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.

Effect of straw return mode on soil aggregation and aggregate carbon content in an annual maize-wheat double cropping system

Contrasting effects of straw and straw-derived biochar applications on soil carbon accumulation and nitrogen use efficiency in double-rice cropping systems

Long-term intensive cultivation leads to the decrease of soil organic carbon (SOC) and soil fertility. Crop residue amendment to soil is documented as an effective measure to increase SOC and improve soil productivity. However, there is limited information on the turnover and storage of crop residue carbon (C) in soil aggregates after the residue is added to soil with low fertility. The objectives of this research were to investigate the distribution and storage of residue C in soil aggregates and its contribution to different physical fractions of SOC, and to quantify the turnover of residue C in soil with low fertility. Soil samples added with 13C-labelled maize straw residue were put into carborundum tubes for two-year long in-situ incubation. Soil aggregates were separated by wet sieving and then physically fractionated. During the whole incubation process, 12–15% of residue C was stably distributed to 2000–250 μm aggregates, while the percentage of residue C distributed to microaggregates (

Distribution and storage of crop residue carbon in aggregates and its contribution to organic carbon of soil with low fertility

Are humic substances soil microbial residues or unique synthesized compounds? A perspective on their distinctiveness

Straw management influences the stabilization of organic carbon by Fe (oxyhydr)oxides in soil aggregates

Isotopic characterization of sequestration and transformation of plant residue carbon in relation to soil aggregation dynamics

This research chose the Typic Hapludoll in the northeast of China and studied dynamics of newly formed humic acid (HA) and fulvic acid (FA) in aggregates after addition of the 14C-labelled wheat residues for 60, 180, and 360 days incubation using the aggregate classification combined with chemistry grouping of humic substances. Based on 14C isotope tracer technology, the results showed that the sorting selection of >2,000-μm and 2,000–250-μm macroaggregates on newly formed 14C-HA and 14C-FA was higher than microaggregates. In the >2,000-μm and 2,000–250-μm macroaggregates, the 14C-HA/14C-FA ratio decreased with the increase of incubation time and the formation of 14C-FA was faster than 14C-HA, which humic substance formation supported lignin theory of Waksman. In the 2,000-μm and 2,000–250-μm macroaggregates may have important significance in the enhancement of soil carbon sequestration, fertility, and relief of elevated atmospheric CO2 concentration.

Dynamics of Newly Formed Humic Acid and Fulvic Acid in Aggregates After Addition of the 14 C-Labelled Wheat Straw in a Typic Hapludoll of Northeast China

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Isotopic characterization of sequestration and transformation of plant residue carbon in relation to soil aggregation dynamics

Dynamics of Newly Formed Humic Acid and Fulvic Acid in Aggregates After Addition of the 14 C-Labelled Wheat Straw in a Typic Hapludoll of Northeast China