Abstract: The poor tillage properties in low-yielding albic soil caused by physical structural obstacles are unfavorable for mechanical tillage operations. To address this problem, we conducted indoor simulation experiments with three types of treatments: tillage layer mixing (TLM, where 10%-50% of the albic soil was incorporated into the surface soil), subsoil mixing (SM, where 10%-50% of the illuvial soil was incorporated into the albic soil), and subsoil fertilization (SF, with gradients of 2%-10% organic fertilizer, straw, and biochar addition, respectively). We analyzed the differential regulatory mechanisms of various soil improvement measures on the plasticity (indicated by liquid limit, plastic limit, and plasticity index), swelling-shrinkage behavior (indicated by shrinkage limit), and optimal tillage period (indicated by shrinkage index) of albic soil. Results showed that TLM improved soil homogeneity and plasticity, shortened the optimal tillage period, and degraded tillage characteristics. SM improved the tillage performance of albic soil by increasing clay content and optimizing the sand-clay ratio, which together extended the optimal tillage period. SF, leveraging the synergistic effects of organic matter, specific surface area, maximum hygroscopic water, and organic carbon, demonstrated superior improvement effects on tillage characteristics compared to TLM and SM. Among these, organic fertilizer enhanced soil water retention capacity (plastic limit increased by 37.5%-58.1%), optimizing soil tillage characteristics. Straw exhibited the most significant regulatory effect on soil swelling-shrinkage behavior (shrinkage limit decreased by up to 41.1%), with the optimal effect achieved at a 6% straw addition. Biochar improved soil tillability by optimizing the hierarchical pore structure, where a 10% addition increased the liquid limit and plastic limit by 7.3% and 14.9%, respectively, while reducing the plasticity index by 7.6% and increasing the shrinkage index by 12.6%. These findings indicated that all three soil fertilization materials could improve the tillage characteristics of low-yielding albic soil. This study would provide theoretical support for the remediation of albic soil barriers and the construction of sustainable tillage systems.

Key words: tillage layer mixing, subsoil mixing, subsoil fertilization, albic soil, tillage characteristics