Dynamics of soil aggregate‐associated carbon as influenced by simulated tillage and runoff

Abstract

Tillage practices and water erosion are the most important anthropogenic and natural processes, respectively, driving soil organic C turnover in agricultural land. The aim of this study was to explore the responses of soil organic C (SOC) turnover to tillage and runoff by comparing the variation of soil aggregate-associated organic C (AOC) and intra-aggregate particulate organic C (iPOC) under simulated tillage and runoff conditions. Soil samples were collected from a native vegetation land with no cultivation history in the Mollisol region of Northeast China. After a series of simulated tillage (ST) and simulated runoff (SR) treatments, the samples were incubated for 30 d and then separated through 2-, 1-, 0.25-, and 0.053-mm sieves by wet-sieving to obtain different aggregate size fractions. Each aggregate fraction was subsequently shaken for 18 h in 0.5% hexametaphosphate to get different intra-aggregate particle size fractions. The proportion of the fractions and their AOC and iPOC were determined. The ST treatment promoted the reaggregation of macroaggregates (>2 mm) by accelerating the turnover of their coarse iPOC (0.25-2 mm), leading to a lower concentration of AOC. Runoff transformed larger aggregates (>0.25 mm) to smaller particles (<0.25 mm) without catalyzing C turnover. Fine iPOC (0.053-0.25 mm) could serve as an indicator for AOC (>1 mm) dynamics, especially associated with tillage operations. Our findings highlight the different influences of tillage and runoff, and the negative effect of tillage on SOC dynamics.

Foreword: Degradation and evolution of Mollisols under different management practices and climate change

“…The inclusion of cover cropping management during the fallow period in soybean monocultures could be an appropriate agricultural management strategy to improve water capture and transport in Mollisols of the Argentinean Pampas region, especially in a Typic Argiudoll. Soil tillage practices and the resulting increase in water erosion is one of the most important anthropogenic processes to drive soil nutrients and SOC turnover in agricultural land. A combination of field study and 30‐d incubation experiment was conducted to explore the responses of surface soil nutrients and SOC turnover to different soil tillage and water erosion patterns in the Mollisol region of Northeast China (Li et al., 2022; Zhao et al., 2022). They found that water erosion played a greater role in controlling the distribution of dissolved OC than tillage erosion, whereas particulate OC distribution was more sensitive to tillage erosion.…”