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Straw return is an effective measure to promote sustainable agriculture by significantly improving soil fertility. At present, few studies have been conducted on the most effective carbon enhancing management measures for various crops. Therefore, we conducted a meta-analysis using data collected from 184 literature sources, comprising 3297 data sets to analyze the carbon increase effects of straw returning in three main crops (rice, maize, and wheat) in China and to explore the influence mechanism of natural factors, soil properties, straw return measures, and cropping systems on the carbon enhancement effect. The study showed that straw return significantly increased soil organic carbon and the rate of increase was higher for wheat at 15.88% (14.74%–17.03%) than for rice at 12.7% (11.5%–13.91%) and maize at 12.42% (11.42%–13.42%), with varying degrees of improvement in other soil physicochemical properties. Natural factors have the greatest impact on the carbon increasing effect of rice fields, reaching 28.8%, especially at temperature between 10 °C and 15 °C, less than 800 mm precipitation, low latitude, and short frost-free period. Maize and wheat are most affected by soil properties, reaching 41% and 34.5% respectively. Furthermore, field management practices also play a pivotal role, organic carbon increasing obviously was observed when the C/N ratio of exogenous nutrients is bigger than 20 with the low initial organic matter. Shallow tillage and less than 7.5 t hm−2 straw returning with 3–10 years to the field are ideal for rice and maize. Crop rotation, especially in drylands, increased soil organic carbon more significantly than continuous. The results of our analysis can provide valuable insights into the effect of straw return on carbon increase. In the future, the soil carbon can be improved by adopting rational cropping patterns and straw return measures with taking into account climate and soil characteristics for different crops. [Display omitted] • The effects of straw return on soil organic carbon in three major crops were studied using meta-analysis. • SOC levels significantly increased for rice, maize, and wheat after straw return. • The impact of natural factors, soil properties, straw return measures, and cropping systems varied for different crops. • The increase in SOC for rice was largely influenced by natural factors, while for maize and wheat by soil properties. [ABSTRACT FROM AUTHOR]

The practice of crop rotation can significantly impact carbon sequestration potential. In exploring whether crop rotation has the potential to improve soil carbon sequestration in China's Loess Plateau, soil organic carbon (SOC), soil water content (SWC), soil bulk density (SBD), and soil pH were compared across the 0–1.0 m soil profile, under four crop rotation patterns: lentil–wheat–maize, wheat–potato–lentil, wheat–maize–potato, and wheat–flax–pea. The lentil–wheat–maize and wheat–maize–potato rotations have been practiced over the past 20 years, while the wheat–potato–lentil and wheat–flax–pea rotations were established in 1978 (~40 year rotations). The results showed that under the 20-year lentil–wheat–maize rotation, SOC was not significantly different to that of the wheat–maize–potato rotation, at 6.81 g kg−1 and 6.91 g kg−1, respectively. However, under the lentil–wheat–maize rotation, SWC (9.81%) and SBD (1.19 Mg m−3) were significantly higher, but soil pH (8.42) was significantly lower than the same metrics under wheat–maize–potato rotation (8.43% and 1.16 Mg m−3, and 8.50, respectively). For the 40-year rotations, SWC (9.19%) and soil pH (8.41) under the wheat–potato–lentil were not significantly different to that of the wheat–flax–pea (8.87%, and 8.40, respectively). SOC (6.06 g kg−1) was significantly lower, but SBD (1.18 Mg m−3) was significantly higher under the wheat–potato–lentil than the wheat–flax–pea (7.29 g kg−1, and 1.15 Mg m−3, respectively) rotations. Soil carbon sequestration for the lentil–wheat–maize and wheat–potato–lentil rotations was co-influenced by SWC, SBD, and soil pH, while for wheat–maize–potato and wheat–flax–pea rotations, it was co-influenced by SWC and soil pH. The economic value of the four studied crops is, in order: potato > maize > wheat > flax. The results of the present study suggest that the lentil–wheat–maize and maize–flax–pea rotations are the most suitable patterns to optimize simultaneous economic and ecological development of the study area. [ABSTRACT FROM AUTHOR]