Positive effects of crop rotation on soil aggregation and associated organic carbon are mainly controlled by climate and initial soil carbon content: A meta-analysis

Understanding the global patterns and controls on soil aggregation and associated organic carbon (OC) is essential to improve soil carbon storage and mitigate climate warming. Crop rotation is an important feature of sustainable agricultural management and influences multiple soil properties. However, the effects of crop rotation on soil aggregation and associated OC remain poorly understood. We conducted a meta-analysis of 2199 paired observations from 53 studies to quantitatively analyze crop rotation-induced changes in soil aggregation and associated OC and elucidate optimal climatic, edaphic, and agronomic factors. Overall, crop rotation improved the proportions of macroaggregates (> 0.25 mm) by 7-14%, aggregate stability by 7-9%, and OC contents in all sizes of aggregates by 7-8% relative to continuous monoculture. Crop rotation increased soil aggregation and associated OC mainly in regions with mean annual temperature between 8 and 15celcius, mean annual precipitation between 600 and 1000 mm, and also in topsoil (0-20 cm) with loamy textures and medium levels of initial soil OC (10-15 g kg- 1), total nitrogen (0.75-1.50 g kg- 1), and pH (6-8). Greater increases in soil aggregation and associated OC induced by crop rotation were associated with sub-soiling, no-till, straw retention, combined manure-inorganic fertilizers, and a lower nitrogen fertilization input rate with more rotation cycles and longer rotation length. Crop rotation effects were especially strong when the previously cultivated crop was soybean. The variance partitioning analysis revealed that variations in crop rotation-induced changes in soil aggregation and associated OC were mainly explained by climate (26-35%) and soil properties (17-34%). The random forest model indicated that climate (mean annual temperature and precipitation) and initial soil OC were the predominant controls on the effects of crop rotation. Overall, these findings suggest that the use of crop rotation can help sequester carbon by improving soil aggregation and associated OC, and highlight the importance of climate and initial soil OC in site-specific crop rotation systems to the sustainability of agroecosystems.