Study On Nitrogen And Phosphorus Loss In Dryland Vegetable Field And Its Prevention And Control

With the improving condition of point source pollution control,agricultural non-point source pollution has become one of the most serious water environmental problems in China.Domestic dryland farmland accounts for 49.43%of the total cultivated land,which makes it an important source of agricultural non-point source pollution.As a significant part of dryland farmland,the vegetable field discharges large amounts of nitrogen and phosphorus into the water body,to investigate the loss pattern of runoff pollutants in the vegetable field,and to provide references for its non-point source pollution control,artificial simulated rainfall runoff experiments were carried out.Experiments took place on the field that cultivates Ipomoea aquatica,under the conditions of four different total rainfall（10,25,50 and 100 mm）and three different rainfall intensities(10,15 and 25 mm·h^-1).On this basis,an interception and recycling scheme was proposed,and its interception effect for runoff volume,nitrogen,and phosphorus was examined.The results indicate that:1.Runoff yield in dryland vegetable field increases with the increasing rainfall intensity and total rainfall.The runoff yield under the total rainfall of25,50 and 100 mm is 37.92、57.33 and 372.12 m3·ha^-1,respectively.The runoff yield under the rainfall intensity of 10,15,and 25 mm·h^-1 is 197.07,381.92 and 649.45 m³·ha^-1,respectively.2.The volume of nitrogen loss increases with the increasing rainfall intensity and total rainfall.The volume of TN loss under the total rainfall of25,50 and 100 mm is 0.064、0.278 and 3.579 kg·ha^-1,respectively.The volume of TN loss under the rainfall intensity of 10,15,and 25 mm·h^-1 is0.67、2.48 and 9.74 kg·ha^-1,respectively.3.The volume of phosphorus loss increases with the increasing total rainfall,and decreases with the increasing rainfall intensity.The volume of phosphorus loss under the total rainfall of 25,50 and 100 mm is 0.002、0.011and 0.058 kg·ha^-1,respectively.The volume of phosphorus loss under the rainfall intensity of 10,15,and 25 mm·h^-1 is 0.061、0.050 and 0.030 kg·ha^-1,respectively.4.Compared with NH₄⁺-N,the nitrogen loss is primarily in the form of NO₃^--N under different rainfall conditions;the particulate phosphorus（PP）is the main form in the phosphorus loss.Under the total rainfall of 25,50and 100 mm,the loss of NO₃^--N accounts for 50.33%⁵6.52%of TN loss,and the loss of PP accounts for 69.64%⁸7.66%of TP loss.Under the rainfall intensity of 10,15,and 25 mm·h^-1,the loss of NO₃^--N accounts for42.40%⁵6.85%of TN loss,and the loss of PP accounts for 77.34%⁹3.44%of TP loss.5.Nitrogen interception is the key element of the dryland vegetable field runoff control under different rainfall conditions.TN discharge can be effectively reduced by controlling the field ditch water level during the runoff period with high nitrogen load.The interception rate is 100%,100%,and 81.67%under different total rainfall.The interception rate under different rainfall intensities is and 100%,63.56%,and 33.98%.6.The nitrogen and phosphorus losses can be effectively reduced by runoff recycling.When the circulated runoff is 200 m³·ha^-1,the runoff can be completely returned to the farmland ecosystem after three cycles.The first cycle has the best effect on nitrogen reduction,the reduction rate ranged from 86.44%⁹4.35%,and most of the phosphorus can be reduced by two remaining cycles,the reduction rate ranged from 76.19%⁹0.10%.