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*Corresponding author’s e-mail: poonambhagat11.pb@gmail.com

Indian J. Agric. Res., 50 (6) 2016 : 542-548Print ISSN:0367-8245 / Online ISSN:0976-058X

Effect of mulching on soil environment, microbial floraand growth of potato under field conditionsPoonam Bhagat*, S.K. Gosal and C.B. Singh

Department of Microbiology and Department of Soil Science,Punjab Agricultural University, Ludhiana-141 004, Punjab, India.Received: 25-02-2016 Accepted: 03-12-2016 DOI: 10.18805/ijare.v50i6.6671

ABSTRACTMulches modify hydrothermal regime, recycles plant nutrients, promote crop development and increase yields. The impactof straw mulch and different doses of recommended nitrogen was studied on soil microbial flora, soil physico-chemicalproperties and plant growth parameters of potato at different time intervals under field conditions. Maximum bacterialpopulation (75× 107 cfu g-1 soil), plant growth promoting rhizobacteria count (63× 105 cfu g-1 soil) and fungal population(69× 103 cfu g-1 soil) were observed with the treatment having rice straw mulch @ 6 tonnes/ha and 100% N-level whilediazotrophic count (42× 105 cfu g-1 soil) was found with treatment having mulch (6t) but no nitrogen fertilizer at 30 DAS.Mulched soil samples gave statistically higher microbial population. The soil pH and the electrical conductivity of soilwere not significantly affected by the different applications. A slight improvement in soil organic content was observed inmulched (0.32%) over unmulched (0.24%) soil samples at 90 DAS. The mineral nitrogen content of soil i.e. ammonical(235.2 kg/ha) and nitrate (156.8 k/ha) nitrogen were greatly affected at 90 DAS by mulching and higher doses of nitrogenfertilization. The altered microbial population helps in improving the various growth parameters of potato plants. Maximumchlorophyll content (1.84 mg/g), maximum dry root-shoot biomass (0.7 g/pl and 5.8 g/pl) and maximum yield (366.8 q/ha)were observed with the treatment having mulch and 100% N-level. It is also concluded that mulch increased the minimumsoil temperature by 2-30C and lower down the maximum by 2 to 80C.

Key words: Nitrogen fertilization, Potato (Solanum tuberosum L.), Rice straw mulch, Soil micro-organisms, Soil temperature

INTRODUCTIONSoil micro-organisms are immersed in a framework

of interactions known to affect plant fitness and soilquality. The soil micro-organisms act as sink and source ofnutrients as these are organic decomposers and hence providemore nutrients to plants. Soil micro-organisms are alsocapable of promoting plant growth through differentmechanisms, such as biological nitrogen fixation (BNF),phytohormone production, phosphate solubilization andsiderophore production. They are also known to participatein many important ecosystem processes such as thebiological control of plant pathogens, nutrient cycling, and/or seedling growth (Persello-Cartieaux et al 2003, Zahir etal 2004). Soil micro-organisms are involved in fundamentalactivities that ensure the stability and productivity of bothagricultural systems and natural ecosystems (Barea et al2005). Soil micro-organisms are greatly influenced by themodern agricultural practices like mulching and N-fertilization. The nutrients in mulch and N-fertilizer have topass through the gut of the microbes in the soil. Thecultivation method (bare soil and mulch) introduceddifferences in the initial counts, evolution and tolerance torefrigeration temperatures for some of the microbialpopulations (Ponce et al 2008). Along with soil covering

techniques judicious application of manures and fertilizersalso increase organic matter level and structural improvementof soil.

Potato is an economically important staple cropbecause of its great yield potential and high nutritive value.In India, more than 80 per cent of the potato crop is raised inthe winter season (Rabi) under assured irrigation during shortwinter days. Mulch helps in retaining soil moisture andmaintaining soil temperature, also prevents soil compactionand has favourable effects on soil physical, chemical andbiological properties such as pH, organic carbon, and waterholding capacity and bulk density of the soil (Singh et al2005). The farmers feel that mulching accentuates the rodentproblem in the crop (Sidhu and Beri 2008). Rice straw mulchincreases albedo and decreases solar energy flux to the soil(Lalitha et al 2010). During night hours, straw mulch keepsthe soil warmer by intercepting the long wave energy fluxfrom soil to air.

