Interactions Of Water And Controlled Release Urea On Physiological Characteristics Of Summer Maize And Its Mechanisms Of High Nitrogen Use Efficiency

Both water and nitrogen managements are very important to regulate maize growth and development and increase maize yield.Field and soil column experiments were conducted in2015 to 2017 at the State Key Laboratory of Crop Biology and the experimental farm of Shandong Agricultural University.In the experiments,we used the summer maize variety Zhengdan958（ZD958）,which is commonly planted throughout China.The field experiment design consisted of two irrigation levels（full[I2]and reduced[I1],525 mm and 263 mm irrigation throughout the growth period,respectively）and five N fertilizer treatments.The soil column experiment employed three levels of water treatment（adequate water[W3],mild water stress[W2]and severe water stress[W1]）and four levels of CRU.We focused on the interaction between controlled release urea and water on the yield and nitrogen use efficiency of summer maize.From the dry matter accumulation and distribution,photosynthetic physiological characteristics,leaf senescence characteristics,root characteristics and absorption and distribution of nitrogen in aboveground and roots,the regulation mechanism of interaction between controlled release urea and water on the growth and development of summer maize was explored in depth.This study will provide theoretical basis for nitrogen fertilizer application in summer maize production and high yield with high efficiency cultivation.The results as follows:1 Controlled release urea and water had significant interaction in improving dry matter accumulation and maize yieldAdequate moisture could effectively promote the accumulation of maize dry matter and ensure the formation of high yield population,which expand the"source"of the"library".Under drought stress,the growth of maize plants was limited,and it had a negative effect on the accumulation of dry matter.Nitrogen application could obviously promote the increase of dry matter accumulation in the upper ground of summer maize.Under same water condition,the accumulation of dry matter increased with the controlled release urea increased.Under normal water condition,the increase of dry matter and yield was not significant when the nitrogen was excess.The interaction of controlled release urea and water on dry matter accumulation and yield was significant,and water was the main effect while controlled release urea was the secondary effect.Under severe water stress,the dry matter production capacity of summer maize decreased,the production and distribution of photosynthate decreased to grain,the yield also decreased,and the increase of nitrogen fertilizer had a positive effect.The yield of high nitrogen treatment under mild water stress was significantly higher than that of other treatments,and there was no significant difference between the yield under the normal moisture content,and the interaction of water and nitrogen in increasing yield was very significant,effectively alleviating the adverse effect.There is no significant difference in the yield of medium nitrogen and high nitrogen treatment under normal water conditions,which indicates that on the basis of suitable nitrogen fertilizer,the production capacity of dry matter will not continue to increase,and the effect of increasing yield is not significant.2 The interaction of controlled release urea and water could improve photosynthetic characteristic of summer maizeAppropriate application of nitrogen fertilizer could alleviate the adverse effects of water stress on photosynthetic characteristics of summer maize,improve the net photosynthetic rate and chlorophyll content,and prolong the duration of high photosynthesis.P_n,G_s,C_i and chlorophyll content of leaves increased with increasing moisture content.Under same water condition,the increase of nitrogen application could significantly increase theΦPSII and F_v/F_m.With the increase of N application,q_p increased obviously,while NPQ decreased significantly.It indicated that proper application of N fertilizer could improve the photochemical utilization of light energy absorption of leaves,and weaken non photochemical utilization.The interaction of controlled release urea and water on photosynthetic characteristics of summer maize has reached a very significant level,and water was the main effect while controlled release urea as secondary effect.High N treatment under mild water stress and middle N treatment under normal water conditions maintain a high chlorophyll content after tasseling,which lays the foundation for high net photosynthetic rate,G_s and C_i.This increased the photosynthetic capacity and increased yield.In this experiment,the interaction of CRU 210 kg hm^-2 with water content 75±5%and cru 315 kg hm^-2 with water content 55±5%were most significant,the chlorophyll content and photosynthetic rate of summer maize increased significantly,which kept higher photosynthetic performance in the late growth period,thus improved the utilization of light energy and high grain yield.3 The interaction of controlled release urea and water could regulate aging process in leaf of summer maizeUnder normal water condition,increasing Nitrogen had no positive effect on improving the activity of protective enzymes,the content of soluble protein and the decrease of MDA content when the N fertilizer reached the level of medium nitrogen.Under water stress condition,the difference between high N and middle N was very significant.It showed that the interaction effect of adding CRU on the activity of protective enzymes and the content of soluble protein and reducing the content of MDA was significant under water stress condition.The effect under severe water stress was significantly lower than that under mild water stress,indicating that the leaf senescence increased when the maize was subjected to severe water stress.Even if increased CRU application,it was difficult to obtain higher yield.In this experiment,the interaction of CRU 210 kg hm^-2 with water content 75±5%and cru 315 kg hm^-2 with water content 55±5%maitained the leaf protective enzyme activity and soluble protein content a high level,and decreased the content of MDA significantly.The interaction between CRU and water had significant effect on the leaf senescence characteristics of summer maize,and water was the main effect.4 The interaction of controlled release urea and water could regulate root growth of summer maizeDrought reduced the absorption of water and nutrients in the soil by root after tasseling,limited the normal growth and development of maize root system,and eventually reducd the dry matter accumulation of root and the aboveground.Under different water conditions,CRU had significant effects on root dry weight,root length,RLD and active absorption area.Under severe water condition,the normal growth and development of root system were inhibited and the effect of increasing CRU was not significant.Under mild water stress,root length,RLD,root total absorption area and active absorption area of root system increased with the CRU increased and the interaction between water and CRU was significant.Under normal water condition,there was no significant difference in root growth between middle N and high N treatment.In this experiment,the combination of CRU 210 kg hm^-2 with water content 75±5%and cru 315 kg hm^-2 with water content 55±5%maitained was more suitable for the growth and development of summer maize root system.5 The interaction of controlled release urea and water could regulate N uptake,translocation and NUE of summer maizeUnder severe water condition,the N movement speed in the soil and root activity were inhibited,which resulted in the reduction of N in the vegetative growth period and the inhibition of the plant growth,and then the construction of N"library"and N accumulation were restricted.The distribution,redistribution and translocation of N were not normal,which seriously affected the N use efficiency.Under mild water stress,increasing N fertilizer increased nitrogen efficiency in soil and compensated for the distribution and translocation of water stress,ensured N distribution and transport,and eventually improved the utilization of nitrogen.Under normal water condition,CRU release N corresponded to the growth rule of summer maize,and the N movement was faster.It was beneficial to the absorption of N and the distribution and translocation of N in the plant.At the same time,the root system kept high activity,which was helpful for the construction of high yield population.Water and CRU could play a synergistic role in N uptake,translocation and distribution.Under drought condition,the compensatory effect of the CRU was observed,and the effect was promoted under normal water condition,especially in N translocation from leaf and stem to ear.In addition,there was no significant difference between high and middle N treatment under normal water condition in plant N absorption,translocation and distribution in various organs,but the ANUE,NUE and PNUE of middle N treatment were significantly better than high N treatment.