2.4. RESEARCH AND DEVELOPMENT OF ORGANIC CROP PRODUCTION IN MALAYSIA

Aini Zakaria and Vimala P. - Strategic Resources Research Center, MARDI - G.P.O. Box 12301, 50774 Kuala Lumpur, Malaysia

Paper presented at 'Expert Group Workshop on Preparation of Technical Guidelines on Organic Cultivation of Tropical and Subtropical Fruits ', 22-26 July 2002, INTAN Bukit Kiara, Kuala Lumpur.

Introduction

Organic farming in Malaysia was incepted by Center for Environment, Technology and Development, Malaysia (CETDEM) in 1986 on a one ha plot in Sungai Buloh. Since then, the organic movement has expanded slowly and to this day covers only 131 ha (Ong, 2001). Awareness of organic farming is mostly confined to the Klang Valley particularly to the educated masses through seminars, demonstrations, exhibitions and conferences largely organised by CETDEM. Organic farming is largely confined to vegetable growing. Very little fruits are grown organically. They are only grown as a side income for the organic growers and the production is erratic. Most of the organic fruits are apples, pears and oranges that are imported largely from Australia, New Zealand, China, Korea and Japan. The local organic fruits sold are papaya and watermelons. Owing to local farmers problems especially on nutrient and P&D management organically, MARDI embarked on research activities in 1999 by identifying the technology gaps in organic vegetable to support the organic growers. Prior to this however, the 1974 Environmental Act has spearheaded the need in utilizing agricultural wastes as organic matter for vegetables and fruits. In this respect, research conducted prior to 1999 only look into the various components singly such as effects of various organic matter on yield of vegetables and fruits and the P&D aspect is non-organic. Research of P&D was often tested on one single crop using inorganic fertilizers. Realizing this, MARDI has just opened a 2 ha plot in 2000 that grow different types of vegetables, of which various Biopesticide, nutrient requirements and cropping design are tested on the same plot.

Research

a. Vegetables

Studies on composts, manures and organic fertilizers for vegetables

Early research on organic vegetables was done by MARDI on CETDEM farm. The first crop of Pak Choy (Brassica chinensis) yielded only 1.8t/ha using chicken dung as the fertilizer. Conventional farming would yield about 16t/ha. The second crop grown with Kangkong (Ipomea aquatica) yielded 7.1t/ha compared to the conventional farming yields of 10.6 t/ha (Samy et.al., 1992).

In organic crop production, inorganic fertilizers are not used. The organic grower has to depend solely on organic nutrient sources that are not fortified. Most of these organic sources are invariably low in nutrient contents compared to inorganic fertilizers. Inevitably, large quantities need to be used to provide all the macro and micronutrients required for optimum

growth and yield of crops. Several investigations on the types and rates of organic fertilizers for organic vegetable cultivation were conducted by MARDI in recent years.

Studies on the yield response of cabbage to Palm Oil Mill Effluent (POME) showed the need for 60 t/ha POME. Yields obtained were 21 t/ha (Vimala et al 1998). With the application of 1.5 t/ha inorganic fertilizer, yields increased to 34 t/ha, indicating that organic fertilizer alone may not always be able to provide sufficient nutrients for high yields. Several organic fertilizers (Table 1) were evaluated on lettuce grown on peat soils (Vimala, et. al., 2000). Results obtained showed that poultry manure out yielded the other organic fertilizers in both the 1st crop and the 2nd crop (Table 2).

Table 1. Nutrient contents of organic fertilizers evaluated on lettuce on peat

Organic source % NutrientN P K Ca Mg C/N ratio

Chicken manure 2.6 2.9 3.4 7.9 1.1 8.3Processed chicken manure 1.9 2.1 2.2 13.8 0.6 11.5Worm compost 1.9 1.7 2.0 6.6 0.6 13.6Kusocom 1.7 1.5 1.7 3.1 0.6 19.2

Table 2. Yield response of lettuce grown on peat to various organic fertilizers

Yield t/haOrganic source 1st crop 2nd cropProcessed chicken manure 24.5a 12.5Chicken manure 22.9a 20.1 Kusocom 21.2ab 8.1Wormcompost 20.1ab 5.2Inorganic fertilizer (600 kg/ha) 15.7b 6.5bControl 9.3c 1.3c

Two new organic fertilizers available in the market i.e. Proseries Organic Fertilizer (POF) and wormcompost were evaluated on Amaranthus sp. (Vimala et. al. 2000; Vimala et. al. 1999). Results obtained showed that chicken manure was a superior organic fertilizer compared to the others (Table 3 and 4). The second crop of amaranthus (bayam), grown without further additions of organic fertiliser, yielded only 50-60 % of the first crop (Table 4) indicating the need for repeated applications of organic fertilizers to sustain yields. The rate of application can however be reduced for succeeding crops on the same plot.

Table 3. Yield of amaranthus sp. with POF and chicken manure

Organic treatment Yield t/ha30 t/ha POF 10.730 t/ha chicken manure 28.3Control 5.7

Table 4. Mean yields of bayam with wormcompost and chicken manure

Organic treatment Yield (kg/2 m x 1 m)1st crop 2nd crop

Worm compost 6.3 3.9Chicken manure 12.3 6.4

Studies on the yield response of vegetables to rates of organic fertilizer (chicken manure) showed the need for about 50 t/ha for tomato, cabbage and brinjal on peat, 20 t/ha for amaranthus on peat and 20 t/ha for lettuce in C. Highlands (Vimala, Salbiah et. al. 2001). Yields obtained with 53 t/ha chicken manure and with inorganic fertilizer (2 t/ha NPK 12:12:17:2) are presented in Table 5.

Comparison of several organic nutrient sources on the yield of lettuce in Cameron Highlands showed that chicken-manure as the sole source of nutrients gave yields equivalent to chicken manure + NPK. All the other organic source gave lower yields compared to organic source + NPK (Vimala, Salbiah et. al. 2001). The nutrient contents of the organic sources and the yields obtained are presented in Tables 6 and 7 respectively.

Table 5. Comparison of yields obtained with chicken manure and inorganic fertilizer

Yield kg/plot (4m x 1m)Treatment Tomato Cabbage BrinjalChicken manure 15.73 14.92 21.64 Inorganic fertilizer 14.20 16.72 22.20Control 2.42 3.85 1.60

Table 6. Nutrient content of some organic fertilizers evaluated on lettuce in Cameron Highlands

% ppm

Organic fertilizer N P K Ca Mg Mn Fe Cu Zn B CN ratioChicken manure 2.59 2.93 3.39 7.97 1.07 475 2505 76 506 39 8.3Processed poultry manure 1.93 2.09 2.21 13.8 0.90 467 7656 58 631 38 11.5PM + sawdust compost 2.01 1.32 1.79 4.70 0.52 278 1088 76 328 71 14.9Wormcompost 0.92 1.95 0.38 9.73 0.64 4.76 3007 69 459 49 21.6PM + sawdust + rice husk compost 0.59 0.23 0.29 0.85 0.09 - - - - - 59.0

Table 7. Yield of lettuce in Cameron highlands grown with and without NPK

Fertilizer Yield (kg/plot)

Yield reduction with only organic fertilizer (%)

Poultry manure 12.96a 4.8Poultry manure + NPK 13.61a -

Wormcompost 8.94b 28.4Wormcompost + NPK 12.48a -PM + sawdust compost 8.47b 32.0PM + sawdust compost + NPK 12.45a -PM + sawdust + rice husk compost 5.28c 47.5PM + sawdust + rice husk compost + NPK 10.05b -

abc = Values followed by the same alphabets are not significantly different at 1%

Studies on green-manures as organic nutrient sources for vegetables

A trial on the incorporation of green-manures on the yield of cucumber showed that green manure alone, applied at 29-37 t/ha gave low yields compared to green-manure + inorganic fertilizer (Vimala et. al. 1999). Thus green manure alone cannot be used as an organic nutrient source. Further research on higher rates of green manures is recommended. Yields of cucumber obtained are presented below (Table 8).

Table 8. Yields of cucumber with green-manure and green-manure + inorganic fertilizer.

Treatment Cucumber Yields (kg/4.5 m2)1 st crop 2nd crop

Green-manure 6.09 5.55Green-manure + 0.6 t/ha NPK 15.05 14.94Green-manure + 1.1 t/ha NPK 21.09 18.89Green-manure + 2.2 t/ha NPK 23.51 18.89

b. Fruits

In the 40's to early 60's, the cultivation of village durians (Durio zibethenus) involved planting of seedlings from seeds and then left to grow amongst forest trees. The only form of fertilizer used is either chicken dung or guano. Most of the trees are not fertilized and left to nature. Some of these trees are still standing and are still yielding about 700-1000 fruits/tree/season. The introduction of cloned durians and systemic planting coupled with the inception of inorganic fertilizer in the 60's led to the withdrawal of organic fertilizers.Currently, the normal planting practice carried out by farmers in planting fruits such as is to apply raw chicken dung at the rate of 5-10 kg per planting hole with inorganic applications of NPK 12:12:24 +TE. The raw chicken dung is placed in bags and left at the base of the tree. However, most farmers are phasing out use of raw chicken dung as it is often associated with diseases, anthracnose in particular (Zabedah, pers.comm.).Oil palm mill discards such as the empty fruit bunch (EFB) and palm oil mill effluent(POME) as organic inputs proved useful in order to sustain crop production on tin tailings. By embedding EFB in layers into a planting hole (Fig. 1), Aminuddin et. al.( 1999) found that yield of papaya increased significantly (Table 9).

Table 9. Yield of papaya on sand tailing with and without EFB

Treatments Yieldkg/plot Fruit no./plot

With 2 layers of EFB 87.3 196.8Without EFB 29.9 63.8

Palm Oil Mill Effluent (POME) applied at 36 kg/plant/year (20 t/ha) on chiku gave yields comparable to POME + NPK (Vimala, Aminuddin et. al. 2001) indicating that POME as the sole source of nutrients can sustain yields. Yields obtained are shown below (Table 10).

Table 10. Chiku yields with organic fertilizer and organic + inorganic fertilizer

Treatment YieldFruit No. per plot

Fruit Yield kg/plot

Average fruit Wt (g)

Fruit No per plant

POME 2483 176 71.6 621POME + NPK (1.5 t/ha) 2639 172 65.3 660

In a trial using compost made from combinations of chicken dung, burnt husk, rice hull and sawdust in the ratio of 3:1:2:5, the yield of papaya and water melon was 50% less when 100% of the compost was used ( Table 11) compared to treatments with incorporation of inorganic fertilizer (Syed, 2001; Zabedah, 2001). The low yields using organic was attributed to the low nutrient content of the compost applied (Table 11.a.). The total soluble solids of the fruits however, were not affected. In the case of water melons, despite the low yields, the size of the fruits had no significant difference with treatments that had inorganic fertilizers.

Table 11. Yield of papaya and watermelons on various combinations of compost

Treatment Papaya WatermelonYield (t/ha)

Wt /fruit (kg)

Total Soluble Solid (%)

Yield (t/ha)

Wt /fruit (g)

Total Soluble Solid (%)

NPK only 20.5b 6.66 8.1 14.0 430 13.7Compost only 24.8a 5.89 7.0 6.6 363 14.0Compost (50%) + Inorganic (50%) 44.6a 6.03 7.2 10.6 428 14.0

Table 11.a. Nutrient content of compost from rice hull, sawdust and chicken dung mixture

Compost material pH CN ratio Nutrient Values in %Rice hull : sawdust : chicken dung : burnt husk 2: 5 : 3 : 1 7.9 59

N P K Ca Mg0.59 0.23 0.29 0.85 0.09

c. Herbs

Misai Kucing (Orthosiphon stamineus sp), Hempedu bumi (Andrographis paniculita) and mengkudu (Morinda citrifolia) have been successfully grown under rubber with application

of only organic fertilizer (processed poultry manure). For misai kucing and hempedu bumi, 30 t/ha of poultry manure applied as basal gave fresh yields of 7.1 t/ha and 2.3 t/ha respectively ( Mohamad Senawi et al 2001; Vimala, Mohd Yusof et.al., 2001)Mengkudu planted under rubber did nor give any significant yield increase with increasing rates (12.5, 25, 37.5, 50 kg/plant) of organic fertilizer applications, indicating that the lowest rate i.e. 12.5 kg/ plant applied in 4 split applications was sufficient for early growth and yield ( June 2000 - Dec 20001). It is interesting to note that there was no significant differences in growth (Fig. 1 and 2) or yield (Table 12) with organic fertilizer only and organic + inorganic fertilizer applications, indicating that organic fertilizer as the sole nutrient source provided sufficient nutrients for early growth and yield of mengkudu under rubber (Vimala, Zulkefly et.al 2002)

Table 12. Yield and fruit number of mengkudu under rubber with organic fertilizer only and organic + inorganic fertilizers

Treatment Yield kg/plot Yield kg/plant Fruit number/plot Fruit no/plantOrganic only 95.33a 5.96 1547a 19.61Organic + inorganic 99.59a 6.22 1371a 19.53

On sand tailings too, there was no significant difference in growth and yield of mengkudu with organic fertilizer only and organic + inorganic fertilizers (Vimala, unpublished). Thus, sufficient rates of organic fertilizer without any inorganic fertilizer application, can sustain the growth and yield of herb crops in Malaysia.

d. Compost

Malaysian organic farmers make use of compost and Bokashi to sustain the soil fertility largely from leftovers of their field harvest. However, some agricultural wastes such as sawdust, rice hull and rice straw form the main compost media. For a 20t heap, 20% constitute chicken dung, 500 kg rice bran, 15 kg microbial inoculum and sawdust make the remaining component. Water is added until the heap reaches 60% moisture level.The compost is overturned after 1 week from the initial mixing and in the 3rd week in which the temperature is often higher than 60oC. This is done manually by a group of farmers or by renting a front end loader for overturning purpose. The composting process takes 3 months to mature. To make a 1 ton Bokashi, farmers add 40% Chicken dung, 60% top soil, 400kg rice bran, 12 kg enzyme and 20L molasses which is diluted to 40L. The temperature of the Bokashi is maintained between 40-50 oC by overturning and covering it with a damp gunny sack. Unlike compost, Bokashi 'matures' within 10 days.About 5 t/ha of compost and 1.5 t/ha of Bokashi are applied onto the vegetable beds one week before planting. Fish meal or bone meal is supplemented thereafter. Research is geared towards quality and consistency in the nutrient values of the composts from agricultural wastes. As an agricultural-based country, Malaysia annually churns approximately 115 tons of agricultural wastes from the oil palm, rice, cocoa, coconut, sugarcane, pineapple and logging industry (Aini et.al, 1992).

Table 13. Composts from various agricultural wastes.

