Effects Of Planting Density And Nitrogen Fertilizer Interaction On The Yield And Water And Nitrogen Utilization Of Spring Maize With Double Furrows

Gansu is the main grain production base of spring maize in China.Planting with reasonable density and applying fertilizer scientifically are important means to restrict the growth and yield formation of spring maize.In this paper,Xianyu 335 was selected as the experimental variety,and three planting densities were set,which were 35000 plants/hm²（D1）,55000 plants/hm²（D2）,and 75000 plants/hm²（D3）.Four nitrogen fertilizer rates,0kg/hm²（N1）,180 kg/hm²（N2）,225 kg/hm²（N3）and 270 kg/hm²（N4）,were applied in dingxi City,Gansu Province.The effects of planting density and nitrogen application rate on growth index,yield,water and fertilizer use efficiency and soil NO₃^--N residue of spring maize were studied.At the same time,meteorological data,soil data and field management data were collected,combined with the measured data of spring maize,parameters of the improved DSSAT model were calibrated,and the simulation accuracy of the model was evaluated.Finally,five groups of nitrogen application schemes were set up,and the spring maize growth was simulated with the verified model,which further discussed the nitrogen application measures to maintain higher yield of farmland ecosystem in central Gansu province.The main research results are as follows:（1）Both planting density and nitrogen application rate significantly affected the growth and yield of spring maize,and the interaction between them was significant.The plant height,leaf area index and population dry matter accumulation of spring maize were significantly increased by increasing planting density and nitrogen application rate,while SPAD value decreased significantly with increasing planting density and decreasing nitrogen application rate.The plant height,leaf area index and dry matter accumulation of spring maize reached the maximum values under high density and medium nitrogen application rate（D=75000 plants/hm²,N=225 kg/hm²）,while the SPAD value reached the maximum values under low density and high nitrogen application rate（D=35000 plants/hm²,N=225 kg/hm²）.D=35000 plants/hm²,N=270 kg/hm²)showed good performance.The yield increased firstly and then decreased with the increase of planting density and nitrogen application rate,and reached the maximum（10203 kg/hm²）in D2N3 treatment（D=55000 plants/hm²,N=225kg/hm²）.In D3 and N0 treatments,panicle length,panicle rows,row grains and 100-grain weight were all lower than those in other treatments.In general,when planting density was55000 plants/hm²and nitrogen application rate was 225 kg/hm²,both yield and yield composition performed well.（2）During the growth period of spring maize,soil moisture showed different performances under different densities and nitrogen application conditions,and the moisture content in the 0-40 cm soil layer fluctuated greatly.At the same time,the effects of density and nitrogen application rate on WUE were significant.The WUE of spring maize treated by D2N3 was 28.6 kg·hm^-2·mm^-1,which was 1.78%to 57.14%higher than that of other treatments.In addition,density and nitrogen application rate significantly affected the accumulation of nitrogen content per plant and population.The nitrogen content of the population at maturity reached the maximum under D2N3 treatment.Properly increasing density and nitrogen application rate could significantly increase the nitrogen content of plant vegetative organs.Cumulative uptake,transport rate and nitrogen content in grains,and nitrogen application rate had a significant effect on nitrogen use indicators.When nitrogen application rate was 225 kg/hm²,nitrogen fertilizer agronomic efficiency（NAE）,nitrogen fertilizer use efficiency（NUE）,nitrogen partial productivity（NPFP）,and Nitrogen Harvest Index（NHI）were the highest.Under the condition of film mulching,a large amount of NO₃^--N was accumulated in the soil after maize harvest due to high nitrogen fertilizer input and low planting density.The nitrate nitrogen residue in 0-100 cm soil layer could be reduced by appropriately reducing nitrogen fertilizer application and increasing planting density.Therefore,considering the yield,nitrogen absorption and transport,water and fertilizer use efficiency,and soil environmental effects,a density of 55000 plants/hm²and a nitrogen application rate of 225 kg/hm²were the best density nitrogen fertilizer combinations under the conditions of this experiment.（3）The improved DSSAT model was calibrated and validated using field trial data.The results showed that the corrected DSSAT model had significant effects on seed yield（n RMSE=14.29%）,flowering（n RMSE=2.17%）,maturity（n RMSE=1.15%）,grain yield（n RMSE=2.29%）,leaf area index（n RMSE=10.2%）and soil moisture content（n RMSE is less than 20%）.The calibrated model was used to estimate 5 nitrogen application rates（112.5kg/hm²,168.75 kg/hm²,225 kg/hm²,281.25 kg/hm²and 337.5 kg/hm²）under 40（1981-2020）meteorological scenarios The results showed that with the increase of nitrogen application rate,until the nitrogen application rate reached 225 kg/hm²,the grain yield,above-ground dry matter accumulation and water use efficiency were all affected increase;when the nitrogen application rate exceeds 225 kg/hm²,these values have a slight downward trend with the increase of nitrogen application rate.Compared with the nitrogen application rates of 281.25 kg/hm²and 337.5 kg/hm²,the nitrogen physiological efficiency（NPE）and nitrogen partial productivity（NPFP）were significantly improved when the nitrogen application rate was 225 kg/hm².Combined with the simulation results of the model,and taking into account factors such as crop yield,above ground dry matter accumulation,water use efficiency,nitrogen physiological efficiency and nitrogen fertilizer partial productivity,this study concluded that 225 kg/hm²was the best fertilizer application rate to maintain high yield and efficiency in the study area under the condition of 55000 plants/hm²planting density.