Evaluating soil quality is of vital importance to strategize fertilization and management practices for sustaining agricultural productivity. Five fertilization practices were carried out for six years under corn-soybean rotation in Mollisols of Northeast China. Two soil quality index models of Nemoro quality index (NQI) and integrated quality index (IQI), and two indicator selection approaches of total data set (TDS) and minimum data set (MDS) were applied for evaluating changes in soil quality index. NQI-MDS, NQI-TDS, IQI-MDS, and IQI-TDS approaches all indicated that six-year crop straw returning and dairy manure application under corn-soybean rotation increase soil quality index at 0-30 cm soil depth. Depended on soil-depth, IQI-MDS is the most suitable soil quality model for evaluating soil quality at 0-10 cm and 10-20 cm, and NQI-MDS at 20-30 cm soil depth. Soil quality index in IQI-MDS at 0-10 cm soil depth is the method to evaluate soybean yield. Integrating crop yield and soil quality index, the six-year organic amendments, especially dairy manure application is the most suitable management practice in promoting soil biochemical, chemical and physical properties under corn-soybean rotation in Mollisols.

Soil microorganisms play critical roles in mediating soil fertility. Exploring the effect of fertilization on soil microbial communities is of great importance to comprehend the sustainability of agriculture. However, the impacts of the application of different fertilization techniques on soil microbial communities remain ambiguous due to inconsistent findings across studies. In this study, we investigated changes in soil microbial communities under different fertilization techniques (chemical fertilizer (CK), organic fertilizer (OF), Bacillus-amended biofertilizer (BF), and Trichoderma-amended biofertilizer (MF)) and analyzed the link between soil fertility improvement and crop yield increase from a microbial perspective. Compared to the CK treatment, the BF and MF treatments increased corn yields by 16.07% and 12.98%, and soybean yields by 17.48% and 15.32%, respectively. BF tends to increase soil available phosphorus, whereas MF demonstrates a more pronounced enhancement in both available phosphorus and NH₄⁺-N contents. These differential effects were primarily linked to changes in the microbial community. Specifically, BF significantly enriched Bacillus, Rhodanobacter, Massilia, Mortierella, and Tetracladium, while the MF selectively increased the abundances of Burkholderia-Caballeronia-Paraburkholderia, Trichoderma, Penicillium, and Sistotrema. Co-occurrence network analysis revealed that biofertilizers enhanced microbial network stability and complexity compared to conventional fertilization techniques. Moreover, structural equation modeling (SEM) confirmed strong and positive relationships between crop yields and the abundances of specific probiotic microorganisms. These findings elucidate the mechanism-specific roles of biofertilizers in agricultural systems and provide novel insights for developing targeted biofertilizer formulations to advance sustainable agricultural practices.

Fertilization practices change soil organic carbon content and distribution, which is relevant to crop rotation and soil aggregates. However, how fertilization management under corn–soybean rotation affects soil organic carbon and aggregate stability at different soil depths in Mollisols is unclear. The effects of 6–yr fertilization under corn–soybean rotation on aggregate stability, soil organic carbon content and storage, and size distribution in soil aggregates were investigated. Five different fertilization practices were carried out in 2013: corn and soybean without fertilizer; corn with chemical fertilizer, soybean without fertilizer; corn with chemical fertilizer, soybean without fertilizer, returning the corn and soybean residues; corn and soybean with chemical fertilizer; and corn with chemical fertilizer, soybean with farmyard manure. Compared with corn and soybean without fertilizer, returning the corn and soybean residues increased bulk SOC content, and enhanced mean weight diameter and geometric mean diameter values at 0–10 cm because of increased water–stable aggregates (WSA) larger than 2 mm proportion and decreased WSA_<0.053mm proportion. Simultaneously, corn with chemical fertilizer and soybean with farmyard manure increased bulk soil organic carbon content but reduced mean weight diameter and geometric mean diameter values at 0–20 cm due to increased WSA_<0.053mm proportion and decreased WSA_>2mm proportion. Altogether, the application of consecutive returning crop residues and chemical fertilizer in alternate years is the most favorable approach for soil organic carbon accumulation and aggregate stability at 0–10 cm under corn–soybean rotation in Mollisols.

Understanding the characteristics of carbon ion beam irradiation-induced mutation is essential to its potential application in plant breeding. A carbon ion beam-mutagenized soybean population was generated from the newly released soybean variety Dongsheng 28, with irradiation dosages of 100 Gy, 120 Gy and 140 Gy. Many phenotypic variations and novel mutants with heritable tendencies including plant height mutants, sterile mutants, early mature mutants, rolled leaves and short petioles mutants, yield-related mutants and lodging-resistant mutants were identified. Diverse variations in seed size, seed protein and oil concentration were found. Increasing irradiation dosage from 100 Gy to 140 Gy increased leaf chlorophyll concentration in M₁ generation, but this effect was significantly reduced in M₂ generation. The activities of superoxide dismutase (SOD), peroxidase (POD) and malondialdehyde (MDA) concentration all showed wider variation in M₁ and M₂ generation, the only exception being that the MDA concentration was similar to the control in the M₂ generation. Overall, we suggest that treating soybean seeds with carbon ion beam irradiation at a dosage of 120 Gy (80 Mev/u) could be effective in soybean mutation breeding.