Effects Of Nitrogen Application And Post-heading Drought Stress On Growth And Development Of Foxtail Millet And Water And Fertilizer Use Efficiency

Foxtail millet is affected by many factors during its growth,among which water and nitrogen fertilizer play important roles.In recent years,with the global warming,the available water resources are decreasing day by day,the excessive input of nitrogen fertilizer leads to the rising production cost,and the environmental problems are aggravating day by day.At present,the agricultural production in our country is in a new agricultural development from pursuing high-yield to stable production,focusing on resource saving and environment-friendly,which is of great significance to the agricultural sustainable development on strengthening water-saving irrigation and optimizing fertilization technology.Therefore,in order to form optimized water and nitrogen regulation measures for millet production,Jigu 22 was used as material and potted with two factors of water and nitrogen,and the interaction effect of water and nitrogen of millet was studied.To explore the effects of different water and nitrogen conditions on the growth and development of millet,agronomic and yield characters,physiological and biochemical characteristics,endogenous hormones,grain quality,photosynthetic physiological characteristics,soil microorganisms and water and nitrogen use efficiency after heading.The following results are obtained:1.Effects of different water and nitrogen treatments on plant growth and water and nitrogen use efficiency of foxtail millet after heading.Compared with the control,the biological yield,grain yield,harvest index and root related indexes were decreased by drought stress at different stages after heading,and the essential amino acid content was increased,especially in the early stage of filling.W₁N₁₅₀had the lowest grain yield,harvest index and fat content,W₁N₀decreased proportion of dry matter distribution in reproductive organs with the lowest yield.Under the same water treatment,nitrogen application significantly increased grain yield,harvest index and root related morphological indices,and total protein and amino acid contents increased,while starch and yellow pigment contents were lower than those without nitrogen application.The damage caused by drought to millet can be alleviated by applying nitrogen,which also improves yield and quality In terms of use efficiency,under the same water treatment,nitrogen application increased water use efficiency,nitrogen transfer in vegetative organs and nitrogen contribution to grain,while nitrogen use efficiency decreased.Drought could increase water use efficiency but decrease nitrogen agronomic efficiency and nitrogen partial productivity.W₁treatment was compared with CK,and the yield increase rate,contribution rate,transfer volume,transfer rate and contribution of dry matter and nitrogen in vegetative organs decreased significantly.2.Effects of different water and nitrogen treatments on physiological and biochemical characteristics of millet after heading.The contents of SOD,PRO and MDA increased under drought stress and recovered somewhat after rehydration,but were still higher than that of control.The activities of NR and GS decreased under drought stress and recovered somewhat after rehydration.ABA content in leaves and roots increased under different treatments,and was more significant without nitrogen application.The contents of IAA and GA in leaves and roots of different treatments were decreased,and the contents in N treatment group were generally higher than those in N₀treatment group.The photosynthetic response curves of different treatments at flowering stage and later grout stage were significantly different.The net photosynthetic rate decreased due to drought stress,and the net photosynthetic rate was the lowest in the N₀group.There were significant differences in the fluorescence properties of leaves under different water and nitrogen treatments at flowering stage and later grout stage.Under the same water treatment,additional nitrogen fertilizer generally increased the values of Fm,Fv/Fm,ΦPSⅡ,PHI（Po）,PHI（Eo）,PI_ABSand Sm,while decreased the levels of Fo,NPQ,PHI（Do）and Vj.Under the same nitrogen level,drought stress at different periods after heading decreased Fm,Fv/Fm,ΦPSⅡ,PHI（Po）,PHI（Eo）,PI_ABSand Sm,but increased Fo,NPQ,Vj and PHI（Do）levels.After heading,SPAD value of millet treated with different water and nitrogen decreased gradually with the passage of time,while SPAD value of leaves was obviously improved by nitrogen treatment.3.Effects of different water and nitrogen treatments on soil microorganisms after millet heading.The number of OTUs of bacteria and fungi at the middle grouting stage was significantly higher than that at the mature stage.W₁N₀had the lowest fungal diversity index,W₂N₁₅₀had a significant difference in bacterial Simpson index,and W₂N₁₅₀had a significantly lower fungal Shannon index than CKN₁₅₀.Nitrogen application significantly increased the fungal diversity index,but generally decreased the bacterial diversity index,but not significantly.The dominant bacterial groups were Proteobacteria,Actinomycetes,Blastomonas,Bacteroidetes,Acidobacteria,Myxomycetes and Firmicutes.The dominant groups of fungi were ascomycetes,basidiomycetes,corycetes and zygomycetes.The species composition of soil bacteria and fungi was similar at phylum level under different water and nitrogen treatments,but the relative abundance was slightly different.There were some differences in the response of soil microorganisms to water and nitrogen input.In conclusion,drought stress at different periods after heading affected yield formation.Nitrogen application could alleviate the damage caused by water deficit to a certain extent and improve water use efficiency.Drought in the early stage of grain filling had a great effect on grain productivity,which resulted in serious yield reduction and significant decrease in nitrogen use efficiency.Compared with the control,W₂N₁₅₀has little yield reduction and higher water efficiency.Therefore,in millet cultivation management,under the condition of normal nitrogen application,appropriate drought exercise at the later stage of grain filling can achieve the effect of water saving and efficiency improvement.