Impact of raindrop diameter and polyacrylamide application on runoff, soil and nitrogen loss via raindrop splashing

Raindrop splashing is one of the driving forces of soil erosion, and it also leads to the loss of soil nutrients. However, the effects of raindrop splashing on nitrogen loss and the mechanisms of detachment are still not well understood, especially under different types of rainfall and soil amendment applications, such as polyacrylamide, which has been widely used to reduce soil erosion. In this paper, indoor artificial rainfall experiments were performed to investigate the impact of the raindrop diameter and polyacrylamide (PAM) applications on runoff and soil and nitrogen losses. Three raindrop diameter treatments (1.52, 2.45 and 3.59 mm) and three PAM application treatments (0, 1.0 and 2.0 g/m(2)) were applied to Kastanozem soil. The results indicated that the infiltration rate, sediment rate and nitrogen concentration in the runoff decreased sharply with the rainfall duration for the first 10 min, but the runoff rate increased under simulated rainfall splashing. In general, the sediment rate for runoff and nitrogen loss increased with the raindrop diameter. The amounts of runoff, sediment, and ammonia and nitrate nitrogen loss were highly reduced with the addition of PAM. The soil and nitrate nitrogen loss decreased with the increasing PAM application rates, and a PAM application rate of 2 g/m(2) was optimized for the soil of the test area. Moreover, the ammonia and nitrate nitrogen concentrations were linearly proportional to the sediment rate in the runoff, and the slopes of the linear regression equations increased with the increasing raindrop diameter but were reduced by PAM application. This study provides effective information on the runoff, soil erosion and nitrogen loss that occur during rainfall splash, and it can improve our understanding of splash erosion and nutrient transport.