Effect of soil conservation measures and slope on runoff, soil, TN, and TP losses from cultivated lands in northern China

Soil and nutrient loss characteristics in cultivated lands are scarcely identified in northern China that could retard reasonable implementation of soil conservation measures. In the present study, seven-year of water, sediment, and nutrient data in 2014–2020 from five cultivated plots in the Miyun Reservoir, Beijing were used to explore runoff, soil, total nitrogen (TN) and total phosphorous (TP) loss characteristics and their responses to soil conservation measures, slope gradients, and rainfall characteristics. Annual soil loss rate (SLR) decreased from 3025.23 t km-2 yr-1 on the plot with no soil conservation measure to 3.47 t km-2 yr-1 on the terraced plot. Contour tillage on gentle slopes decreased soil and nutrient losses and allowed more runoff running downslope. Event-averaged SLR also presented the same trend. Runoff depth decreased insignificantly from 72.83 mm on plot with no soil conservation measure, 68.40 mm on contour tillage plots, to 3.35 mm on terraced plot. Annual TN and TP losses decreased from 344.82 and 27.21 kg km-2 yr-1 on cultivated plot with no soil conservation measure to 11.11 kg km-2 yr-1 and 0.47 kg km-2 yr-1 on terraced plot, respectively. Particulate TN and TP losses contributed over 50% of the total, depending on SLR. This study implies that contour tillage is preferred on gentle slopes, and steep slope should be implemented with terrace or other measures in the study region.