A quantitative review of the effects of residue removing on soil organic carbon in croplands

Abstract

Proper management practices can turn soils into sinks for atmospheric carbon and mitigate global warming. The objective of this study was to determine how crop residue management affects soil organic carbon (SOC) content in croplands. Data were collected from 323 field experiments evaluating the effect of residue management on SOC. From these, 609 paired data of SOC stocks with residue retained or removed (harvested or burned) were extracted. Meta-analytic methods were used to analyze the data using the response ratio (RR) as an effect size. Carbon input data to the soil from roots and aboveground residue were also extracted from 46 experiments that allowed residue carbon retention efficiency to be calculated. The residue harvest produced a mean decrease in the SOC stock of 11% in the topsoil (≤ 30 cm). This drop was only 5% when the residue was burned. Topsoil and subsoil SOC stock were equally impacted by residue management. In warm areas the relaive drop in SOC due to residue harvest was greater than in cold regions (13% vs. 8%). Likewise, the relative impact of residue harvest is greater in poor SOC soils. In contrast, water availability, soil texture, nitrogen fertilization, residue location, experiment duration and residue type did not significantly affect the RR. The annualized SOC change was greater during the first 10 years of the experiments and then decreased. Residue harvest or retaining had only a minimal impact on root carbon input to the soil, but led to a 6-fold difference in aboveground carbon input. The carbon retention efficiency of aboveground residue decreases over time, dropping from an average of ca. 25% in experiments of less than 10 years to ca. 11% in long (>20 yr) experiments. The results showed that the practice of residue retention is important in all soils to maintain the SOC level, but especially in soils from warm regions and in poor SOC soils. The impact of residue harvest is not only confined to the SOC pool in the surface layer but also impacts on the deep soil layers.