In this study, the preparation of apricot kernel shell biochar by a hydrothermal method and its adsorption mechanism for atrazine was studied by scanning electron microscopy (SEM) and infrared spectrum (FTIR) analytical techniques. The results show that the biochar prepared from the apricot kernel shell has an evenly distributed, nonaggregated carbon microsphere structure and contains a large number of oxygen-containing groups. The higher the preparation temperature is, the more functional groups exist and the better the potential adsorption performance is. The adsorption kinetics of atrazine on apricot kernel shell biochar were fitted with a quasi-second-order kinetic equation (R² ≥ 0.995, p < 0.05). The isothermal adsorption data were in accordance with the Freundlich model (R² ≥ 0.911, p < 0.05). The adsorption of atrazine on apricot kernel shell biochar includes two processes: surface adsorption and diffusion. The adsorption capacity of apricot kernel shell biochar for atrazine increases with increasing preparation temperature and decreases with increasing pH and Ca²⁺ concentration. The adsorption mechanism includes hydrogen bonding and hydrophobic interactions. Therefore, biochar prepared from apricot shells, an agricultural waste, exhibits good adsorption performance for atrazine and has a good application prospect in addressing agricultural non-point source pollution, especially in pesticide residue pollution control.

The tillage method in farming systems is essential to develop strategies to increase fertilizer uptake by plant roots and to avoid environmental pollution. The field study aimed to investigate the characteristics of nitrogen and enzyme activities in rhizosphere soil with different tillage methods. Four treatment plots applied with fertilizers were established: continuous rotary tillage (CR), plowing-rotary tillage (PR), continuous no-till (CN) and ploughing-no-till (PN). The total content of nitrogen in chernozem was high during early stages of plant growth, and then it decreased with the maize growth. In the rhizosphere soil, the total N accounted 1314.45, 1265.96, 1120.47, 1120.47, 1204.05 mg·kg⁻¹ of CR, PR, CN, and PN, respectively, which were markedly greater than that of non-rhizosphere soil (1237.52, 1168.40, 984.51, 1106.49 mg·kg⁻¹ of CR, PR, CN, and PN, respectively). At first growth stages, content of NH₄⁺-N and NO₃⁻-N in two soil regions was low, then increased gradually, which followed the order of CR < PR < PN < CN. The rhizosphere soil showed slightly higher concentration of NH₄⁺-N and NO₃⁻-N than non-rhizosphere. The soil enzymes were more active in the rhizosphere soil than that of non-rhizosphere during the whole maize growth stages. Due to minimal damage to the soil environment and optimal soil moisture and temperature, the urease and catalase activities were greatest in the rhizosphere for CN treatment. Therefore, CN was recommended to be used by farmers for the improvement of macronutrient availability and soil enzyme activities in the soil.

Straw return is a common cultivation to improve soil fertility and realize sustainable agricultural development. However, the effect of returning interval on the corn straw humification process in northeast China is little known. In this study, a four-year field trial was conducted to investigate the characteristics of soil carbon sequestration under the annual deep straw return (T1), the biennial deep straw return (T2), and the non-straw return (T3) in Jilin Province, China. In order to precisely evaluate the soil organic carbon density (SOCD), each soil horizon was divided differently according to the actual situation, rather than a fixed thickness. The results show that both the annual and the biennial deep straw return had a significantly positive influence on the content of soil organic carbon (SOC), humic acid, fulvic acid, and humin in the plough pan (straw-applied horizon), compared to the no-straw return. SOC of the cambic horizon and the C horizon in annual straw return was 28.78%, 47.44% higher than the biennial straw return, but it was 27.58% lower in the plough pan. The SOCD in the plough pan in the biennial straw return was higher than the annual straw return, but their difference in the entire soil profile was not significant. However, the conversion rate of straw carbon to SOC was 18.42% in the annual straw return and 21.05% in the biennial straw return. The straw return amount was not a key factor affecting the SOC sequestration in the cold area; it was restricted by the comprehensive effects of the cold weather, the intensity of soil disturbance, C/V and the initial SOC content. In conclusion, the biennial deep straw return was a better management tool, as it generally had an identical quality and quantity of soil organic carbon and a higher straw conversion rate relative to the annual deep straw return.

The interaction between secondary phyllosilicate minerals and straw is crucial for preserving soil organic carbon (SOC) and fertility. However, the specific mechanism through which these minerals affect straw decomposition and its products in northeast China’s black soil remains unclear. In this study, montmorillonite, illite, and vermiculite were mixed with quartz sand and maize straw, inoculated with microbes, and incubated to analyze the effects of different secondary phyllosilicate minerals on the degradation of organic components in maize straw and the formation of soil humus. The results showed that montmorillonite significantly facilitated the decomposition of maize straw hemicellulose and lignin, which decreased by 95.85% and 76.38%, respectively. Conversely, vermiculite decelerated hemicellulose and lignin degradation. Regarding soil organic acids, lactic acid and malic acid were predominant, with the highest content being found after the montmorillonite treatment. Montmorillonite was the most effective in enhancing extractable humic-like substances, which increased by 71.68%. Montmorillonite increased the content of G0 (water dispersion group), G1 (sodium ion dispersion group), and G2 (sodium grinding dispersion group) complexes. The addition of secondary phyllosilicate minerals increased the organic carbon (OC) content in the G0, G1, and G2 samples, with montmorillonite demonstrating the most pronounced effect. Secondary phyllosilicate minerals increased the abundance of fungi, particularly Ascomycota, with the highest abundance being found after the montmorillonite treatment. In conclusion, our results indicated that montmorillonite facilitated the decomposition of lignocellulose in maize straw, enhanced the accumulation of humus, and promoted the formation of organic–mineral complexes. These findings provide valuable insights into the interaction between secondary phyllosilicate minerals and maize straw and have important implications for improving the quality of black soil in northeast China.

Long-term intensive cultivation has degraded soil structure and reduced soil organic carbon (SOC) retention in the black soils of Northeast China. However, the processes underlying SOC accumulation under integrated soil–crop system management (ISSM) remain poorly understood. An 11-year field experiment compared farmers’ practice (FP), high-yield and high-efficiency practice (IP), super-high-yield practice (HY), and ISSM. We assessed SOC stocks, aggregate stability, organic carbon chemistry, extracellular enzyme activities, microbial carbon-use traits, microbial community composition, and microbial necromass carbon (MNC), and used partial least squares path modeling as an exploratory analysis of potential linkages. Compared with FP, ISSM increased SOC content and stock by 87.0 and 77.0%, respectively, and achieved an SOC sequestration rate of 2.8 Mg C ha⁻¹ yr⁻¹. ISSM also increased mean weight diameter and geometric mean diameter by 45.0 and 61.0%, increased microbial biomass carbon and carbon use efficiency by 205.2 and 100.0%, and decreased qCO₂ by 71.1%. Bacterial and fungal necromass carbon increased by 100.0 and 70.0%, respectively. The relative abundance of taxa operationally classified as growth-oriented also increased under ISSM. However, MNC/SOC did not differ significantly among treatments, while SOC aromaticity and hydrophobicity declined. Path analysis suggested that microbial carbon transformation was positively associated with necromass formation, whereas aggregate stability was associated with MNC and SOC retention. These results indicate that ISSM synchronously enlarged SOC and microbial necromass pools through sustained carbon inputs, efficient microbial transformation, and aggregate-mediated physical protection rather than through increased chemical recalcitrance.