CROP ROTATION EFFECTS ON SOIL ORGANIC MATIER AND SOIL MICROBIAl PROPERTIES

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1 Indian J. Agric. Res.: 39 (2}: ,2005 CROP ROTATION EFFECTS ON SOIL ORGANIC MATIER AND SOIL MICROBIAl PROPERTIES S.K DhuII, S. Goyal, KK Kapoor* and M.C. Mundra** Department of Microbiology, CCS Haryana Agricultural University, Hisar , India ABSTRACT Changes in soil organic matter level, microbial bio~ss C, carbon mineralization and various sou- enzyme activities were studied in a crop rotation experiment. It was found that soil organic C and total N level increased by taking three crops or including green manure in the rotation than taking two crops. Microbial biomassc and dehydrogenase activity was highest in pearlmiliet~eat.green manure rotation and was lowest in pearimiuet-wheat rotation. However protease activity was found to be highest in soyabean-wheat-cowpea rotation. INTRODUCTION Crop r:nanagem~ntpractices influence the soil prodl'ctivity by altering the soilenvironment which.' in turn affects transformations of plant residue carbon to soil organic matterthrough the activity of microbes (Ftanzluebbers fit' a/., 1995; Doran et a/., 1996). The benefits of organic manures, crop rotation, greeri manuring and growing legumes for maintaining soil organic matter and fertility have been well established (Campbell et a/., 1991; Gregorich et a/., 1994). Soil and crop management practices exert a considerable. influence on the level of organic matter retained overtime (Campbell et a/., 1992). The living fraction of organic matter, the microbial biomass responds much more quickly to changes in crop management pra<;tices or environmental conditions than soil organic matter (Martens. 1995). Therefore, measurement of soil microbial biomass and its activities provides a sensitive indication of organic matter turnover. Greater knowledge of short and long-term effects of various agricultural management practices or soil biological. properties is needed to assess the contribution of these practices to su<;tainable land management. The present study was undertaken to ascertain the short term changes in soil organic matter level, microbial Corresponding author Department of Agronomy, Haryana Agricultural University, Hisar , India. biomass, carbon mineralization and soil enzym~ activities resulting from different crop rotations. MATERIAL AND METHODS Description by field experiment: In order to identify appropriate cropping system with high productivity, a field experiment with different crop rotations was laid down in 1998 at Haryana Agricultural University, Hisar. The soil of the experimental field was sandy loam (69% sand, 17% silt and 14% Clay) classified as Typic Ustocrept and initially contained 0.43 per cent organic C and 0.04 per cent total N and had ph of 7.9 and electrical conductivity.of 0.25 ds/m. Different crop rotations (Table 1) followed every year were arranged in a completely randomized block design with four replicates each in a plot size of 80 m 2 Soil sampling: All the four plots of each treatment were sampled in May 200l. Samples from ten locations in each plot were taken with an auger to a depth of 15 cm and pooled together. The bulked soil samples of field moist soil from each plot were stored separately in polythene bags at 4 C. The soils were sieved through 2 mm seive and moisture content was adjusted to 50 per cent of 'water holding capacity and incubated at 30 C for 10 days to permit uniform rewetting and allow

