Fate Of Summer Maize Fertilizer Nitrogen Under Different Water And Nitrogen Management Modes In Winter Wheat/Summer Maize Rotation System

Winter wheat/summer maize rotation is the main planting mode in Guanzhong area.Clarifying the impact of water and nitrogen management on the fate of fertilizer nitrogen in the rotation system can provide an important theoretical basis for scientifically formulating water and nitrogen management measures.In order to quantitatively study the fate of nitrogen fertilizer applied in summer maize season under different water and nitrogen management modes in the rotation system,a two-year field micro rotation experiment was conducted from 2019 to 2021 by using ¹⁵N tracer technology.In experiment 1,four irrigation and nitrogen application modes were set up,which were:M1 traditional base application,nitrogen application rate was 210 kg/hm²,and border irrigation was 90 mm at jointing stage;M2 traditional top dressing（50%before sowing and 50%at the big bell-mouth stage）,nitrogen application rate was 210 kg/hm²,and border irrigation was 90mm at the jointing stage;M3 drip irrigation,nitrogen application rate was 210 kg/hm²,and the ratio of nitrogen application was 2:3:3:2 in seedling stage,jointing stage,tasseling stage and filling stage.Full drip irrigation was carried out in the whole growth period according to evapotranspiration;M4 drip irrigation,nitrogen application rate was 150 kg/hm²,which was 28.6%lower than that in M3,and the management of nitrogen and irrigation was the same as that in M3;In experiment 2,the nitrogen fertilizer applied at seedling stage,jointing stage,tasseling stage and filling stage under M4 mode in experiment 1 was tracked by ¹⁵N labeled fertilizer.The two experiments continued to track the residue of labeled fertilizer nitrogen in the last winter wheat season.Drip irrigation was adopted for all winter wheat,with the nitrogen application rates of 255 kg/hm² and 175 kg/hm² respectively,corresponding to the plots with the nitrogen application rates of 210 kg/hm² and 150kg/hm² in summer maize season,and the irrigation amount was determined according to the evapotranspiration for full drip irrigation.In order to provide theoretical basis and technical support for the optimization of water and nitrogen management in the winter wheat/winter wheat rotation system,the absorption,distribution,transport,loss,residue and after-effect of nitrogen fertilizer in different irrigation and nitrogen application modes in the summer maize season and in different periods were studied.The main achievements are as follows:（1）The effects of different irrigation and nitrogen application modes on dry matter quality and nitrogen accumulation of summer maize were studied,and the fate of fertilizer nitrogen in summer maize season under different irrigation and nitrogen application modes was determined.Compared with the two traditional models,drip fertigation significantly increased the above-ground dry matter mass,nitrogen accumulation and fertilizer nitrogen accumulation of summer maize.Under drip irrigation,28.6%nitrogen reduction did not significantly reduce the dry matter mass and nitrogen accumulation of summer maize,while the fertilizer nitrogen accumulation decreased significantly,which may be the effect of large sample error on the significance.After summer maize harvest,the amount of residual fertilizer nitrogen in 0～20 cm soil layer of each treatment was significantly higher than that in the lower soil layer,and the amount of residual fertilizer nitrogen in soil decreased with the increase of soil depth,but the amount of residual fertilizer nitrogen in 80～100 cm soil layer increased significantly under the traditional basic application mode.Drip fertigation can reduce the leaching loss of nitrogen fertilizer to the deep layer of soil and keep the residue of fertilizer nitrogen in the upper layer of soil.The residual amount of fertilizer nitrogen in summer maize was the highest in top dressing mode;drip irrigation with nitrogen could significantly reduce fertilizer nitrogen residue.Under drip irrigation,28.6%nitrogen reduction had no significant effect on fertilizer nitrogen residue in soil.In the two years of the experiment,the fertilizer nitrogen utilization rate of the drip irrigation mode with the nitrogen application rate of 210 kg/hm² was 45.58%and 46.01%respectively,which was significantly higher than the two spraying modes.The loss rate of fertilizer nitrogen of summer maize in the current season was the highest in the base application mode,which was 36.91%and 38.50%respectively.Under the condition of drip irrigation,28.6%nitrogen reduction could significantly improve the utilization rate of fertilizer nitrogen in the current season,up to 50.96%and 55.22%,and the loss rate in the current season was less than 20%.