Effects Of Chlorocholine Chloride On Growth And Nitrogen Use Efficiency Of Summer Maize In North China

Chlorocholine chloride（CCC）is a chloroquatrain inhibiting agent in plant growth,enhancing stress resistance,promoting root development,and regulating nutrient metabolism in plants.In consideration of high nitrogen application rate and low nitrogen utilization efficiency of summer maize in North China,field experiments were conducted using Jingnongke 728（JNK 728）and Zhongshan 909（ZD 909）as materials in Xinxiang experimental station,Henan Province,Institute of Crop Science,Chinese Academy of Agricultural Sciences in 2018 and 2019.With split-plot experiment design,CCC was the main treatment and nitrogen application rate was the secondary treatment,set N₀,N₁,N₂ and N₃ denote the nitrogen application rate of 0 kg hm^-2,62.5 kg hm^-2,125 kg hm^-22 and 187.5 kg hm^-2.The effects of CCC on nitrogen absorption,assimilation,distribution,and accumulation of summer maize under different levels of nitrogen application were measured and analyzed.Moreover,the effects of CCC on maize of nitrogen utilization efficiency and yield of summer maize in North China were clarified.The main results are as follows:1.CCC treatment reduced maize optimum nitrogen application rate and increased maize yield.Under CCC treatment,the optimal fertilizer application of both JNK 728 and ZD 909 were 125 kg hm^-2,which were 33.4%lower than the conventional nitrogen treatment(187.5 kg hm^-2).The maximum yield of JNK728 and ZD 909 in 2018 were 9,977 kg hm^-2 and 12,645 kg hm^-2,respectively,which were increased by7.1%and 0.3%compared with conventional nitrogen treatment,while the maximum yield in 2019 were12,645 kg hm^-22 and 12,587 kg hm^-2,which were increased by 4.1%and 0.4%compared with conventional nitrogen treatment,respectively.2.CCC treatment improved maize photosynthetic performance under low and medium nitrogen application.Under low and medium nitrogen level(62.5 kg hm^-2 and 125.0 kg hm^-2),CCC treatment increased leaf area index and chlorophyll content,JNK 728 were average increased by 8.1%and 8.2%,ZD 909 were increased by 12.4%and 5.2%.The photosynthetic potential and net assimilation rate of JNK728 were increased by 6.1%and 13.8%,ZD 909 were increased by 6.2%and 10.1%,respectively.The net photosynthetic rate of ear leaf of JNK 728 and ZD 909 during the grain filling stage were increased by 16.5%and 11.6%.Therefore,the accumulation of photosynthetic product was promoted,photosynthetic performance was improved,and increased the amount of dry matter accumulation.3.CCC treatment improved maize function leaves key enzyme activity of nitrogen metabolism,and promoted the absorption and utilization of nitrogen under the low and middle nitrogen levels.At the low and medium nitrogen level(62.5 kg hm^-2 and 125.0 kg hm^-2),the activities of the nitrate reductase（NR）,glutamine synthetase（GS）,glutamate synthase（GOGAT）,glutamate pyruvate transaminase（GPT）,and soluble protein content of the leaves of JNK 728 under CCC treatment were increased on average by17.3%,8.7%,12.6%,3.3%,and 12.0%,respectively.The activities of NR,GS,GOGAT,GPT and soluble protein content of the leaves of ZD 909 under CCC treatment were increased on average by 15.0%,10.2%,26.0%,12.6%,and 7.0%,respectively.4.CCC treatment increased the available nitrogen content in 0-60 cm arable soil,and promoted the plant to absorb and utilize nitrogen.Compared to the conventional control treatment,NO₃^--N and NH₄⁺-N concentration in the surface soil during the growth period of summer maize with CCC treatment under different nitrogen application levels were increased.Under low and medium nitrogen application(N₁,N₂:62.5 kg hm^-2,125.0 kg hm^-2),the nitrogen accumulation,nitrogen partial productivity,the agronomic efficiency,and the nitrogen use efficiency ratio of JNK 728 were increased by 8.9%,10.0%,15.7%and24.8%,ZD 909 were increased by 20.9%,5.7%,14.9%and 71.7%,respectively.In summary,CCC treatment improved maize nitrogen use efficiency and grain yield under low and medium nitrogen application.CCC treatment had the best effect on reducing nitrogen and increasing yield at 125 kg hm^-22 application rate.This study provided theoretical guidance for nitrogen reduction,efficiency improvement and chemical controlled cultivation technique of summer maize in North China.