Soil particle-size distribution and aggregate stability of new reconstructed purple soil affected by soil erosion in overland flow

Purpose Artificial soil erosion caused by engineering practices is becoming increasingly severe worldwide. However, little is known about the change of soil structure of new reconstructed purple soil after erosion in the hilly areas of Southwest China. This study aims to analyze the effects of erosion on the soil particle-size distribution (PSD) and aggregate stability of new reconstructed purple soil in the overland flow under different flow discharges, slope lengths, and slope positions. Materials and methods A series of field scouring experiments was conducted. Flow discharges of 5, 15, and 30 L/min were applied in the new reconstructed purple soil plots with different slope lengths (5, 10, 20, 30, 40, and 50 m). Sediment samples were collected in 550-mL bottles. Soil sampling was conducted from the 0-10-cm layers before and after the field scouring experiments. In the laboratory, the pipette method was used to measure the soil PSD and microaggregates. The macroaggregates were determined by the dry and wet sieving method. Results and discussion Silt particles were eroded most at 30 L/min, by 2.11%. The average maximal reduction rate of the mean weight diameter of soil aggregates (MWD) was 20.23% at 15 L/min. Clay loss was maximal at 1.04%, and the average maximal increasing rate of the > 0.25 mm percentage of aggregate disruption (PAD(0.25)) was 0.86% at 5 L/min. The silt and MWD maximally decreased by 7.72% and 1.86%, and the maximal sand and PAD(0.25) increased by 16.70% and 25.18%, which were all observed in the 10-m plot. The percentage of soil aggregates destroyed by the change in the MWD was - 14.32% on the upslope. Silt sediment showed an increasing rate of 6.36% and microaggregate destruction showed a decreasing rate of 13.00% on the middle slope. Microaggregates and clay particles were mainly deposited on the lower slope and the reduction rates of the silt and sand content were smaller than those on the middle slope. Conclusions The effects of erosion on the soil PSD and aggregate stability of new reconstructed purple soil in the overland flow under different flow discharges, slope lengths, and slope positions were obviously different. Soil and water conservation measures should be effectively implemented on the upper slope and a slope length of 10-m soil. The soil PSD and MWD could be used as parameters for prediction of soil erosion on new reconstructed purple soil.