Type of materials and ratio Nutrient values (%) pH Final C:N

ratioN P K Ca MgRice hull : CD :burnt hull 1 : 1 : 0.01 (*) 0.95 1.53 1.53 5.9 0.58 7.9 24Coconut coir dust: CD : burnt hull 0.7 : 1 : 0.01 (*) 2.32 2.08 3.12 7.92 0.89 8.4 12Oil palm frond : CD : burnt hull 1 : 1 : 0.01(*) 2.01 1.44 2.34 5.90 0.67 8.6 13Rice straw : CD* : rice bran : spent molasses from alcohol factory 3.6 : 1 : 0.15 : 1(**) 1.57 0.77 2.83 - - 8.0 15.6

Pineapple trunk : oil palm frond : CD* 1 : 1 : 0.4 (**) 1.51 1.82 2.79 9.99 0.99 - 13.6

CD - Chicken dung(*) Aini and Izham, 2001(**) unpublished data

Quality composts are achieved using materials that are free from heavy metals and through aerobic fermentation. To ensure an aerobic condition, compost heaps are overturned upon reaching 60 oC and moisture maintained at 60%. Initial C:N ratio of 30 offer less volatization of nitrogen and consistent compost maturity. Care should be taken in using sawdust as a compost media as a large portion of wood are treated with chemicals containing heavy metals. Some of the composts made form agricultural wastes are shown in Table 13.

e. Pests and Diseases

High temperatures, humidity and sunshine throughout the year offer an environment conducive for a continuous cycle of pest and diseases. The winter season in the temperate provides a break in the pest life cycle, reducing the pest population and will only increases in the summer months. Weeds are also fast growing in the tropics and some weeds harbour pests. The common practice for organic farmers in Malaysia to reduce the pest population is to spray with wood vinegar and BT sprays.

Studies in use of Biopesticide

Flea beetles (Phyllotreta spp.) form a major pest both in the lowlands and highlands of Malaysia. Several trials were conducted using Biopesticide to test its efficacy in reducing the population. Results show that, tea tree oil and a herbal preparation could be used against flea beetles. Garlic and Neem sprays are not as effective (Sivapragasam and Mohammad Roff, 2002). Table 14 shows the effect of these sprays on the pest number. Other physical measures need to be incorporate to complement the reduction of pest population (Table 15).

Table 14. Mean number of flea beetles per plant and the number of leaves damaged in each treatment

Treatments Mean number of beetles per plant per sampling date

Mean number of leaves damaged per plant

Amyl acetate based Azadirachtin indica 1.9 ab 5.0 ab

Ketone based Azadirachtin indica 0.7 ab 1.8 ab

Azadirachtin excelsea 0.6 b 2.4 ab

(sentang)Garlic spray 2.1 ab 4.0 abUntreated check 3.3 a 3.4 ab

Source adapted from : Sivapragasam and Mohammad Roff (2002)

Table 15. Adult flea beetle populations (mean) on Brassica chinensis in the various Biopesticide and bio based treatments

Treatment 2-day post spray

Mean yield per bed (kg)

Unsprayed check 25.3 ab 3.3 abNeemix 28.3 ab 2.9 abAsystasia gangetica (weed not infested by flea beetles) 39.7 a 2.8 ab

Commercial herbal spray 22.0 ab 3.2 abTea tree oil 20.0 ab 3.6 abNetting 6.7 b 2.6 abPolyethylene sheet 9.7 b 1.7 b

Source adapted from: Sivapragasam and Mohammad Roff (2002)

Use of multiple crops in reducing pest population

Studies showed that by increasing the biodiversity of the cropping system , incidences of pests are reduced. Alate aphids were markedly reduced by 60-65% by intercropping chilli with maize and surrounding chilli with maize (Mohammad Roff and Ho, 1991). Instead of chilli grown as monoculture, it can be bicultural with maize or brinjal or in triculture with brinjal and Leucaena. By doing so, the population of Menochilus sexmaculatus ( a predator of aphids) is increased (Hussein, et al., 1996). Using Indian Mustard ( Brassicca juncae) as a trap crop for major insect pests of lowland cabbage, it can reduce damage caused by Hellula undalis on cabbage yields (Table 16). Insect numbers did not reduce significantly between cabbages grown as monoculture and with Indian mustard . However, it is suggested that Indian mustard be grown as hedgerows in the cabbage system to dilute the pest population on cabbage, based on the smaller insect numbers on it ( Sivapragasam and Loke, 1996).

Table 16. Insect numbers, yield and damage of cabbage grown with and without the Indian Mustard trap crop.

Parameters Cabbage Monocrop Cabbage + Indian Mustard Trap cropInsects and Other ArthropodsPlutella 5.5 7.3 0.5Hellula 2.1 1.5 0.8Spodoptera 2.4 8.9 1.0Flea beetles 6.5 6.3 35.5Predators (spiders/ants/earwigs) 10.3 10.9 3.3

Yield damage (%)Marketable heads 59.6 62.2Hellula damage 17.1 5.7Soft Rot 11.2 12.8

Major Constraints Faced By Malaysian Farmers In Organic Farming

The most critical factor is the certification of organic products without it, consumers question the authenticity of organic produce. Though the Malaysian Certification guideline is already available, the accreditation system is still not implemented. Accreditation by foreign companies is expensive and most farmers cannot afford to pay for the accreditation fees. For those who are able, they will have to raise the price of their product and ensure their market in order to meet the costs. As it is, the price of organic produce is 4-6 times the price of conventional produce.Market outlet is another factor that determines the success of organic farms. Without a specialty store, with no labeling or packaging, the organic produce cannot be differentiated from conventional produce. In Malaysia, organic produce is mostly sold in the Klang Valley , Penang and Johore Bahru in special stores or hypermarkets. Produce especially from the highlands is transported by ordinary lorries exposing the produce to heat, resulting in reduced shelf life.Most consumers are indifferent towards organic produce and are driven by the aesthetic looks of produce and the pricing. They are still unaware of the objectives of organic farming and the impact towards environment and health. Poor quality organic produce such as misshapen fruits, thin, stunted, yellow looking with tell tale signs of pest attack often shun consumers into buying organic fruits and vegetables except those who are health conscious.For farmers to ensure that their land is free from chemical contamination and lesser pest attack, they often settle to areas near forests. In these areas, infrastructure is very much lacking and farmers find difficulty in transporting their produce. To combat P & D, farmers can only access to a limited number of pesticides that often have a very short efficacy shelf life.

Conclusions and recommendations

Chicken manure, either processed or unprocessed but dry (25-30% moisture), is presently recommended as the most suitable organic nutrient source for organic food crop cultivation in Malaysia. Processed chicken manure is preferred by organic growers though it costs more, because of pathogens associated with unprocessed chicken manure. General organic fertilizer recommendations for some crops are presented below. Higher rates of organic fertilizers will be required if marginal soils like sand-tailings are used.

Crop Organic fertilizer Vegetables

Chilli 30 t/ha organic fertilizer as basal, 3 -5 days before transplanting (1st application) 30 t/ha at 60 Days After Transplanting (DAT) (2nd application)

Radish 30 t/ha basal + 10 t/ha (45 DAT)Long bean/French bean 30 t/ha basal + 15 t/ha (45 DAT)

Cabbage 30 t/ha basal + 15 t/ha (50 DAT)Okra 30 t/ha basal + 20 t/ha (50 DAT)Sweet Potato 30 t/ha basal + 10 t/ha (50 DAT)Lettuce 30 t/ha basalBayam 30 t/ha basalGreen soybean 30 t/ha basalHerbsMisai kucing 30t/ha basalHempedu bumi 30t/ha basalMengkudu (1-2years) 3kg / 3months

The aim in organic farming is not to eradicate pests altogether but to maintain a degree of balance between beneficial organisms and pests. Since Biopesticide are limited in the market, other measures must be taken into consideration to reduce the pest population.

Pests Control options

AphidsEnrich soil organically, grow trap crops, apply dormant oil sprays, wash-off from plants, use yellow water pan traps with detergent, use shiny aluminium surface, give adequate water and avoid water stress in plants

Caterpillars Bacillus thuringiensis, neem based sprays, parasitoids and predators

Adult moths Pheromone traps, sticky traps, mechanical barriers, intercropping with tomatoes

Eggs of moth Trichogramma parasitoidsPupal stages in the soil Tillage and exposure

Nematodes Trap crops such as marigoldsFlea beetles Sentang sprays, trap cropsMites Oil spraysWhite flies Dishwashing fluids, parasitoids

To ensure success of organic farming, government portrayal is needed to give the much needed support in creating awareness on food safety and environment to the masses. The research component is also important to look into nutrient, P & D management , cropping systems and labour saving techniques.

REFERENCES

Aini Z., Abdul Aziz B., Suhaimi O., and P. Vimala. 1992. The growing need for organic fertilizer usage and the availability of agricultural wastes in Malaysia. Paper presented at International Conference on "Proper use of Chemical Fertilizers Combined with Organic Fertilizers in Crop Production" Nov. 9-14 1992, Serdang. FFTC-UPM.

Aini Zakaria and Izham Ahmad. 2001. Accelerating Compost Maturity in Some Agricultural Biomass Using Bio-Plus Activator as Inoculum. In Project Final Report "Development and Testing the Effectiveness of BPA Organic Fertilizer on Selected Horticultural Crops and Rice". MARDI- Bio-Organic System & Services Sdn. Bhd. (BOSS).

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Mohammad Roff, M.N. and Ho, B.L. 1991. Maize as a barrier crop in reducing aphids, the virus vector of chilli. MARDI Res. J. 19 (2) :251 -258

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Samy, J., Chan, Y.K. and Sivapragawam, A. 1992. Organic Farming - Has it a Future? Paper presented at the Soil Science Conference. Malaysian Soil Science Society. Kuala Lumpur.

Sivapragasam, A and Loke, W.H. 1996. Indian Mustard as a trap crop for insect pests on cabbages. Report on the collaborative vegetable research program in South East Asia (AVNET-III), 1993-1996.

Sivapragasam, A. and Mohammad Roff, M.N. Effect of Biopesticide and other bio-based treatments against flea beetles, Phyllotreta spp on crucifers. 2002. In proceedings ' Positioning Biopesticide in Pest Management Systems' . 3rd International Conference on Biopesticide. 22-26 April 2002. Kuala Lumpur.

Syed Mohammed, 2001. Water Melon Production Using BOSS Bio-Organic and Bio Foliar Fertilizer. In Project Final Report "Development and Testing the Effectiveness of BPA Organic Fertilizer on Selected Horticultural Crops and Rice". MARDI- Bio-Organic System & Services Sdn. Bhd. (BOSS).

Vimala, P., Aminuddin, B.Y. Ahmad, H., Ghulam, M.H. and Lim, S.P. 2001. Performance of chiku (Achras zapota L.) on sandy tin-tailing soils. Paper presented at 'Soils Sc. Conf'. 17-20 April 2001, Kota Kinabalu, Sabah.

Vimala, P. Mah, S.Y. Mohd Roff, M.N. Ong H.K. Salbiah, H. and Rubiah, W.A. 2000. Organic cultivation of lettuce (Latuca sativa). Paper presented at ' Malaysian Soil Sc. Conf.' 18-20 April, 2000. Johore Baru, Johore.

Vimala, P., Mah, S.Y., Mohd. Roff, Rubiah, W.A. and Salbiah, H. 2000. Yield and growth performance of organically grown bayam (Amaranthus sp.). Trans. Malaysian Soc. Plant Physoil. 9: 273-276.

Vimala P., Mohd Yusoff A., Mohamed Senawi M.T., Abdul Ghani I. and Ahmad Shokri O. 2001. Paper presented at ' Seminar on medicinal and aromatic plants 2001' 24-25 July 2001, FRIM, Kepong, Kuala Lumpur.

Vimala, P. Othman, A.B. Aminuddin, Y. Salbiah, H. and Ruwaida, M. 1998. Comparison of Palm Oil Mill Effluent and chicken manure as organic amendments for cabbage cultivation in the highlands. Paper presented at 'Malaysian Soil Sc. Conf.' 21-22 April 1998, Kuala Lumpur.

Vimala, P. Salbiah, H. and Ong, H.K. 1999. Evaluation of vermicompost on growth, yield and nutrient content of bayam (Amaranthus sp.) grown on peat. In 'Proc. Soil Sc. Conf.' pg 70-81. April 20-21. Seremban, Negeri Sembilan.

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Vimala, P. Ting, C.C., Salbiah, H. Ibrahim, B and Ismail, L. 1999. Biomass production and nutrient yields of four green manures and their effect on the yield of cucumber. J. Trop. Agric. and Fd. Sc. 27(1): 47-55.

Vimala P., Zulkefly S., Mohamed Senawi M.T., and Ahmad Shokri O. 2001.Macronutrient content, uptake and partitioning and heavy metal content in hempedu bumi (Andrographis paniculata) and misai kuching ( orthosiphon stamineus) grown under rubber. Paper presented at' Malaysian Soil Sc. Conf.' 23-25 April, Kangar, Perlis 2002

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Fig. 1. Incorporation of EFB in planting holes on tin tailings

Maturity and stability parameters of composts prepared with a wide range of organic wastes

M.P. Bernai , C. Paredes, M.A. Sánchez-Monedero and J. Cegarra

Department of Soil and Water Conservation and Organic Waste Management, Centro de Edafología y Biología Aplicada del Segura, CSIC, PO Box 4195, 30080 Murcia, Spain

Received 29 January 1997;  revised 22 May 1997;  accepted 24 May 1997.  Available online 18 June 1998.

Abstract

Seven different composts were prepared in a pilot plant by the Rutgers static-pile system using a wide range of wastes: sewage sludge, poultry manure, pig slurry, olivemill wastewater, city refuse and the lignocellulosic wastes cotton waste, maize straw and sweet sorghum bagasse. Their chemical and biological properties were studied at four stages of the composting process: in the initial mixture, at the thermophilic phase, at the end of the active

phase and after two months of maturation. The following maturity indices were established: C/N < 12, Cw < 1.7%, Cw/Norg < 0.55. NH4/NO3 < 0.16, and NH4-N < 0.04%, with a germination index greater than 50%. In addition, some carbon mineralization parameters

could also be used as maturity indices: mineralized-C in 70 days (Cm) < 30%, rapidly mineralizable-C (CR) < 7.2% and a slow mineralization rate (CS × KS) < 0.35% day−1. Maturation indices based on humification of the organic matter and the cation exchange

capacity of different composts could not be found, since the values for mature

compost depended on the wastes from which the composts were made.

