Effect of soybean–wheat rotation on soil aggregation, organic nitrogen and net nitrogen mineralization characteristics: a four-year field study.

Long-term, excessive application of synthetic N fertilizers will reduce soil aggregate stability and N supply capacity in corn–wheat (Zea mays L. – Triticum aestivum L.) rotation. This study aimed to determine the effects of soybean (Glycine max L.) on soil aggregation, soil organic N (SON) and net amount of N mineralization (NANM) in wheat season compared with corn. Three rotation systems, corn–wheat (C-W), soybean–wheat (S-W) and soybean inoculated with Rhizobium-wheat (SR-W) were established in 2017. In wet screening, compared with C-W rotation, the mass proportions of large macro-aggregates (LM%) + small macro-aggregates (SM%) at 0–20 cm was increased by 51.9% and 16.6% under S-W and SR-W rotations, respectively, and was increased by 50.6% and 59.8%, respectively, in the 20–40 cm. The proportions of LM + SM-associated N (LMN% + SMN%), ammonium N (AN) and amino acid N (AAN) were higher under the S-W and SR-W rotations. Furthermore, the NANM of S-W and SR-W rotations increased by 34.1% and 28.6% compared with C-W rotation, respectively, and the non-N benefits of soybean played an important role. In conclusion, the improvement degree of soil aggregation by soybean is an important factor affecting soil N mineralization in wheat season. [ABSTRACT FROM AUTHOR]