Zero tillage and residue retention impact on soil aggregation and carbon stabilization within aggregates in subtropical India

Abstract

Studying the impact of different tillage systems on soil organic matter (SOM) dynamics is essential to define better strategies to improve soil fertility and soil organic carbon (SOC) sequestration. We used density fractionation to assess the changes in SOM in an Inceptisol following nine-years of contrasting tillage under wheat (Triticum aestivum) based cropping systems. The major objective of the study was to investigate the amount of C content within soil aggregates as influenced by tillage and residue management. For this a nine-year old experiment was conducted with two tillage practices in main plots (zero-tillage: ZT and conventional tillage: CT) and four residue management practices in sub-plots (No residue: NR, wheat residue: WR, soybean residue: SR and wheat + soybean residue: WR + SR). The results indicated that SOC content increased by ∼48, 42 and 36%, respectively, in WR + SR, SR and WR plots compared with the NR plots in the 0-5 cm soil layer. The SOC content within macroaggregates were ∼30 and 25% higher in the ZT plots than CT in the 0-5 and 5-15 cm soil depths, respectively. The intra-aggregate particulate organic matter (iPOM) inside microaggregates within macroaggregates (iPOM_mM) was ∼16% higher in the CT than the ZT plots. Tillage management had no significant effect on light fraction inside microaggregates within macroaggregates (LF_mM) and iPOM_mM SOC contents inside microaggregates within macroaggregates (mM) in the surface soil, but residue management improved LF_mM and iPOM_mM SOC contents. The WR + SR, SR and WR plots had ∼73, 40 and 35% more LF_mM SOC content, respectively, than NR plots. Within free microaggregates in the surface soil, the LF_m SOC content was significantly enhanced due to ZT operation by ∼61% than the CT plots but not by crop residue addition. The iPOM_mM and iPOM_m fraction accounted for about ∼35 and 51% of the total SOC content within macroaggregates and microaggregates, respectively. That indicates the role of iPOM fraction in SOC sequestration within the soil aggregates in tropical Inceptisol. Plots under ZT had ∼38% more C content inside microaggregates within macroaggregates (mM) than CT (2.31 Mg ha-1), indicating ZT management could be adopted for C stabilization within aggregates.