Key words: carbon mineralization; composting; compost maturity; compost

stability; maturity index; humification; organic wastes

References

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compost degradation, J. Ferment. Technol. 59 (1981), pp. 215–219.M.S. Finstein and F.C. Miller, Principles of composting leading to maximization of decomposition rate, odor control, and cost effectiveness, Composting of agricultural and other wastesdor control, and cost effectiveness, Elsevier Applied Science Publ (1985), pp. 13–26.K. Haider, Problems related to the humification process in soil of temperate climates, Soil Biochemistry 7 (1992), pp. 55–94.Y. Harada and A. Inoko, Relationship between cation-exchange capacity and degree of maturity of city refuse composts, Soil Sci. Plant Nutr. 26 (1980), pp. 353–362.N.V. Hue and J. Liu, Predicting compost stability, Compost Sci. Utilization 3 (1995), pp. 8–15.D.A. Iannotti, T. Pang, B.L. Toth, D.L. Elwell, H.M. Keener and H.A.J. Hoitink, A quantitative respirometric method for monitoring compost stability, Compost

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PDF (451 K) | View Record in Scopus | Cited By in Scopus (60)A.F. Navarro, J. Cegarra, A. Roig and M.P. Bernal, An automatic microanalysis method for the determination of organic carbon in wastes, Commun. Soil Sci. Plant Anal. 22 (1991), pp. 2137–2144. Full Text via CrossRefA.F. Navarro, J. Cegarra, A. Roig and D. García, Relationships between organic matter and carbon contents of organic wastes, Biores. Technol. 44 (1993), pp. 203–207. Abstract |

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Relationships between total organic carbon and oxidable carbon, Biores. Technol. 57 (1996), pp. 291–295.S.G. Sommers, V. Kjellerup and O. Kristjansen, Determination of total ammonium nitrogen in pig and cattle slurry: sample preparation and analysis, Acta Agric. Scand. Section B 42 (1992), pp. 146–151.F. Zucconi and Bertoldi M. de, Compost specifications for the production and characterization of compost from municipal solid waste. In: M.de Bertoldi, Editor,

Compost: production, quality and use, Elsevier Applied Science, Barking, Essex (1987), pp. 30–50.F. Zucconi, A. Monaco, M. Forte and Bertoldi M. de, Phytotoxins during the stabilization of organic matter, Composting of agricultural and other wastes, Elsevier Applied Science Publ., Essex (1985), pp. 73–85.F. Zucconi, A. Pera, M. Forte and Bertoldi M. de, Evaluating toxicity of immature compost, BioCycle 22 (1981), pp. 54–57. View Record in Scopus | Cited By in Scopus (209)

Composting rice straw with sewage sludge and compost effects on the soil–plant system

L. Roca-Péreza, C. Martíneza, P. Marcillaa and R. Boluda , a,

aDep. Biologia Vegetal, Facultat de Farmàcia, Universitat de València, Av. Vicent Andrés i Estellés s/n, 46100 Burjassot, València, Spain

Received 15 September 2008;

revised 22 December 2008;

accepted 24 December 2008.

Available online 1 February 2009.

Abstract

Composting organic residue is an interesting alternative to recycling waste as the compost obtained may be used as organic fertilizer. This study aims to assess the composting process of rice straw and sewage sludge on a pilot-scale, to evaluate both the quality of the composts obtained and the effects of applying such compost on soil properties and plant development in pot experiments. Two piles, with shredded and non-shredded rice straw, were composted as static piles with passive aeration. Throughout the composting process, a number of parameters were determined, e.g. colour, temperature, moisture, pH, electrical conductivity, organic matter, C/N ratio, humification index, cation exchange capacity, chemical oxygen demand, and germination index. Moreover, sandy and clayey soils were amended with different doses of mature compost and strewed with barley in pot experiments. The results show that compost made from shredded rice straw reached the temperatures required to maximise product sanitisation, and that the parameters indicating compost maturity were all positive; however, the humification index and NH4 content were more selective. Therefore, using compost-amended soils at a dose of 34 Mg ha−1 for sandy soil, and of 11 Mg ha−1 for clayey soil improves soil properties and the growth of Hordeum vulgare plants. Under there conditions, the only limiting factor of agronomic compost utilisation was the increased soil salinity.

Keywords: Rice straw; Compost maturity ; Amended soils; Salinity problems

Article Outline

1. Introduction

2. Material and methods

2.1. Analytical parameters and compost maturity indicators

2.2. Composting piles and sampling

2.3. Pot experiments

3. Results and discussion

3.1. Raw materials characterisation

3.2. Composting monitoring

3.3. Compost maturity

3.4. Effect of compost application on soil properties and H. vulgare growth

4. Conclusions

Acknowledgements

References

1. Introduction

The amount of sewage sludge generated from sewage treatment plants in the Valencian Community (Spain) is around 1 30 000 dry tons per year. Sewage sludge is destined to agriculture, composting, incineration and rubbish dumps. Furthermore, rice (Oryza sativa L.) is an important crop in this area and generates more than 100 million kg of residues per year. This residue is usually burnt in the field in autumn which causes atmospheric pollution and respiratory diseases in the local population. This environmental problem has been reported by Arai et al. (1998) and Torigoe et al. (2000) in Japan. Therefore, eliminating such residues is not only a problem in our region, but in all those areas in the world where this cereal is grown and where sewage treatment plants are located. Besides, this habit contributes to CO2 emissions on a global scale. An attractive alternative to recycling such waste is composting. During composting, it is necessary to know how the physical, chemical and biological parameters evolve over time to improve the process ([Iglesias and Pérez, 1992], [Charest and

Beauchamp, 2002], [Van Heerden et al., 2002] and [Bustamante et al., 2008]).

On the one hand, the use of sewage sludge mixed with different organic waste materials is now usual in composting experiments ([Fang et al., 1999], [Li et al., 2001] and [Mupondi et al., 2006]). Moreover, rice straw has been used as a raw material for mixing compost

with rock phosphate and ammonium sulphate (Zayed and Abdel-Motaal, 2005), swine manure (Zhu et al., 2004), rape cake, poultry manure (Abdelhamid et al., 2004), and dairy manure (Li et al., 2008). According to the report of Iranzo et al. (2004), the characteristics of rice straw and sewage sludge generated in Valencia are complementary for composting; besides, the optimal conditions for blends to reach maximum microbial activity in the first steps of composting have also been documented (Roca-Pérez et al., 2005). However, we

found no works which evaluate the composting process and the compost quality using these wastes exclusively. Therefore, it is necessary to study the evolution of the physical and chemical parameters during the process, and also the effect of particle size given its significant influence on material degradation during composting (Lhadi et al., 2004).

On the other hand, there is a basic need to know the effect of compost application on soils and crops. The study of compost, from sewage sludge, or sewage application on the soil–plant system has been widely reported by numerous authors (e.g. [Bulluck et al., 2002], [De Melo et al., 2002], [González and Cooperband, 2002], [Korboulewsky et al., 2002], [Madejón et al., 2003], [Walker et al., 2004], [Bhattacharyya et al., 2005] and [Bhattacharyya et al., 2007]). However, very few works study the effect of

compost application and assess, at the same time, the limiting factor and the optimum dose to be applied. In this work, compost has been obtained which, at a specific rate, can be applied to soil to increase soil fertility and plant development.

Therefore knowing all these aspects can contribute to recycling and assessing such waste. Hence, the objectives of this work were to (i) characterise the physical and chemical properties of rice straw and sewage sludge generated in Valencia, (ii) study the composting process with these wastes, including the effect of shredded and non-shredded rice straw in pilot-scale experiments, (iii) estimate compost maturity, and (iv) assess the effect of

compost application on both soil properties and Hordeum vulgare growth.

2. Material and methods

Dewatered digested sewage sludge was collected from the Metropolitan sewage industry (EMARSA), and rice straw was obtained from rice soils in the Albufera Natural Park, both located in Valencia (E. Spain).

2.1. Analytical parameters and compost maturity indicatorsColour was determined by Standard Soil Color Charts. Moisture content, oven-dried at 105 °C for 24 h; total organic matter, through weight loss on ignition at 550 °C for 72 h; oxidizable organic carbon by the Walkley–Black method; and total Kjeldahl nitrogen (TKN) by the Kjeldahl method (Bremner and Mulvaney, 1982). The pH and electrical conductivity (EC) of the raw materials and compost were measured in a 1:5 water soluble extract (w:v). The was determined using the KCl extraction method (Mulvaney, 1996). In order to quantify the P2O5, K2O, CaO, MgO, Fe, Mn, Zn, Cu, Ni, Pb, Cd, and Cr contents in the sewage sludge and compost, samples were digested with an acid mixture of HNO3 and HClO4; only HNO3 was used for rice straw. The P concentration was determined by spectrophotometry as molybdovanadate phosphoric acid. The remaining elements were determined by flame atomic absorption spectrometry (Perkin Elmer 2080). Three replicates were done per sample.

The maturity indexes analysed were cation exchange capacity (CEC), humic acids/fulvic acids ratio (CHA/CFA), chemical oxygen demand (COD), and germination index (GI). CEC and COD were determined respectively by Ba(OAc)2 (Harada and Inoko, 1980), and by oxidation with K2Cr2O7 according to Lossin (1971). For the CHA/CFA ratio, extractable carbon (CEX) was determined by 0.1 M Na4P2O7 + 0.1 N NaOH solutions (1:1), and humic acid-like carbon (CHA) after precipitation at pH 1 with sulphuric acid; fulvic acid-like carbon (CFA) was derived from the difference between CEX and CHA (Iglesias and Pérez, 1992). The GI test was carried out on water extracts by mechanically shaking fresh samples for 3 h at a

solid:distilled water ratio (1:10 w/v, dry weight basis); then extracts were centrifuged at 3500 rpm for 10 min and filtered through 0.45 μm membrane filters, and were then diluted (1:1) with distilled water; 5 mL of extract were added to a plastic petri dish lined with germination filter paper; 20 Lepidium sativum L. seeds (Zucconi et al., 1981) were evenly distributed on the filter paper and incubated at 30 °C in the dark for 48 h; six replicates were analysed per sample; the GI was calculated as the average percentage of seeds germinated on petri dishes multiplied by the average length of roots expressed as a percentage of the control with distilled water (Huang et al., 2001).

2.2. Composting piles and samplingIn a previous laboratory-scale experiments with rice straw and sewage sludge were performed; the optimum conditions to achieve greater microbial activity were obtained in blends with a C/N ratio of between 15 and 20, and a moisture content of 60% (Roca-Pérez et al., 2005). In order to achieve such conditions, two static piles were prepared by blending sewage sludge with shredded (P1) and non-shredded rice straw (P2) at a ratio of 2.6:1 (w/w fresh weight), and 10 L of water were added. The pilot-scale composting piles were designed by means of constructing a composting apparatus according to Hanajima et al. (2001). The piles measured 1.0 × 0.8 × 0.75 m. A geotextile draining sheet was positioned at the base to facilitate passive aeration. Electronic thermometers were placed at three different depths: top (50 cm from the base); middle (35 cm from the base) and bottom (10 cm from the base). Three more were placed at the centre, east and west. Temperatures were taken daily. A representative composed sample, of approximately 2 kg of three subsamples at differently located piles, was collected. Subsamples were taking at the base, middle and surface of the piles. Each sample was divided into two parts. One was refrigerated (4 °C) until the pH was reached, and the EC and the analyses were performed; the other was oven-dried at 30 °C for 48 h, and pulverised. Several samples were taken during the composting process at different times.

2.3. Pot experimentsThe experimental design was based on the method described in the UNE standard (1996). To carry out the experiment, clayey soil (calcaric Luvisol, FAO, 1998) and sandy soil (albic Arenosol, FAO, 1998) were used. Both soils were located in the outskirts of the city of Valencia. Then, 6 previously germinated barley seeds (H. vulgare L.) were used per pot, and these were kept in a growth chamber at constant temperature, light and humidity (70% of field capacity of soils). Pots were filled with 250 g of dry soil (passed through a 2 mm sieve) and with compost from P1 in the following proportions (w/w): 0.0%; 0.2%; 0.8%; 1.5%; 3.0%, 6.0% and 100% for clayey soil, and 0%; 1%; 2%; 4%; 6%; 10%, 20% and 100% for sandy soil. Likewise, 3 pots were seeded per dose. After a 10 d growth period, soil was carefully removed, plants were washed, and their dry weights were determined after being placed in an oven at 60 °C for 24 h. The experiment was done in triplicate. Soil analyses such as pH, soil organic matter (SOM), TKN, available P, and EC were performed as previously reported by Roca-Pérez et al. (2002). Stable aggregates (SA) were determined by the Henin and Feodorff method (Fortun et al., 1989). To assess the effects of compost -amended soil on H. vulgare L. plants, the root/shoot (R/S) ratio index was determined; for this purpose, studies have been conducted to demonstrate the variation in the R/S ratio in terms of fertilizer dose ([Maschnner, 1995], [Cronin and Lodge, 2003] and [Xu et al., 2004]).

3. Results and discussion

3.1. Raw materials characterisation

The characteristics of the sewage sludge and rice straw used to prepare the piles for composting are shown in Table 1. In general, most of the parameters analysed fall within the ranges obtained by Iranzo et al. (2004). Nevertheless, the EC value and the Cu and Pb contents of the sewage sludge used are lower than the values presented in the aforementioned work, which could be due to seasonal variations in waste water characteristics from the EMARSA treatment plant. The N and C contents in rice straw are similar to those obtained by Abdelhamid et al. (2004), whereas the pH and EC present higher values to those obtained by these authors. This is owing to the different substrate/water ratio used to determine these parameters. It should be pointed out that the characteristics of the raw materials are compatible for carrying out composting.

Table 1.

Physical and chemical characteristics of raw materials (dry weight basin). Mean (standard deviation).

Parameter Sewage sludge Rice straw

Colour 7.5Y 2/1 2.5Y 7/6

Density (g cm−3) 1.01 (0.01) 0.05 (0.00)

Moisture content (%) 79.0 (2.0) 10.0(0.3)

pH (H2O)a 7.5–7.7 8.4–8.6

EC (dS m−1) 3.10 (0.60) 6.95 (0.61)

Oxidizable organic carbon 20.0 (0.6) 34.0 (1.0)

Total organic matter (%) 60 (2) 78 (1)

Total Kjeldahl nitrogen (%) 3.0 (0.1) 0.7 (0.1)

C/N ratio 7.0 (0.5) 48.0 (2.0)

P2O5 (%) 3.6 (0.3) 0.2 (0.1)

K2O (%) 0.30 (0.02) 1.90 (0.01)

Parameter Sewage sludge Rice straw

CaO (%) 11.00 (1.00) 0.85 (0.03)

MgO (%) 1.3(0.2) 0.6 (0.0)

Fe (mg kg−1) 31 200 (2700) 310 (3)

Mn (mg kg−1) 165 (9) 92 (2)

Zn (mg kg−1) 1100 (80) 29 (1)

Cu (mg kg−1) 230 (20) 9 (1)

Ni (mg kg−1) 53 (3) 6 (0)

Pb (mg kg−1) 50 (20) 2 (0)

Cd (mg kg−1) 2.55 (0.05) n.d.

Cr (mg kg−1) 210(20) n.d.

EC: electrical conductivity; n.d.: not detected.

a Range.

3.2. Composting monitoringDuring this process, physical changes were observed: colour, volume, weight, moisture (Table 2), odour and structure. At day 0, blends were highly fibrous, malodorous, of the black and yellow colour of sewage sludge (black, 7.5Y 2/1) and rice straw (yellowish, 2.5Y 7/6), respectively. The predominant colour of the blend was yellowish grey (2.5Y 5/6), while that at the end of composting process was a consistent dark brown colour (10YR 3/2, P1) to brownish black (10YR 3/2, P2), with a cloddy structure and pleasant odour resembling that of wet forest soil: the colour and odour characteristics were of brown earth with a soil forest surface horizon rich in Mull-humus. From the 4–6th day, a large amount of fungi mycelium and white mushroom appeared. With both piles, the volume and weight decreased considerably at the end of the process, particularly in the compost obtained in P1 (37% and 54%, respectively); after a little rubbing, this compost was sieved through

a 12 cm sieve while the reject material of the compost of P2 was 15% in weight. In general, the moisture content in both piles decreased to reach values of 40–42% (Table 2), so it was not necessary to add water; it was also interesting to note that no lixiviate production was observed, and this may be owing to the correct adjustment of humidity and also to the specifications of the composting apparatus which, to a certain extent, favoured water vapour condensation inside the lid and its return to the piles; in that sense, Haug (1993) reported that the most adequate initial humidity content for the blend to be processed is around 60%, and this was verified for these two residues in previous laboratory experiments by Roca-Pérez et al. (2005). All these facts confirmed the importance of particle size for preparing a good blend and their significance on the humification process linked to browning and to the organic matter stabilisation.

