Objective Given that field experiments on soil nutrient loss in the black soil region of Northeast China are currently insufficient, this study analyzes the characteristics of runoff, sediment generation, and nitrogen loss on gentle slope farmland, aiming to provide a scientific basis for regional soil erosion control and prevention.

Methods In the Qinggou small watershed in Nanguan district, Changchun city, Jilin province, six runoff plots were established at the hydraulic erosion observation station. Three slope gradients of 3°, 6°, and 9° were set up, along with two tillage patterns: conventional downhill ridge tillage (corn) and straw-covered downhill ridge tillage (corn). Based on monitoring data of runoff and soil loss production from May to September 2024, the characteristics of nitrogen loss (total nitrogen, nitrate nitrogen, and ammonium nitrogen) during the runoff and sediment generation were analyzed in the conventional tillage and straw-covered runoff plots.

Results 1) Nitrogen loss in runoff and sediment accounted for 56.15% and 43.85% of total nitrogen loss, respectively. The loss of nitrate nitrogen and ammonium nitrogen in runoff accounted for 53.32% and 8.34% of nitrogen loss in runoff, respectively. 2) With the increase of slope, runoff and sediment generation increased, and the loss of total nitrogen in sediment generation and total nitrogen and nitrate nitrogen in runoff also increased, while the change in ammonium nitrogen loss in runoff was not obvious. The nitrogen concentration showed a pattern consistent with the loss amount. 3) Straw cover had a significant inhibitory effect on runoff, sediment generation, and nitrogen loss. At slopes of 3°, 6°, and 9°, the runoff control efficiency was 95.55%, 89.37%, and 90.62%, respectively, and the sediment control efficiency was 95.56%, 89.03%, and 99.95%, respectively. 4) Nitrogen loss is significantly positively correlated with runoff and sediment generation, with correlation coefficients of 0.99 (P < 0.05) and 0.96 (P < 0.05), respectively. Runoff was mainly related to rainfall and the interval time between rainfall events that produce runoff and soil loss.

Conclusions Implementing straw mulching on slopes of different gradients can effectively reduce runoff, sediment generation, and nitrogen loss, but it can lead to an increase in nitrogen concentration in the runoff. The nitrogen loss from sloped farmland is mainly determined by the amount of runoff and sediment generation.