Effects of different mulching measures on soil physicochemical properties and phosphorus fractions in orchards in the southeast hilly region of China

Soil phosphorus plays an important role in the soil ecological environment and sustainable development of the fruit industry in the soil hilly region of southern China, but the impact of different mulching measures on soil available phosphorus and phosphorus fractions in orchards remains unclear. In this study, soil basic physicochemical properties, available phosphorus, inorganic phosphorus fractions and their interrelationships under natural grass cover (NG), film mulch (FM) and clean tillage (CK) in orchards were explored. Compared to CK treatment, both FM and NG treatments have been shown to increase the contents of soil organic carbon (SOC), total nitrogen (TN), and available nitrogen (AN). Additionally, compared with the FM treatment, the NG treatment increased total phosphorus (TP), total potassium (TK), available potassium (AK), and soil acid phosphatase (S-ACP), resulting in greater improvements in soil fertility. The NG treatment increased the contents of aluminium-bound phosphate (Al-P) and iron-bound phosphate (Fe-P) in the 0–40 cm soil layer, whereas the FM treatment decreased the contents of Fe-P and Al-P and increased the content of occluded phosphate (O-P). Compared with the CK treatment, the NG treatment significantly increased the available phosphorus in the 0–40 cm soil layer, whereas the FM treatment significantly decreased it. Redundancy analysis revealed that pH and S-ACP were the main factors affecting soil phosphorus components. Al-P, Fe-P, and S-ACP were the three factors with the highest correlations with available phosphorus. However, according to multiple stepwise analyses, only Al-P was directly related to available phosphorus. Overall, in the southeast hilly orchards, the NG treatment improved soil nutrient and enzyme activity and is considered an effective strategy to increase the biological effectiveness of phosphorus while reducing leaching losses.