Journal of the Indian Society of Soil Science, Vol. 62, No. 3, pp 224-234 (2014)

Soil Nutrient Availability and Enzyme Activities under Wheat-Greengram Crop Rotation as Affected by Rock Phosphate Enriched

Compost and Inorganic Fertilizers

P.C. Moharana, D.R. Biswas*, A.K. Patra1, S.C. Datta,R.D. Singh, Lata2 and K.K. Bandyopadhyay3

Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute,New Delhi, 110012

The aim of this study was to evaluate the effect of rock phosphate (RP) enriched rice straw compost, FYMand inorganic fertilizers on changes in nutrient availability and enzyme activities in soil during differentphysiological growth stages under a wheat-green gram crop rotation in an Inceptisol. The matured RPenriched compost contained higher bioavailable P as well as total P content compared to farmyard manure.Data revealed that application of inorganic fertilizers and RP enriched compost or FYM either alone or incombination resulted in significant build-up in soil organic carbon, mineral N, Olsen-P and NH4OAc-K aswell as enzyme activities compared to unfertilized control plots during different physiological growth stagesof wheat and green gram. Plot receiving 50% NPK+RP enriched compost resulted in 100.8, 95.2 and 100.0per cent greater build-up in Olsen-P over unfertilized control in crown root initiation (CRI), flowering andmaturity stage of wheat, respectively. Irrespective of treatments, build-up of mineral N, Olsen-P and NH4OAc-K decreased in all the growth stages of green gram as compared to values obtained in wheat. Thedehydrogenase and phosphatase activities (alkaline and acid) were higher in flowering stage than maturityand CRI stages of wheat. While, higher enzyme activities were obtained during pod formation in greengram. The results demonstrated that enriched compost could be prepared using low-grade RP with rice strawand used as an alternate nutrient source for improving crop yields, maintaining soil nutrient availability andenzyme activities.

Key words: Residue recycling, rock phosphate, enriched compost, nutrient availability, enzyme activities

*Corresponding author: (Email: drb_ssac@yahoo.com)Present addresses1Indian Institute of Soil Science, Nabibagh, Berasia Road,Bhopal, Madhya Pradesh2Division of Microbiology, Indian Agricultural Research Insti-tute, New Delhi, 1100123Division of Agricultural Physics, Indian Agricultural ResearchInstitute, New Delhi, 110012

Management and recycling of farm wastes of diverseorganic sources into quality compost is becoming verypopular these days. Preparation and use of mineralenriched compost has become an important compo-nent of sustainable cropping systems and receivedmuch interest in recent years as a means of increasingsoil organic matter and serves as the potential sourceof nutrients for plant growth. It is estimated that ap-proximately 550 million tonnes (Mt) of crop residuesare produced in India per year. The major share is therice residues which are usually burnt in the fields,particularly in northern parts of Indo-Gangetic Plains

of India to save labour as well as to enable tillage andseeding machinery to work efficiently and to sow thenext crop of wheat without loss of time. As a result,substantial amounts of potent organic matter and nu-trients are lost besides polluting the environment(Yadvinder-Singh et al. 2005). The alternative meansto utilize crop residues and recycle them back to theagricultural field is by composting technology, whichis recognized as an economical and sustainable op-tion for management of agricultural waste and can befollowed at the local site of the produce, thus reducethe ill effects of residue burning (Biswas 2011). Inrecent years, interest in composting has also increasedbecause of the social demand for an environmentalfriendly waste treatment technology and advent of or-ganic farming. It is the most acceptable methods ofrecycling of organic matter and agriculture residues(Gaind et al. 2009; Antil and Raj 2012; Sharma et al.2014).

2014] NUTRIENT AVAILABILITY AND ENZYME ACTIVITIES UNDER WHEAT-GREEN GRAM 225

Cost of water soluble phosphatic fertilizers hasincreased tremendously in India in recent times be-cause of importing raw materials like high-grade rockphosphate (RP) and sulphur, imposing heavy burdenon government exchequer. A substantial amount ofRP is available in India, but most of them are low-grade and unsuitable for manufacturing of commer-cial P-fertilizers as well as for direct use as a sourceof P to crops, particularly in neutral and alkaline soils(Narayanasamy and Biswas 1998). An alternativemeans of improving the availability of P from RPcould be incorporating them into composting mass,wherein the organic acids produced during the de-composition of fresh organic matter help in the solu-bilization of P from RP into plant available form(Biswas and Narayanasamy 2006; Biswas et al. 2009).

Soil enzymes regulate the transformation of nu-trients in soil required for plant growth (Saha et al.2008). Transformation of organic P through enzymaticreactions and immobilization of P in the biomass playan important role in P cycling and are likely to beaffected by P amendments. However, there is limitedinformation available on the effect of enriched com-post prepared using crop residues and low-grade RPin soils under field conditions in intensive croppingsequence on changes in soil available nutrients andenzymes activities during crop growth stages in awheat-green gram crop rotation. The present studywas therefore aimed to prepare and assess the impactof rock phosphate enriched compost and chemical fer-tilizers on soil nutrient availability and enzyme activi-ties during different physiological growth stages un-der wheat-green gram crop rotation in an Inceptisolof Indo-Gangetic Plains of India.

