Effects Of Film Mulching And Nitrogen Fertilization On Maize-Wheat Growth And Utilization Of Water And Nitrogen

Focusing on the problems of imbalance of rainfall and crop demand,increasing residual pollution of PE film,and common over-use of nitrogen fertilizer in the arid regions of Northwest China,we will explore planting strategies to improve yield,increase water-and nitrogen-use efficiencies,and reduce environmental pollution.It is of great significance for dryland agriculture to stabilize yield,increase income,and green development.This paper studies the rotation of summer maize and winter wheat in semi-humid and drought-prone areas.The trial design for summer maize included four planting patterns（flat planting without mulching（FNM）,ridge-furrow with biodegradable film mulching（RBM）,ridge-furrow with plastic film mulching（RPM）,and flat planting with full plastic film mulching（FFM））and four nitrogen-fertilization rates（0（N0）,90（N90）,180（N180）and 270（N270）kg/hm²）,for winter wheat,1)planting patterns included FNM and RPM,N-fertilization rates were same as summer maize,and 2)two fertilization methods（all N fertilizer applied as basal fertilizer（BN）,and 60%applied as basal fertilizer and 40%applied as topdressing（TN））with FNM based on N-fertilization rates in plots of summer maize.The effects of different film mulching and N application on soil moisture,temperature,mineral nitrogen content,gaseous nitrogen（NH₃ and N₂O）emissions,post-harvest soil nutrients,crop growth and physiology,grain filling dynamics,source-sink regulation,N uptake,evapotranspiration partitioning,utilization of water and nitrogen,yield and economic benefit were studied.The N application rate was optimized by multi-objective,and the optimal rotation strategy of summer maize-winter wheat was put forward based on various indicators.The main results were as follows:（1）Film mulching and N application increased soil water,temperature,and nutrients but decreased gaseous nitrogen（NH₃,N₂O）emissionsFilm mulching increased soil water storage and temperature,and the effect of increasing temperature and moisture retention was FFM>RPM>RBM.Nitrogen application decreased soil water storage and temperature due to promoting crop canopy growth and aggravated with the increase of N application,while TN was beneficial to increase soil water storage and temperature.Film mulching and N application increased the accumulation of soil mineral nitrogen.The accumulation of soil mineral nitrogen in FFM was the highest（271.6 kg/hm²-472.2 kg/hm²）and mainly concentrated in the shallow layer.N180 and N270 also led to the accumulation of soil mineral nitrogen in the 0-200 cm soil layer and transported to the deep layer.However,the TN could reduce the accumulation of soil mineral nitrogen（3.6%-10.4%）.Nitrogen fertilization also reduced soil organic matter and p H,which is detrimental to soil health.In addition,film mulching and TN reduced the fluxes and cumulative emissions of gaseous N,which is beneficial to reducing environmental pollution and nitrogen loss,while nitrogen application is the opposite.（2）Film mulching and nitrogen application improved the physiological growth of summer maize and winter wheatFilm mulching and N application increased plant height,LAI,aboveground dry matter mass,chlorophyll content,net photosynthetic rate,plant N accumulation,and N ratio in stems and ears at harvest,but decreased the N content in leaves at later stages.It was beneficial to increase yield,among which FFM and N180 had the best effect,while TN reduced physiological growth indexes and N accumulation in plants.Analyzing the root growth of summer maize,we found that increasing root length density and root weight was beneficial to increasing dry matter accumulation,water use efficiency,and yield.Compared with RPM,RBM decreased root growth in 0-10 cm soil layer（4.8%-35.1%）,but increased root activity;nitrogen application increased root growth in shallow layers,root-shoot ratio,and root activity of RBM.（3）The mechanism of the effect of film mulching and nitrogen application on yield was revealedIn the simulated grain filling dynamics of summer maize,the overall effect of RBM in promoting grain filling was better than that of RPM,and RPM entered grain filling earlier than RBM;nitrogen application mainly increased the grain filling rate and prolonged the grain filling time of RPM.At N90,the grain reached the maximum grain filling rate at the earliest,while N180 performed the best in the gradually increasing,fast increasing,and slowly increasing stages of grain filling.In the source-sink regulation of winter wheat by film mulching and N application,soil water storage and soil temperature at milk stage increased the establishment of the initial sink,while soil mineral nitrogen coordinated the source-sink balance;the leaf area and dry matter at the flowering stage,the chlorophyll content at 18 days post-anthesis,the number of grains per spike and the spike number had a decisive role in improving yield.Therefore,mulching with N application increased the yield components,yield（6.2-21.6%）,and net income（387-2273 RMB/hm²）of summer maize,of which FFM had the best effect,while RPM reduced the planting area,resulting in a decrease in the spike number（29.8%）,yield（13.3%,except for N0）and net income（1899-3365 RMB/hm²,except for N0）of winter wheat;N fertilization improved yield components and increased yield（28.6%-208.0%）and net income（2133-14484 RMB/hm²）,among which N180 was the best,while TN increased the number of grains per spike of winter wheat but decreased the spike number,and TN in N180 plot showed the best performance.（4）The effect of film mulching and nitrogen application on the water-and nitrogen-use efficiencies was clarifiedReducing water consumption and increasing plant transpiration or decreasing soil evaporation was beneficial to increasing WUE.In the partitioning of evapotranspiration,film mulching reduced soil evaporation（12.1-24.5 mm）,while increasing plant transpiration was related to N application and precipitation;N application mainly increased plant transpiration in reproductive growth stages of FNM and RPM,and the effect on soil evaporation was related to precipitation.During the whole growth period,film mulching reduced ET（4.7%-34.6%）,and RBM>RPM>FFM,N application increased ET（6.3%-19.1%）,among which N180 and N270 were the largest,and TN was beneficial to reduce ET.Analyzing the water-and nitrogen-use efficiencies,we found that film mulching improved the water-and nitrogen-use efficiencies of summer maize and different mulching patterns had their advantages,while RPM reduced the WUE（11.5%,except N0）,NUE（16.5%）,and N partial productivity（13.3%）of winter wheat;N fertilization only improved WUE and NUE（except for N270）,while TN favorably increased NUE and N harvest index.Combining yield and water-and nitrogen-use efficiencies,the optimal nitrogen application rates in a single season for each planting pattern of summer maize and winter wheat were obtained,and the RBM for summer maize and FNM with TN for winter wheat were beneficial to improving the productivity and N utilization of the rotation system.To sum up,mulching planting and suitable N application were beneficial to improving soil environment,promoting crop growth,increasing yield and water-and nitrogen-use efficiencies,and reducing soil N residues and gaseous N emissions.In the summer maize season,RBM reduced residual film pollution and had similar effects to RPM,while FNM and TN were beneficial to increasing the yield and efficiency of winter wheat and reducing soil N residues in rotation.Therefore,169 kg N/hm² for summer maize with RBM and 120kg N/hm²（using TN）for winter wheat with FNM is the best pattern for summer maize and winter wheat rotation in arid regions to achieve stable grain growth and green development.