Research On Nitrogen And Phosphorus Loss Law In Typical Sloping Arable Land In Xiangxi River Watershed

The Xiangxi River as the largest tributary of Three Gorges Reservoir in Hubei province,it is an important water source watershed for local residents living and production.Due to the steep slope of arable land,as the local residents in Xiangxi River basin in order to pursue high-yield crops,and excess fertilizer resulting in a surplus of nitrogen and phosphorus,making a lot of nitrogen and phosphorus along with rainfall runoff flows into the river,resulted in a greater threat of the safety of water quality the environment in Xiangxi River and Bay.Therefore,it based on field surveys Xiangxi River basin and consult relevant literature,selected local typical soil in sloping-lime soil in the field for artificial rainfall simulation experiment.The study for the runoff and sediment regularity on lime soil under different rainfall intensities and different slope and different vegetation coverage and the study for the soil loss regularity with the nitrogen and phosphorus under different rainfall intensities different vegetation coverage.The results are as follows:（1）Through the observation to the phenomenon of runoff and sediment on the runoff plot yield and discoveries that the characteristics of surface runoff and sediment are the same under different rainfall intensities and different slope and different vegetation coverage,among the runoff with the extension of the runoff time show that first to increase then gradually to maintain,the loss of sediment concentration are expressed as the extension of the runoff time show that first tends to reduce and final to balance.The TP and TN loss from runoff under different rainfall intensities and different slope showed the initial runoff are the largest,after as the rain continued showing a slow decrease and finally tends to balance,the TP and TN loss from the runoff sediment as the runoff time continued showed that first to increased then to decreased.（2）With the rainfall intensity,slope increased and coverage reduced,the surface runoff and sediment loss volume has significantly increased trend.With the increase of rainfall intensity and slope,the initial runoff time was significantly advance;With the increase of vegetation coverage,the initial runoff time was significantly prolonged.（3）The loss of phosphorus in Lime soil based mainly in the form of sediment,the loss of TP in runoff mainly PP-based,accounting for more than 80%;the proportion of lime soil nitrogen loss in runoff and sediment are rather,specific performance that on the strong rain the N in the soil loss in the form of runoff dominant,accounting for 57.79%;on the moderate intensities the N in the soil loss in the form of sediment dominant,accounting for 54.45%N;Under the three slope,the loss of TN in the runoff are the dominant form of runoff.The runoff loss of TN mainly NO₃^--N-based,the loss of NH₄⁺-N concentration is far less than the loss of NO₃^--N concentration.The loss of subsurface runoff TN mainly particulate nitrogen-based on strong rain,accounting for more than 75%,the loss of subsurface runoff TN mainly dissolved-based on moderate intensities,accounted for more than60%.（4）On the different rainfall intensities and different slope,the cumulative loss amount of nitrogen and phosphorus in surface runoff as the runoff period being a significant linear correlation.