Study On Surface And Vertical Transport Characteristics Of Nitrogen And Phosphorus In Sloping Farmland Of Red Soil In Poyang Lake Region

Red soil is a kind of zonal soil in China.It is mainly distributed in the hilly area to the south of the Yangtze River.Due to the concentrated rainfall and heavy rain,thin soil layer,easy to be eroded,frequent agricultural activities and unreasonable plant distribution and other reasons,soil erosion and non-point source pollution are imminent.The loss of nitrogen and phosphorus in slope farmland not only leads to the decline of soil fertility,but also easily causes algae and other plankton to proliferate rapidly,the dissolved oxygen content of water decreases,and the water quality deteriorates.It is an important source of non-point source pollution.Jiangxi is the central area of red soil distribution in China,and the slope farmland in Poyang Lake area is the most concentrated in Jiangxi Province,which is typical and representative.In this paper,slope runoff plot test,indoor soil column simulation test and soil leakage plot test were carried out in Jiangxi soil and water conservation ecological science and technology park.In order to study the characteristics of nitrogen and phosphorus output from sloping farmland,12 runoff plots were set up on the same slope,including bare slope land(LL),slope tillage(SP),conventional tillage + straw mulch(dcfg),slope tillage + hedgerow(spzwl),and ridge farming(HP).Through indoor soil column simulation test and soil leakage plot test,the vertical output characteristics of nitrogen and phosphorus in slope farmland were studied by two treatments: bare and covered.After observation,sampling,testing and analysis during 2016-2018,the main conclusions are as follows:(1)Different soil and water conservation measures have an important impact on Soil and water loss of slope farmland.The results showed that: dcfg > HP > spzwl > SP > ll;the order of sediment reduction benefits was: HP > dcfg > spzwl > SP > ll.The results showed that dcfg had the best sediment reduction benefit(74.70%)and HP(91.66%).(2)Compared with the traditional tillage along the slope,the intercepting rates of total nitrogen output from surface runoff by ridge planting + hedgerow,straw mulching and ridge cultivation on cross slope were 69.79%,33.56% and 66.14% respectively,and the interception rates of total phosphorus output were 65.76%,90.17% and 80.00%,respectively.(3)Nitrogen and phosphorus were mainly lost with erosion sediment in the process of surface runoff and erosion sediment.The difference of nitrogen and phosphorus content distribution in surface runoff and erosion sediment of straw mulching runoff plot was the smallest.Under this measure,nitrogen accounted for 45.53% and 54.47% of surface runoff and erosion sediment,respectively,and phosphorus accounted for 15.76% and 84.24% respectively.In the other four measures,the nitrogen and phosphorus contents in the runoff plots were 74.18% ～ 89.83% and 96.11% ～ 98.42%,respectively.Organic nitrogen is the main nitrogen in erosion sediment,and inorganic nitrogen in surface runoff.(4)Through the leaching test,it is concluded that the leaching solution is dominated by nitrogen,and the leaching amount of phosphorus is small.In the process of experiment,the nitrogen concentration generally shows a decreasing trend;in the process of red soil leaching,nitrogen is mainly in the form of nitrate nitrogen,which is the main form of nitrogen loss in red soil and an important threat to water nitrogen pollution.Compared with bare red soil,the accumulation of total nitrogen and total phosphorus decreased by 19.4% and 23.3% respectively under straw mulching treatment in intermittent leaching test;the soil and water conservation measures with straw mulching could inhibit the leaching of nitrogen,especially nitrate nitrogen,and also inhibit the leaching of phosphorus.(5)Nitrogen in runoff of red soil slope farmland is mainly nitrate nitrogen.Mulching measures can reduce surface runoff by changing the hydrological process of slope,thus reducing nitrogen loss with surface runoff.However,mulching measures have the risk of increasing soil and underground runoff and nitrogen loss in deep layer.The results of this study revealed the characteristics of nitrogen and phosphorus migration in red soil slope farmland in Poyang Lake area,which provided theoretical basis for nutrient transfer research of red soil slope farmland and other types of soil slope farmland,provided theoretical supplement for soil and water loss and non-point source pollution research,and provided reference for soil and water conservation production practice.