Materials and Methods

Mass Production and Analysis of Enriched CompostMass production of RP enriched rice straw com-

post was done at the Biomass Utilization Unit of IARIas per the procedure outlined earlier by Biswas andNarayanasamy (2006). For this, RP was obtained fromRajasthan State Mines and Minerals Ltd., Udaipur,Rajasthan. The powdered RP (100-mesh particle size)had 8.81% total P, 0.002% water soluble P (WSP),1.29% citrate soluble P (CSP), 6.5% Ca, 5.6% Mg,0.10% Fe, and 665, 21.7 and 41.7 mg kg-1 of Mn, Cuand Zn, respectively. Rice straw was collected fromthe Research Farm of IARI, New Delhi. It containedtotal carbon (C) 49.8%, total N 0.53%, C/N ratio 93.9,total P 0.04%, total K 1.07%, and Fe, Mn, Cu and Zncontent of 262, 33, 12 and 49 mg kg-1, respectively.The composting was done layer-wise, where rice straw

was spread on the floor of an area approximately 20m × 2 m. A layer of RP (2% P, w/w) was spread overrice straw. Then a layer of fresh cattle dung wasspread over the composting mass as natural inocu-lants for faster decomposition. Water was added so asto maintain the moisture content about 50-60%throughout the composting period. Mechanical turn-ings were employed at 30, 60 and 90 days ofcomposting to provide adequate aeration, thoroughmixing of composting mass and uniform decomposi-tion.

Fresh samples of matured compost (120-days-old) were drawn from three different locations anddivided into two portions. The first portion was keptin a refrigerator at 4 oC and used subsequently foranalysis of total N, mineral N (NH4

+-N + NO3--N) and

enzyme activities like dehydrogenase, acidphosphatase and alkaline phosphatase; whereas theother portion was oven-dried at 65±1 °C for 24 h,ground to pass through a 2-mm sieve, and analyzedfor pH, EC, total C, N, P and K as well as Olsen-P,WSP, CSP and NH4OAc-K as per the standardprocedures. The pH and EC were measured usingcompost: water ratio of 1:5. Total C content wasdetermined by the ignition method. Total N contentwas determined by the micro-Kjeldahl method(Bremner and Mulvaney 1982). For determination oftotal P and K, the di-acid digestion (HNO3:HClO4::9:4) method was followed. Total P content wasdetermined by a spectrophotometer after developingvanadomolybdo-phosphoric yellow colour complex,while total K was determined by a flame photometer.Mineral N (NH4

+-N + NO3--N) was determined by the

method as outlined by Keeney and Nelson (1982).Olsen-P was determined using 0.5 M NaHCO3 (pH8.5) extract (Olsen et al. 1954), while available Kwas determined using 1 N NH4OAc (pH 7.0) (Hanwayand Heidel 1952). Dehydrogenase activity wasmeasured as per the method of Klein et al. (1971)while, phosphates activity was measured as per theprocedure outlined by Tabatabai and Bremner (1969).Water soluble carbon (WSC) was analyzed byextracting sample with water followed by estimationof carbon by wet digestion method (Walkley andBlack 1934). Bio-available P consisting of WSP andCSP was determined as per the procedure outlined byFertiliser (Control) Order (FCO 1985). Similarprocedures were followed for characterization offarmyard manure (FYM) and RP enriched compost.

Experimental Details and Soil AnalysesThis experiment was conducted from November

2011 to November 2012 under a wheat-green gram

226 JOURNAL OF THE INDIAN SOCIETY OF SOIL SCIENCE [Vol. 62

cropping system at the Research Farm, Indian Agri-cultural Research Institute, New Delhi. Representa-tive composite sample from surface soil (0–15 cmdepth) was collected from the experimental field forinitial soil properties. The soil belongs to Inceptisol,member of coarse loamy, non-acid, mixed hyperther-mic family of Typic Haplustept. Some of the physico-chemical properties of the experimental soil were: tex-ture sandy loam with sand 67.2%, silt 14.8% and clay18.0%; pH 8.1, EC 0.35 dS m-1, CEC 10.5 cmol(p+)kg-1

soil, organic C 3.2 g kg-1, mineral-N 21.2 mg kg-1,Olsen-P 12.4 kg ha-1 and NH4OAc-K 145 kg ha-1.

