Improvement effect of soil layer mixing and corn straw addition on albic soil

Mixing the albic horizon with the illuvium horizon can break the poor soil structure of albic soil, while straw input is an effective way to enhance soil nutrient content. We conducted an incubation experiment to analyze the changes in soil liquid limit, plasticity index, mechanical composition, distribution of stable aggregates, and soil organic carbon content under different mixing ratios of the albic horizon and illuvium horizon (1:0, 2:1, 1:1, and 1:2), along with the addition of 1% corn straw. We further verified the impacts with a soybean field experiment. The results showed that with the increasing proportion of illuvium horizon soil, the liquid limit of the soil increased, and the plasticity index increased from 16.0% to 23.0%, 27.0%, and 31.0%, respectively. The suitability of albic soil for cultivation was enhanced. The stability indicators of soil aggregates, such as clay content, percentage of aggregates larger than 0.25 mm (R_>0.25), average weight diameter (MWD), geometric mean diameter (GWD), increased, with MWD and GWD increasing by 42.9%, 44.9%, 46.9% and 27.7%, 27.7%, 29.8%, respectively. At the same mixing ratio, straw addition increased soil R_>0.25 and enhanced aggregate stability. Soil mixing and straw addition, as well as their interaction, had significant effects on soil R_>0.25, MWD, and GMD. The treatment with soil mixing ratio of 1:1 and straw addition resulted in the highest R_>0.25, reaching 66.6%. Soil mixing reduced soil organic carbon content, while straw addition significantly increased soil total organic carbon and aggregate organic carbon content at various particle sizes. This indicated that the combination of soil layer mixing and straw addition synergistically promoted the formation and stability of soil aggregate structure by increasing soil clay and organic carbon content, thereby improving soil structure and fertility. Field results showed that the application of machinery could achieve approximately 1:1 mixing of albic soil horizon and illuvium horizon. Compared with conventional deep loosening control, the soybean yield increased by 7.2% after the mixing operation and full straw return. This model had significant promotion effect in the improvement of albic soil.