Construction effect of fertile cultivated layer in albic soil. Ⅱ. Effects of deep tillage with organic materials on nutrient contents and pH in tillage layer of albic soil.

White slurry layer of albic soil has low fertility and poor nutrient availability. Organic material return to fields is a primary agricultural management practice for enhancing soil fertility. We examined the variations of soil nitrogen, phosphorus and potassium nutrient contents and pH of the topsoil layer (0-15 cm) and subsoil (15-35 cm) layers of albic soil under different treatments, including deep tillage at 35 cm without organic materials (T), straw deep mixing at 35 cm (T+S), organic fertilizer deep mixing at 35 cm (T+M), combined straw and organic fertilizer deep mixing at 35 cm (T+M+S), and conventional tillage at 15 cm without organic materials as the control (CK). Compared to CK, the T+S treatment significantly increased the contents of total N (TN), total P (TP), total K (TK), available N (AN), available P (AP), and available K (AK) in both the topsoil and subsoil layers. Compared to the T treatment, the T+S treatment showed significant increases in AN, AP, and AK in both soil layers. The T+M and T+M+S treatments had significantly higher total and available nutrient contents in both the topsoil layer and subsoil layer than other treatments, with the T+M+S having the highest total and available nutrient contents. Compared with CK, the contents of TN, AN, AP, and AK in the topsoil layer soil increased significantly by 34.8% and 36.4%, 20.5% and 29.0%, 112.3% and 118.0%, and 39.5% and 49.5% under the T+M and T+M+S treatments, respectively. Correspondingly, these parameters in the subsoil layer increased significantly by 68.6% and 72.3%, 39.4% and 46.3%, 124.9% and 131.2%, and 50.4% and 64.9%, respectively. The treatments T, T+S, T+M, and T+M+S increased the abundance indices (subsoil layer nutrient content/topsoil tillage layer nutrient content) of TN, AN, AP, and AK in subsoil layer by 5.3%-12.4%, 4.8%-5.5%, 11.4%-14.4%, and 18.0%-20.7%, respectively. Our results indicated that deep mixing of organic materials induced by deep tillage effectively mitigated the decrease in TN, AN, AP, and AK content in the topsoil layer, while simultaneously increased nutrient content in the subsoil (white slurry layer). The pH values in the 0-35 cm soil layer increased by 0.01, 0.09, 0.17, and 0.14 under the four treatments, respectively. In summary, deep mixing of organic materials into the soil enhances soil fertility in both the topsoil and subsoil layers of albic soil, and the treatments with organic fertilizer alone or in combination with straw would be the most effective practice.