Experimental Study On The Changes Of "Three Nitrogens" In The Process Of Nitrate Nitrogen Migration In Farmland Soil Beside River

With the growth of China's economy and the development of agriculture,the problem of pollution of freshwater resources has become increasingly serious.Among them,the pollution caused by agricultural fertilization to soil and groundwater has attracted the attention of countries all over the world.Nitrate nitrogen is one of the main components of nitrogen fertilizer,and it is also the main pollutant of farmland groundwater pollution.Most rural areas have low utilization efficiency of nitrogen fertilizer.Most of the nitrogen fertilizer residues in the soil will be transferred to the deeper soil or even groundwater by rainwater infiltration.This is the main way to lose nitrate nitrogen migration and also has great threat to the human health.In addition,the Riverside farmland is a typical common farmland form.The unified whole of surface water and groundwater formation has different effects on nitrogen than a single groundwater system.Once one of the systems is contaminated,it will easily cause further migration of pollutants and conversion.Therefore,studying the transformation and conversion of nitrate nitrogen under this system has a great significance for reducing nitrogen pollution and transformation in farmland and repairing contaminationIn this paper,the experiment trough indoor soil tank was used to simulate the riverside farmland system,and the farmland soil of the riverside was collected as experimental materials.By setting different surface water-groundwater relationship gradients and using different soils,the process of nitrate nitrogen entering the soil from the surface was simulated and research.The spatial distribution characteristics of nitrate nitrogen in soil under different periods and different water levels were analyzed,and the corresponding contents of ammonia nitrogen and nitrite nitrogen were also analyzed.Mainly got the following conclusions:(1)Without the influence of surface water and groundwater,the process of nitrate nitrogen move to the deep layer of soil is mainly vertical transfer.20 L of 0.5 g/L sodium nitrate solution was applied to the surface of the soil.After 24 h,the nitrate nitrogen in the soil increased by 77% on average,30% in 30 cm,and the average increase in 50 cm was only 7 %.However,after the addition of microorganisms to the soil,the increase in nitrate nitrogen in the soil decreased.(2)Surface water recharge groundwater experiments show that soil with a depth of10 cm is less affected by surface water,and the nitrate nitrogen in the soil is reducedfrom the initial 16.12 mg/kg to the end of 8.96 mg/kg,mainly due to surface watering.The soil at a depth of 30 cm is affected by the water level gradient of 110 cm-30 cm.The nitrate nitrogen content of the soil on the side not affected by surface water does not decrease significantly during the whole experimental period.Due to the replenishment of surface water,Nitrate nitrogen in the river lateral soil is greatly reduced into groundwater.The soil at a depth of 50 cm is affected by the water level gradient of 90cm-30 cm.At this depth,the nitrate nitrogen in the soil near the river is stable from the initial stage of the experiment,and then gradually decreases,while the nitrate nitrogen in the soil on the the far river,The nitrate nitrogen from the upper layer of the soil was accumulated,and the content reached the highest on the 18 th day of the experiment,and then began to decrease.(3)After the experimental soil supplemented with microorganisms,in the surface water recharge groundwater experiment,the soil with a depth of 10 cm is also not affected by the recharge of surface water.However,the decline rate of nitrate nitrogen content in soil was significantly higher than that in natural soil experiments,from the initial 14.90 mg/kg to the end of the 32 nd day experiment,it was 6.75 mg/kg.The soil at a depth of 30 cm is also affected by the water level gradient of 110 cm-30 cm.Unlike the natural soil experiment,the nitrate nitrogen in the soil side of the far river is continuously reduced from the initial 13.37 mg/kg to the 31 st day.At the end of the experiment,it dropped to 5.96 mg/kg.The soil at a depth of 50 cm also showed a continuous decrease from the beginning of the experiment,and there was no case where the soil side of the far river first increased and then decreased.(4)When the soil is polluted by more severe nitrate nitrogen,the accumulation of nitrite nitrogen is prone to occur in the long-term anoxic environment of the soil.This situation is particularly obvious in natural soils,and the deeper the depth,the nitrite The higher the cumulative amount of nitrogen.However,soils using additional microorganisms can reduce the accumulation of nitrite nitrogen by denitrification,and almost no nitrite nitrogen is detected in the soil during the experiment.(5)Ammonia nitrogen in the soil is not easily damaged or migrated by infiltration and leaching,but in the soil with long-term saturated water,ammonia nitrogen will be significantly reduced.