The field experiment was carried out to assessthe impact of the RP enriched compost and FYM withand without chemical fertilizers on soil nutrient avail-ability and enzyme activities in a wheat-green gramcrop rotation. Six nutrient management practices con-sisted of T1: control, T2:100% recommended dose offertilizer (100% NPK), T3: FYM @ 5.0 t ha-1 (FYM),T4: RP enriched compost @ 5.0 t ha-1 (RP enrichedcompost), T5: 50% NPK+ FYM @ 5.0 t ha-1 (50%NPK+FYM) and T6: 50% NPK+ RP enriched com-post @ 5.0 t ha-1 (50% NPK+RP enriched compost)were followed. The experiment was laid out in a ran-domized block design having plot size of 3.5 m × 4 meach with three replications. Wheat (Triticumaestivum) var. HD-2851 was grown as the first cropand green gram (Vigna radiata) was grown as thesecond crop to evaluate the direct and residual effectsof different nutrient management practices. The rec-ommended doses of nitrogen (120 kg N ha-1), phos-phorus (60 kg P2O5 ha-1) and potassium (60 kg K2Oha-1) as well as other treatments were computed as perthe treatment combinations. Urea and diammonium

phosphate (DAP) were used as the source of N, whileDAP and muriate of potash (MOP) were used as thesource of P and K, respectively. Whole quantities ofenriched compost, FYM and NPK fertilizers were ap-plied at the last ploughing and mixed thoroughly intothe soil.

Soil samples were collected from each plot atthree physiological growth stages of wheat (crownroot initiation, CRI; flowering and maturity) and greengram (flowering, pod formation and maturity) and ana-lyzed for organic C (Walkley and Black 1934), min-eral N (Keeney and Nelson 1982), Olsen-P (Olsen etal. 1954), NH4OAc-K (Hanway and Heidel 1952) aswell as enzyme activities like dehydrogenase activity(Klein et al. 1971), acid and alkaline phosphatase ac-tivities (Tabatabai and Bremner 1969).

Statistical AnalysisThe data were analysed for comparing means

employing analysis of variance and computing criti-cal difference of different nutrient management dur-ing different physiological growth stages on soil nu-trient availability and enzyme activities using SPSSwindow version 16.0 (SPSS Inc., Chicago, USA).Duncan multiple range test (DMRT) was performedto see the difference between the treatments.

Results and Discussion

Quality of RP Enriched Compost vis-à-vis FYMThe quality of the matured RP enriched rice

straw compost vis-à-vis FYM in terms of their chemi-cal composition and enzyme activities are presentedin table 1. It is evident that total C content in RP

Table 1. Characteristics of rock phosphate enriched compost and FYM (mean ± standard deviation)

Quality parameters RP enriched compost FYM

pH 7.74 ± 0.10 7.47 ± 0.17Electrical conductivity (EC, dS m-1) 3.72 ± 0.08 2.45 ± 0.13Total organic C (TOC, %) 22.8 ± 0.90 34.6 ± 1.2Water soluble C (WSC, %) 0.11 ± 0.04 0.02 ± 0.003Total N (%) 1.51 ± 0.06 1.39 ± 0.03C/N ratio 15.1 ± 0.35 24.9 ± 0.48NH4

+-N (mg kg-1) 423 ± 31 393 ± 28NO3

- -N (mg kg-1) 611 ± 60 549 ± 27Total P (%) 2.42 ± 0.03 0.46 ± 0.06Olsen-P (g kg-1) 1.12 ± 0.07 0.65 ± 0.12Water soluble P (WSP, %) 0.11 ± 0.003 0.36 ± 0.04Citrate soluble P (CSP, %) 1.54 ± 0.06 0.08 ± 0.01Total K (%) 1.29 ± 0.02 1.11 ± 0.02NH4OAc-K (%) 0.55 ± 0.12 0.50 ± 0.05Dehydrogenase activity (µg TPF h-1 g-1 compost) 85.5 ± 6.5 82.3 ± 7.4Alkaline phosphatase (µg PNP h-1 g-1 compost) 1530 ± 25 997 ± 15Acid phosphatase (µg PNP h-1 g-1 compost) 723 ± 3 405 ± 23

2014] NUTRIENT AVAILABILITY AND ENZYME ACTIVITIES UNDER WHEAT-GREEN GRAM 227

enriched compost decreased substantially to 22.8%compared to the initial total C in rice straw (49.8%).On the other hand, total N content was increased to1.51% in RP enriched compost compared to initialtotal N content in rice straw (0.53% N). The total Cand N content in FYM used in this study for compari-son was 34.6 and 1.39%, respectively. The loss oftotal C in the matured RP enriched compost is attrib-uted to the oxidation of organic matter (total C) asCO2 and generation of heat during composting pro-cess. The increase in total N in enriched compost overthe initial value of N in raw rice straw may be due tothe net loss of total C as CO2 and water by evapora-tion during composting. This might also be due tomineralization of N with the progress of compostingperiod. The results are in agreement with the workdone by Biswas and Narayanasamy (2006) and Biswaset al. (2009).

