The threshold of nitrogen and phosphorus loss in runoff on degraded Ferralsols of Fujian province, southern China

Loss of soil nutrients in runoff accelerates eutrophication of surface waters. This study found out the critical of rainfall intensity and slope angles of total nitrogen and phosphorus in surface runoff for degraded Ferralsols in southern China. We established plots (1.5 m × 0.5 m × 0.3 m; length × width × height) to investigate the effects of rainfall intensity (1.0, 1.5, 2.0 mm min−1) and slope gradients (10°, 15°, 20°) on runoff rate, total nitrogen and total phosphorus loss rates and dynamic factors. Our results indicated that a slope gradient of 15° is suitable for controlling TN and TP losses in degraded Ferralsols, 1.5 mm min−1 is the critical rainfall intensity of nitrogen and phosphorus loss in runoff in our study, runoff rate determines runoff-associated TN and TP losses, and runoff shear force is the dynamic factor for nitrogen and phosphorus losses. Our study might also be helpful for predicting water erosion and non-point source pollution in large scales and natural slope scales and building a model of soil erosion watershed scales.