Both mulching and N-fertilization combinedlyaffect the microbial population, the combined technique helpsthe agriculturally important soil micro-organisms to bloom.Mulching has a stimulating effect on soil microbes andthrough this on soil fertility (Csaba et al 2007).

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MATERIALS AND METHODSField experiment was conducted in sandy loam soil

at Punjab Agricultural University, Ludhiana. Potato seedlingswere sown in bed system and field was primarily analysedfor physico-chemical properties and microbial populationcount. The soil sampling was done by collecting rhizosphericsoil (0-15 cm) from four randomly selected points in eachplot. The experiment was laid out in RBD in triplicate usingfour different nitrogen levels (0, 75%, 100% and 125%) ofthe recommended dose of N-fertilizer i.e. 0, 135 kg/ha,180kg/ha and 225 kg/ha, respectively and rice straw mulching(6 tonnes ha-1) was done in half of the field.Microbial count/enumeration: The enumeration ofdifferent micro-organisms was done using standard spreadplate technique. The bacterial count was enumerated onnutrient agar (Wright 1933) media plates, fungi enumeratedon glucose yeast extract (GYE) media, diazotrophsenumerated on Burk’s agar and PGPR’s on King’s Bmedia.Soil physico-chemical properties: The physico-chemicalproperties were determined at different time intervals. Soiltexture was determined by feel method, soil pH and electricalconductivity (EC) were determined using L1 glass electrodepH meter (Jackson 1958) and Sol bridge (Richard 1954)respectively. Organic carbon (OC) content was determinedby Walkley and Black’s (1934). Chlorophyll content wasestimated by Anderson and Boardmann (1964) method.Root-shoot biomass was observed at different time intervalsby drying the samples in an oven at 65ºC till a constant dryweight will be obtained.Yield and yield parameters: Yield was taken at harvestand was measured by taking the weight of potatoes onweighing balance. Number of potatoes per plant were alsocounted.RESULTS AND DISCUSSION

The effect of mulching and different levels of N-fertilization was studied on soil microbial flora, physico-chemical properties of soil and yield of potato crop.Microbial count: At different time intervals, differentmicrobes were enumerated in mulched and unmulched potatofield having different N-levels. At zero day of the experiment,the initial bacterial count, diazotrophs count, PGPR’s andfungus count was found to be 42 × 106, 8× 105, 56× 104 and16× 103 cfu g-1 soil respectively. The count was observed tobe statistically higher when compared to zero day count andmaximum increase was found with treatment T3 (havingmulch + 100% N-level) followed by T4 (mulch + 125% N-level), T2 (mulch + 75% N-level), T7 (unmulch + 100% N-level) and T8 (unmulch + 125% N-level). At 60 DAS and90 DAS (Table 1) the microbial count was found to be low.The diazotrophic count was maximum with treatment T1(mulch + 0 N-level).

It was observed that microbial population was morein mulched soil than unmulched soil. The increasedrhizospheric bacterial population in mulched crops alsoreported by Tiquia et al (2002). The increase in microbialcolonies/population may be due to increasing organic carboncontent of the soil due to mulching which is considered asone of the major constituents of the food supply for micro-organisms. Nitogen fertilization also imposes effect ongrowth of microbes. The management practices such asfertilization, crop rotation, application of organicamendments and tillage favours the growth of micro-organisms (Workneh and Van Bruggen 1994). The similarfindings were reported by Shashidhar et al (2009), Mukherjeeet al (1991) and Wu et al (1993). The air temperature wasrecorded very low during the experiment but microbial countwas found good in mulched soil in the low temperature.Mulching increased soil microbial flora and helped inmaintaining favourable soil temperature for microbial growth(Aguero et al 2008). Temperature plays pivotal role in thegrowth of plants. The potato crop was cultivated fromOctober to January in Punjab State, India. This period is notsuitable for the optimum growth of microbes as thetemperature is very low during December and January. Inthe present study, the maximum rise in soil temperature by2.90C was observed in mulched soil as compared to unmulchsoil with respect to air temperature. The sun’s energy passedthrough the mulch and heated the air and soil beneath themulch directly and then the heat was trapped by thephenomenon of “greenhouse effect” (Hu et al 1995).Physico-chemical properties: The physico-chemicalproperties of the soil were determined at different timeintervals, soil pH was observed to be 7.3, electricalconductivity (EC) was 0.32dSm-1, organic carbon (OC) was0.23%, ammonical and nitrate nitrogen as 29.41 and 141 kgha-1 respectively at zero day. There was no considerablechanges observed in them till 30 DAS. A change was foundin N content of the soil with increasing number of days dueto N-fertilization. At 60 DAS OC was recorded slightlyincreased with mulched soil samples (Table 1).