The C/N ratio in enriched compost markedly de-creased (15.1) compared to the raw rice straw whichhad a C/N ratio of 93.9. In case of FYM, the C/Nratio was 24.9. It is reported that the C/N ratio is oneof the main characteristics that describe the maturityof compost. It gives an indication of N availability forthe process of biological degradation, and the decreasein this ratio with composting time has been widelyreported as an indicator of maturity for compostingprocesses (Biswas et al. 2009). The narrowing of C/Nratio with the progress of composting is because ofdecomposition of organic matter wherein the C con-tent of the compostable mixtures decreased with timedue to loss of carbon as CO2 in respiration, while Ncontent per unit material increased, which resulted inthe decrease of the C/N ratio. Similar results in de-crease in total C and increase in total N content perunit of material during the decomposition of differentorganic wastes were reported by other workers(Nishanth and Biswas 2008).

Farmyard manure had a lower P content (0.46%)than RP enriched compost (2.42% P). The increase intotal P is attributed to contribution of P from RP inenriched compost. The result confirms the findings ofearlier work of Biswas and Narayanasamy (2006).However, it was observed that enriched compost hadlesser amounts of WSP content than FYM; while asubstantial improvement in CSP content was noticedin enriched compost compared to FYM, indicatingthat RP enriched compost had greater amounts of bio-available P (WSP+CSP) than FYM. The carbonic acidand organic acids produced during the decompositionof organic matter solubilize apatite in the RP, result-ing in the release of phosphate and calcium into thesolution (Biswas et al. 2009). Enriched compost also

had greater amounts of dehydrogenase, acid and alka-line phosphatase activities compared to FYM, indi-cating the better quality of enriched compost producedusing rice straw mixed with RP.

Changes in Soil FertilitySoil organic carbon

It is evident that the soil organic carbon (SOC)content increased significantly due to various nutrientmanagement practices in all the physiological growthstages of wheat as compared to unfertilized controlplot (Table 2). The SOC content improved signifi-cantly in plots receiving application of enriched com-post and FYM alone as well as in combination with50% NPK as compared to 100% NPK (T2) in allgrowth stages of wheat. At CRI stage, SOC contentincreased by 46.2 per cent with 100% NPK treatedplot over unfertilized control plot (3.7 g kg-1). Fur-ther, these values increased by 85.5 and 69.8 per centwith combined application of 50% NPK+FYM (T5)and 50% NPK+RP enriched compost (T6), respec-tively. Similar trend in improvement in SOC contentsdue to different nutrient management were also ob-served at flowering and maturity stages of wheat. It isevident that with the advancement of physiologicalgrowth stages of wheat, SOC status decreased fromCRI stage to maturity stage irrespective of treatments.Data also revealed that SOC was significantly influ-enced by residual effect of various nutrient manage-ment practices during different physiological growthstages of green gram (Table 2). Data showed thatSOC varied from 3.4 to 4.9 g kg-1 in flowering; 3.3 to4.8 g kg-1 in pod formation and 3.1 to 4.4 g kg-1 inmaturity stage of green gram due to different treat-ments. The plot receiving 50% NPK+FYM resultedin significantly higher SOC in all the growth stagesof green gram as compared to other treatments exceptplot receiving 50% NPK+RP enriched compost. Atflowering stage, SOC increased by 26.1 per cent with100% NPK treated plot over control, while, these val-ues increased by 44.2 and 32.1 per cent with com-bined application of 50% NPK+FYM and 50%NPK+RP enriched compost, respectively.

The improvement in enhancing SOC in plot re-ceiving 50% NPK along with enriched compost maybe attributed to balanced and integrated use of inor-ganic and organic sources of nutrients. This may beattributed to enhanced crop growth which in turn, re-sulted in increased below-ground organic residues(e.g., root biomass, rhizodeposition, root exudatesetc.), and thus raised the SOM status. The increasedSOM in enriched compost amended plots also may beattributed to slower break down rate (less and con-

228 JOURNAL OF THE INDIAN SOCIETY OF SOIL SCIENCE [Vol. 62

stant mineralization rate) of enriched compost in soil.Kundu et al. (2007) reported that soil organic C con-tent improved in fertilized plots as compared to theunfertilized plots due to C addition through the rootsand crop residues, higher humification rate constant,and lower decay rate. Similarly, in a long-term ex-periment, Moharana et al. (2012) observed that theSOC was considerably greater in soils receiving FYMalong with NPK fertilizer than in plots receivingmerely NPK fertilizer. In this study, the combinationof organic and inorganic fertilization enhanced theaccumulation of SOC, which is consistent with otherstudies (Majumdar et al. 2008; Banger et al. 2009).

