Soil erodibility after the removal of wood chip mulch: A wind tunnel experiment

Numerous field studies have investigated the effects of mulching on soil wind erosion. However, little is known about the changes in soil erodibility after removing the mulch layer. In this paper, we measured the physicochemical properties and aggregate characteristics of soil from an urban park after removing the mulch layer and estimated wind-erodible materials emission by wind tunnel experiments. Wood chips at 4,500 g m⁻² (mulch thickness of 5 cm, R5), 6,300 g m⁻² (mulch thickness of 7 cm, R7), and 8,100 g m⁻² (mulch thickness of 9 cm, R9) were used for mulching an area in Yuanmingyuan Park from October of 2019 to the end of February of 2021. The following four treatments were listed: unmulched soil (CK), R5, R7, and R9. Compared with CK, the soil moisture content (SM), the macro-aggregates (>0.25 mm) ratio (M > 0.25), the wind erodible fraction (WEF), and the dry aggregate stability (DAS) of R5, R7, and R9 were significantly increased after mulching (P < 0.05), whereas the soil organic matter content (SOM) was only slightly increased. The calcium carbonate contents (CaCO₃) varied greatly among the different treatments. Based on the wind tunnel experiments, the distribution of wind erosion materials near the soil surface (0 to 30 cm) was fitted to logarithmic, power, and exponential functions (R² ranged between 0.7179 and 0.9859). The particle size distribution of all wind-erodible materials was unimodal, and the proportion of coarse particles (250 to 100 μm) was highest. Compared with the CK, the average wind erosion rate (AWER) of R5, R7, and R9 was decreased by 48.44%, 65.04%, and 70.03%, respectively, after mulching. The AWER was significantly (P < 0.01) negatively correlated with SM, M > 0.25, WEF, and DAS, and negatively correlated with CaCO₃ and SOM. The CaCO₃ was significantly (P < 0.05) positively correlated with M > 0.25, WEF, and DAS. Overall, despite the relatively short mulching period (16 months), wood chip mulch improved the physicochemical properties and aggregate characteristics of soil and decreased erodibility.