Study On Water And Nitrogen Distribution And Growth Characteristics Of Summer Maize Based On RZWQM-2 Model

The amount of water and nitrogen applied plays an extremely critical role in the growth and development of crops.The traditional belief is that increasing water and fertilizer application rates can significantly increase crop yields,so most growers are accustomed to using high water and high fertilizer to pursue high crop yields.However,this highly irrational water and fertilizer application system not only fails to maximize the benefits,but also leads to leaching of large amounts of water and nitrogen from the soil to deeper soils,reducing the efficiency of water and nitrogen utilization,which in turn pollutes the groundwater table and brings about agricultural surface pollution.Therefore,in the context of"ensuring food security and sustainable agricultural development",we urgently need to investigate a reasonable water and fertilizer application system to improve water and nitrogen use efficiency and pursue high crop yields while reducing the risk of agricultural surface pollution.In this study,we investigated the effects of different water and nitrogen conditions on the water and nitrogen distribution and growth characteristics of summer maize using the RZWQM2 model and field experiments to address the problems of low water and nitrogen use efficiency and deep leakage during the growing period of summer maize in China.Based on the validated RZWQM2 model,we simulated the variation curves of soil water content,NO₃^--N concentration,NH₄⁺-N concentration and crop growth characteristics of summer maize under different water and fertilizer conditions in the 0-100 cm soil layer during the whole fertility period.The simulation results were used to analyze the effects of different water and fertilizer application conditions on soil water content,soil nutrients and crop growth characteristics of summer maize;and the possible reasons for this pattern were discussed from the perspectives of crop time-variability,meteorological factors time-variability and soil structure time-variability,which can provide a theoretical basis for the improvement of local summer maize yield,reduction of surface source pollution and development of high standard farmland.The main results of the study are as follows:（1）The parameters of the root zone water quality model（RZWQM2）were rate determined and its applicability was verified.The RZWQM2 model could simulate summer maize soil water content,NO₃^--N,NH₄⁺-N（0-40 cm）plant height,LAI,biomass,and yield better,in which the measured and model simulated values in the validation group agreed at d=0.791-0.997>0.5,with standard root mean square error n RMSE<30%and mean relative error|MRE|<30%;the RZWQM2 model was not effective in simulating the distribution of NH₄⁺-N in 40-60 cm soil was not effective and could not meet the experimental requirements,where d=0.410-0.508,n RMSE>30%,|MRE|>30%;in terms of simulation accuracy,the moisture module was better than the growth module better than the nutrient module.（2）The patterns of effects of different lower limits of water control and N application levels on soil water content in the 0-100 cm soil layer during summer maize fertility were obtained.The effect of different water and nitrogen conditions on soil water content of 0-60 cm was greater than that of 60-100 cm;when N application level was in the range of 120 kg·hm^-2-320kg·hm^-2,increasing N application level reduced soil water content transiently and tended to increase soil water content for the whole fertility period;when the lower limit of soil moisture was in the range of 60%θ_f-80%θ_f,increasing the lower limit of moisture control significantly increased the number of irrigation at the pre-pulling and filling stages of summer maize.The lower limit of soil moisture was in the range of 60%θ_f-80%θ_f,and increasing the lower limit of moisture control significantly increased the number of irrigations at the pre-pulling and filling stages of summer maize,as well as significantly increased the soil water content of each layer.（3）The effects of different water control limits and nitrogen application levels on the distribution of NO₃^--N and NH₄⁺-N concentrations in the 0-100 cm soil layer during summer maize fertility were obtained.The NO₃^--N concentration and NH₄⁺-N concentration in each soil layer were significantly increased by increasing the level of nitrogen application,and the increase of NO₃^--N concentration in the same soil layer was greater than that of NO₃^--N;the NO₃^--N concentration in the surface soil decreased and the NO₃^--N concentration in the deep soil increased by increasing the lower limit of moisture control,while the peak of NH₄⁺-N concentration in each soil layer slightly decreased.The peak concentration of NH₄⁺-N decreased slightly in all soil layers.（4）The patterns of effects of different lower moisture control limits and N application levels on height,root depth,leaf area index（LAI）,biomass and yield of summer maize were revealed.When the lower limit of soil moisture in the 0-40 cm soil layer was controlled in the range of 60%θ_f-80%θ_f and the level of N application was in the range of 120 kg·hm^-2-320 kg·hm^-2,the height,above-ground biomass,below-ground biomass and yield of summer maize showed an increase followed by a decrease when the lower limit of moisture control was increased,and the increase of N application had a significant promotion effect on them.The maximum root depth of summer maize at the lower limit of water control showed a significant decrease and was significantly promoted by increasing the nitrogen application level.