Effect of integrated nutrient management on soil carbon storage and enzymatic activity under rice-wheat cropping system
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Date
2017-05
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
An ongoing long-term field experiment established in 1983 on beni silty clay loam soil at Norman E. Borlaug Crop Research Centre of the Govind Ballaph Pant University of Agriculture and Technology, Udham Singh Nagar, Uttarakhand (India) was selected to study the long term effect of various rates of chemical fertilizers and fertilizer substitution with organic manures (farmyard manure, mung straw and wheat straw). Continuous application of fertilizers either alone or in combination with organic sources decreased the soil pH with lowest pH value of 7.01 in the treatments where 25% of recommended dose of N-fertilizers was substituted by mung straw. However, a reverse trend was obtained in case of EC of soil with maximum increase of 46% in treatment where integration of fertilizers and FYM was done in 50: 50 ratio. But no significant difference was observed in values of soil bulk density among different treatments upto 30 cm depth. Continuous cultivation of rice-wheat cropping system for 32 years could not sustain the initial level of N in all the treatments however level of soil phosphorus was increased in all the treatments over initial value with maximum increase of 48% in treatment where recommended dose of nitrogen was applied through both fertilizers and mung straw. The level of available potassium was decreased with sole application of fertilizers but increased slightly with integration of fertilizers with either FYM or mung straw.
In both surface and sub-surface soil organic carbon content was increased significantly in treatments receiving either fertilizers alone or in combination with organic manures over control, however, none of the treatment was able to maintain initial soil organic carbon status. Integrated nutrient management raised organic carbon content to a higher level as compared to fertilizers alone. Similar trend was followed in soil organic carbon stock and total carbon. In surface soil highest values of soil organic carbon (1.19%), soil organic carbon stock (22.49 t ha-1) and total carbon (1.57%) were observed in treatments where 50% of N-fertilizer was substituted through mung straw. Active pool (Cfrac1 and Cfrac2) of soil organic carbon contributed more to total carbon in comparison to contribution of passive pool (Cfrac3 and Cfrac4). Application of inorganic fertilizers cause slight increase in carbon fractions but increase was higher when integrated nutrient management was done. In the surface soil Cfrac1, Cfrac2, Cfrac3, and Cfrac4 constituted about 32.4-37.3%, 15.7-16.4%, 6.9-8.2%, 17.0-22.3% respectively, of total carbon and about 27.8-32.0%, 14.2-15.9%, 3.9-7.2% and 17.3-21.7% respectively, of total carbon in the sub-surface soil. Maximum increase of 78.02% in urease activity was recorded in the treatment where 50% of recommended fertilizer dose substituted through green gram straw. Maximum increase of 84.0%, 76.38% and 130.27% in dehydrogenase, alkaline phosphatase and acidc phosphatase activity, respectively was recorded in the treatment where 50% of RDF was substituted through FYM. So, it can be concluded that farmyard manure and green gran straw were best organic sources with respect to soil fertility and can be used as substitute of chemical fertilizers.