Studies Of Farmland Water Transformation And Soil Nitrogen Transport Experiment

In this paper,farmland spring corns in Hailiutu river basin from 2014 to 2016 were taken as examples.Analysis of farmland crop water consumption by stable hydrogen and oxygen isotope tracer techniques,combined with the law of nitrogen translocation and transformation based on field sampling,in order to provide theoretical basis for reasonable irrigation and protection of shallow groundwater in sandy farmland with shallow groundwater depth.Research shows:In the study area,the meteoric water line is expressed as δ=7.5137δ¹⁸O-0.0691（R²=0.8545）.In the process of rainfall,there is evaporation and fractionation,and the rainfall effect is obvious.The rainfall is the direct source of recharge of groundwater in Hailiutu river basin.The soil vertical profile with the increase of soil depth,evaporation decreased;The root water uptake of crops is greatly affected by rainfall and irrigation.In less precipitation in 2015,maize mainly absorbs shallow soil（30cm above）water supplied by precipitation and part of deep soil（30cm below）water supplied by capillary rising after the rain;After irrigation,maize mainly absorbs mixed soil water with precipitation and irrigation supplies.In the 2016 years of abundant rainfall,soil moisture content is higher;After irrigation or heavy rainfall,there is a replacement of soil water phenomenon,so 2016 spring corn water source is more single;The maize mainly absorbs the shallow soil water supplied by precipitation after the rain;After irrigation,corns mainly absorb soil water supplied by irrigation.From the direct contrast method and the isotope linear mixed model,the water absorption law of spring maize in the different growth period was "shallow-deep-shallow".At the heading stage,the depth of water absorption reached the deepest,and the root system had basically developed completely,so the water absorption of root is mainly developed in the vertical direction during this period,but the shallow water absorption will increase as it rains.After heading date,the root system is fully,the water intake of the spring maize is still dominated by the deep soil water,but under the effect of irrigation,the depth of water absorption will become shallow;The period of grouting to waxy,water absorption of corn roots began to become shallow with time goinig until the end of the waxy ripening,corn leaves began to wither,the required water is greatly reduced,the root water depth maintained at the surface.The results showed that the small amount of rainfall in the maize seedling stage contributed to the mineralization and nitrification of soil organic nitrogen and enhanced the ability of soil nitrogen supply,thus it was suggested that a small amount of irrigation should be carried out at the seedling stage of maize.During the jointing and heading period,due to the small amount of nitrogen applied,and crop roots have deep water,so we should be appropriate to increase the amount but reduce the number of irrigation,enhanced crop deep nitrogen,to avoid the surface soil moisture content has been high and weaken the soil mineralization nitrification capacity.After heading,due to the larger amount of the second fertilizer,irrigation should be based on a small number of times,to avoid nitrate leaching and leaking in the soil.Ammonium nitrogen （NH₄⁺） is easily adsorbed by soil,and nitrogen leakage in the field is mainly nitrate nitrogen （NO₃^-）.The main reason for the leakage of nitrate nitrogen is prolonged rainfall.In the case of more annual rainfall,the soil nitrogen leaching was especially serious,the nitrate nitrogen content in groundwater was as high as 97.6mg/L,and the nitrogen loss rate of farmland was 60%.It is suggested to change the local irrigation and fertilization methods,switch to drip irrigation,to facilitate the control of irrigation and fertilization,reduce the nitrogen leakage and loss rate in the field,and reduce the risk of groundwater pollution.