2 Vol. 39, No Treatments Table 1. Annual crop rotations followed in the experiment Annual crop rotations T 1 Pearlmillet - Wheat- Greenmanure (Pennisetum glaucum) (Triticum aestivum) (Sesbaria aculeata) T z Pearlmillet - Mustard - C ~en gram (P. glaucum) (Brassica juncea) (Vigna radiata) T 3 Soyabean - Wheat - Fodder CowPea (Glycine max) (T aestivum) (Vigna unguiculata) T 4 Arhar - Wheat (Cajanus cajan) (T aestivum) To Pearlmillet - Potato - Green gram (P. gla'xum) (Solanum tuberosum) (\I. radiata) T 6 Pearlmillet Field pea Fodder Maize (P. glaucum) (Pisum sativum) (Zea mays) T 7 Cotton - Wheat (Gossypium hirsutum) (T aestivum) T s Pearlmillet - Wheat (P. glaucum) (T aestivum) microbial activity to equilibrate after initial disturbances. Sub samples of each soil were. air dried and ground for chemical analysis. Microbial biomass measurement: Soil microbial biomass C was measured by fumigation-extraction method of Vance et al. (1987), Three replicate 25 g portions of each soil were weighed into 100 ml capacity beakers and fumigated with ethanol free chloroform for 24 h in a vacuum desiccator. After chloroform removal the soils were extracted with 100 ml 0,5 M,~S04 for 30 min on a rotary shaker (160 revolutions per minute). Three replicates of unfumigated soils were extracted similarly at the time fumigation commenced. The organic C in the soil extracts was measured by dichromate oxidation method (Kalembasa andjenkinson, 1973) andthe soil microbial biomass carbon{bc) was calculated from BC =2.64 x EC Where EC is organic C extracted from fumigated soil minus organic C extracted from unfumigated soil. Enzyme activities: Soil dehydrogenase activity was measured by the method of Casida et aj. (1964) and soil protease activity was determined by the'method of Ladd. and Butler (1992). Carbon mineralization: Carbon mineralization was measured by measuring CO 2 evolution from soil over a four week period. Fifty gram moist soils were taken in 500 m,l capacity Erlenmayer flasks, Ten millilitres of 0.1 N NaOH contained in a test tube was placed inside each flask and flasks Were sealed airtight with rubber corks and incubated at 30 C. The CO 2 absorved in NaOH was measured by back titration with HCl using phenolphathalein indicator after addition of 2 ml of saturated BaCI 2 The amount of CO 2 evolved was converted to CO 2 -C and percentage of. C mineralized was calculated from the initial amount of C present in the soil. Other analytical methods: 'Soil ph was measured by using systronics 331 ph meter in 1:2.5 soil to water, suspension. Soil organic C was measured by dichromate oxidation (Kalembasa and Jenkinson, 1973) and total N was measured by Kjeldahl methods (Bremner and Mulvaney, 1982). RESULTS AND DISCUSSION The soil samples were analysed for

3 130 INDIAN JOURNAL OF AGRICULTURAL RESEARCH Table 2. Effect of different crop rotations on soil ph, electrical conductivity, organic C and total N Treatments ph EC Organic C Total N C/N (ds/m) (%) (%) ratio T j T2 T 3 T 4 T s T 6 T 7 T s COat 5% NS various parameters after three years of experimentation. There was no effect of different rotations on soil ph and electrical conductivity (Table 2). High buffering capacity of the soil did not allow drastic changes in soil ph. The maximum amount of soil organic C and total N were observed with pearlmilletpotato-greengram rotation (Ts)and lowest amount was present in cotton-wheat rotation (T a ). Generally more build up of soil organic matter was observed in treatments having three crops in the rotation compared to treatments with two crops in a year. There was significant decline in soil C:N ratioby inclusion of Sesbania acujeata green manure in the rotation. This is due to nitrogen contribution to the soil through green manure. Green manuring may activate priming action of soil organic matter. The build up of soil N in the treatment T1 was observed after green manuring because of addition of N through green manure to soil N pool (Deikmann etal., 1996). Soil C and N content provide an indicator of build up of soil organic matter. The above ground portion of crops was removed except green manure and the contribution of only root biomass in the build up of soil organic matter has been manifested in the present study. The incorporation of crop residues would have resulted in more build up of soil organic matter (Goyal et al., 1999). Soil microbial biomass C was significantly affected by different crop rotations NS (Table 3). Microbial biomass C was highest in treatments receiving green manure or having three crops in the rotation compared to two crop in the rotation. Lowest microbial biomass C was observed in treatment having cottonwheat rotation. The size of microbial biomass C is governed by the various management practices such as crop rotation, organic amendments, fertilization and crop residue management. SesQania aculeata green manure provides readily available C and N which leads to more development of microbial biomass. Different crop rotations affected the different soil enzyme activities. Dehydrogenase activity was highest in pearlmillet-wheat-green manure rotation and was lowest in pearlmilletwheat rotation. Protease activity was also affected by different crop rotations and was highest in soyabean-wheat-cowpea rotation and was lowest in cotton-wheat rotation. Higher protease activity was observed in soils receiving green manure and three crops and lower enzyme activity were observed in treatments with two crops in the rotation. Soil enzyme activities are closely related to the soil organic matter content (Jenkinson and Ladd, 1981 j Frankenberger and Dick, 1983). Similar observations were made during the present study. The CO 2 -C evolved was minimum in rotations with two crops (T4' T 7, T a )compared to rotationswith three crops (Table 4). Similarly the percentage of soil C mineralized was