Table 2.

Characteristics of the blends and the compost in P1 and P2 after 90 days of composting (dry weight basin). Mean (standard deviation).

Parameters P1 P2

Initial mixture Compost Initial mixture Compost

Colour 2.5Y 5/6 10YR 3/2 2.5Y 6/8 10YR 3/3

Volume (m3) 0.44 0.28 0.48 0.35

Weight (kg) 98 45 98 52

Moisture (%) 60.3 (3.5) 39.9(1.5) 60.3 (3.5) 42.0(1.6)

pH (H2O)a 8.29-8.61 6.83-7.21 7.63-8.65 7.03-7.12

EC (dS m−1) 3.34(0.14) 3.67 2.95 (0.08) 3.80 (0.06)

OOC (%) 26.8(1.4) 22.7 (0.4) 31.4(0.6) 18.4(0.1)

TOM (%) 69(1) 53(1) 69(1) 48(1)

TKN (%) 1.6(0.2) 2.3(0.1) 1.6(0.3) 1.9(0.1)

Parameters P1 P2

Initial mixture Compost Initial mixture Compost

(mg kg−1)

3420 (10) 120(1) 3340 (10) 540 (60)

C/N ratio 18.0(1) 9.8 (0.7) 20.0(1) 10.6(0.9)

P2O5 (%) 1.7(0.2) 2.5 (0.2) 1.7(0.2) 2.7 (0.6)

K2O (%) 1.1 (0.1) 1.2(0.1) 0.9(0.1) 1.1 (0.1)

CaO (%) 5.3 (0.3) 9.0(1.0) 5.2 (0.2) 9.2 (0.8)

MgO (%) 0.9 (0.1) 1.2(0.1) 0.8(0.1) 1.2(0.1)

Fe (mg kg−1) 13900(1100) 18200 14000(1000) 19200(600)

Mn (mg kg−1) 120(10) 200 (20) 170(10) 220(10)

Zn (mg kg−1) 500 (30) 700 (60) 510(20) 610(40)

Cu (mg kg−1) 100(20) 170(20) 100(10) 170(10)

Ni (mg kg−1) 23(2) 36(4) 26(1) 39(2)

Pb (mg kg−1) 22(5) 94(15) 22(2) 99(6)

Cd (mg kg−1) 1.0(0.0) 1.2(0.0) 1.7(0.1) 2.5 (0.0)

Cr (mg kg−1) 94(6) 150(20) 96(4) 152(8)

Cha/Cfa 0.23 1.40 0.29 0.48

CEC (cmol(+) kg−1) 60(4) 108(11) 63(7) 98(5)

Parameters P1 P2

Initial mixture Compost Initial mixture Compost

GI (%) 21 106 29 86

COD (mg g−1) 34.0 (0.7) 20.0(1.4) 55.0 (2.6) 16.0(0.9)

EC: electrical conductivity; OOC: oxidizable organic carbon; TOM: total organic matter; TKN: total Kjeldahl nitrogen; Cah/Caf: humic acid carbon/fulvic acid carbon ratio; CEC: cation exchange capacity; GI: germination index; COD: chemical oxygen demand.

a Range.

Variation in temperature during the composting process plays a selective role in both the evolution and succession of the microbial communities maximising the sanitisation, biodegradation rate and the microbial diversity ([Hassen et al., 2001] and [Zhu et al., 2004]). In this study, the temperature profiles (data not shown) indicated that the core temperature was the highest in each pile. A rapid increase of temperatures was observed in the first 24 h. However, the average temperature between the piles indicates significant differences (Table 3). Indeed, although the thermophilic phase lasted for approximately 15 d in both cases, the time which passed with temperatures over 55 °C was 48–144 h for P1, depending on the location of the probe, and only 8 h at the centre of P2; the maximum temperatures reached inside P1 and P2 were 72.0 and 55.2 °C, respectively, which contrasts with the ambient temperature (18–25 °C). Hanajima et al. (2001) found maximum temperatures to be in the same locations (Table 3). These facts indicate that previous sample treatment as well as the way the blend is prepared are extremely important operations, and confirm the need to shred rice straw to facilitate its contact with sludge, as well as the convenience of turning with a view to favouring the sanitisation of all the product. The temperatures obtained in P2 also suggest that increased heat loss may have taken place because of the large size of the fibrous particles which excessively encouraged atmospheric air to enter. In this sense, the enhancement of the degradation processes during composting was related to smaller particle size (Lhadi et al., 2004). Conversely however, and bearing in mind the USEPA criterion (1994), the compost from P2 would not be acceptable in sanitisation terms; Iranzo et al. (2004) demonstrated that incubating blends of these residues at 62 °C for 48 h avoided the presence of enteric bacteria, streptococci and Salmonella spp.; unlike the blends that did not reach adequate incubation temperatures. This confirms the important role that temperature plays in composting thermophilic phase for pathogenic reduction.

Table 3.

Maximum temperature and duration of temperatures above 55 °C in the pilot-scale experiment during the composting process with rice straw with sewage sludge.

Locations P1 P2Hanajima et al. (2001)

East Centre West East Centre West Right Centre Left

Maximum temperature (°C)

Top 64.7 69.3 63.2 47.0 54.2 49.0 64.2 69.2 52.8

Middle 65.7 72.0 67.2 45.8 55.2 49.6 73.4 77.3 77.2

Bottom 63.0 62.8 59.9 48.8 53.2 48.0 61.8 66.6 62.2

Duration (h) of temperature above 55 °C

Top 96 120 84 0 0 0 34 51 0

Middle 108 144 132 0 8 0 84 126 102

Bottom 60 65 48 0 0 0 42 113 55

The concentrations of macronutrients (N, P, K, Ca, Mg), micronutrients (Fe, Mn, Zn, Cu, Ni, Cr) and toxic metals (Cd, Pb) in both composts increased at the end of process (Table 2). The Zn, Cu, Ni, Cr, Cd and Pb values in our composts were all below the maximum limits established by Spanish legislation currently in force on Class C (BOE, 2005). Conversely, the concentration decreased at the end of the process in both piles.

Fig. 1 shows the evolution of both the pH (Fig. 1a) and C/N ratio (Fig. 1b) during composting. It was reported that the pH value could be affected by composting raw materials and other uncertain factors (Zhu et al., 2004). In this study, the pH of both piles slightly increased during the first days of the composting process, and then decreased during the composting period. At the end of the process, both piles had a similar pH (7.07 P1 and 7.09

P2). The rise in pH may be related to the NH3 released, resulting from the degradation of organic matter through microbial activities, while the decrease in pH, which took place later, was caused by ammonium volatilisation. Similar profiles have been observed in other composting processes using raw materials like de-inking paper sludge (Charest and Beauchamp, 2002), and citrus waste (Van Heerden et al., 2002). Nevertheless, our results showed a short initial period (about 3–4 d) with a high pH, while the elevated pH in other works lasted longer. This fact could be related with the characteristics of the raw materials in our piles which resulted in less release of NH3.

Full-size image (13K)

Fig. 1. Changes in pH (a), and C/N ratio (b) during composting of rice straw and sewage sludge. Bars represent standard deviations. P1 (■), P2 (□)

The initial C/N ratio of the composting blend was 18 (P1) and 20 (P2), and these values decreased approximately to 10 in both piles after 90 d (Table 2). Firstly, this parameter increased in both cases, which was due to an initially strong nitrogen loss in the form of ammonium; later, the C/N ratio tends to decrease during the process (Fig. 1b), which is likely due to an effect of the N concentration caused by a release of C in the form of CO2, and also to water loss through evaporation during the mineralisation of organic matter. These facts agree with those reported by Kapetanios et al. (1993), and Fang et al. (1999). Moreover, the pH and C/N ratio values in the final composts indicated good compost development in both piles in relation to organic matter biodegradation; in this sense, it is well-known that mineral soils with a high soil organic matter content (8–20%), a neutral pH, and a C/N ratio of about 10, showed a high level of biodegradation and humification of fresh soil organic matter.

3.3. Compost maturityThe virtual absence of ammonium nitrogen in the final compost is a good indicator of their maturity (Riffaldi et al., 1986). In this study the NH4-N content, in the final

composts, was 120 and 540 mg kg−1 in P1 and P2, respectively; these facts were consistent with other reports ([Riffaldi et al., 1986] and [Zucconi and De Bertoldi, 1987]); thus, Zucconi and De Bertoldi (1987) established that an ammonium nitrogen value below

400 mg kg−1 indicates mature compost; this may indicate that the composting process of P2 was slower. These facts are directly related to the increased EC which is due to material losses caused by organic matter biodegradation, evaporation, volatilisation and subsequent concentration, all of which are typical composting process mechanisms. This verification is robust and is done upon the basis of weight loss, oxidizable organic carbon, total organic matter and (Table 2).

Although no universally accepted criterion exists, it is known that CEC, CHA/CFA, COD and GI are good indicators of maturity and compost quality. The values obtained for these indicators are shown in Table 2. In this study, the CEC values obtained in the compost were 108 (P1) and 98 (P2) cmol(+) kg−1; these values were higher than 60 cmol(+) kg−1. By using the criterion of Harada et al. (1981), these results indicated that both

composts were mature. The CHA/CFA ratio may be considered an indicative parameter of either the polymerisation grade or the molecule size of the humus-type polymers (Iglesias and Pérez, 1992). The compost obtained in P1 presented a CHA/CFA ratio of 1.40, whereas that of P2 was 0.48. Iglesias and Pérez (1992) considered that a compost

was mature when this ratio exceeded 1; given this parameter, we can therefore consider that the final product of P2 was not mature compost. This result contrasted with that reported by Bustamante et al. (2008) while co-composting distillery wastes with animal manures. This report indicated that the CEC revealed major organic matter humification in contrast with the humification ratio and the humification index. The conclusion drawn was that humification indexes did not show the expected evolution and that they could not be used to assess compost maturity. In this study, the values obtained with CEC and the CHA/CFA ratio in both composts, in relation to the initial values of the blends, revealed how the composting process contributes greatly to organic matter humification; however, the CHA/CFA ratio was more selective than CEC to be able to differentiate compost maturity in relation to the composting monitoring process.

Another analysis to assess compost stability is COD (Lossin, 1971). When comparing the COD values at the start and the end of the process, the initial COD values of both piles were higher than those obtained at the end of the process as a result of biological activity and organic matter biodegradation. We observed a substantial reduction of this parameter in both composts which indicated a good stability grade.

The GI is a parameter used to assess phytotoxicity; if its value is below 50%, the compost presents high phytotoxicity ([Zucconi et al., 1981] and [Solano et al., 2001]). The results obtained after 90 d of composting reveal that germination percentage in both piles was over 50%. It should be highlighted that this percentage in the P1 compost was higher (106%) than that obtained in P2 (86%). In short, our results showed that, when studying the different parameters related with the compost maturity status, only the

compost obtained from P1 was positive in all the maturity analyses carried out.

3.4. Effect of compost application on soil properties and H. vulgare growthThe agricultural use of an organic amendment such as compost with sewage sludge, which contains a relatively high content of salts and heavy metals, may seem hazardous for soils and crops, and such measures must be assessed and controlled. However, this kind of

compost provides nutrients and organic matter to the soil–plant system which must also have to be studied. The final objective is clear: suitable handling and avoiding unnecessary environmental risks.

The effect of applying compost based on sewage sludge on the soil–plant system has been widely studied by many authors. Thus, applying compost or sludges on soil improved physical properties ([Caravaca et al., 2002] and [González and Cooperband, 2002]), increased nutrient content ([De Melo et al., 2002] and [Korboulewsky et al., 2002]), fertility (Madejón et al., 2003), and biological and enzymatic activity (Bulluck et al., 2002). It has also been verified that adequate doses of municipal solid waste compost -amended soil improved the mineral nutrition of plants when the soil was poorly fertile as a result of an increase of SOM ([Bulluck et al., 2002], [Madejón et al., 2003] and [Abdelhamid et al., 2004]); otherwise it may be used within the safety limits as an organic supplement (Bhattacharyya et al., 2005), as an alternative to cattle manure for supplying lowland rice with potassium (Bhattacharyya et al., 2007), or for increasing the plant-available concentration of heavy metals from amended-soil (Walker et al., 2004), etc. Nonetheless, very few works have been conducted which assess the effect of applying compost and which also study the optimum dose and the limiting factor for its use. For such reasons, this work, on the one hand, has assessed the effect of applying different doses of mature quality compost (the compost from P1) as an organic amendment on some physical, chemical and nutritional properties of one soil in which vegetable crops were grown under plastic (greenhouse sandy soil, albic Arenosol) and of another in which citrus fruits were grown (clayey soil, calcaric Luvisol) (Table 4). On the other hand, this study has studied the effect on barley growth (H. vulgare L.) under laboratory conditions. It is very important to know these aspects as they may help to lay the foundations towards the complete recycling of these residues in Valencia as the place where they are produced, the location of the sewage water plant and the soils to which the compost is applied, are only a few km distance and would, therefore, avoid the very high costs involved in transporting the materials.

Table 4.

Physical and chemical properties of sandy and clayey amended-soils with different doses of compost from P1. Mean (standard deviation).

Compost dose %

w/w

pH 1:2.5 H2Oa

EC 1:5 dS m−125 °C

TKN (%)P2O5 mg 100 g−1 SOM (%) SA (%)

Sandy soil

09.22–9.34

0.04 (0.01) 0.00(0.00) 0.0 (0.0)0.08 (0.00)

0.40 (0.05)

17.60–7.96

0.16 (0.02) 0.00(0.00) 5.5 (0.6)0.29 (0.06)

0.70 (0.06)

2 6.84– 0.40 (0.09) 0.03(0.04) 15.5(1.3) 0.71 0.85

Compost dose %

w/w

pH 1:2.5 H2Oa

EC 1:5 dS m−125 °C

TKN (%)P2O5 mg 100 g−1 SOM (%) SA (%)

7.46 (0.07) (0.06)

46.75–7.01

0.57 (0.02) 0.09(0.00) 23.2(1.4)1.64 (0.02)

1.39(0.10)

66.37–6.99

1.14 (0.28) 0.16(0.01) 29.3(1.9)2.81 (0.11)

1.70 (0.22)

106.45–6.81

1.45 (0.03)0.22 (0.06)

39.8 (2.9)4.28 (0.67)

4.50 (0.58)

206.24–6.70

2.68 (0.21)0.42 (0.10)

57.4 (4.5) 8.49(0.17)9.50 (0.99)

Clayey soil

0.07.94–8.06

0.21 (0.06) 0.19(0.06) 13.8(1.1)2.68 (0.25)

21(1)

0.27.88–7.98

0.31 (0.09)0.21 (0.09)

15.6 (0.9) 2.78(0.19) 25(2)

0.87.81–7.97

0.42 (0.05)0.24 (0.04)

18.5(1.3)2.91 (0.28)

27(2)

1.57.65–7.83

0.48 (0.09)0.29 (0.09)

21.2(1.8)3.21 (0.31)

30(4)

3.07.45–7.55

0.70 (0.06)0.35 (0.12)

25.3(1.9)3.81 (0.20)

37(2)

6.06.75–7.25

1.15(0.10)0.48 (0.07)

39.8 (3.4)5.01 (0.67)

42(5)

EC: electrical conductivity; TKN: total Kjeldahl nitrogen; SOM: soil organic matter; SA: stable aggregates.

a Range.