（2）The fate of fertilizer nitrogen in summer maize and rotation period under different irrigation and nitrogen application modes was revealed.The rotation cycle utilization rate of drip irrigation was significantly higher than that of the two spreading modes.Under the condition of drip irrigation,28.6%nitrogen reduction had no significant effect on the rotation cycle utilization.The residual rate of fertilizer nitrogen and the final residual rate after rotation period in top dressing mode were the highest in summer maize,and the loss rate of rotation period in base application mode was significantly higher than that in other treatments.As far as the residual fertilizer nitrogen in summer maize season is concerned,the absorption of residual fertilizer nitrogen in the previous crop by winter wheat is the highest in the top dressing mode,and the utilization rate of residual fertilizer nitrogen in the subsequent crop is the highest in the drip irrigation mode;Due to the large amount of fertilizer nitrogen residue in the 80～100 cm soil layer of the previous basal application mode,it was leached below 100 cm in the winter wheat season,resulting in a significantly higher loss rate than other treatments.There was no significant difference in the residual fertilizer nitrogen rate of summer maize in winter wheat season under different irrigation and nitrogen application modes.（3）This paper studied the absorption,distribution,transport and residue of nitrogen fertilizer applied at different stages in summer maize under drip irrigation,and explored the fate of nitrogen fertilizer applied at different stages in the growth process of summer maize.In the same growth period,the absorption and accumulation of nitrogen fertilizer applied at different stages in the upper part of summer maize plants were as follows:tasseling fertilizer≥jointing fertilizer>seedling fertilizer>grain filling fertilizer.Compared with the fertilizer nitrogen applied in other periods,the absorption and accumulation of tasseling fertilizer in summer maize decreased significantly.The utilization rate of seedling fertilizer,jointing fertilizer and tasseling fertilizer in summer maize was more than 50%,and the residue rate and loss rate were less than 30%.During the two years of the experiment,the residual amount of fertilizer nitrogen applied in different periods in the soil decreased with the increase of soil depth,and the residual amount in 0～20 cm soil layer was significantly higher than that in the lower soil layer.The residue rate of filling fertilizer was the highest in the summer maize season,reaching 66.85%and 56.00%respectively,which was significantly higher than that in other periods,and was prominent in 0～20cm soil layer.（4）The fate of fertilizer nitrogen applied at different stages of summer maize season in winter wheat/summer maize rotation cycle under drip irrigation was determined.The absorption and accumulation of fertilizer nitrogen residues in the above ground organs of winter wheat at different stages of the previous crop was the highest in the filling fertilizer residue,which was significantly higher than that of seedling fertilizer,jointing fertilizer and tasseling fertilizer.After winter wheat harvest,the residue of filling fertilizer was still the largest in 0～100 cm soil layer.The fate of fertilizer nitrogen applied at different stages of summer maize in rotation period showed that the utilization rate,residue rate and loss rate of fertilizer nitrogen applied at different stages of summer maize rotation cycle varied from 43.54%to 74.11%,6.30%to 16.01%and 17.26%to 40.45%respectively.The utilization rate of male pulling fertilizer rotation was the highest,and that of grain filling fertilizer rotation was the lowest.In conclusion,drip irrigation can significantly improve the utilization rate of fertilizer nitrogen in winter wheat/summer maize rotation system;the decrease of nitrogen application rate by 28.6%significantly increased the fertilizer nitrogen use efficiency of summer maize in the current season,and had no significant effect on the dry matter mass,nitrogen accumulation and nitrogen use efficiency of winter wheat/summer maize rotation cycle.In addition,compared with seedling fertilizer,jointing fertilizer and tasseling fertilizer,the utilization rate of 20%nitrogen topdressing in the current season and rotation period of summer maize in the filling stage was lower,and the residue and loss were higher.Therefore,it is recommended to adopt the drip irrigation nitrogen application mode with the nitrogen application rate of 150 kg/hm² for summer maize,and reduce the proportion of nitrogen application after the filling stage.