Effect of soil thickness on crop production and nitrogen loss in sloping land

Soil thickness is a useful soil quality indicator. This study aimed to characterize the effects of soil thickness on crop yield and water and nitrogen loss in sloping land. A seven-year experiment was conducted in the purple soil sloping land of Southwest China, which included six soil thickness of 20, 40, 60, 80, 100 and 120 cm. The crop yield, surface runoff, leaching and nitrogen loss were measured. The results showed that the crop yield increased as soil thickness increased from 20 cm to 120 cm. Regression analysis showed that the yield of spring maize and summer maize plateaued when the soil thickness increased to 118 cm, and the yield of winter crops still increased with soil thickness when the soil thickness was more than 120 cm. The total runoff decreased as the soil thickness increased from 20 cm to 120 cm. The surface runoff, leaching and total runoff under 120 cm soil thickness were 50.4 %, 72.3 % and 65.8 % lower than those under 20 cm thickness. The nitrogen loss through leaching accounts for 97.5 % of the total nitrogen loss. The total nitrogen loss decreased with the increase of soil thickness, and the average annual total nitrogen loss in 20, 40, 60, 80, 100, 120 cm soil thickness were 36.6, 25.1, 21.5, 16.9, 10.5 and 7.2 kg ha−1, respectively. Regression analysis showed that the total runoff was efficiently reduced when soil thickness reached 160 cm, and the total nitrogen loss was efficiently reduced when soil thickness reached 140 cm. These critical soil thickness values provided references for the design of high-yield cropping systems and environment benefit evaluation in purple soil sloping land.