Effects Of Planting Density And Nitrogen Application On Yield And Water And Nitrogen Use Of Degradable Film-Covered Summer Maize

The uneven distribution of rainfall and low water and nitrogen utilization efficiency in the arid areas of northwest China are the main factors limiting agricultural development.Ridge and furrow plastic film planting can preserve soil moisture,suppress evaporation,improve soil water and heat,promote crop growth,and effectively improve crop water and nitrogen utilization efficiency.The negative effects of residual film on soil characteristics,crops,and environmental pollution are positively correlated with the amount of residual film in the soil.Degradation film coverage can effectively improve this problem.However,the planting density and nitrogen application rate for high yield and efficient utilization of water and nitrogen under degraded plastic film coverage conditions are still unclear.Choosing a suitable planting density for the local area and optimizing nitrogen fertilizer management to achieve optimal yield,high yield,cost saving and environmental friendliness is an important measure for sustainable agricultural development.In this study,summer maize was studied at planting densities（D1:40,000 plants/hm²,D2:60,000plants/hm²,D3:80,000 plants/hm²）)and nitrogen application levels（N1:60 kg/hm²,N2:120 kg/hm²,N3:180 kg/hm²,N4:240 kg/hm²,N5:300 kg/hm²）,and flat the crop without mulch and no N application CK was used as the control treatment.The impact of degradable plastic film covering on the physiological growth,dry matter accumulation,yield,water and nitrogen utilization efficiency,and economic benefits of maize.Propose a planting density and nitrogen application model for high yield and efficient water and nitrogen utilization of summer maize covered with degradable plastic film in the arid areas of northwest China.The main research findings are as follows（1）Mulching significantly increased soil water storage,with soil water storage decreasing and then increasing from 0-100 cm during the reproductive period.The increase in planting density will reduce the soil water storage capacity of 0-100 cm during the growth period of summer maize.With the increase of nitrogen application rate,soil water storage significantly decreased,but there was no significant difference between N4 and N5 treatments under D3 planting density.The accumulation of soil nitrate nitrogen gradually decreases with the increase of soil depth,and nitrate nitrogen accumulation is mainly concentrated in the upper and middle layers of soil.The accumulation of nitrate nitrogen in 0-100 cm soil accounts for 68.41%to 70.22%of the accumulation of nitrate nitrogen in 0-200 cm soil.As the nitrogen application rate increases,the accumulation of soil nitrate nitrogen significantly increases,but an increase in planting density will reduce the accumulation of soil nitrate nitrogen in the0-140 cm soil layer.（2）Planting density significantly increased the leaf area index and aboveground dry matter accumulation of maize,but significantly reduced stem diameter and chlorophyll content.Nitrogen application can significantly increase maize plant height,stem diameter,and chlorophyll content.Compared with D1,the chlorophyll content of D2 and D3 decreased by an average of 4.02%and 9.40%,and the dry matter accumulation increased by an average of 8.91%and 44.63%.As the nitrogen application level increases,the accumulation of aboveground dry matter first increases and then decreases.Under different densities,the accumulation of dry matter reaches its maximum at D1N3,D2N3,and D3N4,respectively.Compared with D1N3 and D2N3 treatments,D3N4 prolonged the rapid growth period by 2-4 days,and the maximum dry matter accumulation rate（Vmax）increased by 26.42%and4.36%.Nitrogen application significantly increases pre flowering transport and post flowering production,while planting density significantly increases post flowering production and the contribution rate of post flowering production to grain yield,thereby increasing yield.（3）Planting density and nitrogen application level have a significant impact on yield and its components.Planting density significantly increases maize yield by improving population production levels.As the nitrogen application rate increases,the yield,ear length,ear diameter,number of grains per row,and 100 grain weight show a pattern of first increasing and then decreasing.Different planting densities reach their maximum yield under D1N2（8455 kg/hm²）,D2N3（9463 kg/hm²）,and D3N4（12804kg/hm²）treatments,respectively.Compared with D1N2 and D2N3 treatments,D3N4increased total investment by 16.21%and 7.50%,but net benefits increased by63.11%and 44.10%（P<0.05）.Increasing planting density and nitrogen application significantly increased the water consumption of maize throughout its entire growth period,and appropriate densification can improve the water use efficiency of maize.D3 showed an average increase of 7.27%and 10.31%in planting density WUE compared to D1 and D2.As the nitrogen application level increases,WUE first decreases and then increases.Increasing planting density can increase NAE,NRE,and NPFP of maize,while increasing nitrogen application levels actually reduces NAE,NRE,and NPFP of maize.Selecting yield,water use efficiency（WUE）,and nitrogen use efficiency（NUE）as evaluation indicators,comprehensively considering the interaction effect between planting density and nitrogen application level.The results showed that when the nitrogen application level was 162.85-192.24 kg/hm²and the planting density was 77551-8000 plants/hm2,the obtained crop yield,WUE,and NUE could reach 95%of the maximum comprehensive benefits,ranging from11632 to 12212 kg/hm²,37.46 to 38.24 kg·hm^-2·mm^-1,and 70.36 to 72.61 kg/kg,respectively.At this time,NAE,NRE,NPFP,and NHI were 33.43-44.20 kg/kg,38.28-46.79%,59.66-79.15 kg/kg,and 65.52-67.62%,respectively.Reasonable adjustment of nitrogen application rate and planting density can regulate the growth structure of crop populations,while improving yield,water and nitrogen utilization efficiency,and reducing environmental pollution risks,which is of great significance for the healthy and sustainable development of dryland agricultural production.When the nitrogen application amount is 162.85-192.24 kg/hm²,and the planting density is 77551～80000 plants/hm²,it is recommended to be the composite pattern of planting density and nitrogen application amount of maize with high efficiency and high yield under degradable film mulching in the northwest dry region.Different corn varieties have their own suitable planting densities.In the future,further in-depth research can be conducted by combining variety,density,and nitrogen application factors,combined with ammonia volatilization,greenhouse gas emissions,etc.,to provide a more scientific and reasonable theoretical basis for the nitrogen density combination planting of corn.