Study On The Effects Of Nitrogen Fertilizer Combined With Biochar On The Water Physiological Characteristics Of Foxtail Millet

Millet（Setaria italic.L）,also known as foxtail millet,has become one of the important food crops in loess arid areas because of its advantages of drought resistance,poor soil resistance and strong stress resistance.Reasonable fertilizer ratio and good management mode are of great significance to improve the quality and yield of millet.In order to clarify the effects of different C/N ratios on physiological growth indexes,hormones and enzyme activities in roots and leaves of millet,the millet variety Jingu 21 was used as the research object under two water conditions of T0（natural drought）and T1（supplementary irrigation）.The 12 treatments were C1 10 g·m^-2 biochar,C2 15 g·m^-2 biochar,C3 20 g·m^-2biochar and C4 25g·m^-2 biochar treatments,N1 6 g·m^-2 nitrogen fertilizer,N2 9g·m^-2 nitrogen fertilizer and N3 12 g·m^-2 nitrogen fertilizer interactive treatments.Comprehensive analysis of different biological carbon and nitrogen fertilizer on soil moisture,millet growth and development,yield,water use efficiency,physical and chemical indicators and physiological function of millet.The results show that:（1）The interaction treatment of C2 and C3 combined with N2 and N3 contributes to the growth and storage of soil moisture content.The four C/N interaction treatments showed a significant increase of 15.14%-17.53%compared to CK during the jointing stage,and a significant increase of 27.31%-65.28%compared to CK during the heading stage.（2）The interaction treatment of C2 and C3 combined with N2 and N3 is beneficial for the distribution and construction of millet root morphology.During the growth and development process from jointing stage to heading stage,the root length of C2N3 treatment increased by 52.89%compared to CK,the total root surface area of C3N3 treatment increased by 50.73%compared to CK,and the root volume of C3N3 treatment increased by 108.13%compared to CK.（3）There is an optimal threshold for C3N3 application,which can effectively regulate the biomass accumulation and yield distribution of millet stems,leaves,and ears.The stem biomass accumulation of C4N3 and C3N3 treatments during the mature stage significantly increased by 33.85%and 32.74%compared to CK,respectively.The leaf and ear biomass accumulation of C3N3 treatments significantly increased by 33.33%and 66.23%compared to CK,respectively;The yield of C3N3 treatment was the highest,with a significant increase of 78.17%compared to CK.（4）The combination of C/N application and timely supplementary irrigation after drought can significantly improve the WUE of millet.Under T0 and T1 water conditions,the WUE of C3N3 treatment reached the highest value,significantly increasing by 77.67%and75.86%compared to CK,respectively.T1 showed an overall increase of10.34%compared to T0.（5）Moderate application of C/N and supplementary irrigation measures have a positive effect on endogenous hormones and enzyme activities in foxtail millet.Moderate drought stress can increase hormone and enzyme activity content and enhance crop stress resistance.In the C/N combination application,C3N3 treatment showed the most stable response to supplementary irrigation,with a decrease of 33.75%in root ABA content and an increase of363.89%in JA content;The highest increase in ABA content in C3N3 treated leaves was123.79%.Under T1,the content of SOD,POD,and CAT in the leaves treated with C3N3 was the lowest,decreased by 49.69%,10.61%,and 19.90%compared to CK,respectively.The MDA content was the highest,increased by 14.01%compared to CK.（6）There is a significant correlation between Pn and Tr,Ci,Gs in moderate C/N application.There is a significant positive correlation between Pn and Tr,Gs,while there is a negative correlation with Ci.Under T1 conditions at heading stage,the Pn,Tr,and Gs treated with C3N3 increased by 41.96%,43.33%,and 55.54%compared to CK,respectively.The Ci content was the lowest,decreasing by 16.46%compared to CK.In summary,a reasonable C/N combination application can significantly promote crop growth and development,improve physiological functions,and have a good regulatory effect on the accumulation of millet biomass,providing theoretical support for high-yield and efficient cultivation of foxtail millet.