Effects Of Straw Returning And Reduced Fertilization On Runoff Nitrogen And Phosphorus Loss In Rice And Rapeseed Rotation Fields

China is a large agricultural country,rice-rape rotation is one of the important planting methods in China,and agricultural production produces a large number of crop straws.The unreasonable and ineffective use of crop straw resources leads to agricultural non-point source pollution.At the same time,farmers use a large amount of chemical fertilizers in agricultural production to increase crop yield.Excessive fertilization leads to the decline of soil fertility,the loss of nitrogen and phosphorus in farmland,further aggravating agricultural non-point source pollution.On the premise of improving the utilization rate of crop straw resources and reducing the application amount of chemical fertilizer,it increases crop yield,reducing non-point source pollution and promoting the sustainable development of agriculture.In this paper,through the two-year field experiment in Tongcheng during 2018-2019,we established three different treatment modes,namely,non-straw returning treatment(CF),straw returning treatment(JG),and straw returning+reducing fertilizer treatment(JG+JL).We research the influence of straw returning and reduced fertilization on nitrogen and phosphorus loss from surface runoff,crop yield,nutrient absorption and soil nutrient status in rice-rape rotation fields.The main results were as follows:(1)The total nitrogen loss was the largest in rice and rape seasons.Nitrate nitrogen was the main form of runoff nitrogen loss in rape season,nitrate nitrogen loss in rice season was slightly higher than ammonium nitrogen loss,soluble phosphorus was the main form of runoff phosphorus loss in rice season and rape season.Compared with conventional fertilization(no straw returning)treatment,the total nitrogen loss respectively decreased by 2.25%and 13.07%under conventional fertilization+straw returning treatment and reduced fertilization+straw returning treatment.(2)Under the rice and rape rotation mode,straw returning and reduced fertilization were beneficial to slow down the loss of nitrogen and phosphorus in farmland runoff.The loss amount and concentration of nitrogen and phosphorus in the treatment of reduced fertilization+straw returning were basically lower than those in the treatment of conventional fertilization+straw returning and conventional fertilization(no straw returning).Compared with conventional fertilization+straw returning and conventional fertilization(no straw returning)treatment,the nitrate nitrogen loss was 24.89%and 26.08%on average.The loss of soluble phosphorus in the treatment of reduced fertilization+straw returning was 0.146 kg/hm~2 and 0.014kg/hm~2,compared with the treatment of conventional fertilization+straw returning and conventional fertilization(no straw returning).(3)Fertilization and rainfall affected the loss of nitrogen and phosphorus in farmland surface runoff,and the effect of base fertilizer application and heavy rainfall was more obvious.(4)Straw returning and reduced fertilization increased rice yield.Compared with conventional fertilization(no straw returning)treatment,conventional fertilization+straw returning treatment and reduced fertilization+straw returning treatment increased rice yield by 171.91 kg/hm~2 and 252.55 kg/hm~2 on average.The yield of rape decreased slightly in each treatment in rape season,and the increase or decrease of crop yield was related to the amount of crop nutrient uptake.(5)The contents of total nitrogen,total phosphorus,total potassium and available phosphorus in the soil of rice season and rape season increased,compared with the initial stage of the experiment.The contents of total nitrogen,total potassium and available potassium in the soil of rape season increased,compared with the conventional fertilization(no straw returning)treatment,and the p H decreased.Soil p H,organic matter,total nitrogen and total phosphorus contents increased in rice season compared with conventional fertilization(no straw returning),while available phosphorus contents decreased.The p H of rape season was lower than that of conventional fertilization(no straw returning),and decreased by 0.12～0.15.Compared with conventional fertilization(no straw returning)treatment,the total potassium content of rape season increased by 0.8 g/kg and 1.33 g/kg in the treatment of reduced fertilization+straw returning,respectively.Compared with conventional fertilization(no straw returning),soil p H in rice season increased slightly,conventional fertilization+straw returning and reduced fertilization+straw returning treatments increased by 4.88%and 7.32%,respectively.The decrease of soil available phosphorus in the rice season was affected by straw returning.The soil available phosphorus content in rice season was 0.84%and 9.46%lower in the treatment of reduced fertilization+straw returning and conventional fertilization+straw returning than in the treatment of conventional fertilization(no straw returning).