| Large-scale rice cultivation will lead to a series of ecological and environmental problems,such as surface water quality contaminated by drainage water from paddy fields.This paper takes rice fields as the research object,and aims to study the loss of nitrogen,phosphorus and other components under different irrigation and fertilization conditions in Honghe Farm of Sanjiang Plain,as well as the water quality and quantity monitoring tests of typical irrigation and drainage channels at different levels in the irrigation area.And the generation and migration characteristics of agricultural non-point source pollution in irrigation areas will also be considered.(1)The drainage method and Penman formula are estimated the water withdrawal in the experimental area,and the rice water requirement is calculated by the indirect calculation method.After calculating the effective rainfall of the paddy field,the actual value of the dewatering amount is measured according on the spot.In the analysis of the drainage water on May 20,the drainage water accounted for 95% of the drainage water;but on July 27,the drainage water accounted for 33% of the drainage waterbecause of the rice growth cycle entered a period of higher water consumption.It shows that,the crop growth cycle and weather are the chief factors of water withdrawal and drainage water of rice cultivation in Northeast China.(2)Cross-experimental comparison was used to analyze the effect of flooded water surface height,fertilizer application rate and herbicide on farmland water quality.The impact of flooded water surface height on farmland water quality status was small,while the application of chemical fertilizers has a more obvious effect on total nitrogen,ammonia nitrogen,total phosphorus and other nutrient elements.To a certain extent,the use of herbicides has bad effect on ammonia nitrogen.In addition,the consistency of water quality changes at different monitoring points can be analyzed by the time series of different monitoring points to judge the situation of being affected by external factors further.The results show that the consistency of the law of different indicators with time is poor,indicating that external factors have little effect on it.(3)At the same time point,we can get that the nitrogen(total nitrogen,ammonia nitrogen)concentration has a peak in the vertical direction,which has a downward trend with time(only at a depth of 0-60mm)by the analysis of the changes in the concentration of pollutants in the vertical direction(soil depth)and the horizontal lateral seepage(field edge soil).It shows that the vertical infiltration pollutant concentration may be has small effect on total phosphorus concentration due to the downward shift of the nitrogen fertilizer on the soil surface after fertilization with the peak value caused by the field underwater infiltration.Besides,the results of lateral seepage are consistent with that of the vertical seepage pollutant concentration.(4)There is no obvious linear relationship between the water withdrawal and the drainage water volume and the discharge compliance by the analysis of the relationship between the water withdrawal and the discharge load.Relevant regression formulas of field water pollutant concentration and water withdrawal,farmland water residence time,temperature and fertilizer use can be obtained by regressed calculations.Moreover,the mechanism of farmland dewatering pollution formation is further clarified from the perspective of regression parameters and fitting parameters. |
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