Effects of Forestry Waste Mulching on Plantation Soil Fertility, Enzyme Activities, and Microbial Communities in China

The application of forestry waste as organic mulch on soil represents an increasingly recognized management practice. However, studies on how different mulching strategies regulate soil fertility and microbial community responses remain limited. In this study, a field experiment was conducted in plantation forest soil with four treatments: no mulching, fresh forestry waste mulching, composted mulching, and layered mulching. The results indicated that the layered mulching treatment significantly increased the soil comprehensive fertility index by 6.67% relative to the no mulching treatment. Both composted mulching and layered mulching treatments significantly reduced soil bulk density (2.26%–5.26%), increased pH (0.36%–0.48%) and organic matter content (21.90%–25.23%), and markedly enhanced urease (22.45%–26.41%) and protease activities (51.72%–62.68%). Under fresh forestry waste mulching, soil available phosphorus and available potassium increased by 23.21% and 27.07%, respectively, whereas improvements in the soil comprehensive fertility index, enzyme activities, and microbial communities were limited. Bacterial communities were highly responsive to mulching treatments, with composted mulching and layered mulching treatments significantly altering their structure, while fungal communities were comparatively stable across treatments. RDA and Mantel tests linked bacterial shifts mainly to total nitrogen, available potassium, and bulk density, and fungal variation mainly to total nitrogen (all p < 0.05). This study indicates that a layered mulching strategy simulating forest litter layers can enhance soil fertility and enzyme activity and provides an option for improving soil quality through the utilization of forestry waste.