In general, the results obtained showed that dose- compost application decreases the pH, and increases SOM, N, P, SA and EC from both the amended soils. These data agree with the results reported by (Bulluck et al., 2002), (Caravaca et al., 2002), (Korboulewsky et al., 2002), (Madejón et al., 2003), (Abdelhamid et al., 2004) and (Walker et al., 2004) and Bhattacharyya et al. (2005), among others, and they indicate that compost -amended soil improves soil properties and fertility. Soil reaction is a chemical property that is directly related with soil fertility. In our study, the drop in the pH was accounted for by the huge effect that organic matter has on soil; indeed, the pH dropped rapidly when compost was applied. This is an extremely positive effect on basic soils of a calcareous nature and one that will contribute to the bioavailability of micronutrients like Fe to minimise the ferric chlorosis problem. This drop in pH, along with the increase of the SOM, N and P contents, is another positive and outstanding fact, and suggests that solubility in field conditions may take place in a parallel fashion. This is particularly interesting with P and Fe as it may well be related with their increased mobility owing to the drop in pH which takes place when this type of soils has been amended with organic matter.

Furthermore from the soil fertility viewpoint, physical properties are fundamental for the adequate development of the plant’s root system. The relationships between the soil’s physical conditions and plant growth are highly complex, but it is totally accepted that roots must do a job that not only depends on a pressure that must be overcome, but also on the volume of soil to be moved. Thus, root growth takes place effortlessly in well-structured soils of good porosity, decent thickness and suitable bulk density. In this work we verified that the process of applying compost reduced the bulk density in both soils (data not shown) and also increased the amount of SA (Table 4). This improvement of the soil’s physical fertility was also due to the supply of organic matter as a result of adding compost, which improved soil structure and, in turn and most probably, encouraged porosity- and water retention-related properties.

Nonetheless, doses over 2% in sandy soil and 0.8% in clayey soil considerably increased EC values (Table 4). It is well-known that EC (1:5 w/v soil-extracts) values over 0.4 dS m−1 lead to salinity problems in soils. So by applying this criterion, the adequate doses of our compost were calculated at 34 Mg ha−1 for sandy soil and 11 Mg ha−1 for clayey soil, estimated at 1000 m3 of soil volume. This difference between the doses in our soils is logical as soils with a sandy texture require a greater amount of organic matter than clayey soils for any effects to be noted. It is also interesting to stress that, from a residue minimisation viewpoint; these doses could be increased if we were to consider that both soils are actually of a depth higher than 10 cm.

With regard to the risk of heavy metal pollution to soils, if we apply these doses and bear in mind the Royal Decree RD 1310/1990 on the application of sludges, the amount of heavy metals involved does not, hypothetically, represent a risk of heavy metal accumulation in

soils. In addition, it should be pointed out that the heavy metals in the Mediterranean soils where they accumulate present a very low bioavailability ([Gímeno-García et al., 1995] and [Romaguera et al., 2008]).

All the aforementioned demonstrate that soil indeed directly responds to this type of compost, and that there is no limit to doses in terms of pH, SOM, N, P and SA. Nonetheless, the effect on EC indicated, a priori, that increased soil salinity may be a limiting factor for this kind of compost to be used in agriculture. This affirmation, along with the fact that the difference obtained in the doses to be applied in accordance with the soil type suggests the need of adequate information in order to handle compost in accordance with soil conditions.

Finally, the effect of applying sewage sludge-derived compost on the plant has also been thoroughly studied. Therefore, steps were taken to verify that this application increased the nutrient content on lettuce ([Simeoni et al., 1984] and [Xu et al., 2004]), orange (Madejón et al., 2003) and largeleaf pondweed (Cronin and Lodge, 2003) production. In the two experiments realised in this study, when determining the length and weight of the root and the shoot separately, the plant response was noted in the form of a typical dose–reponse curve according to the concentration of a nutrient (data not shown). Nonetheless, and for the purpose of assessing the effect of applying our compost on mineral nutrition and plant growth at the same time, an index was employed which jointly assessed root and shoot development, this being the R/S ratio expressed as dry matter. A drop in the R/S ratio clearly indicates more suitable nutritional characteristics which lead to better plant growth (Maschnner, 1995). Then, based on the results obtained from determining this index, applying our compost to soil at the various indicated doses brought about a positive response of barley growth which was grown under laboratory conditions (Fig. 2). This figure clearly illustrates that all the doses applied, except for 100% (R/S = 0.92), encouraged better plant growth in relation to the control (R/S = 0.83 to sandy soil and R/S = 0.79 to clayey soil); in relation to barley, this indicates that all the doses, except for raw compost, are feasible. This may be due to the excellent tolerance of this plant to salinity. Nonetheless, the variability of the R/S relationship in terms of the compost doses applied to soil indicated that the lowest R/S ratio values were 0.37 for barley grown in sandy soil with doses of 4 and 6% (Fig. 2a), and 0.45 for barley grown in clayey soil with a dose of 0.8% (Fig. 2b). Any doses either higher or lower than these triggered the inverse plant performance as the R/S ratio value increased. These facts, along with the effect of the compost on soils, undoubtedly confirmed that the optimum dose to obtain the best effect on the soil–plant system were 34 Mg ha−1 for sandy soil and 11 Mg ha−1 for clayey soil. In addition, the main limiting factor of this type of compost to be used in agriculture is not the effect it had on barley, rather the increased on soil salinity. This affirmation is very important as we have not found any such assertion in the bibliography we consulted, which indicates the need to assess the compost dose–response effect on different soil–plant systems.

Full-size image (21K)

Fig. 2. Effect of compost doses amended-soils on the root/shoot (R/S) ratio of Hordeum vulgare plants in pot experiments: (a) sandy soil; (b) clayey soil.

4. Conclusions

The results obtained confirmed that rice straw and sewage sludge generated in Valencia (E. Spain) to be used, alone, in a composting process are highly compatible. Two experiments were carried out whose variable was shredded and non-shredded rice straw. In general, both experiments showed a similar pattern of performance; however, after 90 d of composting, the most selective parameters of the process development, as well as the compost maturity

indicators, were the rejected material and compost structure, the maximum temperatures reached and the times at which the temperatures remained above 55 °C, the

content, and CHA/CFA ratio. This, undoubtedly, confirmed that shredding rice straw is necessary prior to preparing a good blend in order to favour composting process of these wastes and to guarantee quality compost in sanitisation terms.

A sandy soil and a clayey soil were amended with different doses of mature compost which were, in turn, strewed with barley seeds. The results indicated a direct soil and

plant response with the different doses of this type of compost. There was no limit noted of the dose to be applied when assessing the pH, organic matter, N, P and SA in the soil and barley growth. Nonetheless, the effect on both the EC of the soil and root growth indicated that the increased salinity in the soil was the limiting factor of this type of compost for it to be used in agriculture. Also, results suggest the need for suitable information in order to handle the compost in accordance with each soil–plant system condition.

Future composting experiments on an industrial scale and steps to compost -amended-soil on a field scale must be carried out with the purpose of confirming the results obtained in this work and to make a treatment process available which is compatible with sustainable development.

Acknowledgements

The authors wish to thank the regional government (Generalitat Valenciana: GV-CAPA00-03), the City Council of Valencia (BIOCOMPOST project), the Ministry of the Environment

(MMA 4.3-141/2005/3-B) and the Ministry of Education and Science (CGL2006-09776) for their financial support.

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Effects of pulp mill solids and three composts on early growth of tomatoes

J. Simone Levy and Barry R. Taylor ,

Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia, Canada B0H 1X0

Received 9 September 2002;

revised 27 January 2003;

accepted 9 February 2003. ;

Available online 1 April 2003.

Abstract

Compost has been proposed as a means of simultaneously diverting organic materials from landfills while producing a valuable product that improves tilth, organic matter content and nutrient supply of agricultural soils. Composts manufactured from different source materials may have markedly different properties however, even if they meet all regulatory requirements. We compared the capacity of composts made from three different combinations of organic wastes (horse manure and bedding, mink farm wastes, municipal solid waste (MSW) and sewage sludge) along with clarifier solids from a chemo-thermomechanical pulp mill, to enhance the growth of tomato (Lycopersicon

esculentum L.) seedlings grown in nutrient-poor organic potting soil. Germination and seedling emergence of tomatoes, cress (Lapidium sativum L.) or radish (Raphanus sativus L.) were tested to assess phytotoxicity of the four amendments. Mink farm compost and horse manure compost stimulated root and shoot growth of tomato seedlings but MSW compost and pulp mill solids were strongly inhibitory. MSW compost and unamended potting soil also inhibited seedling emergence and pulp mill solids produced stunting and deformities in radish and cress seedlings. Both toxic constituents and nutrient imbalances may be responsible for the growth-inhibiting effects of these amendments. Application of pulp mill solids to agricultural soil without composting may lead to deleterious effects on vegetable crops.

Author Keywords: Compost ; Pulp mill solids; Growth rates; Phytotoxicity

Article Outline

1. Introduction

2. Methods

2.1. Soil amendments

2.2. Tomato seedling emergence and growth

2.3. Toxicity tests

2.4. Statistical analysis

3. Results

3.1. Emergence of tomato seedlings

3.2. Growth of tomato seedlings

3.3. Toxicity tests

4. Discussion

5. Conclusions

Acknowledgements

References

1. Introduction

Commercial production of compost from organic materials produced by farms, households or industries has been promoted as a means of simultaneously reducing the volume of organic wastes being dumped in landfills while producing a useful product that benefits gardens and agricultural soils. Compost can act as an effective surface mulch, increase the concentration of soil organic matter, improve tilth and water-holding capacity, suppress weeds, and provide a long-term supply of nutrients as the organic material decomposes (Ozores-Hampton and Obreza, 1999; Evanylo and Daniels, 1999). For these

reasons, composting has been advocated as one component of sustainable agriculture ( Arrougé et al., 1999; Edwards et al., 2000).

One of the barriers to large-scale use of composts and similar soil amendments made from waste materials is the need for a product of consistent and predictable quality (Baarth, 1999). Different varieties of the same product, as produced by different processes or manufacturers, must have essentially similar benefits for plant production if the amendment is to be used for agriculture or horticulture. Maintaining predictable compost quality is a particular problem when the material is produced from sources such as municipal solid waste (MSW), pulp mill solids or feedlot waste as a means of reducing an organic waste stream. In these operations, the process must be optimized for both efficiency of waste disposal and quality of end product, which demands that some compromise be made in both.

Most jurisdictions in North America and Europe now have regulations stipulating the minimum quality standards which composts must meet for commercial sale (CCME, 1997; Baarth, 1999). Nevertheless, composts from different feedstocks or prepared by different methods can have significantly different chemical compositions even while meeting regulatory standards for nutrient content, maturity and physical composition. The chemical structure of the organic material in compost can vary in numerous ways that are non-linear and difficult to quantify. If these differences translate into difference in soil-amendment properties or fertilizer value, they hinder the expansion of compost use because the quality of different materials is unpredictable.

An important source of organic material for composting or soil restoration that is largely untapped is solid waste from the pulp and paper industry. Settled solids from the wastewater treatment plant of a typical pulp mill consist of expanded fibres of pulverized wood, rich in lignin and unused cellulose but low in soluble organic substances. Some nitrogen and phosphorus may be added during wastewater processing to speed decomposition (Evanylo and Daniels, 1999). Even after settling and drying, the solids have a high water content ( Thompson et al., 2001).

Disposal of this material, variously referred to as clarifier solids or pulp mill sludge, presents a problem for the mill. Some of it may be incinerated, but the high water content impedes efficient combustion. Disposal by landfilling, the most common disposal method, is costly and faces increasingly stringent environmental regulations (Arrougé et al., 1999; Jackson et al., 2000). Using settled solids as a soil amendment on farmland is an attractive alternative because it allows for some cost recovery, improves soil physical properties and recycles the carbon into the soil ( Chantigny et al., 2000; Gagnon et al., 2001).

A number of researchers have reported substantial benefits to physical characteristics of low-carbon soils from amendment with pulp mill solids or de-inking paper sludge (Fahmy et al., 1999; Chantigny et al., 1999 and Chantigny et al., 2000; Gagnon et al., 2001). Benefits include increased organic matter content, augmented formation of macroaggregates, improved moisture-holding capacity and stimulated bacterial enzyme activity. The pulp mill solids may be biologically active, however, and their chemical composition may be unstable because decomposition is still actively proceeding. The carbon:nutrient ratios are likely to be high; the only significant N or P content is that which is added during wastewater treatment. These properties could cause unpredictable or detrimental effects on crops through phytotoxicity ( Evanylo and Daniels, 1999) or immobilization of nitrogen ( Bellamy et al., 1995; Simard et al., 1998). Cocomposting with a complementary high-nitrogen feedstock

may relieve these deficiencies while maintaining the soil-building properties of the wood residues ( Arrougé et al., 1999; Baziramakenga et al., 2001).

In this study, we examined the growth-promoting properties of compost produced from three very different feedstocks and composting processes, along with clarifier solids from a pulp mill that are currently being applied to farmland. Our hypothesis was that chemical quality of the initial feedstocks would be reflected in the final products, and hence predictable differences in early growth of a crop plant (tomato) would be produced from the different composts. We also hypothesized that the clarifier solids would prove less beneficial to plant growth than compost because of their instability and high carbon:nitrogen ratio. We suspected that phytotoxicity from clarifier solids might reduce their value as a soil amendment.

2. Methods

2.1. Soil amendmentsWe used experimental compost of three kinds in these experiments (Table 1). Race Track compost was manufactured in static piles using horse manure and bedding straw from a stable. Mink compost was made by an in-vessel process from bedding material and pelted carcasses from a mink farm. Both composts were cured for several months after the thermal phase had finished. The third compost was produced from combined sewage sludge and MSW from the Municipality of Lunenburg, Nova Scotia. The Lunenburg facility uses a rolling drum to mix and aerate the feedstocks continuously during the thermophilic stage of composting. The fresh compost is then cured for several months on a concrete pad. The compost in our sample was produced at Lunenburg in 1998; the composting process used there has since been modified.

Table 1. Chemical composition (g kg−1), pH, electrical conductivity (EC, mS cm−1) and respiration rate (mg CO2 g−1 d−1) of the composts and pulp mill solids

Figures in parentheses are standard deviations.

