Response Of Soil Erosion And Nutrient Loss To Rainfall Factor And Slope In Loess Region

Water and soil loss from the soil erosion of the sloping farmland in the upper reaches of the Fenhe River Basin has become the main influencing factor of sediment deposition and eutrophication of the Fenhe Reservoir.Up to now,most of researches have focused on the relationship between soil erosion,nitrogen loss characteristics of sloping farmland and rainfall,slope and other single factors.However,there are relatively few studies on the effects of rain intensity and land slope on runoff depth,sediment loss and nitrogen loss of under different underlying surfaces.Especially in the upper reaches of the Fenhe River,the little research on this topic has been found.The data of runoff,sediment loss and nitrogen loss under natural rainfall conditions in the runoff plots,which was established in the upper reaches of the Fenhe River,were used in this study to analyze the laws of soil and water erosion,and nitrogen loss and the effect of rain intensity and slope on runoff,sediment loss and nitrogen loss under the four underlying surfaces.The underlying surface includes maize,potato,bare land,abandoned farmland.A compound factor model based on rain intensities,and land slope was put forward to predict runoff depth,sediment loss and nitrogen loss under the different underlying surfaces.The main conclusions are as follows.(1)Runoff depth and sediment loss under four underlying surfaces showed a significantly positive correlation with rainfall(P),maximum 10 min rain intensity(I10),maximum 30 min rain intensity(I30),product of rainfall and average rain intensity(P×Im),product of rainfall and maximum 10 min rain intensity(P×I10),product of rainfall and maximum 30 min rain intensity(P×I30),respectively,but the correlation with Im was not significant.The correlation coefficient between runoff depth,sediment loss with P×I10,P×I30 was bigger than that of I10 and I30.The relationship between runoff depth,sediment loss and rainfall factors showed good consistency.The runoff depth and sediment loss of the four underlying surfaces increased with the increase of rain intensity and slope.Under moderate and high rainfall intensity,the ability of maize field to reduce runoff depth and sediment loss was the strongest.When the slope was 7 degrees,the ability of abandoned farmland to reduce runoff depth and sediment loss was the strongest.(2)There was a significantiy positive correlation between the nitrogen loss under four underlying surfaces and I10,I30,P×I10 and P×I30,but there was no significant correlation with Im and P×Im.I30 was mostly correlated with nitrogen loss in the single rainfall factors.There was a linear,logarithmic or quadratic function relationship between nitrogen loss from different underlying surfaces and I10 and I30.Under different rain intensity and slope grade,the nitrogen loss concentration was in the order of high rain intensity> medium rain intensity> low rain intensity,and for different slops it was 17°> 12°> 7°.And the nitrogen loss concentration stability time was advanced with the increase of rain intensity and slope.When the slope was 7 degrees,the ability of abandoned farmland to reduce nitrogen was the strongest.When the slope was 12 and 17 degrees,the best one for reducing nitrogen loss was maize.(3)Compared with pearson correlation analysis results,the partial correlation analysis between runoff depth,sediment loss,nitrogen loss and rain intensity and slope showed that the correlation coefficients were improved.The effects of slope on runoff depth,sediment loss and nitrogen loss was greater than rain intensity.From the above results,the following conclusions can be drawn:(1)Maize could be used as the preferred crop variety for sloping farmland in areas with high rainfall intensity,and abandoned farmland made a significant role in soil and water conservation under mild slope conditions.(2)Slope was the main factor affecting soil and water loss and nitrogen loss under low and medium rainfall intensity.Therefore,in the management of sloping farmland,measures such as terrace renovation,furrow and ridge planting should be taken to reduce the impact of slope on soil and water loss and nitrogen loss.