Effects of Topsoil Water and Nitrogen Control on the Movement and Residual Effect of Nitrate Accumulated in Deep Soil Profile

【Objective】The purpose of this study was to study the effects of topsoil water and nitrogen control on the movement and residual effect of nitrate accumulated in deep soil profile in north China.【Method】The injection technique of labeled NO3--N was adopted in a field micro-plot experiment.Nitrogen applied at 0 and 150 kgN·hm-2 N and two irrigation modes were designed.The four treatments were N0W1,N0W2,N150W1,N150W2.The labeled NO3--N was injected in 110 cm soil profile.【Result】Under this condition,the distribution of residual amount of 15N in each soil profile after wheat harvest was: N0W2N150W2N150W1N0W1.The labeled 15N moved at vertical distance.It moved 30 cm to the top soil profile and 50 cm to the lower.In addition to N0W2,the other treatments with the cumulative peak position than the mark down 30 cm;After maize harvest,most 15N was detected in 100-160 cm.The residues of 15N of N0W1 reduced significantly;The utilizations of residual 15N by maize were: 5.5%,2.2%,1.7% and 1.5%,and N0W1N150W2N150W1N0W2.Maize roots were distributed in 0-20 cm,and N treatment was higher than non-fertilizer treatment,topsoil water and nitrogen control affected root development in the middle and lower.【Conclusion】Less nitrogen and reasonable water stress promoted the growth of maize roots in subsoil layers which accelerated the absorption of nitrate accumulated in deep soil profile.Nitrogen does not promote the use of maize residue N,nitrogen and traditional irrigation of plow layer will enhance the accumulation of nitrate in the deep,and thus resulting in the security threat to groundwater.