Effects of Artificially Crushing Bedrock by Rotary Tillage on Soil Infiltration: A Field Study in a Shallow Hillslope in China

In purple soil areas of China, there is a traditional practice of breaking up bedrock to obtain soil matrix by hoeing. Purple soil is formed by the development of mud shale with low hardness and high brittleness, which is easy to break under mechanical action. Research on the effect of deep vertical rotary tillage (DVRT) in breaking up the bedrock on soil infiltration performance is still lacking. This study selected a hillslope with 18 cm, 25 cm, and 40 cm soil depths at the upper, middle, and lower slopes, respectively. They investigated differences in soil infiltration capacity after DVRT and rotary tillage (RT) and identified the main controlling factors responsible for differences. The effects of different bedrock fragment contents (RFC, range 0-70%) and the bedrock size (0-5, 5-10, 10-20 mm) on saturated hydraulic conductivity (Ks) were investigated with laboratory tests by constant head method. Results are that (1) stabilized soil infiltration rates for the DVRT treatment increased by 150% and 81% relative to the RT treatment at the upper and middle slope positions, and the lower slope position decreased by 80%. (2) The Kostiakov model shows that the DVRT broken bedrock promotes soil infiltration performance on the upper and middle slopes but inhibits this at lower slope. (3) With increased RFC, saturated hydraulic conductivity decreased and then increased, and RFC thresholds existed to change the inhibition/promotion effect. The thresholds for bedrock fragments with grain sizes of 0-5, 5-10, and 10-20 mm were 74%, 59%, and 53%, respectively. It is suggested that DVRT can regulate the soil infiltration in shallow hillslopes and promote rainwater in-situ utilization.