Effects of organic mulching on soil aggregates, main microbial groups, and enzyme activity in Chinese hickory plantation

A field experiment was conducted on a Chinese hickory (Carya cathayensis Sarg.) plantation using two types of hickory husk mulching: fresh and composted husk mulching (FHM and CHM, respectively). Soil samples were collected 90, 180, 270, and 360 days after husk mulching to determine the effects of the treatments on soil nutrients, aggregates, microbial communities, and nutrient cycling-related enzyme activities. We found that soil pH and organic carbon content (SOC) increased by 4.10–12.16% and 13.72–76.39% after FHM and CHM treatment, respectively. FHM and CHM treatments increased the proportion of > 2000 μm aggregates by 15.71–24.74% and decreased the proportion of < 250 μm aggregates by 7.87–38.25%. The total soil microbial, fungal, bacterial, and actinomycete biomasses significantly increased after husk mulching (P < 0.05). The α-glucosidase, β-glucosidase, and leucine aminopeptidase activities increased 29.17%–99.55%, 27.03%–49.19%, and 40.35%–118.47% after the husk mulching treatments, respectively. Soil pH, organic carbon, available potassium, and the proportions of aggregates of > 2000 μm and 1000 – 2000 μm were the main factors influencing the soil microbial community composition. Partial least squares path modeling demonstrated that husk mulching increased soil enzyme activity through altering the composition of the main microbial groups. Organic mulching may affect soil aggregate microstructure through increasing SOC and influencing the composition of the main microbial groups, directly affecting enzyme activities. Overall, the husk mulching treatments increased SOC as well as soil stability and decreased pH, describing the benefits of the application of this soil management practice in sustainable agroforestry.