4 Vol. 39. No.2, Table 3. Microbial biomass anc enzyme activities in soils with different crop rotations Treatments Microbial biomass C Dehydrogenase activity Protease activity (mg/kg soil) (I-Ig TPF/soil/24hr) (I-Ig tryosine/g soiljh) Treatments Table 4. Carbon mineralization of soils under different crop rotations Cumulative COz-C evolved (mg/kg soil) Incubation period (weeks) ' Percentage of soil C mineralized in 4 weeks minimum in treatments T4 and T7' The rate of C mineralization increasedwith three crops in the rotation including a green manure crop. The variable amount of C mineralization indicates variable amount of labile C accumulated in response to different crop rotations (Gregorich eta/., 1994). The percent soil C mineralized is dependent on the accumulation ofsoil organic C in relation to various rotations. Although the amount of C mineralized wasdifferent in different rotations but there was less variations in the per cent C mineralized. This is because of less variations in the total soil C sequestered in soil in response to various rotations. Rotations producing more root biomasswith high lignin content can help in soil organic C sequestration (Lal, 2002). It is concluded from this study that taking three crops and green manuring is a betteroptionfor improving soil organic matter level and biological properties vital for soil productivity particularly under tropical conditions where maintenance of soil organic matter levels is a problem. REFERENCES Bremner, J.M. and Mulvaney, C.S. (1982). In: Methods of Soil Analysis. Part 2. Chemical and Microbiological Properties (Page, A.L. et al., eds.) American Society of Agronomy, Madison. pp 595. Campbell, CA et al. (1991). Can J. Soil Sci., 71: Campbell, c.a. et al. (1992). Can. J. Soil Sci., 72: Casida, L.E. Jr. et al. (1964). Soil Sci., 93: Diekmann, K.H. etal. (1996). BioI. Fertil. Soils, 21:

5 132 INDIAN JOURNAL OF AGRICULTURAL RESEARCH Doran, J.W eta/. (1996). Adv. Agron., 56: Frankenberger, WT. Jr. and Dick, WA (1983). Soil Sci. Soc. Am. J., 47: Franzluebbers, A.J. et a/. (1995). Appl. Soil Ecol., 2: Goyal, S. et a/. (1999). Bioi. FertiJ. Soils, 29: Gregorich, E.G. et a/. (1994). Can J. Soil Sci., 74: Jenkinson, D.S. and Ladd, J.N. (1981). In : Microbial Biomass in Soil (paul, EA and Ladd, J.M. eds.) Soil Biochemistry, Vol. 5. Dekker, New York. pp Kalembasa, S.J. and Jenkinson, D.S. (1973).. J, Sci. Food Agric., 24: Ladd, J.M. and Butler, J.HA (1972). Soil Bioi. Biochem., 4: Lal, R. (2002). Environ. Pollut., 116: Martens, R. (1995). Bioi. Ferti/. Soils, 19: Vance, E.D. et a/. (1987). Soils BioI. Biochem., 19: