Soil nitrogen in farmland ecosystems is affected by climate, soil physical and chemical properties and planting activities. To clarify the effects of these factors on soil nitrogen in sloping farmland quantitatively, the distribution of soil total nitrogen (TN) content, nitrate nitrogen (NO₃-N) content and ammonium nitrogen (NH₄-N) content at depth of 0–100 cm on 11 profiles of the Luanhe River Basin were analyzed. Meanwhile, soil physical and chemical properties, climatic factors and NDVI (Normalized Difference Vegetation Index) were used to construct a structural equation which reflected the influence mechanism of environmental factors on soil nitrogen concentration. The results showed that TN and NO₃-N content decreased with the increase of soil depth in the Luanhe River Basin, while the variation of NH₄-N content with soil depth was not obvious. Soil organic carbon (SOC) content, soil pH, soil area average particle size (SMD) and NDVI6 (NDVI of June) explained variation of TN content by 77.4%. SOC was the most important environmental factor contributing to the variation of TN content. NDVI5 (NDVI of May), annual average precipitation (MAP), soil pH and SOC explained 49.1% variation of NO₃-N content. Among all environmental factors, only NDVI8 (NDVI of August) had significant correlation with soil NH₄-N content, which explained the change of NH₄-N content by 24.2%. The results showed that soil nitrogen content in the sloping farmland ecosystem was mainly affected by natural factors such as soil parent material and climate.

This study investigates spatial characteristics of annual and decadal precipitation in the Huaihe River basin. Daily precipitation data, obtained from meteorological gauges, are analyzed for a 51-year period, from 1961 to 2011. Precipitation is analyzed in grids (5 km²) with respect to temporal variability. The spatial distribution and intensity of annual rainfall (mm/10 year), determined by the linear regression method, reveals a slight increase of 3 mm/10 year over the basin. However, the trend did not present a significant change at 95% significance level in the most of basin. Precipitation is mostly increasing for each ten-year periods during the total 51 years. The annual precipitation randomicity was calculated from the non-uniform coefficient Cv (coefficient of variation) test and showed a significant non-uniform spatial distribution, indicating that randomicity of annual rainfall was the moderate variability. The Pettitt test determined that the abrupt change points occurred mainly in 1965, 1975 and 2002. Wavelet analysis showed that cyclic variations appeared almost every 5 to 10 years, accounting for 36% of the basin area. Meanwhile, these cycles tended to be delimited by the abrupt change points. This study aims to provide insights for water resources management, mitigation of climate change effects and water supply in the Huaihe River basin and surrounding watersheds.

Changes in water and sediment conditions in the Upper Yellow River Basin (UYRB), which contains the ecological barrier and “water tower” of the entire Yellow River Basin, directly affect the development of the downstream ecological environment. In this study, the impacts of recent and potential land use and climate changes on runoff and sediment load were investigated through statistical analysis, land-use maps, scenario estimations, and hydrological modelling. The temporal trends and abrupt changes in hydro-meteorological elements from 1957-2010 were analysed using linear regressions and moving-t tests. Transformations in land use from 1990 to 2014 were determined using a transfer matrix analysis. The back propagation neural network was constructed to modify and integrate several general climate models, and it projected the climate change evolution characteristics in the UYRB from 2021 to 2100 under different emission scenarios. On this basis, the effects of recent and potential land use and climate changes on runoff and sediment load were quantified using the Soil and Water Assessment Tool (SWAT) hydrological model and fifteen climate scenarios, respectively. The results show a significant decreasing trends for both runoff and sediment loads with warmer and wetter climate conditions in the past 50 years. An abrupt change in runoff occurred in 1990, and a notable change in sediment load occurred in 2000 which was defined as the dividing year of the study period. The warm and wet climate characteristics of the UYRB will continue from 2021 to 2100. Over the past 20 years, the transformation of land use in the URYB has intensified. Therefore, land use changes between 1990 and 2000 show significant increasing wetland trends and decreasing bare land and grassland trends. The SWAT simulation results indicated that climate changes have had a more significant impact on runoff than land use changes in the past 20 years, increasing runoff by 6.32%. Both land use and climate changes have great impacts on sediment load reduction. For the next 80 years, the potential land use change demonstrated greater impacts on runoff and sediment load than climate changes. The runoff and sediment load exhibited different trends under various climate conditions and emission scenarios. The results obtained in this study can provide useful information for water resource management, soil and water conservation, and ecological protection in the UYRB.

Water and soil losses from sloping farmlands potentially contribute to water eutrophication and land degradation. However, few studies explored the combined effects of ridge direction and ridge width on surface runoff and soil losses of sloping farmlands. Twenty-seven experimental plots (8 m long and 4 m wide) with nine treatments (three ridge direction: cross ridge, longitudinal ridge, and oblique ridge; and three ridge width: 40, 60, and 80 cm) were adopted under natural rainfall conditions for two years in the Luanhe River Basin of China. Results indicated that ridge direction had significant effects on runoff and sediment yield (p < 0.05). The ridge width had no significant effect on runoff and sediment yield. No significant interaction effect was found between ridge direction and width on runoff and sediment yield of the sloping farmland based on statistical analyses. Compared with cross-ridge (CR) tillage and oblique-ridge (OR) tillage, longitudinal-ridge (LR) tillage significantly decreased runoff by 78.9% and 64.9% and soil losses by 88.2 and 83.5%, respectively (p < 0.05). The effects of ridge directions on runoff and sediment yield were related to rainfall grade. When the rainfall grade reached rainstorm, the runoff yield under CR, LR, and SR had significant differences (p < 0.05). The runoff under LR and OR treatment was 5.16 and 3.3 times, respectively, of that under CR. When the rainfall level was heavy rain or rainstorm, the sediment yield under LR was significantly greater than that under CR. The sediment yield was 13.45 times of that under CR. Cross-ridge tillage with a ridge width of 40 cm is an optimally effective measure of soil and water conservation on sloping farmland in arid and semiarid regions of China.