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Increasing soil organic carbon (SOC) is a widely accepted strategy to offset greenhouse gases and improve soil quality. Straw return can modify SOC dynamics and increase its stock, which are also i...

We quantified the effects of different straw return modes on soil organic carbon (SOC), total nitrogen content (TN) and C:N ratios in a wheat/maize double‐cropping agricultural system by analysing their content in different soil aggregate sizes and density fractions under four modes of straw return: (a) no return/retention of wheat and maize straw (Control); (b) retention of long wheat stubble only (Wheat Stubble); (c) retention of long wheat stubble and return of chopped maize straw (Mixed); and (d) return of chopped wheat and maize straw (Both Chopped). The Mixed and Both Chopped straw return modes produced the highest crop yields. Relative to the Control, SOC stock was 9.6% greater with the Mixed treatment and 14.5% greater with the Both Chopped treatment, whereas the Wheat Stubble treatment had no effect on SOC. Mixed and Both Chopped significantly enhanced TN stock relative to the Wheat Stubble and Control treatments. Compared with the Control, the Mixed and Both Chopped treatments increased the mass proportions of large macroaggregates and reduced the silt plus clay fraction; Mixed and Both Chopped caused a significant increase in SOC and TN in large and small macroaggregates; the Mixed treatment significantly increased SOC content in the coarse and fine intra‐aggregate particulate organic matter (iPOM) density fractions of large macroaggregates, whereas Both Chopped increased SOC in the coarse iPOM, fine iPOM and mineral‐associated organic matter (mSOM) density fractions of both large and small macroaggregates; and Mixed and Both Chopped enhanced TN content in coarse iPOM and fine iPOM within small macroaggregates. Although the Mixed treatment was slightly less effective at improving C sequestration in agricultural fields than the Both Chopped treatment, the Mixed treatment may nonetheless be the optimal plant residue management mode in terms of minimizing time and labour due to its ability to improve soil structure, maintain organic carbon levels and provide a means of sustainable crop production in intensive wheat/maize double‐cropping systems.

Crop residue is a commonly used organic soil amendment in summer maize (June–October)–winter wheat (October–June of next year) rotation systems. However, the effects of different straw return modes on soil aggregation and soil organic carbon (SOC) stocks in different water-stable aggregates have not been extensively investigated in these cropping systems. The objective of this study was to quantify the long-term (7 yr) impact of C input on the SOC content of four soil aggregate size classes (large macroaggregates; small macroaggregates; microaggregates, silt plus clay fraction) and in explicit SOC fractions (free light fraction, free LF; intra-aggregate particulate organic matter, iPOM; mineral-associated matter, mSOM) within the top 40 cm of soil in a wheat–maize double cropping system in Northwest China. Four treatments were examined: (i) no return (control); (ii) return of wheat straw only (WR); (iii) return of maize straw only (MR); and (iV) return of both maize and wheat straw (MR-WR). Over the experimental period, the change in SOC under the four treatments ranged from −0.96 to 5.83 Mg ha −1 and a significant linear relationship between SOC change and cumulative C input (R 2 = 0.9882, P fine iPOM > coarse iPOM > free LF. Straw return significantly increased the C stock in iPOM and mSOM relative to the control. Coarse iPOM was the most sensitive indicator of C change and mSOM was the main form of SOC under long-term straw return. A significant linear relationship existed between cumulative C input and the mass proportion of macroaggregates as well as the C content of SOC fractions (or aggregate fractions). Soil depth had a significant influence on almost all measurements, with greater values observed in the 0–20 cm layer than in the 20–40 cm layer. Overall, return of both maize and wheat straw was the best strategy for improving soil structure, soil organic carbon, and crop yield. However, straw return from one crop was sufficient to maintain initial SOC levels, and conserved straw could be used for cellulosic feedstocks.

Soil organic carbon (SOC) and inorganic carbon (SIC) are important carbon reservoirs in terrestrial ecosystems. A large portion of carbon from stover enters the atmosphere after stover return. Howe...

Increasing organic carbon sequestration in agricultural soils is important for improving soil fertility and mitigating climate change. Wood ash is generally applied as a potassium fertilizer, but the effects of simultaneous incorporation of wood ash and crop straw on the turnover of soil organic carbon (SOC) and inorganic carbon (SIC) are not well understood. In this study, a 118-day lab incubation experiment was conducted using a calcareous soil (with 10 years of continuous maize cropping history) to study the effects of adding wheat straw, wood ash and lime. Our study showed that straw addition led to an increase in both SOC (19%) and SIC (3%). Wood ash and lime addition decreased CO2 emission by 182 and 1210 mg kg-1 and increased SIC by 125 and 1001 mg kg-1 during the incubation, respectively, which was due to supply of CaO from wood ash and lime. The increase of SOC content was 2.4% due to the addition of lime. In addition to straw addition enhanced straw-derived OC content, the addition of lime also increased straw-derived OC content by 34.5%. This study demonstrated that lime was more effective in reducing CO2 emission and and enhancing SOC than wood ash. In conclusion, adding lime to calcareous soil might be an effective method of enhancing carbon sequestration and slowing climate change.