The experiment was done on sandy loam soil andsandy soils have low water holding capacity, the rice strawmulch helps in retaining the moisture in the soil. Mulchesprevent loss of water from the soil by evaporation (Yaun etal 2009). Mulching and N-fertilization had no effect on soilpH. The results were similar with Carrera et al (2007),Ashworth and Harrison (1983), Carter and Johnson (1988)who also reported that most mulching materials do notstrongly affect soil pH. Similarly, there was also no effect ofmulching and N-fertilization on electrical conductivity ofsoil. Over the years the soil electrical conductivity of Punjabstate virtually remained unaltered reported by Benbi and Brar(2009). The OC content was observed to be changed slightly.Powlson and Jenkinson (1981), Schnurer et al (1985),

544 INDIAN JOURNAL OF AGRICULTURAL RESEARCH

Tabl

e 1:

Effe

ct o

f m

ulch

ing

and

N-fe

rtiliz

atio

n on

diff

eren

t m

icro

bial

pop

ulat

ion

and

soil

phys

ic-c

hem

ical

pro

perti

es a

t di

ffere

nt ti

me

inte

rval

s

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Persson and Kirchmann (1994) also reported that the totalsoil organic matter content changes slowly after mulching.Shashidhar et al (2009) who also found no measurableincrease in organic carbon content in paddy straw. The resultsshowed that there was an increase in nitrification potentialof the soil after application of mulch and high dose ofnitrogen fertilizer due to the N-mineralizable process whichincreased the supply of NH4

+. A high increase in nitrificationpotential after the application of cover cropping system wasalso observed by Kandeler and Eder (1993). The findingswere corroborated with the studies of Geiger et al (1992)and Insam et al (1991) who found that the combination ofresidues plus fertilizer resulted in greater enhancement ofsoil fertility parameters.Root-Shoot biomass: The root-shoot fresh and dry weightswere observed at different time intervals viz 30, 60 and 90DAS. At 30 DAS, the maximum root fresh weight (10.2 g/pl) was observed with treatment T4 followed by treatmentT3 (9.1 g/pl) while dry weight (0.7 g/pl) was observedmaximum with treatment T3 followed by the treatment T2(0.6 g/pl) though there was non-significant increase in thetreatments. At 60 DAS and 90 DAS, the maximum root freshweight (18.2 g/pl and 20.2 g/pl) and dry weight (1.6 g/pland 2.1 g/pl) was found with treatment T3. The shoot freshweight (97 g/pl) and dry weight (5.8 g/pl) was observedmaximum with treatment T3 followed by the treatment T4(85 g/pl and 5 g/pl) at 30 DAS. Similarly, at 60 DAS and 90DAS, the maximum shoot fresh weight (185 g/pl and 280 g/pl) and dry weight (17.2 g/pl and 26.4 g/pl) was found withtreatment T3 followed by the treatment T4 (11.5 g/pl and 20g/pl respectively). It was observed in all the treatments thatroot-shoot dry weight was significantly higher in mulchedplants over the unmulched plants (Fig 1a, 1b,1c and 1d).

