The mechanisms of nutrient output through water flow from sloping farmland with slight rocky desertification in a karst region

Abstract

Nutrient loss from sloping farmland with rocky desertification in karst regions leads to low farmland productivity and non-point source pollution. The mechanisms of nutrient outputs through water flow in such contexts under different rainfall intensities and slope angles were studied by using artificial rainfall simulation. Research showed that surface water flow occurred when the rainfall intensity was between 30 mm • h-1 and 50 mm • h-1, and the nutrient (TN, TP, TK) output through water flow showed the same pattern. Nutrient output through water flow was dominated by nutrient loss from surface and subsurface water flows when the rainfall intensity was ≥ 50 mm • h-1. Rainfall intensity was found to be a dominant driver in comparison to slope angle and for limestone soil of the karst region in Southwest China, but slope angle only had a significant effect on TP output through surface water flow. The largest proportion of nutrient output was associated with surface flow, a lower proportion was associated with subsurface flow, and the lowest proportion with underground flow. The nutrient output through underground water flow directly led to groundwater pollution, although it was not large. The results of this study provide a theoretical reference for the control of nutrient output through water flow and the management of nonpoint source pollution in karst regions.