[Transport of Nitrogen and Phosphorus from Sloping Farmland with Thin Purple Soil Overlying Rocks]

In a sloping farmland plot(1500 m²) of purple soil with underlying fractured mudrock in Southwest China, field monitoring and sampling campaigns were undertaken to explore the mechanisms of surface and subsurface transport of nitrogen and phosphorus upon two representative rain events in the summer of 2015. The results indicated that:1depths of surface runoff and subsurface fracture flow as well as average colloid export flux were dependent on antecedent soil wetness and rainfall amount, while discharge dynamics and colloid peak concentration were determined by rainfall intensity; 2nitrogen export was mainly in dissolved forms through subsurface fracture flow, however, phosphorus was mainly transported in particle-associated forms through surface runoff; 3the transport of nitrogen and phosphorus was strongly influenced by hydrological processes, with nitrogen and phosphorus transport being controlled by fracture flow and surface runoff, respectively. Our findings contribute significantly to the knowledge of nitrogen and phosphorus export from sloping farmland with thin soil underlain by fractured rock upon rainfall, and on the other hand this study provides reliable field data in support of developing effective approaches for controlling agricultural non-point source pollution of N and P and identifying key hydrological processes to be manipulated.