Long-term Use of Balanced and Integrated Nutrient Management Improved Soil Aggregation and Carbon Stabilization in a Maize-wheat Cropping Sequence

Sustainable nutrient management practices have the potential to enhance carbon (C) storage capacity of agricultural soils that may help offset increasing atmospheric CO2 concentration. Nutrient management practices on long-term basis differentially influence aggregates and distribution of soil organic C (SOC) present within aggregates, which in time may affect C stabilization. The present study assessed the impact of long-term application of fertilizers for 44 years either alone or integration with farmyard manure (FYM) on bulk density, SOC and C pools, potassium permanganate oxidizable C (KMnO4), aggregate stability and distribution of C fractions within different size aggregate under maize-wheat cropping sequence. The application of 100%NPK+FYM significantly (P< 0.05) improved soil aggregation and mean weight diameter (MWD). The percent of macro-aggregates (MacroA) and meso-aggregates (MesoA) was maximum in 100%NPK+FYM followed by NPK and the minimum in the control treatment. Irrespective of aggregate classes, TOC (g kg-1 aggregate) was maximum in 100%NPK+FYM treatment with an average of 8.42 g kg-1 aggregate as compared to control (5.05 g kg-1 aggregate). If averaged across the treatments, TOC concentration in aggregates followed the order MacroA> MesoA>MicroA. Correspondingly, results for KMnO4-C were similar in different treatments and aggregate classes. Application of FYM with inorganic fertilizers (NPK) or NPK showed a significant increase in all oxidizable organic C fractions particularly recalcitrant C fraction, which reflects the stable nature of OC as compared to very labile and labile C fractions. In general, C present in mineral fraction and large-sized aggregates (MacroA) has higher recalcitrant fractions of SOC as compared to small-sized aggregates (MesoF and MicroF). The study concluded that long-term balanced and integrated nutrient management improved soil aggregation, C distribution within aggregates, and C storage capacity of soils under maize-wheat. Carbon associated with macro aggregate and a mineral fraction has more recalcitrant C fraction compared to meso and micro aggregate fractions.