Do moisture conservation practices influence stability of soil organic carbon and structure

Abstract As soil erosion is a major threat for global food security, soil and water conservation (SWC) structures are essential in degraded lands of the tropics facing water scarcity. However, some fundamental questions regarding the impact of SWC measures on soil aggregate stability, organic carbon (SOC) pools within bulk soils and aggregates, and biological activities remain unexplored. A 11-year study was conducted, involving a combination of tree (Emblica officinalis) + grass (Cenchrus ciliaris) + legume (Stylosanthes seabrana), comparing in-situ soil water storage measures, staggered contour trenches (SWC1), continuous contour trenches (SWC2), stone mulch (SWC3), and vegetative barriers (SWC4), to a control (SWC0). We calculated three novel indices: biological activity index (BAI), oxidative stability (OXS), and normalized soil stability index (NSSI). SWC1 and SWC2 reduced soil erosion by ~63% and 51% compared to SWC0. Labile C concentration improved by ~47, 31, and 15% for SWC1, SWC2, and SWC4 compared to SWC0. SWC1 and SWC2 had 50 and 33% greater recalcitrant C than SWC0, respectively, in the top layer. Considerably higher amount of aggregate associated C was observed with SWC1 and SWC2 than with SWC0. NSSI values of SWC1 and SWC2 were ~1.92- and 1.87-fold higher than that of SWC0 in the upper layer. BAI was improved by 1.34–2.65 times under SWC conditions compared to the control. For macroaggregates, OXS of C for SWC1 and SWC2 were ~12% higher than that for SWC0 at the surface. Overall, fruit and pasture yield under SWC1 were ~51 and 82% higher than SWC0, respectively. System water productivity was ~61% higher for SWC1 compared with SWC0. Therefore, staggered contour trenching or continuous contour trenching could be recommended for improving soil structural stability and SOC storage and for reducing soil erosion in degraded lands of semi-arid, dry, tropical regions.