Soil Aggregation and Associated Organic Carbon as Affected by Long Term Application of Fertilizer and Organic Manures under Rice-Wheat System in Middle Gangetic Plains of India

Abstract

The long-term impact of integrated nutrient management practices on soil organic carbon (SOC), aggregate stability and distribution of C in different aggregate fractions were studied. The experiment is being conducted in a sandy clay loam (Udic Ustrochepts) at Bihar Agricultural University, Sabour since 1984 under rice-wheat rotation. Changes in total water stable aggregates (WSA), mean weight diameter (MWD), aggregate associated C and bulk soil C were measured. Application of 50%NPK+ 50% N through FYM in rice, 100% NPK in wheat increased the SOC, WSA, MWD and associated C over the control (no NPK fertilizer or organics). The SOC content in 0-15 cm soil layer increased from 3.6 g kg-1 under no-fertilizer (control) to 7.7 g kg-1 soil under the INM treatments. Macroaggregates constituted 37-60% of total WSA and the proportion of microaggregates ranged from 19 to 30%. Addition of FYM, wheat straw and green manure increased macroaggregate fractions, with a concomitant decrease in microaggregate fractions. Among the macroaggregates, 0.25-0.50 mm fraction constituted the largest proportion and had higher C density compared to microaggregates. The MWD was significantly higher in plots receiving 50%NPK+ 50% N through FYM in rice (1.36 mm), 100% NPK in wheat or 50%NPK+ 50% N through CR in rice (1.28 mm), 100% NPK in wheat or 50%NPK+ 50% N through GM in rice (1.29), 100% NPK in wheat (1.18mm) as compared to control (0.89 mm). It may be concluded that application of 50%NPK+ 50% N through FYM in rice and 100% NPK in wheat can sustain the soil C in a better way and contribute in mitigation of global warming.