Soil aggregation and distribution of carbon in a sandy loam soil of Trans Gangetic plains under integrated nutrient management practices in rice-wheat cropping system

Abstract

The effects of different integrated nutrient management practices on soil aggregation, bulk density and aggregate associated carbon after 26 years of ricewheat cropping system on a sandy loam soil of Ludhiana were studied. The total Water Stable Aggregates (WSA) at wheat harvest ranged between 78.6 and 85.8% under different treatments. Application of NPK either through inorganic fertilizers or through combination of inorganic fertilizers and organics such as Farm Yard Manure (FYM) or Crop Residue (CR), or Green Manure (GM) significantly increased the amount of water stable aggregates, aggregate ratio, Mean Weight Diameter (MWD) and Geometric Mean Diameter (GMD). The macro-aggregates comprised 35.3 to 48.9% of the total WSA compared to 36.5 to 43.3% as micro-aggregates. The amount of macro-aggregates was lowest in the control plot and it was higher in the plots treated with organics. Application of FYM, CR and GM significantly improved the formation of macro-aggregates as compared to control. The proportion of micro-aggregates decreased with the application of organics. Among the macroaggregates, the 0.25-0.50 mm fraction constituted the greatest proportion (17- 21.6%). Plots receiving FYM showed the highest MWD (0.56 mm) and the control plots had the lowest MWD (0.43 mm). Meagre variation was observed in all the structural indices among the organically amended treatments. Carbon concentration was higher in macro-aggregates as compared to micro-aggregates and application of organics resulted in the greatest increase in C concentration in various aggregate size fractions over control.