The results indicated that mulching favoured betterdevelopment of roots by protecting the plants fromenvironmental stresses. These findings were similar with theresults obtained by Lynch and Tai (1989), De la Morena etal (1994), Lynch and Rowberry (1997) that plant height andbiomass were increased in the presence of mulch and N-fertilization. There was a significant increase in stem biomasswith mulch and high N-level according to Alam et al (2007).The altered micro flora also helped in better availability ofplant nutrients (Kennedy and Smith 1995) and play animportant role in nitrogen cycling, nitrogen fixation andmineralization processes in all ecosystems (Neill et al 1997).Chlorophyll content: The total chlorophyll content was foundto be significantly higher with treatment T3. At 30 DAS,maximum total chlorophyll content was observed to be 1.84mg/g followed by treatment T4 (1.24 mg/g). Similarly at 60DAS and 90 DAS, the maximum total chlorophyll contentwas found to be maximum with treatment T3 i.e, 0.84 mg/gand 0.61 mg/g respectively followed by treatment T4 i.e,0.53 mg/g and 0.29 mg/g respectively. With the increasing

Fig: 1a, 1b, 1c, 1d & 1e shows effect of altered micro flora on rootfresh weight, root dry weight, shoot fresh weight, shoot dry weightand total chlorophyll content at different time intervals respectively.

a

b

c

d

e

546 INDIAN JOURNAL OF AGRICULTURAL RESEARCH

number of days total chlorophyll content was observed tobe decreased (Fig 1e). It was observed that the totalchlorophyll content in mulched potato leaves was found tobe significantly higher as compared to unmulch potato leaves.

The investigation showed that with mulching andN-fertilization, the rhizospheric microbial population wasincreased which resulted in more decomposition of nutrientsinto inorganic forms i.e. major availability of nutrients(Sainju et al 2001) to plant and hence, resulted in vegetativegrowth of the plant (Gao et al 2009), which might haveresulted in more leaf area. These findings were alsocorroborated with the findings of Gangawar et al (2000) whoreported that paddy straw mulch showed maximum leaf yield.According to Jacks et al (1955) the increase in leaf area wasdue to better soil moisture retention, creation of favourablesoil temperature, suppression of weed growth, improved soilstructure, high status nutrients in soil and well developmentof root system because of mulching. Higher nitrogen levelis also known to affect the leaf area, which results in morephotosynthesis. The addition of nitrogen ensuresmaintenance of photosynthetically active leaves for longerduration (Millard and Marshall 1986).Yield: In the present study, the maximum potato tuber yieldwas recorded as 366.8 q/ha with treatment T3 followed bytreatment T4 (364.1 q/ha). Maximum yield with 100% N-level was statistical at par with treatment having 125% N-level in mulched potato plants. In unmulched potato plantsthe maximum yield (349.3 q/ha) was found with treatmentT8 followed by treatment T7 (324.3 q/ha). There wasincrease in the yield of mulched potato plant over theunmulched though the increase was not significant (Fig 2aand 2b).

The investigations revealed that mulch increasessoil moisture and nutrients availability to plant roots, in turnleading to higher yield (Tolk et al 1999 and Liu et al 2002).According to Shiri-e-Janagard (2009), the highest yield perplant was obtained by applying 160 kg N/ha, this dose wasapproximately similar to the dose provided in the treatmenthaving 100% N-level. A significant increase in wheat yield

due to mulching and higher biomass in mulched crops ascompared to unmulched crops were also reported by Gao etal (2009).CONCLUSION

It is concluded from the results obtained thatapplication of mulch enhances the soil microbial populationdue to addition of nutrients into the soil which may resultedin enhanced microbial activity. The enhanced microbialpopulation increased the plant growth parameters i.e. totalchlorophyll content, root-shoot biomass and the yield ofpotato due to more availability of nutrients to the plant. Thegrowth parameters were significantly higher in the mulchedplants over the unmulched plants. The treatment havingmulch and 100% nitogen level of recommended dose wasfound to be most effective in all the parameters studied.

a

b

Fig: 2a &2b shows effect of altered micro flora on number oftubers per plant and yield of potatao at harvest respectively.

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