Effects Of Nitrogen Forms On Nitrogen Uptake And Utilization And Yield Formation Of Maize Varieties With Different Low Nitrogen Tolerance

In order to increase the yield of maize,excessive fertilization is common in maize production,which leads to a series of problems such as low nitrogen efficiency,high production cost and environmental pollution.Selecting nitrogen efficient varieties is an effective measure to improve nitrogen efficiency and reduce nitrogen dosage.Due to the different types and forms of nitrogen fertilizer supplied in agricultural production,the potential of its absorption and utilization by plants is also different.Therefore,selecting the appropriate nitrogen form according to the characteristics of maize varieties can improve the nitrogen utilization rate,reduce the nitrogen dosage,reduce production cost and environmental pollution,which is conducive to resource saving and sustainable development.This study was conducted in Zhongjiang Experimental Base of Sichuan Province from 2021 to 2022.Low nitrogen tolerant cultivar ZH311 and low nitrogen sensitive cultivar XY508 were selected in the previous stage as materials.0 N,urea,NH₄⁺-N:NO₃^--N=1:0,NH₄⁺-N:NO₃^--N=0:1,NH₄⁺-N:NO₃^--N=1:1 five levels,through the field experiment,the effects of nitrogen form on the growth and development of maize varieties with different low nitrogen tolerance and physiological characteristics,material production,nitrogen absorption and utilization and transport characteristics,nitrogen supply balance in maize production system,etc.The main research results are as follows:1.Low nitrogen tolerant cultivar ZH311 had lower biomass than low nitrogen sensitive cultivar XY508 at the early growth stage,and entered the rapid growth stage later,but the duration was longer.Moreover,ZH311 maintained a higher material accumulation rate（4.42-63.61%higher）from the large flared stage to maturity stage,so the accumulation of dry matter and nitrogen and grain yield after spinning were higher.It also showed greater advantage under low nitrogen conditions（26.53%higher in 2022 without nitrogen application）.In the early growth stage,ammonium nitrogen treatment significantly increased plant biomass,entered the rapid growth stage earlier and lasted longer,but in the late growth stage,the matter accumulation rate was significantly lower than other nitrogen treatments,plant biomass was lower,and the proportion of dry matter allocation,dry matter transport and assimilation amount of female panicle was lower,so the yield was lower.The plants under ammonium nitrate combined treatment had high efficient substance accumulation,the duration of rapid accumulation period was short,but the maximum growth rate and average growth rate had obvious advantages（9.77-68.33%and 8.55-56.61%higher than other nitrogen treatments,respectively）,and the proportion of dry matter allocation in female paniculae was higher.The dry matter transport and reaccumulation ability was stronger,so the yield of the two varieties was higher.The yield of the two varieties under the average ammonium and nitrate combined treatment was2.59-11.59%higher than that under the other nitrogen treatment.The overall performance of single application of nitrate nitrogen was better than that of urea treatment,and the promotion effect of XY508 was more significant.2.Compared with XY508,the low nitrogen tolerant variety ZH311 had a higher growth rate of leaf area index and chlorophyll content in the early and middle growth period,the leaf area duration was longer（22.47%higher）,and the leaf photosynthetic capacity improved faster.The time to enter the leaf area decay stage was later（about 7 d later）,and the leaf senescence rate was lower in the later growth stage,and the leaf green retention was stronger.The activities of nitrate reductase,glutamine synthetase and soluble protein content were higher than those of XY508 after the large trumpet stage（especially at the filling and maturity stages）,and the photosynthetic performance and nitrogen metabolism of leaves were more obvious under the condition of low nitrogen,which resulted in the improvement effect of nitrogen application of XY508 was more significant than that of ZH311 at the later stage.At the early stage,the single application of ammonium nitrogen effectively increased the leaf area index,chlorophyll content,net photosynthetic rate and PSⅡactivity of leaves,nitrate reductase and glutamine synthetase activities of leaves,and soluble protein content of the two cultivars,but the improvement effect was poor after spinning.Compared with other nitrogen treatments,the initial time of leaf area decay was earlier,the duration of leaf area was lower,and the chlorophyll degradation rate was higher at the later growth stage,especially for XY508.In the middle and late growth period,ammonium nitrate combined treatment had the best effect on the photosynthetic performance and nitrogen metabolism of maize leaves,and the effect on ZH311 was more obvious.The overall performance of the two cultivars treated with only nitrate nitrogen was better than that of urea treatment,and the promotion effect of XY508was more significant.3.Compared with low nitrogen sensitive variety XY508,low nitrogen tolerant variety ZH311 had higher nitrogen uptake efficiency,nitrogen use efficiency and nitrogen partial productivity.In particular,the nitrogen uptake and use efficiency were 28.78%and 34.52%higher,respectively,and the apparent nitrogen loss and nitrogen loss rate were effectively reduced（20.63%and 26.77%lower,respectively）.The physiological efficiency of nitrogen fertilizer was lower than XY508,and 48.89%lower in 2022,reaching a significant level.Nitrogen dry matter production efficiency and physiological nitrogen utilization efficiency of both cultivars were significantly improved by single application of ammonium nitrogen,and soil residual inorganic nitrogen reserves were reduced after harvest.In addition,plant nitrogen accumulation was low at the later growth stage,so apparent nitrogen loss was significantly increased.The effects of ammonium and nitrate combined treatment on nitrogen uptake efficiency,nitrogen use efficiency,agronomic nitrogen use efficiency and nitrogen partial productivity of the two varieties were better than those of other nitrogen treatments.In the later growth stage,higher soil nutrient supply capacity was maintained,and high nitrogen uptake by crops was promoted,thus reducing apparent nitrogen loss.Especially for ZH311(51.04-149.40 kg·hm^-2 less than other nitrogen treatments).For XY508,nitrogen uptake efficiency and nitrogen use efficiency were improved by nitrate treatment alone compared with urea treatment（18.46%and 37.35%higher,respectively）,and nitrogen loss was reduced effectively.The difference between treatments was more obvious under low soil fertility condition.The results of ZH311 and ZH311 treatments were different from each other due to the influence of soil and climate.In conclusion,the phenotype and physiological characteristics of low-nitrogen tolerant varieties were more advantageous than those of low-nitrogen sensitive varieties,which mainly included:longer leaf area duration before and during growth,faster improvement of leaf photosynthetic capacity,lower leaf senescence rate at later stage,and stronger leaf green retention,which were important material basis for improving dry matter accumulation.In the later stage,the leaves had stronger nitrogen metabolism,higher nitrogen absorption and utilization efficiency,and lower nitrogen apparent loss,which were the key to improve nitrogen accumulation.The important factors to achieve high yield of maize were to maintain high assimilate accumulation capacity while ensuring the full transport of pre-anthesis stored substances to the grain.The advantages of varieties were more obvious under low nitrogen condition.Compared with urea,a common form of nitrogen fertilizer used in maize production,the single ammonium nitrogen treatment had stronger promoting effect on plant growth and substance accumulation in the early stage,but had worse effect in the late stage.On the contrary,ammonium and nitrate combined treatments performed better in the middle and late growth stages than other nitrogen treatments.In most cases,nitrogen-only treatment performed better than urea treatment,but there were obvious genotypic differences between the two varieties.XY508 was more significantly affected by nitrogen-only treatment.