Mineral NMineral N (NH4

+ -N + NO3- -N) in soil increased

significantly due to application of RP enriched com-post and FYM with and without inorganic fertilizersduring different physiological growth stages of wheatthan unfertilized control (Table 3). Among the nutri-ent management practices, significantly higher amountof mineral N in soils were observed in 100% NPKtreated plots in all the growth stages of wheat. It was

observed that plot receiving 100% NPK increasedmineral N by 93.3, 130.3 and 112.6 per cent overcontrol in CRI, flowering and maturity stages, respec-tively. While, treatment receiving enriched compostmaintained significantly lower mineral N at CRI stage,but registered higher build-up in mineral N at the lat-ter stages, particularly at maturity. Further, it was ob-served that combined application of 50% NPK+RPenriched compost registered mineral N which was atpar with 100% NPK treated plot, but out yieldedhigher mineral N in all the growth stages of wheatthan sole application of enriched compost or FYM.Data revealed that significantly higher amounts ofmineral N in soils were observed in treatments receiv-ing 50% NPK +RP enriched compost which resultedin 91.4, 142.0 and 119.7 per cent greater build-up inmineral N over unfertilized control in flowering, podformation and maturity stages of green gram, respec-tively (Table 3). Sole application of FYM or RP en-riched compost resulted in significantly lower mineralN in all the physiological growth stages of green gram.In general, build-up of mineral N decreased in all thegrowth stages in green gram grown on residual fertil-

Table 2. Changes in soil organic C content during different physiological growth stages of wheat and green gram grown insequence as affected by application of RP enriched compost

Treatment Soil organic C (g kg-1) content underWheat (direct effect) Green gram (residual effect)

CRI Flowering Maturity Flowering Pod formation MaturityT1: Control 3.7d 3.6d 3.5c 3.4c 3.3c 3.1bT2: 100% NPK 5.4c (46.2)# 4.7c (30.3) 4.3b (24.2) 4.3b (26.1) 4.3ab (27.1) 3.7b (14.0)T3: FYM 6.2b (67.4) 5.7ab (56.8) 4.7b (33.8) 4.5ab (31.9) 4.3a (29.7) 4.0ab (22.9)T4: RP enriched compost 5.7bc (55.7) 5.5bc (50.7) 4.6b (31.4) 4.3ab (26.5) 4.1b (21.8) 3.8b (15.2)T5: 50% NPK+FYM 6.8a (85.5) 6.4a (76.3) 5.6a (61.5) 4.9ab (44.2) 4.8a (43.9) 4.8a (45.5)T6: 50% NPK+RP enriched compost 6.3ab (69.8) 6.2a (72.6) 5.4a (53.9) 4.5a (32.1) 4.4ab (31.5) 4.2ab (28.6)# Figure in parentheses indicate per cent increase over control* For each parameter, different lower case letter within the same column indicate that the treatments are significantly different atP<0.05 according to DMRT for separation of means

Table 3. Changes in mineral-N in soil during different physiological growth stages of wheat and green gram grown in sequenceas affected by application of RP enriched compost

Treatment Mineral N (mg kg-1) content underWheat (direct effect) Green gram (residual effect)

CRI Flowering Maturity Flowering Pod formation MaturityT1: Control 37.7d 47.9e 43.7e 37.8d 33.0d 36.8dT2: 100% NPK 72.8a (93.3)# 110.3a (130.3) 92.9b (112.6) 58.8bc (55.6) 58.5c (77.0) 64.3b (74.7)T3: FYM 46.1c (22.4) 72.7d (51.7) 60.3d (37.9) 43.1d (14.0) 50.5c (52.8) 55.5c (50.7)T4: RP enriched compost 56.8b (50.7) 88.8c (85.4) 76.1c (74.1) 55.1c (45.9) 59.4c (79.7) 64.5b (75.4)T5: 50% NPK+FYM 59.1b (57.1) 101.0b (110.8) 92.4b (111.4) 64.6b (70.9) 69.2b (109.6) 70.0b (90.2)T6: 50% NPK+ RP enriched 71.3a (89.3) 112.7a (135.2) 102.1a (133.5) 72.3a (91.4) 79.9a (142.0) 80.8a (119.7)compost# Figure in parentheses indicate per cent increase over control* For each parameter, different lower case letter within the same column indicate that the treatments are significantly different atP<0.05 according to DMRT for separation of means

2014] NUTRIENT AVAILABILITY AND ENZYME ACTIVITIES UNDER WHEAT-GREEN GRAM 229

ity compared to values obtained in wheat (direct ef-fect) irrespective of treatments. According to Reesand Castle (2002) application of manures leads to anenrichment of the soil N pool, and increases the effi-ciency of organic fertilizer by releasing higher min-eral N. Organic manures release mineral N slowly,which help in supplying higher mineral N to crops,particularly latter stages of crops. A major proportionof basal dose of fertilizers transforms into mineral Nand utilized by the crop during initial stages of cropgrowth because of more requirement of N at the earlystage. These results suggest that integrated nutrientmanagement was more persistent in supplying min-eral N in soil than only chemical N fertilizers.Whereas, application of 100% organic could not main-tain the level of mineral N in soil than that obtainedunder inorganic or integrated sources.