Our fourth organic soil amendment was settled clarifier solids from a local pulp mill. The mill uses a chemo-thermomechanical process to separate cellulose from softwood feedstock, mostly spruce and balsam fir. No chlorine is used in the mill. Wastewaters from the pulping process are treated in aerated lagoons with additions of nitrogen and phosphorus to speed microbial degradation. Settled solids from the second lagoon are dewatered to produced a grey, wet, low-density material consisting mostly of semi-decomposed, pulverized wood fragments. Some of this material is now being used as a composting feedstock, but previously it was applied directly to farmland.

The four soil amendments varied substantially in their physical and chemical properties (Table 1). Reaction ranges from acid to circumneutral. Salinity, as estimated from electrical conductivity, was higher in the three composts than in the pulp mill solids. MSW

compost would be considered slightly saline; the other materials were non-saline.

All three composts were rich in nitrogen, leading to low C:N ratios and presumably rapid release of N. The C:N ratio for pulp mill solids, on the other hand, was well over 30, suggesting that N might be immobilized or slowly released from this material, at least initially. All four amendments were enriched in phosphorus, as judged by C:P ratios, although the pulp mill solids were less extremely so than the composts (Table 1).

Rates of microbial respiration on the three composts were low and similar, as would be expected for mature organic matter. The clarifier solids, however, still supported a vigorous microbial community, as indicated by respiration rates 5–8 times higher than that of

composts (Table 1). Respiration rates of clarifiers solids were correspondingly more variable among samples and through time.

The amendments also varied in particle size, as determined by wet sieving (Fig. 1). MSW compost was dense and contained a greater proportion of the largest particles (>4

mm) than the other two composts. Mink compost, by contrast, was very fine, and was over 40% composed of particles <2 mm diameter. The pulp mill solids stood apart from the composts by the near total absence of fine particles (0.15%). This material was a wet, sticky mass of light fragments. Our sample was 80% moisture.

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Fig. 1. Proportions of three particle sizes (wet sieved) in three kinds of compost and clarified solids from a pulp mill.

2.2. Tomato seedling emergence and growthWe tested the efficacy of the three composts and pulp mill solids to enhance germination and growth of tomato seedlings. We chose tomatoes (Lycopersicon esculentum L.) because they are a common vegetable crop, the plants are demanding of nitrogen, they grow quickly and are easy to grow in pots under lights. Our study concentrated on the early growth stages of the plants, where nutrient deficiencies or inhibitory effects were likely to be most apparent, and therefore differences among treatments would be easiest to observe. We counted the number of shoots successfully emerging from the soil and measured the growth rates of the seedlings. The latter measurements

reveal the growth promoting potential of the amendments, while the former reveals any phytotoxicity. Subsequent experiments (toxicity tests) examined phytotoxicity more closely.

Tomatoes were grown in square plastic pots, 9 cm (3.5 in.) in top width by 10 cm high. Six aliquots of each soil amendment were combined with potting soil in a 50:50 v/v ratio and thoroughly mixed. Because of differences in density and moisture content, the mass of compost differed between treatments. Volume aliquots more closely reflect how composts are applied to fields and gardens. We chose a high ratio of compost to soil to exaggerate the effects of soil amendments and thereby make treatment differences easier to observe.

The soil used for mixing was a commercial potting soil (pH 5.6), sold locally in garden stores. It consisted of finely divided peat augmented with perlite and vermiculite to enhance aeration. There was no other mineral content. Although branded a “potting soil”, this material is impoverished in nutrients, especially N, and produces poor plant growth without fertilizer. It therefore served as a neutral control against which to compare the stimulatory effects of the amendments. Six control pots filled with potting soil alone were included in the experiment.

Five tomato seeds (“Purple Prince”, McKenzie Seeds, Brandon, MB) were planted in each pot. Pots were maintained under fluorescent “grow lights” maintained approximately 5 cm from the tops of the plants. Light intensity at the leaf tops (mean ± SD) was 64 ± 6.9 μmol photons m−2 s−1. Pots were maintained under a 16:8 h light:dark cycle. Pots were watered with room-temperature, dechlorinated Antigonish tap water as needed. Pots were placed in random order under the lights and re-arranged every two days.

The number of seedlings successfully emerging in each pot was recorded for each treatment after one week and again after two weeks. Beginning in the second week, and continuing for the next eight weeks, the height of the stem from soil to the base of the top leaves was measured. After four weeks, when individual seedlings began to be crowded, plants were thinned to two per pot by cutting off the smaller individuals with a razor blade at soil level. Data are reported as means for each pot regardless of the number of stems.

After nine weeks the plants had reached the capacity of the pots. Along with the final height measurement, the number of leaves and the length of the longest leaf on each plant were also determined. Plants were then removed from the pots and separated from soil by gentle washing under flowing water. Plants were divided into roots and shoots by cutting at soil level with a razor blade. Average dry mass of roots and shoots from each pot was determined after drying at 70 °C for 48 h.

2.3. Toxicity testsGermination and early growth of tomatoes suggested phytotoxicity in some treatments. Therefore, all four soil amendments, as well as potting soil, were assessed for phytotoxic potential using seed germination and seedling emergence tests. The methods used were modifications of established toxicity tests used in the assessment of composts and contaminated soil (Warman, 1999; Kapanen and Itävaara, 2001).

Water-soluble material was extracted from three replicates of each amendment and potting soil by adding 60 ml of soil or amendment, representing 12–34 g dry mass, to 120 ml distilled water in a 250-ml beaker and agitating gently on a shaker for 1 h. A sample of the elutriate was then decanted from the beakers and clarified by filtration under suction through a

Whatman #1 glass-fibre filter. To test germination, 5 ml of each elutriate was added to the bottom of a petri dish containing a glass-fibre filter to imbibe the water. Five radish seeds (Raphanus sativus L. “Scarlet Globe”, McKenzie Seeds, Brandon, MB) were placed in each dish, covered, and incubated at room-temperature (23 °C) in darkness for 5 d. Successful germination was taken as unambiguous emergence of both the epicotyl and the hypocotyl. Controls were germinated in distilled water.

Several tests were carried out to explore the unexpectedly low tomato seed germination in soil mixed with MSW compost (see Section 3). A dilution assay was used to quantify the strength of phytotoxicity. Because the potting soil itself appeared to be slightly inhibitory of seed germination, this experiment used a local silt-loam soil (pH 5.0) as diluent. The sieved soil (<2 mm) was taken from the A horizon of a stony, Humo-Ferric Podzol developed in a river floodplain near Antigonish and was typical of agricultural land in northern Nova Scotia. MSW compost was diluted with field soil to create compost concentrations of 100%, 50%, 25% and 12.5% by volume. The compost

was coarse-sieved (<4 mm) to remove large particles. Five replicates of each dilution were used to fill square plastic pots, 7 cm (2.75 in.) in width and 5.5 cm tall. Each pot was planted with five radish seeds, remoistened with an atomizer, covered in transparent plastic to retain moisture, and incubated under ambient light for one week. Controls used 100% field soil.

Phytotoxicity in MSW compost may have been associated with its relatively high pH (Table 1). To test this possibility, we lowered the pH of a well-mixed, 400-ml sample of

MSW compost to 5.3 from 7.4 by adding 3 ml dry weight of low-molecular-weight organic acids (a mixture of tartaric, malic and citric acids). Three replicate, 7-cm pots were filled with pH-adjusted MSW compost and five tomato seeds were planted in each. Silt-loam field soil was used as a control. Emergence was scored after five days, when control pots had achieved >80% emergence. The plants were maintained for three weeks under ambient light, watered as needed with room-temperature, dechlorinated tap water. Height of each plant was then measured.

Effect of pulp mill solids on seedling emergence was tested with seeds of both radish and cress (Lepidium sativum L. “Extra Triple Curled”). Six replicate 7-cm pots were filled with either pulp mill solids or potting soil (control). For each of the two test species, five seeds were planted in each pot, covered with soil or pulp mill solids, moistened with distilled water, and incubated at room-temperature, under grow lights, for five days. Successful emergence was taken as extension of the epicotyl out of the soil and spreading of the cotyledons. After 18 days, (watered as needed with distilled water) the seedlings were assessed visually for stunting and deformity using a subjective scale from 1 (no difference from control) to 3 (severe stunting or deformity). Results are expressed as the average for each pot.

2.4. Statistical analysis

Weekly data on growth of tomatoes were analysed using Analysis of Variance for a repeated-measures design, followed by Tukey’s Multiple Comparisons Test, where appropriate, to separate significantly different treatments. Scheffé’s Test (Zar, 1996) was used to compare specific pairs or groups of treatments. Tomato leaf length and root and shoot weights, as well as seedling germination and emergence tests and chemical measurements, were all compared

using one-way Analysis of Variance followed by Tukey’s Test or Scheffé’s Test. All statistical analysis used the STATISTIX software package (Analytical Software, 1999).

3. Results

3.1. Emergence of tomato seedlingsThere were clear differences in the success of tomato seedling germination and emergence among the different organic amendments. MSW compost was strongly inhibitory: no seedlings emerged in this treatment in the first week, out of 30 seeds planted (Fig. 2(a)). The potting soil itself also inhibited germination (mean 1.2 seedlings emerged out of 5 after 1 week), as did the mink compost. Race track compost and pulp mill solids produced the most rapid emergence, averaging over 70% after one week (Fig. 2(a)).

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Fig. 2. Success of emergence of tomato seedlings (a) one week or (b) two weeks after planting in peat-based potting soil mixed with compost or pulp mill solids (50:50, v:v). Error bars are standard deviations. Columns with the same letter above them are not significantly different (p<0.05).

By the end of the second week, germination was far more complete in all treatments. Nevertheless, significant differences remained (Fig. 2(b)). All the seedlings emerged from the Race Track treatment, and over 80% emerged from Mink and Pulp Mill Solids. There was still significant inhibition in the potting soil (62% emergence) and the MSW compost (50% emergence). No seedlings emerged in two of the six replicates in the MSW compost treatment. No more seedlings emerged in any treatment after two weeks.

3.2. Growth of tomato seedlingsGrowth of the emerged seedlings was rapid in all treatments initially but declined toward the end of the experiment, probably because the plants were becoming limited by the size of the pots (Fig. 3). ANOVA on growth rates identified two distinct groups (p<0.05). Growth rates in Mink compost and Race Track compost were similar to that in potting soil, while rates in MSW compost or pulp mill solids were significantly slower. There were no differences in growth rate within either of these two groups. The difference in growth rate was apparent from the outset of the experiment, and remained more or less constant for the duration (Fig. 3).

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Fig. 3. Growth of tomato seedlings in peat-based potting soil amended with composts or pulp mill solids. Different letters indicate significantly different growth rates over the

9-week experiment. Vertical bar shows the average standard deviation.

The differences in growth rate among the treatments was reflected in the final masses of the plants. Final shoot mass in mink compost was significantly greater than shoot mass in all other treatments (Fig. 4). ANOVA and Tukey’s Test separated the remaining treatments into three overlapping groups, with Race Track compost at one end and Pulp Mill solids at the other (Fig. 4). Shoot mass in pulp mill solids was significantly less than in all other treatments except MSW

compost (p<0.05). Final shoot mass in the pulp mill solids was barely one-third of that in Mink compost (Fig. 4).

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Fig. 4. Final dry mass of tomato shoots (above the zero line) and roots (below the zero line) after nine weeks, with significant differences (p<0.05) indicated by different letters. Error bars are standard deviations.

Differences in root mass of tomato seedlings at the end of the experiment paralleled those for shoots but were less pronounced. ANOVA and Tukey’s Test recognized three overlapping groups of treatments, running from largest (mink compost) to smallest (potting soil) in the order listed in Fig. 4. Tomatoes grown in pulp mill solids, which produced tomatoes with the smallest shoot mass, also produced the smallest root mass among all the amendments. Tomato root mass in pulp mill solids and potting soil were not significantly different, but root mass in pulp mill solids was significantly less than the average for all three composts (Scheffé ’s Test, p<0.05).

There were only small differences among treatments in number of leaves per plant and length of the longest leaf (Table 2). Tomato seedlings in mink compost had the largest leaves and the greatest number of them, while those in potting soil had the least. The remaining treatments ranged between these extremes in the same order as growth rates (Fig. 4), though few of the treatment differences were significant. Mean leaf length of tomatoes grown in pulp mill solids was significantly less than the mean for all compost amendments (Scheffé’s Test, p<0.05), but there was no difference in mean number of leaves.

Table 2. Number of leaves per plant and length of the longest leaf from tomato plants grown in peat-based potting soil amended with compost or pulp mill solids

Data are means and (standard errors). Means in the same column superscripted with the same letter are not significantly different (p<0.05).

3.3. Toxicity testsPoor emergence of tomato seedlings in the MSW compost treatment and potting soil, as well as poor growth in pulp mill solids, suggests that some of these amendments may be phytotoxic. None of the aqueous extracts from composts, pulp mill solids, or potting soil inhibited germination of radish seeds. Mean germination in all treatments was at least 94% (100% in extract from Race Track compost) , and not significantly different (p>0.05) from germination in distilled water (100%).

Emergence tests with whole amendments produced stronger evidence of phytotoxicity. In the serial dilution assay, undiluted MSW compost produced severe inhibition of seedling emergence: Only one seed successfully germinated and emerged in any of the five replicate pots, a 4% success rate (Fig. 5). Toxicity diminished swiftly with dilution: emergence success in 50% MSW compost and lower dilutions averaged at least 92%, marginally better than in the field soil used as a control (84%). Hence, phytotoxicity in MSW compost appears only at very high concentrations, which may not commonly occur in the field.

Full-size image (9K)

Fig. 5. Success of emergence of radish seedlings one week after planting in MSW compost diluted with silt-loam soil (control). Error bars are standard deviations. Columns with the same letter above them are not significantly different (p<0.05).

The phytotoxicity of MSW compost was reversed by lowering the pH. Mean emergence success of tomatoes in undiluted MSW compost adjusted to pH 5.3 was 86%, again slightly better than in the field-soil control (80%). Mean stem height after 3 weeks (±SD) was 86.2 ± 20.7 mm in the MSW compost and 80.8 ± 13.1 mm in soil, a non-significant difference (p>0.05).

Undiluted pulp mill solids did not inhibit germination of either radish or cress, but did produce serious growth inhibition. Mean seedling emergence of radish in pulp mill solids was 90%, not significantly less than in control soil (100%). Emergence was slightly less successful for cress in pulp mill solids (83%) but still not significantly different from controls (93%). Both species suffered serious deformity when germinated in pulp mill solids, however. On the three-step scale of stunting and deformity compared with control seedlings, all the replicates of cress scored 2 or 3 (mean 2.8) and all but one of the radish replicates scored 2 or 3 (mean 2.2). These seedlings were smaller, lighter coloured and misshapen (curled) compared with the seedlings growing in soil, and had necrotic patches on the leaves.

4. Discussion

The four organic amendments used in these experiments did produce conspicuous differences in growth of young tomatoes. Our original hypothesis that the growth response would be predictable from the origins and chemistry of the amendments was supported by the response to two of the composts and to fresh clarifier solids from a pulp mill. The potting soil was an appropriate negative control for these experiments because it provided physical support and water holding capacity for the plants but little in the way of mineral nutrition. Therefore the nutritive value of any soil amendment can be judged by the degree of stimulation of plant growth which it produces when added to potting soil.

