Effects of Chemical Fertilizer Reduction Combined with Straw and Organic Fertilizer Application on Soil Acidification Mitigation and Erosion Control

[Objective] To demonstrate that appropriate application of straw and organic fertilizer can effectively improve soil quality, have a positive effect on soil acidification mitigation and erosion control. [Method] Acidified red soil was used as the research object and a comparative analysis was performed for the effects of conventional fertilization (CK), chemical fertilizer reduction (30%), straw returning (6 000 kg/hm2, FSM0), and the combination of chemical fertilizer reduction (30%) coupled with straw returning (6 000 kg/hm2) and different gradients of organic fertilizers (1 500, 3 000, 4 500 and 6 000 kg/hm2) (FSM1, FSM2, FSM3, and FSM4) on soil properties at different stages of rapeseed growth and rapeseed yield. [Results] The reduction of chemical fertilizers combined with straw and organic fertilizer application significantly (p < 0.05) improved soil acidity and nutrient status. Compared with CK, soil pH increased by 0.05~0.25 unit under the five treatments, while exchangeable H+, exchangeable Al3+, and exchangeable acids decreased by 10.82%~39.81%, 5.18%~22.10% and 5.67%~23.90%, respectively. Additionally, the total exchangeable base increased by 7.63%~34.68%, and the total nitrogen and organic matter contents in the soil also significantly increased (by 19.22%~62.86% and 18.43%~61.50%, respectively). Analysis of soil mechanics properties indicated that with the increase of organic fertilizer application, soil shear strength was significantly enhanced, while the cohesion and internal friction angle exhibited a trend of first increasing and then decreasing. Under FSM2 treatment, the shear strength, cohesion, and internal friction angle all reached their peak values, with a respective increase of 22.22%, 20.06% and 11.38% relative to CK. Economic benefit analysis revealed that FSM2 had the highest net income. [Conclusion] Based on soil acidification improvement, fertility enhancement, structural improvement, and rapeseed economic benefits, chemical fertilizer reduction (30%) coupled with straw returning (6 000 kg/hm2) and 3 000 kg/hm2 organic fertilizer application can be recommended as the optimal management strategy. The results of this study can provide a scientific foundation for improving soil acidification and increasing crop yields.