Nitrogen Transport And Impact On Crop Physiology Under Sewage Irrigation At Different Groundwater Depth

Experiment of nitrogen transport, transformation and crop physiology under different ground water depths was investigated, followed by dynamics of nitrate and ammonium transport in soil and ground water, the impact of sewage irrigation on physiology of winter wheat and corn(including the leaf area index, the crop height, the dry matter accumulation and the output), the effect of sewage irrigation on winter wheat quality and yield, the BP Neural Network model of nitrate transport in soil, the estimating index and method of sewage irrigation to environment were discussed. The results are benefit for using of sewage in agriculture safely, protecting soil and groundwater environment, easing water shortage problem, promoting the development of economy and society sustainbly. The field experimental plots are located in the experimental field for crop water interaction and Hongmen experimental station of Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences. Four kinds of water quality (the sewage, half sewage, reused water and clean water)and two kinds of irrigation quota(1200 m3/hm2,900 m3/hm2) were designed in the former experimental treatments, observation items included the soil moisture, nitrate and ammonium content in soil, water quality,the starch, the protein, the nitrogen,the phosphorus, the potassium content,residual of heavy metal in winter wheat grain. Three kinds of groundwater depth and two kinds of irrigation quota were designed in the latter experimental treatments, observation items included the soil moisture, nitrate and ammonium content in soil, water quality,the nitrate content in groundwater, ground water depth.The result of the study indicates:(1)The result of barrel experiment indicates that the ammonium is located mainly in the upper soil zone(0～20cm),the nitrate is increased gradually from upper soil zone to lower soil zone under different treatments. the starch content in winter wheat grain of larger water amount treatment is higher than that of smaller water amount treatment under the same water quality condition.On the contrary, the protein content in winter wheat grain of larger water amount treatment is lower than that of smaller water amount treatment.When the irrigation amount is the same, the protein content in winter wheat grain is that sewage treatment is higher than that of the half sewage, the reused water, and the clean water. Under the smaller irrigation amount treatment, the yield of the sewage, the dilution sewage and reused water treatments increase 12.71%,9.57% and 1.14%, comparing with the clean water treatment. Under larger irrigation amount treatment, the yield of the sewage, the dilution sewage and reused water treatment increase 12.22%, 5.05% and 2.12% comparing with the clean water treatment. The content of nitrogen,phosphor, kalium in winter wheat grain of the sewage treatment are higher than clean water treatment.There is no obvious difference about the residual heavy metal content in the winter wheat grain under different treatments. (2)The experiment of nitrate and ammonium transport in soil under different ground water depths of sewage irrigation showes that after sewage irrigation, the nitrate content in soil at different layers increases noticeably, comparing to the before irrigation. The treatment of more sewage amount, the more nitrate content was tested between 0 to 200 centimeter depth of soil, under the same groundwater depth treatment. The treatment of more groundwater depth, the more nitrate content was tested between 0 to 200 centimeter depth of soil, under the same irrigation quota. It shows that the depth of nitrate transpot is affected by groundwater depth and irrigation amount.But there is no obvious effect for the ammonium content in soil under different groundwater depth.(3)The experiment of nitrate transport in groundwater under different groundwater depths of sewage irrigation showes that, 10 days after sewage irrigation of winter wheat, the nitrate concentration in groundwater increase 21.15%,15.49% and 4.92% ,comparing with the before irrigation,in lower irrigation amount treatments.The nitrate concentration in groundwater increase 58.42%,38.98% and 27.2% ,comparing with the before irrigation in larger irrigation amount treatments.10 days after sewage irrigation of corn, the nitrate concentration in groundwater increase 34.67%,24.94% and 20.89% ,comparing with the before irrigation , in lower irrigation amount treatments.The nitrate concentration in groundwater increase 46.81%,15.48% and 10.07%, comparing with the before irrigation in larger irrigation amount treatments.It indicates that the larger irrigation quota, the more nitrate was test in soil solution and groundwater under the same groundwater depth. the less groundwater depth,the more nitrate was test in the groundwater under the same irrigation quota,also,the larger risk of pollution of groundwater by nitrate increases under shallow groundwater depth.(4)Field experiment of crop physiology showes that the sewage irrigation can promote the growth of winter wheat,especially in the leaf area index, the dry matter accumulation and the output. Following factors, including ground water depth, water quality,irrigation water amount,have a deep impact on colony density of winter wheat before harvest.The treatment of lower irrigation quota is of more benefit to the leaf area index and crop height of winter wheat than that of higher water treatment. The treatment of water depth 2m of ground water depth is the best for the growth of winter wheat under the same irrigation amount and fertilizer amount condition. There is no obvious difference between the leaf area index and crop height of corn under different treatments.(5)Based on the dynamics of nitrate transport under sewage irrigation,the BP Neural Network model of nitrate transport was developed at different groundwater depth.The input parameters of this model include the leaf area index,the crop height, the evapotranspiration of reference crop(ET0),which symbolized the crop physiology and climate condition, ground water depth, soil water content.The output parameters include nitrate concentration of different depth of soil. The optimal topology structure of this model is 10:12:7. The result shows that the model has a high precision. It will expand the research area of nitrogen transport in soil.(6)Following the sewage irrigation experiment,fuzzy evaluation theory was applied in estimating the effect of sewage irrigation to environment,correlative computer software of this model was developed. It was tested in the irrigation area of Henan province.It indicates that this method has a high precision for estimating the impact of sewage irrigation on the environment.The innovation points of this research are as follows.The new effect factor, groundwater depth,was considered in analysis of the impact of sewage irrigation to crop physiology in this research field;following the experiment of nitrogen transport in Laboratory,the field experiment of nitrogen transport and the mechanism of groundwater pollution were conducted in different groundwater depths under sewage irrigation,the risk of groundwater pollution was studied;Based on the dynamics of nitrate transport under sewage irrigation,the BP Neural Network model of nitrate transport was developed at different groundwater depth,the impact of estimating index and the method of the sewage irrigation on environment were studied,the software of these models were developed,which was easy to apply.