Variation of soil aggregates in response to soil water under short-term natural rainfalls at different land use

The red soils of China, South America, and Africa are highly weathered inherently infertile soils that have high erosion risks and low soil organic carbon levels. In an effort to protect these soils, they are being converted from annual crops to woodlands in China. However, under such a land use change, soil aggregate stability variation (a key factor of soil erosion) to short-term rainfall events is not clear. The objective of this study was to investigate the influence of rainfall type, soil water contents, and vegetation on short-term changes in the aggregate stability of red soils. Surface (0-20cm) aggregate stability, SWC and dynamics (Delta theta) (differences of SWC on the sampling day and prior to the sampling), rainfall, and plant root distribution (0-60cm) were monitored from 2017 to 2018 under fir (Taxodiaceae), rapeseed (Bassica napus) and Osmanthus fragrans land use. The results demonstrated that the aggregate size distribution and aggregate mean weight diameter were impacted by the soil water content prior to the precipitation and plant species. Plants such as fir, lowered the soil water content which improved short-term aggregate stability. Variation of aggregate under each type of rainfall was attributed to different change of SWC among plants, which was further confirmed by significantly negative relationships between aggregate fractions (<0.5mm) and SWC (theta(0) and theta(0.5), on the sampling time and half day prior to sampling) under all plants. Differences of aggregates as influenced by SWC among plants was also attributed to different plant root distribution and relative root absorption of soil water rate (RASW(r)) [r between SWC and root percentage (d=1-3mm) was 0.99]. The study suggested that plant types should be carefully selected for their ability to protect the soil and the findings will also provide a theoretical basis for land restoration.