Study On The Risk Of Precipitation To Nitrogen Loss In Rice Season

The growth of rice is mostly in the state of steeping field.After nitrogen application,nitrogen is difficult to be fully absorbed by rice in the short term.When encountering heavy precipitation or excessive irrigation,the surface water rises rapidly,and runoff generates easily,resulting in a large amount of nitrogen loss to the surrounding area.And a series of environmental problems are triggered.At present,there are many studies on agricultural non-point source pollution,but there are few studies on the relationship between precipitation and nutrient loss in rice fields,especially in Chaohu area.In this paper,the author analyzed the 50-year precipitation characteristics of Chaohu City and filtered the potential high-incidence period of rice-sea runoff.Through using the barrel-planting experiment,the author filtered the suitable water level for rice growth and development and the suitable polyaspartic calcium salt(PASP-Ca).And the nitrogen loss of rice paddy was analyzed by combining the precipitation characteristics of Chaohu City.This paper is aimed at reducing the risk of nutrient loss in Chaohu rice fields and providing countermeasures to reduce agricultural non-point source pollution.The main conclusions are as follows:(1)The annual precipitation and the precipitation in the rice field in Chaohu City showed an upward trend from 1968 to 2017,and the rates of change were 28.66mm/10a and 16.7mm/10a,respectively.The ratio of annual extreme precipitation to annual precipitation showed a downward trend with a rate of change of 0.002/10a.The ratio of extreme precipitation in rice season to precipitation in rice season showed a downward trend with a rate of change of 0.004/10a,indicating the 50-year annual precipitation in Chaohu City.And the precipitation in the rice season showed a gradual tendency to be uniform and gradually reduced by the influence of extreme precipitation.In the past 50 years,the average annual precipitation of Chaohu City has remained at the level of general year of water and the frequency of general year of water has the highest frequency of 22 times,accounting for 44%of the total frequency.The annual precipitation of the abundance and dryness of rice in the rice season is basically the same,and the distribution is relatively uniform.Compared with the annual precipitation,the annual distribution of precipitation in the rice season is relatively less affected by the annual precipitation distribution.(2)The recommended water level of the paddy field is 3cm,and the depth of flooding should not exceed 10cm.When the surface water level was based on 3cm,the surface water in the middle of the wet season only overflown during the base fertilizer period,the number of days was 2.3d.The average overflow runoff depth during the base fertilizer period was 19.7 mm.The average concentration of NH4+ in the overflow runoff was 2.76 mg/L,the average concentration of NO3-was 0.19 mg/L,and the average concentration of TN was 5.55 mg/L.In Pingshui,only the panicle stage overflowed,and the number of days was 0.7d.The average runoff overflow depth during the panicle stage was 14.37 mm.The average concentration of NH4+ in the overflow runoff was 0.12 mg/L,the average concentration of NO3-was 0.11 mg/L,and the average concentration of TN was 0.91 mg/L.The dry season does not overflow during the fertilizer season.At the same time,9 days after nitrogen application could be used as a key period to prevent nitrogen loss in paddy fields,and 0.3%concentration of PASP-Ca could be used as a source of control material,so that the average concentration of NH4+ in field water was 3.9%lower than conventional fertilization,NO3-The average concentration was 24.8%lower than conventional fertilization.(3)Appropriate countermeasures can be taken for the risk of loss of runoff in rice fields,for example:3cm is the irrigation water level;choose the appropriate fertilization time to avoid the high precipitation period;choose suitable fertilizer or 0.3%concentration of PASP-Ca could be used as a source of control material to reduce pollution;reservoir,circulating water.