| The problem of excessive irrigation and nitrogen application has long existed in North China,therefore,it is of great significance to study the appropriate water and nitrogen management measures for winter wheat summer maize rotation system.In this study,the winter wheat summer maize rotation under drip irrigation was adopted.The field experiment of winter wheat and summer maize rotation system was carried out continuously from 2018 to 2021.In the winter wheat season,three irrigation levels and four nitrogen application levels were set,the three irrigation levels were 80 mm,60 mm and40 mm,respectively,represented by W80,W60 and W40;four nitrogen application levels as 250,167,83 and 0 kg ha-1were set respectively,which are represented by N3,N2,N1 and N0;At the same time,a control treatment（W0N3）was set in which only 10 mm topdressing water（W0）was applied and the nitrogen application level was N3;in addition,a bare land control treatment（BL）with the same irrigation method as W0 treatment was also set.In summer maize season,the nitrogen application level was the same as that of winter wheat,and the BL control treatment was retained.Because there was a lot of precipitation during the growth period of summer maize in this region,there was no irrigation levels treatment in the summer maize season,and the irrigation amount of each treatment was the same.The main research conclusions are as follows:（1）When the soil water in the upper soil layer（0-60 cm）was insufficient in winter wheat and summer maize seasons,the soil water consumption rate in the lower soil layer（60-140 cm）would rapidly increase.In summer maize season,When the soil water in the 0-60 cm soil layer was high and could meet the water consumption demand of crop,the soil water consumption was mainly concentrated in the 0-60 cm soil layer,and soil evaporation could compensate for the difference in water consumption in the 0-60 cm soil layer caused by nitrogen deficiency,which showed that nitrogen deficiency would not significantly reduce the soil water consumption in the 0-140 cm soil layer;However,when the soil water in the 0-60 cm soil layer was too low to meet the water consumption demand of crop,the soil water consumption rate in the 60-140 cm soil layer increased rapidly,and the nitrogen deficiency would significantly reduce the soil water consumption in the 60-140 cm soil layer,which showed that the nitrogen deficiency significantly reduced the soil water consumption in the 0-140 cm soil layer.（2）In winter wheat and summer maize seasons,with the reduction of nitrogen application,the ratio of soil ammonium nitrogen to nitrate nitrogen content would gradually increase.The irrigation level had no significant effect on the total nitrate nitrogen content in the 0-140 cm soil layer of winter wheat,but the higher irrigation amount resulted in the reduction of soil nitrate nitrogen content in the 0-40 cm soil layer.When winter wheat was mature,the average nitrate nitrogen content of each nitrogen application level decreased year by year,but for the average values of N3 and N2 treatment,the changes from the second to the third season were less than 0.2 mg kg-1.When summer maize was mature,the nitrate nitrogen content of each nitrogen application level also decreased year by year..（3）In the three growth seasons of winter wheat,when the amount of irrigation increased from W60to W80 treatment and the amount of nitrogen fertilizer increased from N2 to N3 treatment,there was no significant increase in above-ground biomass.In summer maize season,the content of nitrate nitrogen in the 0-140 cm soil layer before sowing in 2018 was 13.02 mg kg-1,which could meet the growth demand of summer maize.When the amount of nitrogen application in 2019 and 2020 did not exceed that of N2 treatment,the increase of nitrogen application would promote the growth of summer maize.With the increase of years,due to the consumption of soil nitrogen by low nitrogen（N1 and N0）treatment and its negative effect on soil environment,the growth and development of crops under low nitrogen treatment became weaker year by year.Water deficiency would only reduce the relative content of chlorophyll in flag leaves of winter wheat at the end of its growth period.Water deficiency would promote the increase of amino acid content in winter wheat grains.（4）After the winter wheat grain almost completely lost its nitrogen assimilation ability,the flag leaf still had the nitrogen assimilation ability and would transport nitrogen to the grain for a period of time,while severe water deficiency would end nitrogen transport from flag leaf to grain earlier.Nitrogen deficiency would make winter wheat and summer maize sacrifice the total nitrogen content of vegetative organs to ensure the total nitrogen content of grains.Under the condition of sufficient nitrogen,the amount of nitrogen assimilation（NA）of winter wheat was higher than the amount of nitrogen translocation（NT）,while nitrogen deficiency would reduce NA and NT,and the rate of NA decline was greater.（5）For winter wheat grain yield,when the nitrogen application amount of winter wheat and summer maize reached N2 treatment,and the irrigation amount of winter wheat reached W60 treatment,the crop demand could be met.For summer maize grain yield,when the nitrogen application rate was higher than the N2 treatment,increasing nitrogen application had no significant effect on grain yield.Nitrogen deficiency would reduce the water use efficiency（WUE）of winter wheat and summer maize,and appropriately reducing the amount of irrigation would increase the WUE of winter wheat.Nitrogen deficiency would increase partial factor productivity of applied nitrogen（NPFP）of winter wheat and summer maize,and water deficiency would decrease NPFP of winter wheat.In conclusion,compared with other higher irrigation and nitrogen application schemes,the yield and WUE of winter wheat W60N2 treatment and summer maize N2 treatment would not be significantly reduced,and the NPFP would also be slightly increased,which was an efficient and high-quality water and nitrogen management scheme under this experiment condition. |
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