Olsen-PApplication of RP enriched compost and inor-

ganic fertilizers to wheat had an immense impact ondynamics of P release during different physiologicalgrowth stages of crop because of mineralization of Pfrom RP enriched compost as evident from the greaterbuild-up in Olsen-P in soil (Table 4). At CRI stage,plots receiving 50% NPK+RP enriched compost re-sulted in significantly higher Olsen -P than other treat-ments. Greater amounts of Olsen-P in soil were main-tained due to 50% NPK+RP enriched compost treatedplot in flowering and maturity stages of wheat. It isevident that treatment receiving 100% NPK recordedsignificantly higher Olsen-P at CRI stage than RP en-riched compost alone because of presence of higheramount of water soluble P in the former. However,RP enriched compost registered greater amount ofavailable P at the latter stages, particularly at maturitywhich is comparable to 100% NPK treated plots. It is

also evident that the amounts of Olsen-P in soil de-clined gradually in 100% NPK treated plot with theadvancement of physiological growth stages of wheat,while these values were increased gradually due to50% NPK+RP enriched compost treated plot. Thismight be due to the fact that P content in RP enrichedcompost, being less soluble, released P slowly andmaintained greater amounts of P in soil at the latterpart of the crop growth than the former which is morewater soluble form and subjected to greater fixationin soil.

Significant release of available P due to com-bined use of inorganic fertilizers and enriched com-post clearly indicates the beneficial effect of integratednutrient management in enhancing available P in soilsduring different growth stages of wheat. It is alsoevident that enriched compost had a considerable re-sidual effect on subsequent crop as evident fromgreater build-up on Olsen-P in soils. This may be at-tributed to increased availability of P (citrate solubleand organic P) in RP enriched compost than FYM(Biswas and Narayanasamy 2006). The released phos-phate was then immobilized into the microbial cellsas evidenced by higher water soluble, citrate solubleand organic P contents in the final product. Increasein available P content during growth stages of wheatmay be attributed to the microbial P present in RPenriched compost which acts as a slow release fertil-izer due to its slow rate of decomposition and pro-vides available P to plants for a longer period insteadof fixation and/or precipitation in soil minerals as incase of commercial water soluble P-fertilizer (Vermaet al. 2013). This might be due to the fact that themajor P fraction added through RP enriched compostis in the organic pool, which mineralized slowly withtime (Biswas and Narayanasamy 2006). That is whyincrease in available P content in soil with P addi-

Table 4. Changes in Olsen-P in soil during different physiological growth stages of wheat and green gram grown in sequence asaffected by application of RP enriched compost

Treatment Olsen-P (kg ha-1) in soil underWheat (direct effect) Green gram (residual effect)

CRI Flowering Maturity Flowering Pod formation MaturityT1: Control 12.1e 12.6c 13.0d 12.1d 11.6d 11.1cT2: 100% NPK 21.3ab (76.5)# 21.5ab (70.1) 19.9c (53.5) 17.1c (41.4) 16.0bc (37.9) 15.0b (35.3)T3: FYM 15.7d (29.6) 17.1b (35.2) 18.6c (43.7) 15.8c (30.8) 15.7c (34.9) 15.6b (41.0)T4: RP enriched compost 18.2cd (50.4) 19.2b (52.0) 20.8bc (60.5) 19.9b (64.9) 19.0b (63.3) 17.3b (55.7)T5: 50% NPK+FYM 20.2bc (66.9) 20.9ab (65.7) 22.5b (73.6) 20.3b (68.4) 18.5b (59.4) 17.4b (57.4)T6: 50% NPK+ RP enriched 24.3a (100.8) 24.6a (95.2) 25.9a (100.0) 23.5a (94.7) 22.6a (94.8) 21.7a (95.6)compost# Figure in parentheses indicate per cent increase over control* For each parameter, different lower case letter within the same column indicate that the treatments are significantly different atP<0.05 according to DMRT for separation of means

230 JOURNAL OF THE INDIAN SOCIETY OF SOIL SCIENCE [Vol. 62

tions through inorganic fertilizer and RP enrichedcompost is expected with the advance of growth stagesof wheat.

NH4OAc-KSignificant build-up in NH4OAc-K was observed

due to application of organic and inorganic fertilizerseither alone or in combination in different physiologi-cal growth stages of wheat over control (Table 5).Plots receiving 100% NPK maintained significantlyhigher NH4OAc-K in all the growth stages of wheatthan others except plots receiving 50% NPK+RP en-riched compost which was at par. Plots receiving100% NPK increased NH4OAc-K by 38.2, 44.2 and42.3 per cent higher over control in CRI, floweringand maturity stages, respectively. In general, higheramounts of NH4OAc-K were found in the floweringstage followed by pod formation and maturity stageof green gram irrespective of treatments. It was evi-dent that plot receiving 50% NPK+RP enriched com-post increased NH4OAc-K by 29.5, 26.5 and 26.7 percent higher in flowering, pod formation and maturitystages of green gram, respectively over control

