Environmental loss is primarily caused by soil, water, and nutrient loss, and runoff is associated with nutrient transport and sediment loss. Most existing studies have focused on one influencing factor, namely slope gradient or rainfall intensity, for slope erosion and nutrient loss, but the joint effects of the two factors have rarely been researched. In this context, the impact of slope gradients (0°, 5°, 10°, and 15°) and rainfall intensities (30, 40, 50, 60, 70, and 80 mm/h) on soil erosion and nutrient loss on the sloping fields of Miyun Reservoir were explored using the indoor artificial rainfall simulation testing system. Based on the results of the study, the variation of runoff coefficient with slope gradient was not noticeable for rainfall intensities <40 mm/h; however, for rainfall intensities >40 mm/h, the increased range of runoff coefficient doubled, and the increase was the fastest under 0° among the four slope gradients. The slope surface runoff depth and runoff rate showed positive correlations with the rainfall intensity (r = 0.875, p < 0.01) and a negative correlation with the slope gradient. In addition, the cumulative sediment yield was positively related to the slope gradient and rainfall intensity (r > 0.464, p < 0.05). Moreover, the slope surface runoff-associated and sediment-associated loss rates of total nitrogen (TN) rose as the rainfall intensity or slope gradient increased, and significant linear positive correlations were found between the runoff-associated TN loss rate (NLr) and the runoff intensity and between the sediment-associated NLr and the erosion intensity. In addition, there were positive linear correlations between slope runoff-associated or sediment-associated TN loss volumes and rainfall intensity, surface runoff, and sediment loss volumes, which were highly remarkable. The slope gradient had a significant positive correlation with the slope surface runoff-associated TN loss at 0.05 (r = 0.452) and a significant positive correlation with the sediment-associated TN loss at the level of 0.01 (r = 0.591). The rainfall intensity exhibited extremely positive correlations with the slope surface runoff-associated and sediment-associated TN loss at 0.01 (r = 0.717 and 0.629) Slope gradients have less effect on nitrogen loss on sloped fields than rainfall intensity, mainly because rainfall intensity affects runoff depth. Based on the findings of this study, Miyun Reservoir may be able to improve nitrogen loss prevention and control.

Soil erosion of sloping farmland in the Miyun reservoir area in Beijing has become a serious issue and has threatened the ecological environment and safety of the reservoir area. We used the Taishizhuang Village Non-point Source Pollution Prevention & Control Base in the Miyun reservoir as a study area and performed a comparative analysis of the physicochemical properties of soil of the upper, middle, and lower slopes of the Scutellaria baicalensis + Buchloe dactyloides plot (Treatment 1, T1), Morus alba + Buchloe dactyloides plot (Treatment 2, T2), Salvia miltiorrhiza + Cynodon dactylon plot (Treatment 3, T3), Platycodon grandiflorus + Cynodon dactylon plot (T4), and a barren land control plot (Control check, CK), to explore how different hedgerow patterns affect the soil’s physicochemical properties, anti-erodibility, and fractal characteristics. We found the following: (1) The primary soil mechanical composition included sand particles in the upper slopes, whereas it was soil fine particles in the middle and lower slopes. (2) The fractal dimension of the slope soil showed a significant negative correlation with sand particles (R2 = 0.9791) while being positively correlated with silt particles (R2 = 0.9635) and clay particles (R2 = 0.9408). (3) All hedgerow patterns increased soil nutrients, with the Morus alba + Buchloe dactyloides hedgerow plot increasing the soil total nitrogen (STN), soil total phosphorus (STP), and soil organic matter (SOM) content by 213.89–282.69%, 55.56–58.15%, and 29.77–56.04%, respectively. (4) The Morus alba + Buchloe dactyloides hedgerow plot significantly decreased the soil erodibility factor K value, improved soil anti-erodibility, and reduced soil erosion. (5) The K value of the soil erodibility was significantly negatively correlated with clay particles, soil fractal dimension, and STP (p < 0.01); positively correlated with sand particles; and negatively correlated with silt particles, STN, and SOM. Therefore, the Morus alba + Buchloe dactyloides hedgerow planting contributes to clay particle conservation, soil nutrient content improvement, soil structure optimization, and soil anti-erodibility enhancement.

Excessive, long-term chemical fertilizer application adversely affects soil quality and maize yield. The combined application of biochar with chemical fertilizer can increase maize yield and improve soil fertility. A four-year field experiment was conducted to determine soil physio-biochemical properties and maize yield under a soybean–maize rotation in the black soils of Northeast China. There were five treatments, including no fertilization (CK), fertilizer (NPK), fertilizer + biochar (15.75 t·hm−2, BC1), fertilizer + biochar (31.50 t·hm−2, BC2), and fertilizer + biochar (47.25 t·hm−2, BC3). Compared with CK, the number of macroaggregates and the average weight diameter of soil aggregates in BC2 treatment increased significantly by 10.3% and 24.5%, respectively. The soil pH in the study area was 7.03, and it increased in all treatments except for BC1. The highest pH of 7.17 was recorded in NPK and BC2 treatments, which was around the optimal soil pH. In contrast to the CK and NPK treatments, the biochar application increased soil organic carbon (SOC) and total nitrogen (TN) content. The BC2 treatment improved soil C/N and increased the copy number of soil bacteria by 25.6% compared to CK. The combined application of chemical fertilizer and biochar was better than NPK treatment alone, and improved soil mechanical composition and fine soil particle contents (powder and clay). Mixed biochar with chemical fertilizer application also significantly increased maize yield and the weight of 100 grains increased from 9.5% to 10.9% compared to CK. The maize yield of the three fertilizer and biochar treatments was higher than treatments with applied chemical fertilizer alone, in the order of BC2 > BC3 > BC1 > NPK > CK (BC2 treatment increased by 34.8%). Additionally, the maize yield was significantly and positively correlated with soil aggregates, organic carbon and total nitrogen (p < 0.05) as well as the 100-grain weight (p < 0.01). The application of 31.50 t·hm−2 (BC2 treatment) of biochar can enhance soil physicochemical properties and improve maize yield.

Surface flow (SF) and subsurface flow (SSF) are important hydrological processes occurring on slopes, and are driven by two main factors: rainfall intensity and slope gradient. To explore nitrogen (N) migration and loss from sloping farmland in the Miyun Reservoir, the characteristics of total nitrogen (TN) migration and loss via SF and SSF under different rainfall intensities (30, 40, 50, 60, 70, and 80 mm/h) and slope gradients (5°, 10°, and 15°) were studied using indoor stimulated rainfall tests and mathematical models. Nitrogen loss via SF and SSF was found to increase exponentially and linearly with time, respectively, with SSF showing 14–78 times higher loss than SF. Under different rainfall intensities, SSF generally had larger TN loss loading than SF, thereby indicating that SSF was the main route for TN loss. However, the TN loss loading proportion via SF increasing from 14.03% to 35.82% with increasing rainfall intensity is noteworthy. Furthermore, compared with the measurement data, the precision evaluation index Nash-Suttcliffe efficient (NSE) and the determination coefficient (R2) of the effective mixing depth model in the numerical simulation of TN loss through SF in the sloping farmland in the Miyun Reservoir were 0.74 and 0.831, respectively, whereas those of the convection-dispersion equation for SSF were 0.81 and 0.811, respectively, thus indicating good simulation results. Therefore, this paper provides a reference for studying the mechanism of N migration and loss in sloping farmland in the Miyun Reservoir.