Effects of fertilization on soil aggregation, carbon distribution and carbon management index of maize-wheat rotation in the north-western Indian Himalayas

Abstract

The impacts of the resource conservation practices can be evaluated in short-term through carbon management index (CMI) that conceptualizes the carbon lability and soil aggregation. To test this hypothesis, we investigated the labile organic carbon (LOC) pool and CMI in relation to runoff, soil loss and maize-wheat system productivity on 2% sloping crop lands of Indian Himalayan region in a study (2009–2014) where different nutrient management practices were adopted. Results showed that all integrated nutrient management (INM) practices (mineral) fertilizers with different organic sources like farmyard manure (FYM), vermi-compost (VC), green manure (GM) and poultry manure (PM) enhanced soil aggregation compared with only mineral fertilization (NPK). Among all the treatments, the highest water-stable macroaggregates ( + 25%) in the 0–5 cm soil layer were recorded in 50% NPK + 50% FYM (7.5 t ha−1) treatment. Aggregate size of >2000, 250–2000, 53–250 and <53 µm had ∼18, 26, 34 and 18% higher soil aggregate-associated organic C in topsoil than 5–15 cm soil layer, respectively. Decreasing trend of soil aggregate-associated C was observed with decrease in size fraction from >2000 to <53 µm. Plots with fertilization of 50% NPK + 50% GM (1.8 t ha−1) had significantly higher Walkley-Black carbon (WBC), total soil organic C (TOC), LOC, macroaggregate-associated C concentrations, and soil aggregation than other treatments. In the NPK + FYM treatment, LOC was ∼16% significantly higher in topsoil than the sub-surface soil. CMI varied from ∼17–48% to 15–41% among the nutrient management practices in the 0–5 and 5–15 cm soil layers, respectively. Significant positive correlation was found between CMI with maize yield (r = 0.944; n = 28; p = 0.008), wheat yield (r = 0.942; n = 28; p = 0.005), and negative correlation with runoff (r = −0.818; n = 28; p = 0.042) and soil loss (r = −0.847; n = 28; p = 0.045). FYM, GM, VC and PM with mineral fertilization decreased soil degradation compared to only mineral fertilization and unfertilized control plots, and FYM and GM sources were the best among all the organic sources. The highest wheat equivalent yield (WEY) was recorded with 50% NPK + 50% FYM (∼6.0 t ha−1) while similar WEY was recorded in rest of 50% organic sources. Relationships revealed that the single value CMI can be used for the assessment of soil degradation in the sloping crop lands.