Dehydrogenase ActivityData revealed significant variations in dehydro-

genase activity in soils due to different nutrient man-agement practices under present wheat-green gram ro-tation (Fig. 1). It was evident that plots receiving100% NPK increased dehydrogenase activity by 31.7per cent over control. While, plots receiving FYMand RP enriched compost resulted an increase in de-hydrogenase activity by 39.3 and 47.1 per cent overcontrol, respectively. Dehydrogenase activity in-creased further due to conjoint use of either FYM orRP enriched compost with 50% NPK by 53.9 and69.5 per cent, respectively over control. Irrespective

of treatments, dehydrogenase activities were higher inthe flowering stage than CRI and maturity stages ofwheat. Significantly higher dehydrogenase activitywas maintained due to application of 50% NPK+RPenriched compost even in all the physiological growthstages of green gram than other nutrient managementpractices (Fig. 1). It improved dehydrogenase activityby 82.4, 47.0 and 47.1 per cent over control at flow-ering, pod formation and maturity stages of greengram, respectively over control.

Dehydrogenase activity is considered an indica-tor of overall microbial activity because it occurs in-tra-cellularly in all living microbial cells, and it islinked with microbial respiratory processes (Bolton etal. 1985). Therefore, the use of dehydrogenase activ-ity as an index of microbial activity has been sug-gested by many workers (Nannipieri et al. 1990). Useof different nutrient management promoted a signifi-cant increase in dehydrogenase activity in wheat andgreen gram rhizosphere compared to control. In gen-eral, the peak dehydrogenase activity was observed inflowering stage and then declined subsequent. Thelower values of dehydrogenase activity after flower-ing may be explained by the fact that addition of morestable organic matter may not improve the microbialactivity for a longer duration (Marzadori et al. 1996).Saha et al. (2008) observed that manure applicationincreased soil dehydrogenase activity significantly.The present results suggest that application of FYMand RP enriched compost directly or indirectly influ-ences the enzyme activity, which in turn regulatesnutrient transformation. Application of balanced andintegrated use of nutrients improved the organic mat-ter status of soils, which enhanced dehydrogenase ac-tivity. It was also observed in the present study thatdehydrogenase activity is less influenced by mineralN fertilization, which is in agreement with the studies

Table 5. Changes in NH4OAc-K in soil during different physiological growth stages of wheat and green gram grown insequence as affected by application of RP enriched compost

Treatment NH4OAc-K (kg ha-1) in soil underWheat (direct effect) Green gram (residual effect)

CRI Flowering Maturity Flowering Pod formation MaturityT1: Control 158d 156d 151c 149d 143e 136eT2: 100% NPK 219a (38.2)# 225a (44.2) 215a (42.3) 199a (33.5) 191a (33.9) 178a (30.9)T3: FYM 181c (14.4) 186c (19.0) 178b (17.3) 169c (13.4) 158d (10.7) 155d (14.1)T4: RP enriched compost 192bc (21.6) 200b (28.3) 190b (25.8) 173c (16.4) 162cd (13.5) 159cd (16.4)T5: 50% NPK+FYM 196b (23.7) 200b (28.3) 191b (25.9) 182bc (21.9) 169c (18.3) 168bc (23.1)T6: 50% NPK+ RP enriched 217a (37.3) 219a (40.2) 214a (41.5) 193ab (29.5) 180b (26.5) 173ab (26.7)compost# Figure in parentheses indicate per cent increase over control* For each parameter, different lower case letter within the same column indicate that the treatments are significantly different atP<0.05 according to DMRT for separation of means

2014] NUTRIENT AVAILABILITY AND ENZYME ACTIVITIES UNDER WHEAT-GREEN GRAM 231

of Kautz et al. (2004). The stronger effects of FYMor RP enriched compost on dehydrogenase activitymight be due to more easily decomposable compo-nents of organic matter on the metabolism of soil mi-croorganisms.

Phosphatase activityAlkaline phosphatase activity increased signifi-

cantly due to application of RP enriched compost andinorganic fertilizers in different physiological growthstages of wheat than control (Fig. 2). Among the nu-

trient management practices, significantly higheramount of alkaline phosphatase activity was observedin 50% NPK+RP enriched compost treated plots inall the crop growth stages. It was observed that plotreceiving 100% NPK increased alkaline phosphataseactivity by 13.1, 21.7 and 32.6 per cent over controlin CRI, flowering and maturity stages, respectively.While, plot receiving RP enriched compost alone in-creased alkaline phosphatase activity by 36.4, 33.5and 47.0 per cent in CRI, flowering and maturitystages, respectively. Further, it was observed that com-

*Error bars represent standard deviation of the mean.**T1: Control; T2: 100% NPK; T3: FYM; T4: RP enriched compost; T5: 50% NPK+FYM; T6: 50% NPK+RP enriched compost

