Migration And Transformation Of N And P In Rice Paddy Fields Under Different Water And Fertilizer Management Practices

Rice is the main food crops which is greatest quantity of irrigation water and fertilizer consumption,jianghan plain is the main area of rice cultivation in China,but now also face many problems,such as increased fertilizer use,large loss of nutrients in rice fields and severe seasonal water shortage.Fertilization and water management are important factors affecting nitrogen and phosphorus migration in farmland.Therefore,according to the regional characteristics,the characteristics of rainfall and the growth period of rice irrigation and drainage water characteristics of jianghan plain region,puts forward a set of water-saving section fertilizer production,reduce farmland drainage?permeability?of water pollution and accepted by farmers water management technology is imperative,at the same time can provide reference for prevention and control of agricultural non-point source pollution.This experiment was done in two aspects:Experiment 1:Experimental research on reducing fertilization for paddy field under wastewater from aquaculture pond used for irrigationLocal conventional fertilization and irrigation practice was regarded as a contrast?CK?,some researches were conducted by field experiment under reduction of chemical fertilizer?nitrogen and phosphorus fertilizers?that are absorptive effect of paddy field on nitrogen and phosphorous from pond aquaculture wastewater,influences of that water irrigated paddy field on surface water and leakage water quality,and on nutrient absorption of rice and the yield.The results are as follows,i)Ammonium?NH₄⁺?N?,nitrate nitrogen?NO₃^??N?,total nitrogen?TN?,dissoluble phosphorous?DP?,particulate phosphorous?PP?and total phosphorous?TP?in pond aquaculture wastewater can be effectively removed by paddy field ecosystem,the removal rate increased with the reduction of fertilization.The TN removal rate under100%,80%and 60%of conventional fertilization treatment were 25.1%?38.9%and50.5%while the TP removal rate were 56.4%?71.2%and 76.2%,respectively.The main forms of nitrogen and phosphorus removed were NH₄⁺?N?NO₃^??N and PP.ii)In addition,the mass concentration of NH₄⁺?N,NO₃^??N,TN,DP,PP and TP from surface water and leakage water in paddy field showed a declining trend with the reduction of fertilization.Under 80%and 60%of conventional fertilization treatment the mass concentration of TN and TP in surface water were 5.8%and 23.4%,20.8%and 35.5%lower than that from CK,respectively while in leakage water the number were 18.3%and 27.5%,23.1%and 45.8%.iii)Considering the nutrient uptake and yield,pond aquaculture wastewater was irrigated into paddy fields during rice growing stage,the yield of the conventional fertilization treatment was the highest,compared with CK treatment can increase 2.3%,the nitrogen and phosphorus uptake increased by 4.4 kg·hm^-22 and 2.0 kg·hm^-2,respectively,the yield and nitrogen uptake of the 80%conventional fertilization treatment was similar to CK,but the yield,nitrogen and phosphorus uptake of the 60%conventional fertilization treatment was decreased significantly compared with CK treatment.iiii)In the period of rice growth,100%CF,80%CF and 60%CF in nitrogen uptake of top soil was increased averagely by 3.8%,-2.3%and-10.1%,the phosphorus uptake was increased averagely by 3.3%,-4.2%and-10.7%,respectively;Among all the treatments,the soil total N,available N,total P and available P content increased with the decrease of soil depth in 0⁶0 cm soil layer,but in the same soil depth was decreased with the fertilization decreasing,for this reason,pond aquaculture wastewater irrigation did not increased nitrogen and phosphorus content in soil profile under reducing nitrogen and phosphorus fertilizer.It is recommended that pond aquaculture wastewater was irrigated into paddy field,can save chemical fertilizer by 20%and freshwater quantity by 5700 m³·hm^-2,during the whole period of rice growth.Comprehensive consideration the economic and environmental benefits under consideration in rice cultivation,it is recommended that fertilization is about 80%of the local conventional fertilization when pond aquaculture wastewater was irrigated into paddy field.Experiment 2:Experimental Research on Nitrogen Management Based on Emission Controlling for Paddy FieldIn order to improve paddy water and fertilizer management measures in Jiang Han Plain,field plot experiment with two irrigation regimes?conventional flooding irrigation,CF;shallow irrigation and deep storage,SIDS?and three nitrogen?N?managements?farmers'fertilization practice,FFP;30%urea+70%controlled release compound fertilizer,30%N+70%CRF;optimized and reduced nitrogen fertilizer application,OPT-N?were carried out to study the effects of water and fertilizer managements on losses of N and phosphorus?P?,nutrition uptake of rice and nutrition accumulation of soil during different growth stages.The results are as follows,i)compared with CF,SIDS reduced the irrigation quantity,total water use,runoff and leakage by 41.7%,18.5%,45.8%and 21.9%,respectively,but increased rainfall utilization rate by 16.2%.The amount of total N?TN?from runoff and leakage was 32.6%³5.9%and 22.8%³2%lower in SIDS than in CF.SIDS also decreased the amount of total P?TP?from runoff and leakage by 36.4%⁵3.1%and 16.2%³3.3%,respectively.Meanwhile,the paddy runoff and leaching losses of TN and TP from re-greening to jointing and booting stages accounted for more than 70%of the whole growing season.ii)compared with FFP,30%N+70%CRF and OPT-N decreased runoff of TN by19.7%²9.2%and 15.1%²5.2%,leaching losses of TN by 25.4%⁵1.7%and 20.9%²6.4%,leaching losses of TP by 18.4%²4.5%and 20.4%³1.6%,respectively,but no obvious difference was found in runoff of TP.iii)considering the nutrient uptake of rice and nutrition accumulation of soil,compared with FFP,SIDS increased net photosynthetic rate?Pn?,stomatal conductance?Gs?,intercellular CO2 concentration?Ci?and transpiration rate?Tr?during from tillering stage to filling stage of rice,SIDS increased tillering stage,full panicle stage and mature period of aboveground dry matter accumulation by 17.5%,35.0%and 4.0%,respectively;in addition,SIDS increased yield by 4.4%,but had no significant effects in N and P accumulation of soil?0—40 cm depth?.Compared with FFP,30%N+70%and OPT-N improved 5.6%and 0.4%yields with the high and stable available N and available P of soil?0—20 cm depth?.In generally,the combination of SIDS and 30%N+70%CRF can be effective in saving water,reducing N and P losses,promoting rice yields and improving soil fertility.