The strongest growth stimulation was observed in treatments with mink-farm compost and race track compost, both of which were chemically stable and rich in both

nitrogen and phosphorus. The greater final mass in the mink compost treatment compared with the race track treatment does not correspond exactly with their relative C:N or C:P ratios (both are slightly greater in race track compost) , but the differences between them are too small to distinguish. While tomatoes grown in potting soil alone increased in stem length at the same rate as the mink and race track treatments, the plants in

compost -amended treatments were bushier and leafier, which translated into a substantially greater aboveground mass at the end of the experiment.

In contrast, plants grown in high concentrations of clarifier solids from a pulp mill grew more slowly than plants in most other composts (except MSW), and were dramatically smaller both above and below ground at the end of the experiment. Tomatoes in this treatment were even smaller and less vigorous than those grown in potting soil alone. Again, the poor value of pulp mill solids as a soil amendment is not unexpected given their chemical composition. This material, being largely pulverized wood fragments enriched with nutrients to speed decomposition, is lower in N concentration than any of the composts tested (Table 1). The high C:N ratio (36:1) and rapid respiration rate of pulp mill solids imply that strong immobilization of N by an actively growing microbial community is likely. Plants in this treatment had thin, spindly stems and were all falling over by the end of the experiment, which is consistent with N deficiency. Experiments with cress and radish also showed strong evidence of nutrient deficiencies or imbalance within two weeks of seedling emergence.

The severity of the growth impairment we observed is perhaps surprising given that the C:N ratio of the pulp mill solids we used (36:1) was relatively low for wood residues. Similar materials used elsewhere have had C:N ratios in excess of 100:1 (Simard et al., 1998; Fahmy et al., 1999; Chantigny et al., 2000; Gagnon et al., 2001). The C:N ratio of pulp or paper sludges depends on the proportions of primary and secondary sludge in the mix, and the treatment system used at the mill ( Bellamy et al., 1995). In field experiments, pulp mill solids have been applied to low-C soils and mixed by tilling, which perhaps reduces the severity of N-immobilization. Our experiments combined pulp mill solids with organic soil that was itself deficient in N, which would be expected to exacerbate microbial immobilization of N. The solids we used also supported a rapid rate of microbial activity.

The pulp mill solids were also much lower in P than any of the composts and had a high C:P ratio (178:1). Nevertheless, tomato plants grown in potting soil mixed with pulp mill solids did not exhibit obvious signs of P deficiency (compact growth, purple discolouration on the leaf veins and undersides). These symptoms were observed in the tomatoes grown in potting soil alone. Therefore P deficiency appears to have been at least partially relieved by the addition of pulp mill solids. This result is contrary to the observation of P deficiency symptoms in both the MSW and Race Track treatments, both of which had a higher P content, and a much lower C:P ratio, than pulp mill solids (Table 1). A plausible explanation is that the P in pulp mill solids was added to the effluent lagoons to speed wastewater treatment, and may not have been incorporated into stable organic matter, as it would be in the more completely decomposed composts.

Less explicable is the unexpectedly poor performance of plants grown in MSW compost from Lunenburg. This material is stable and well-decomposed. It is well supplied with

phosphorus and has the lowest C:N ratio of any of the amendments tested (Table 1). Nevertheless, MSW compost produced no stimulation of growth of tomato plants relative to controls grown in potting soil, and is strongly phytotoxic to seeds and seedlings at high concentrations.

Two aspects of the apparent phytotoxicity of MSW compost are salient. First, toxicity in the dilution assay with a silty loam soil showed strong inhibition of seedling emergence only in undiluted compost, whereas a 50% mixture with potting soil produced an effect of the same strength. Second, the phytotoxicity appears to be pH-sensitive.

The first observation may be an interaction with the diluent. The potting soil itself inhibits emergence of tomato seedlings, and its potency is only slightly less than that of MSW

compost (Fig. 2). Consequently, a 50:50 mixture of MSW compost and potting soil would be approximately equivalent to undiluted MSW compost in terms of phytotoxic potency, which is indeed what we observed. When MSW compost is mixed with silty loam soil, which does not impair seedling emergence, only the effect of the

compost is felt, and potency diminishes quickly with dilution. The irony remains, however, of a commercially available potting soil that is toxic to vegetable seeds.

The MSW compost was unique among the amendments in our experiment for its circumneutral pH. While a pH of 7.4 would certainly not be hazardous to plants, tomatoes grow best in acid soils, in the pH range of 5–6 (Brady and Weil, 1999). Hence, the unexpected lack of stimulation of tomato growth in soils amended with MSW compost,

compared with the other composts tested, may have arisen at least partially from the high pH that this compost would impose. Such an effect would be felt over the lifetime of the plant, and so would be most clearly expressed in tomato growth rates and final weights.

That factor alone, however, is insufficient to explain the powerful inhibition of seedling emergence in high concentrations of MSW compost. A short-term response such as impaired seed germination or emergence is more indicative of a chemical toxicant, presumably an organic constituent of the compost. Because we used small organic acids to reduce the pH (to avoid inorganic reactions with clay particles) it is possible that a priming effect from stimulated microbial decomposition of recalcitrant, cyclic compounds (Kuzyakov et al., 2000) was in part responsible for the removal of toxicity at pH 5.3. This is unlikely, however, because seedling emergence tests began immediately after the compost sample was acidified. A priming reaction would take some time for decomposition to proceed.

MSW compost had the highest electrical conductivity of all the amendments (Table 1), suggesting that salinity may have contributed to its inhibitory effects. This is unlikely, however, because the MSW compost was only mildly saline, and aqueous extracts, which presumably would be rich in salts, did not inhibit seed germination. Phytotoxicity based on salinity would also not be expected to be pH-dependent. Finally, mink compost, though only slightly less saline ( Table 1), strongly stimulated plant growth.

It is more probable that the compost contains an organic compound that is phytotoxic at neutral pH and not easily extractable with water. The toxic effect is only significant in nearly undiluted compost, so any reasonable degree of mixing with soil would attenuate it. Phytotoxicity from this amendment is conceivable in the field if a soil were heavily topdressed with MSW compost without subsequent tillage. Presumably, successive improvements in the composting process at the Lunenburg facility have removed any residual inhibition.

5. Conclusions

It appears then that two mechanisms of inhibition may have been active in those amendments that inhibited or failed to stimulate growth of tomato seedlings. The stronger effect of pulp mill solids is largely nutritional, while the effect of MSW may be primarily toxicological. Phytotoxicity apparently inhibited seed germination and emergence. Nutrient deficiencies or imbalances then determined how well the remaining plants grew. Both phytotoxicity and

nutrient availability may have been active in treatments with MSW compost, which failed to stimulate growth of even those tomato seedlings that survived germination.

Our results cannot be directly extrapolated to field crops because compost would not normally be applied at the concentrations that we used in our experiments. Nevertheless, our results suggest that applying fresh pulp mill solids to farmland, unless supplemented with inorganic N fertilizer, may be ill-advised because of the potential for nutrient immobilization. This result was predicted from the chemical composition of the amendment. The more complicated effects of MSW compost, however, were unexpected, and illustrate that important qualities of compost may not always be apparent from standard nutritional analysis.

Acknowledgements

We are indebted to Dr. P.R. Warman, Nova Scotia Agricultural College, for providing samples of the different kinds of compost, as well as for data on their chemical composition. Clarifier solids and data on their chemical composition were generously provided by C.J. MacLellan and Associates, Antigonish, Nova Scotia.

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The effects of composts produced by a simple composting procedure on the yields of Swiss chard (Beta vulgaris L. var. flavescens) and common bean (Phaseolus vulgaris L. var. nanus)

Dorothea C. Smith , , a, Vihitha Behareeb and Jeffrey C. Hughesa

a Soil Science, School of Applied Environmental Sciences, University of Natal (Pietermaritzburg), Private Bag X01, Scottsville 3209, South Africa

b Microbiology and Plant Pathology, School of Applied Environmental Sciences, University of Natal (Pietermaritzburg), Private Bag X01, Scottsville 3209, South Africa

Accepted 20 April 2001

Available online 7 November 2001.

Abstract

The effect of four composts, produced by a simple process, on the yield of Swiss chard and common bean was studied in two glasshouse pot experiments. The composts

which differed in raw material (garden refuse, market and garden refuse) and turning frequency (0×, 6×) were applied at three rates (0, 25, 50% (m/m)) to a sandy soil with and without low applications of inorganic fertiliser. In both the experiments, the soil–compost mixtures out-performed the soil alone irrespective of the amount of fertiliser added. Swiss chard produced the highest total leaf fresh mass on composts made from market and garden refuse. The yield was further significantly improved when the composts had been turned or when the proportion of compost was increased from 25 to 50%, but the addition of fertiliser had no significant effect on the total yield. In contrast to the results for Swiss chard, the application of compost produced from garden and market refuse which had undergone turning had a negative effect on the yield of common bean, especially when the proportion of compost was increased to 50% and when fertiliser was added. Common bean performed the best when grown on soil mixed with compost made exclusively from garden refuse. With the exception of the treatments which contained compost made from turned market and garden refuse, adding fertiliser and increasing the proportion of compost generally led to higher numbers of pods and seeds and increased total seed dry mass. The contrasting responses of the two crops to the applied composts are believed to be caused by differences in the crops’ nutrient requirements and salinity tolerances. In order to maximise yields, compost raw materials and turning frequency need to be carefully chosen to produce

composts particularly suited to specific crop requirements.

Author Keywords: Compost ; Common bean; Swiss chard; Glasshouse plant experiment

Article Outline

1. Introduction

2. Materials and methods

2.1. Composts

2.2. Soil

2.3. Glasshouse experiments

2.3.1. Swiss chard

2.3.2. Common bean

2.4. Statistical analysis

3. Results

3.1. Swiss chard

3.2. Common bean

4. Discussion

5. Conclusions

Acknowledgements

References

1. Introduction

The majority of the South African rural population lives in areas characterised by infertile soils which are often highly susceptible to erosion. The observed practice of removing all crop residues from fields and community gardens prior to planting or sowing of the following crop serves to further deplete the soil of nutrients and organic matter. To maintain soil fertility, the nutrients removed with the crop at harvest must be returned in the form of inorganic fertiliser, manure or compost. The use of adequate amounts of chemical fertiliser to compensate for the loss of nutrients and to improve the crop yield, however, is usually too costly for small-scale farmers. The application of compost has been shown to positively affect, inter alia, the structure, porosity, water-holding capacity, compression strength, nutrient content, and organic matter content of the soil (Mays; Pinamonti and Zorzi, 1996 and Smith, 1996) and to improve plant growth, crop yield and crop quality ( Pinamonti and Zorzi, 1996; Rodrigues et al., 1996 and Smith, 1996). Therefore, the aim of the present study was to address the need for increased food production and soil conservation by establishing a practice of converting source-separated organic domestic refuse and crop residues into compost which can be used in family and community gardens and by small-scale farmers as a sustainable organic soil amendment. To this end, a low-cost and low-technology process was required. Composting in heaps or small windrows was considered to be the method most suited to rural communities where labour is generally available but financial restrictions prohibit mechanisation of the composting process. To ensure the beneficial integration of composts into rural crop production systems, it was necessary to investigate the effects of compost raw materials, composting process and compost application rates on crops which can improve the nutritional status of the rural population. Several authors ( Sikora, 1996; Gagnon and Neilsen) reported positive effects on crop yield following the combined application of compost and inorganic fertilisers. Since for many small-scale farmers, the use of high amounts of inorganic fertiliser is not feasible due to the high costs involved, a treatment consisting of

compost amended with small amounts of inorganic fertiliser was included in the present plant experiments.

2. Materials and methods

2.1. CompostsThe four composts used in this study differed in raw material (garden refuse collected from private households (branches cut into pieces of approximately 10 cm length and long moribund grass) with and without vegetable and fruit waste from the municipal market) and the frequency of turning during the composting process (no turning, turned six times) and were the composite samples of four replicates. Some of the chemical characteristics of the composts are given in Table 1.

Table 1. Some chemical properties of the composts made from garden refuse (G) and market and garden refuse (MG), with turning (T) and without turning (N)

Composting took place under field conditions in two rows, each of eight adjoining compartments, to accommodate the treatments and their replicates. The compartments were constructed of wooden framing covered with polyethylene sheet. Each compartment had a volume of approximately 3 m3. The commonality of the framing between neighbouring heaps and between the two rows ensured that the loss of heat and moisture from the compost

heaps was minimised. The experimental set-up thus resembled a continuous windrow. All compost heaps were erected on wooden pallets to encourage aeration and leachate drainage. The raw materials were thoroughly mixed and water was added to each treatment until a water content of approximately 70% (on wet basis) was reached. Half of the treatments were turned six times during the composting process, while the remaining heaps were left unturned. Water was frequently added to all treatments in order to maintain their water content above 70%. To protect the composts from heavy rain, as well as to prevent water and heat loss, all treatments were covered with a 10 cm layer of hay. Although visual evaluation suggested that compost maturity was reached earlier, the composting process was terminated only after 335 days. At this time, the majority of tests which had been conducted continuously since the beginning of the experiment indicated that the organic matter in the composts had reached chemical and biological stability.

Prior to their use in the glasshouse experiments all composts were air-dried. The replicates of each treatment were combined, thoroughly mixed and sieved to pass a 7 mm screen to remove undegraded wood. Composts made from garden refuse only, which still contained undegraded wood after passing the 7 mm screen, were further screened through a 2 mm sieve.

2.2. Soil

The soil used in both glasshouse experiments was a loamy sand (9.7% clay, 11.5% silt, 78.8% sand) taken from the eluviated horizon of a Cartref soil form (Soil Classification Working Group, 1991), Typic Haplaquept ( Soil Survey Staff, 1990). It had a cation-exchange capacity of 4.83 cmolc kg−1 and an electrical conductivity of 19 μS cm−1. The pH of the soil was 5.91 when measured in distilled water and 4.97 when measured in 0.01 M CaCl2 solution. The concentrations of total carbon and total nitrogen were 1.16 and 0.09%, respectively. The concentrations of some extractable nutrients were 0.12 cmolc kg−1 K, 2.06 cmolc kg−1 Ca, 1.13 cmolc kg−1 Mg, 3.6 mg kg−1 P, 1.0 mg kg−1 Zn and 10.2 mg kg−1 Mn. Prior to use, the soil was air-dried and passed through a 2 mm sieve.

2.3. Glasshouse experimentsExperiments were conducted to monitor the effects of compost application and inorganic fertiliser addition on the growth of two vegetable crops, chosen because of their high nutritional value and their frequent cultivation in the rural communities of KwaZulu-Natal, South Africa. The first experiment was carried out with Swiss chard (Beta vulgaris L. var. flavescens) which is a heavy feeder and responds well to organic fertiliser (Hadfield, 1995). Common bean (Phaseolus vulgaris L.) and cowpea (Vigna unguiculata L. Walp.) are important grain legume crops which supply a large part of the daily protein requirement of the people in many developing countries (Fageria et al., 1991). Of these, the common bean (P. vulgaris L. var. nanus) was chosen as the experimental crop for the second plant trial.