Fig. 2. Changes in alkaline phosphatase activity in soil as affected by RP enriched compost, FYM and inorganic fertilizerapplication during different physiological growth stages of wheat and green gram

* Error bars represent standard deviation of the mean.**T1: Control; T2: 100% NPK; T3: FYM; T4: RP enriched compost; T5: 50% NPK+FYM; T6: 50% NPK+RP enriched compost

Fig. 1. Changes in dehydrogenase activity in soil as affected by RP enriched compost, FYM and inorganic fertilizer applicationduring different physiological growth stages of wheat and green gram

232 JOURNAL OF THE INDIAN SOCIETY OF SOIL SCIENCE [Vol. 62

bined application of 50% NPK+RP enriched compostresulted in 50.3, 42.9 and 56.9 per cent greater alka-line phosphatase activity in CRI, flowering and matu-rity stages, respectively. Significantly higher amountsof acid phosphatase activity was maintained in plotsreceiving 50% NPK+RP enriched compost in all thegrowth stages of wheat over plots receiving 100%NPK as well as RP enriched compost applied alone(Fig. 3). Plots receiving 50% NPK+RP enriched com-post resulted in 76.4, 130.6 and 133.9 per cent greaterbuild-up in acid phosphatase activity over control.Similar trend on acid phosphatase activity was ob-served in case of green gram grown on residual fertil-ity (Fig. 3). Plots receiving 50% NPK+RP enrichedcompost resulted in 113.0, 106.2 and 106.1 per centgreater acid phosphatase activity over control in flow-ering, pod formation and maturity stages, respectively.These values for 100% NPK treated plots were 36.1,38.4 and 24.7 per cent over control in respectivestages.

Phosphatases are inducible enzymes excreted byplant roots and soil organisms, which can be stimu-lated by P starvation (Tarafdar and Jungk 1987).Therefore, phosphatase activities have been regardedas an important factor in maintaining and controllingmineralization rate of soil organic P, and a good indi-cator of P-deficiency (Vance et al. 2003). Mainte-nance of acid phosphatase activity in unamended con-trol soil confirms the report that organic manure/com-post did not alter the enzyme-substrate affinity, whilemineral fertilizer reduced this affinity or changed thecomposition and activity of soil microbiota

(Masciandro et al. 2000). The phosphatase activityincreases when the sources of nutrients have an equili-brated balance between C and N (Nannipieri 1994).Thus, integrated use of manures and fertilizers hadgreater phosphatase activity than 100% NPK as evi-denced in our present study.

Pearson’s correlation matrix revealed the exist-ence of significant linear relationship (P<0.01) be-tween soil nutrient availability and enzyme activity asinfluenced by different nutrient management (Table6). It was observed that SOC was significantly andpositively correlated with mineral N, Olsen-P andNH4OAc-K in both wheat and green gram. Similarly,SOC was correlated with all enzymes assayed exceptalkaline phosphatase in wheat. Mineral N also showedpositive correlations with Olsen-P, NH4OAc-K, dehy-drogenase, alkaline phosphatase and acid phosphataseactivity. Strong relationships were noticed betweenOlsen-P with NH4OAc-K, dehydrogenase, alkalinephosphatase and acid phosphatase activity. It was alsorevealed that NH4OAc-K maintained positive relation-ship with dehydrogenase, alkaline phosphatase andacid phosphatase activity. Further, dehydrogenase ac-tivity shared a strong correlation with alkaline phos-phatase and acid phosphatase activity, which are in-volved in P transformation.

ConclusionsThe results demonstrated that application of rock

phosphate enriched compost in combination with 50%inorganic fertilizer is the most desirable in order toimprove nutrient availability and enzyme activities in

*Error bars represent standard deviation of the mean.**T1: Control; T2: 100% NPK; T3: FYM; T4: RP enriched compost; T5: 50% NPK+FYM; T6: 50% NPK+RP enriched compost

Fig. 3. Changes in acid phosphatase activity in soil as affected by RP enriched compost, FYM and inorganic fertilizer applica-tion during different physiological growth stages of wheat and green gram

2014] NUTRIENT AVAILABILITY AND ENZYME ACTIVITIES UNDER WHEAT-GREEN GRAM 233

soil. Thus, it can be concluded from the present studythat enriched compost could be prepared using low-grade rock phosphate and rice straw which could beused as an alternate nutrient source for maintainingsoil nutrient availability and enzyme activities, thereby50% costly chemical fertilizers could be saved.

AcknowledgmentsThe senior author thanks to the Indian Agricul-

tural Research Institute, New Delhi for providing fi-nancial support as senior research fellowship duringhis research work and the Head, Division of Soil Sci-ence and Agricultural Chemistry, Indian AgriculturalResearch Institute, New Delhi for providing facilitiesfor successful completion of the research works.

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Received 29 April 2014; Received in revised form 31 July 2014; Accepted 30 September 2014