Study On The Characteristics Of Nitrogen Losses From Slope Farmlands During Maize Growth Stages In Purple Soil Region

Purple soil is a high productivity rock,which is shallow soil surface occur ersion easily under rainfall in Sichuan hilly basin.Nitrogen loss in runoff and sediment yield reduces soil productivity and results in eutrophication.So the research object is the scattered and simulated rainfall combined with runoff plot were employed to study the nitrogen loss during maize?Zay mays L.?growth stages under different slope gradients?10°?15°?20°?,different rainfall intensities(1.0 mm min^-1?1.5 mm min^-1?2.0 mm min^-1)and different erosion phase?sheet erosion?interrill erosion?rill erosion?,which were for the characteristic of nitrogen loss in slope farmland and the relationship between nitrogen loss and maize growth.The research laid the foundation for effective prevention the nitrogen loss in slope farmland and the sustainable agricultural development of Sichuan hilly basin.The main results are presented as follows:?1?Runoff and sediment yield increased first with rainfall duration,and the values tended to peak to the end of rainfall during maize growth stages under different slope gradients.The rate of surface runoff and sediment yield increased as slope gradients increased,and were maximum at seedling stage.The rate of interflow increased as slope gradients decreased,and were maximum at tasseling stage.The rate of nitrogen losses in surface runoff and sediment yield increased as slope gradients increased,and was up to maximum at seedling stage which the average was 5.83 mg m^-2 min^-1 and 0.94 mg m^-2min^-1,respectively.The rate of nitrogen losses in interflow decreased as slope gradients increased,and reached maximum at elongation stage which the average was 27.32 mg m^-2min^-1.Under slope gradient of 20°,the proportion of nitrogen losses in surface runoff and sediment yield to total nitrogen losses was up to 21.78%-35.67%and 2.02%-3.60%,respectively.Under slope gradient of 10°,the proportion of nitrogen losses in interflow was up to 88.15%-91.77%.?2?Runoff and sediment yield increased with increasing rainfall duration and became stable to the end of rainfall during maize growth stages at the rainfall intensity of 1.0 and1.5 mm min^-1.Runoff and sediment yield increased with rainfall duration at the rainfall intensity of 2.0 mm min^-1.The rate of surface runoff and sediment yield increased as rainfall intensities increased,and were maximum at seedling stage.The rate of interflow increased as rainfall intensities decreased,and were maximum at tasseling stage.The rate of nitrogen losses in surface runoff and sediment yield increased as rainfall intensities increased,and was maximum at seedling stage which the average was 5.25 and 0.80 mg m^-2 min^-1,respectively.The rate of nitrogen losses in interflow decreased as slope gradients increased,and was maximum at elongation stage which the average was 28.34 mg m^-2min^-1.Under rainfall intensity of 2.0 mm min^-1,the proportion of nitrogen losses in surface runoff and sediment yield to total nitrogen losses was up to 17.05%-36.37%and2.04%-4.55%,respectively.Under rainfall intensity of 1.0 mm min^-1,the proportion of nitrogen losses in interflow was up to 83.58%-90.18%.?3?Runoff and sediment yield also increased first with rainfall duration,and the values tended to peak during maize growth stages at sheet erosion and rill erosion,but were volatility at interrill erodion.The rate of runoff and sediment yield were rill erosion>interrill erosion>sheet erosion during maize growth stages.The rate of surface runoff and sediment yield was maximum at seedling stage.The rate of interflow was maximum at elongation stage.Nitrogen losses in surface runoff,interflow and sediment yield were maximum at rill erosion during maize growth stages,and the average rate of nitrogen loss was 14.97,52.88 mg m^-2 min^-1 and 5.06 mg m^-2 min^-1.The rate of nitrogen losses in surface runoff of sheet erosion was maximun at seedling stage and elongation stage,and was maximum at elongation stage and seedling stage during interrill erodion,respectively.The rate of nitrogen losses in interflow during erosion terrace was maximum at elongation stage.The rate of nitrogen losses in sediment yield during erosion terrace was maximum at seedling stage.?4?The variation trend of nitrogen loss in runoff and sediment yield with rainfall duration was same with runoff and sediment yield during maize growth stages under different slope gradients,rainfall intensities and erosion terraces.Under 15°slope gradient and 2.0 mm min^-1 rainfall intensity,the proportion of nitrogen losses in surface runoff and sediment yield to total nitrogen losses was maximum.Under 10°slope gradient and 1.0mm min^-1 rainfall intensity,the proportion of nitrogen losses in interflow was maximum.Rill erosion was the main erosion terrace of nitrogen loss in surface runoff,interflow and sediment yield during rainfall duration.Interflow were the main channels for nitrogen losses,and nitrate nitrogen was the main form of nitrogen loss during the rainfall process.