2.3.1. Swiss chardThe variables investigated in the experiment with Swiss chard (cv. Fordhook Giant) were the

compost raw materials (garden refuse (G), market and garden refuse (MG)) and the turning frequency (frequent turning (T) and no turning (N) during the composting process), as well as the compost: soil ratio (25:75 and 50:50 (m/m)) and the addition of small amounts of inorganic fertiliser. Pots (2-l) were filled with soil (2000 g) and the different soil–

compost mixtures (25% compost: 447 g compost  + 1340 g soil; 50% compost: 765 g compost  + 765 g soil). The fertiliser used contained 6.5% N, 2.7% P, 13.0% K, 7.0% Ca, 2.2% Mg, 7.5% S, 0.15% Fe, 0.024% Mn, 0.024% B, 0.005% Zn, 0.002% Cu and 0.001% Mo. It was applied to the soil– compost mixtures in salt form at rates of 0 and 1.205 g per pot. Pots filled with soil only and soil amended with 1.205 and 2.410 g fertiliser served as controls. The experiment was designed as a 4-factorial experiment plus three controls in five randomised blocks. Prior to planting each pot was watered to 90% of the water holding capacity. Swiss chard seedlings of uniform size (four mature leaves) were selected and one seedling was planted in each pot. Tap water was used to irrigate the plants. Water was added daily to maintain the potting mixtures at close to water holding capacity. During the experiment insecticides were applied when necessary. The average maximum temperature recorded in the glasshouse was 27°C (21–35°C) and the average minimum temperature was 15°C (10–20°C). The experiment lasted for 119 days. During this period, the Swiss chard was harvested four times (first harvest 5 weeks after planting, thereafter every 4 weeks). At the first three harvest times, only the largest

leaves of each plant, as well as very small leaves with no potential for further growth, were removed at their base and their fresh mass and dry mass (after drying at 60°C for 4 days) were determined. At the end of the experiment (fourth harvest) all remaining leaves were removed, irrespective of their size, and their fresh and dry mass was determined.

2.3.2. Common beanThe variables tested in the experiment with common bean (bush bean, cv. Wartburg) were essentially the same as those tested in the experiment with Swiss chard with the addition of an extra control treatment (soil amended with 3.616 g fertiliser per pot). The experiment was thus designed as a 4-factorial experiment plus four controls in five randomised blocks. The amounts of soil and composts in the bean experiment were 2500 g (soil control), 400 g compost  + 1200 g soil (25% compost) and 600 g compost  + 600 g soil (50% compost) per pot. Each potting mixture was moistened to 90% of the water holding capacity and six bean seeds were sown in each pot. Two weeks later, the number of seedlings was reduced to two plants per pot. All pots were watered daily with tap water to water holding capacity, to ensure that the plants never suffered from water stress. Insecticides and fungicide were applied when necessary. The average maximum temperature in the glasshouse was 33°C (20–41°C) and the average minimum temperature was 21°C (16–24°C). The experiment was terminated after 83 days and the response of the beans to the treatments was assessed by the determination of the number of seed pods and seeds produced, and the determination of the total seed dry mass (after drying at 60°C for 4 days).

2.4. Statistical analysis

Statistical analyses for both the experiments were performed using the GENSTAT 5 for WINDOWS statistical software package (Release 4.1, 3rd Edition, Genstat 5 Committee of the Statistics Department, IACR-Rothamsted Experimental Station, Harpenden, Hertfordshire, UK, 1997). The statistical significance of the experimental treatments was determined by subjecting the data to analysis of variance and differences between means were compared using least significant differences at P<0.05.

3. Results

3.1. Swiss chardThe leaf fresh mass of the Swiss chard grown on the different treatments is shown in Fig. 1. The highest yields of leaf fresh mass were obtained when the Swiss chard was grown on soil–

compost mixtures. Swiss chard grown on soil without compost produced significantly less leaf fresh mass, as was expected since only small amounts of inorganic fertiliser were applied. The raw material used to produce the compost significantly affected the total fresh mass of the harvested leaves. Swiss chard grown on compost made from a mixture of market and garden refuse had a higher yield than Swiss chard grown on compost made from garden refuse alone. Turning of the compost during the composting process also had a significant effect on the total fresh mass. Composts which had been turned yielded the highest fresh mass. Furthermore, increasing the proportions of compost in the soil– compost mixture from 25 to 50% (m/m) improved the total yield of Swiss chard not only significantly, but also substantially. On an average, the total leaf fresh mass was increased by 68% (23–106%). The addition of fertiliser to the soil– compost mixtures, however, had no significant effect on the total leaf fresh mass. When the Swiss chard was grown on the soil– compost

mixtures, the first two cuts yielded most of the total leaf fresh mass. On soil alone, the

bulk of the leaf fresh mass was harvested at the first cut and subsequent cuts contributed little to the total yield. The analysis of the treatment effects on the yield of the leaf fresh mass obtained at each harvest showed that the compost raw material significantly affected only the yield of the first cut, when Swiss chard grown on compost made from market and garden refuse produced the highest yields. No significant effect of the compost raw material was observed at any of the following harvests. The addition of fertiliser to the soil– compost mixtures also significantly improved only the yield of the first harvest, later it had no effect on the leaf fresh mass production. Whether the compost had been previously turned did not influence the yield of the first harvest, but significantly increased the yield of the second, third and fourth cuts. At all harvests the soil–

compost mixtures containing 50% (m/m) compost produced significantly higher yields than those mixtures containing only 25% (m/m) compost.

Full-size image (29K)

Fig. 1. Leaf fresh mass per plant (average of five replicates) of Swiss chard grown on soil with different additions of compost (0, 25 and 50% (m/m)) and fertiliser (0 and 1.205 g per pot (soil– compost mixtures); 0, 1.205 and 2.410 g per pot (soil only)). The composts applied were MGN ( compost made from market and garden refuse without turning), MGT ( compost made from market and garden refuse with turning), GN ( compost made from garden refuse without turning) and GT ( compost made from garden refuse with turning).

Although the leaf dry mass of Swiss chard was affected by the treatments in a similar way as the leaf fresh mass, some differences were observed. Whether the composts had been made from garden refuse with or without market refuse did not significantly affect the total leaf dry mass of the Swiss chard. However, when higher interactions are considered, as in the case of the total leaf dry matter of Swiss chard grown on soil with 25% (m/m) compost addition, compost made from market and garden refuse was superior to that made from garden refuse only (Fig. 2). Furthermore, the yield of Swiss chard grown on soil fertilised with 1.205 g fertiliser per pot and mixed with compost which had previously been turned was significantly higher when the compost raw material was a mixture of market and garden refuse. As for the leaf fresh mass, the leaf dry mass obtained at the first cut was significantly influenced by the compost raw material, the quantity of compost used in the soil– compost mixture and the fertiliser addition. However, also significant was whether the compost had been turned. Composts which had previously been turned yielded higher leaf dry mass at the first

harvest than those which were produced without turning. The dry leaf yield of the consecutive harvests followed the same trends as those of the leaf fresh mass.

Full-size image (27K)

Fig. 2. Leaf dry mass per plant (average of five replicates) of Swiss chard grown on soil with different additions of compost (0, 25 and 50% (m/m)) and fertiliser (0 and 1.205 g per pot (soil– compost mixtures); 0, 1.205 and 2.410 g per pot (soil only)). The composts applied were MGN, MGT, GN and GT.

3.2. Common beanThe effects of the composts applied in different quantities with and without fertiliser supplementation on the number of seed pods and seeds are illustrated in Fig. 3 and Fig. 4, respectively. Beans grown on soil– compost mixtures produced significantly more seed pods and seeds than beans grown on soil only, irrespective of the amount of fertiliser added. The number of seed pods and seeds was also significantly affected by the

compost raw material. The soil– compost mixtures which contained compost made from garden refuse yielded significantly more seed pods and seeds than those which contained compost made from market and garden refuse. Whether or not the compost had been turned during the composting period, generally had no effect on the number of seed pods and seeds produced. Only when the compost was made from market and garden refuse did turning affect the seed and seed pod production and significantly less of both was produced when the compost had been turned. With the exception of the treatment MGT/50% compost/ 1.205 g fertiliser per pot, increasing the amount of compost in the potting media from 25 to 50% (m/m) increased the number of seed pods and seeds per pot significantly, although not always substantially. The application of inorganic fertiliser to the soil– compost mixtures also had a significantly positive effect on the number of seed pods and seeds, with the same exception. When grown on soil without compost, beans produced significantly more seed pods and seeds when the fertiliser application was increased from 0 to 2.410 or 3.616 g per pot and from 1.205 to 3.616 g per pot.

Full-size image (23K)

Fig. 3. Number of seed pods per pot (average of five replicates) produced by beans grown on soil with different additions of compost (0, 25 and 50% (m/m)) and fertiliser (0 and 1.205 g per pot (soil– compost mixtures); 0, 1.205, 2.410 and 3.616 g per pot (soil only)). The composts applied were MGN, MGT, GN and GT.

Full-size image (24K)

Fig. 4. Number of seeds per pot (average of five replicates) produced by beans grown on soil with different additions of compost (0, 25 and 50% (m/m)) and fertiliser (0 and 1.205 g per pot (soil– compost mixtures); 0, 1.205, 2.410 and 3.616 g per pot (soil only)). The composts applied were MGN, MGT, GN and GT.

The total seed dry mass (Fig. 5) followed the same trends as for the number of seed pods and the number of seeds in almost all aspects. The only difference was that the seed dry mass of the beans was significantly affected by the turning of the compost during the composting process. Turned composts produced lower seed dry masses. However, the statistical analysis showed that this was mainly due to the significant effect of turning when the composts had been made from market and garden refuse. When the composts were made purely from garden refuse, no significant differences between those which had been turned and those which were produced without turning were detected, as was the case previously for the number of seed pods and seeds.

Full-size image (23K)

Fig. 5. Seed dry mass per pot (average of five replicates) produced by beans grown on soil with different additions of compost (0, 25 and 50% (m/m)) and fertiliser (0 and 1.205 g per pot (soil– compost mixtures); 0, 1.205, 2.410 and 3.616 g per pot (soil only)). The composts applied were MGN, MGT, GN and GT.

4. Discussion

The positive yield response of Swiss chard, grown on a sandy soil, to compost applications is believed to be primarily a reaction to the nutrients contained in these composts. Swiss chard is a heavy feeder (Hadfield, 1995) and thus, benefited from applications of composts with high nutrient concentrations. This was reflected in high crop yields when grown on soil amended with composts made from market and garden refuse and composts which had been turned during the composting process. It is, however, surprising and potentially important, that the application of composts made from market and garden refuse significantly affected only the first cut, while composts which had been turned led to significantly higher yields throughout the experiment. This was in spite of the fact that the differences in nutrient content between

composts which had been turned and those which had not, were smaller than the differences between composts made from market and garden refuse and those made solely from garden refuse ( Table 1). The positive effect of the composts which had been turned during the composting process on the consecutive yields might have been the result of a slower, but continuous release of nutrients throughout the experiment due to the higher cation-exchange capacities detected in the turned composts.

The results of the experiment with common bean showed that bean yield generally reacted positively to the nutrients supplied by the treatments as long as the electrical conductivity of the composts was not too high. An electrical conductivity (saturated paste) higher than 2–3 dS m−1 is known to result in marginal necrosis in many plant species (Rosen et al., 1993). Beans are considered to be salinity-susceptible crops with a salinity threshold of about 1 dS m−1 (Maas and Hoffman, 1977). The salinity of the composts used in the plant experiment ( Table 1) was the highest in compost made from market and garden refuse which had been turned during the composting process (2.069 dS m−1 in a 1:10 compost: water suspension) and the 50% (m/m) soil– compost mixtures will have exceeded the salinity threshold of 1 dS m−1 in the saturated paste, explaining the low yields from this treatment. The higher salinity of the composts made from market and garden refuse might also explain why, in spite of their higher nutrient content, they produced lower bean yields than composts made purely from garden refuse. When comparing composts made from the same raw materials, those which had been turned had approximately twice the electrical conductivity than those which were produced without turning (Table 1). The frequent turning of the compost, however, did not

influence the bean yield when the compost was made from garden refuse but it significantly decreased the yield when the compost raw material was market and garden refuse which on its own already contributed greatly to the compost’s salinity. The low application of inorganic fertiliser given to half of the soil– compost mixtures exacerbated the salinity problem of the compost made from turned market and garden refuse and decreased the yield even further. In contrast, the yield of the beans grown on the other soil– compost mixtures was significantly improved by the nutrients added in the fertiliser. In an experiment carried out with pepper, Roe et al. (1997) also observed that composts combined with low rates of fertiliser generally produced higher yields than other treatments.

Although an investigation of the effect of compost addition on the physical and microbiological properties of the soil– compost mixtures was beyond the scope of this paper, it cannot be excluded that the yield of both crops might also have been affected by changes in these properties.

5. Conclusions

In South Africa, as in many other developing countries, small-scale farmers often cannot afford to use inorganic fertilisers in the quantities necessary to produce satisfactory crop yields. The aim of this research was, therefore, to establish a simple practice of converting source-separated organic domestic refuse and crop residues into compost which can be used as sustainable organic fertiliser. The results of the experiments with Swiss chard and common bean have shown that composts which are produced by simple technology have considerable potential for use as fertilisers in small-scale farming. This study further demonstrated that composts can be produced to suit the nutritional requirements of different crops by altering the composition of the compost raw materials and the turning frequency during the composting process. The incorporation of wastes such as fruit and vegetable refuse in the raw material mixture of the compost and frequent turning are suggested to produce a nutrient-rich and relatively more saline compost which can, even at high application rates, beneficially be used for crops with a great demand for nutrients and a tolerance of saline conditions (e.g. Swiss chard). Frequent turning during the composting process also increases the cation-exchange capacity of the compost which is believed to promote a continuous release of nutrients over an extended period of time. Composts made from raw materials which contain less nutrients can be used to grow crops with a lower nutritional requirement and crops which are more susceptible to salinity. Adjusting the raw material mixture and the turning frequency of the compost

as well as the compost quantity to take into account the nutrient requirements and the salt tolerance of the crop to which the compost is going to be applied results in a more efficient use of the nutrients contained in the compost and is a prerequisite to avoid problems associated with salt stress. The application of small amounts of fertiliser together with compost is recommended if salinity is not considered to be yield-limiting and the financial gain from the increased yield exceeds the cost of the fertiliser.

Acknowledgements

The financial support of the National Research Foundation (NRF), Pretoria, via Grant number 2034682 is gratefully acknowledged. The authors wish to thank Mr. Ken Leisegang and Mr. Ian Sumner from Sunshine Seedlings Services for the donation of the Swiss chard seedlings,

Mr. Gavin Smit, School of Agriculture and Agribusiness for the application of the pesticides in the greenhouse, and Mr. Harvey Dicks, School of Mathematics, Statistics and Information Technology for his assistance with the statistical analyses. Some of the chemical analyses of the soil and composts were provided by the Soil Fertility and Analytical Services Laboratory at Cedara, KwaZulu-Natal Department of Agriculture and Environmental Affairs.

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