| Rational application of nitrogen fertilizer is the key measure to obtain higher target yield in crop production in the world today.Application of nitrogen fertilizer can increase crop yield and quality.However,excessive application of nitrogen fertilizer will not only lead to the decrease of crop yield and quality,but also cause serious environmental pollution.In this study,under the winter wheatsummer maize rotation system,field plot experiment,15 N micro-plot experiment and soil culture experiment were combined,and five treatments were set up in field plot experiment and soil culture experiment: No nitrogen fertilizer(0N),nitrogen fertilizer reduction 30%(70%N),nitrogen fertilizer reduction 30%+ biological humic acid(70%N+b HA),major nitrogen fertilizer(100%N),major nitrogen fertilizer + biological humic acid(100%N+b HA);Four treatments were set up in the15 N microzone experiment: Nitrogen reduction by 30%(70%N),nitrogen reduction by 30%+biological humic acid(70%N+b HA),major nitrogen(100%N)and major nitrogen + biological humic acid(100%N+b HA)were applied to study the effects of nitrogen reduction by 30% combined with biological humic acid on soil nitrogen supply,fertilizer nitrogen direction and crop yield.The aim is to provide theoretical basis and technical support for realizing regional nitrogen reduction.The main research results are as follows:1.Compared with nitrogen application alone under the corresponding fertilizer rate,100%N+b HA and 70%N+b HA treatments could increase the dry matter accumulation,nitrogen accumulation and grain yield in the above-ground part of the crop at jointing,flowering and maturity stages of wheat and at jointing,silking and maturity stages of maize.The effect of 70%N+ b HA treatment was more significant,and the above-ground dry matter accumulation was increased by 5.8%-14.1%,nitrogen accumulation by 10.9%-19.5%,and grain yield by 12.4%-14.2%,respectively.During the jointing and flowering stages of wheat,the net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of maize were increased by 6.3%-16.2%,5.2%-23.5% and 2.9%-14.0%,respectively,and the intercellular CO2 concentration(Ci)was decreased by 8.4%-12.0%,respectively.Pn,Gs,Tr and Ci under 70%N+b HA treatment have significant differences compared with 70%N.2.Urease activity and nitrate reductase activity of 2.70%N+b HA treatment decreased by 5.5%~17.4%and 3.4%~18.1%,respectively,compared with 70%N treatment and 100%N+b HA treatment,ammonia volatilization rate decreased.The volatilization rate of 70%N+b HA ammonia is the lowest except for 0N treatment.Compared with 70%N+b HA,the gene copy number of AOA-amo A,AOBamo A and nif H increased by 14.2%,19.8% and 17.0% in wheat flowering stage and 18.4%,16.2%and 13.5% in maize silking stage,respectively,and the difference was significant.3.Compared with 70%N+FA and 70%N,nitrogen fertilizer combined with biological humic acid can increase nitrate nitrogen content and decrease ammonium nitrogen content in topsoil except in the flowering stage of wheat in 2021.Nitrate nitrogen content increases by 6.5% to 49.2%,and ammonium nitrogen content decreases by 1.9% to 27.5%,respectively.Compared with 100%N+FA and 100%N,the nitrate nitrogen content increased by 1.4% to 51.5%,and the ammonium nitrogen content decreased by 4.9% to 20.5%.Compared with nitrogen application alone,100%N+b HA and70%N+b HA treatments could increase soil microbial biomass nitrogen content by 6.4%-57.5% and2.2%-16.3%,respectively.4.15 N isotope tracer test results showed that compared with 70%N+FA treatment,total nitrogen uptake in above-ground part increased by 18.1%,and fertilizer 15 N uptake increased by 35.3%,and there was no significant difference between total nitrogen uptake in above-ground part and fertilizer15 N uptake in 70%N+FA treatment and 100%N treatment.When biological humic acid was applied at 100%N level,the increases of total nitrogen uptake in different parts of wheat and nitrogen uptake in fertilizer were smaller than those at 70%N level.Compared with 70%N treatment,the residual nitrogen in 0-80 cm soil increased by 7.6%,and the residual nitrogen in 0-20 cm soil layer increased by 12.8%,and the residual nitrogen in 0-20 cm soil layer under 70%N+FA treatment was 12.0%higher than that under 100%N treatment.5.Nitrogen fertilizer combined with biological humic acid could improve partial productivity of nitrogen fertilizer and nitrogen use efficiency.Compared with 70%N treatment,nitrogen partial productivity and nitrogen use efficiency of 70%N+FA treatment were significantly increased by12.6%-14.2% and 6.6%-9.9%,respectively.The highest fertilizer recovery utilization rate of70%N+FA treatment increased by 8.1% compared with 70%N treatment and 9.5% compared with100%N treatment.The highest fertilizer soil residue rate of 70%N+FA treatment increased by 2.0%compared with 70%N treatment and 6.4% compared with 100%N treatment,and the differences were significant.After one year rotation,the total fertilizer recovery efficiency of 70%N+FA treatment was the highest,which increased by 10.1% compared with 70%N treatment and 14.8%compared with 100%N treatment.The total loss rate decreased by 11.9% compared with 70%N treatment and 14.9% compared with 100%N treatment,and there were significant differences.6.Combined application of nitrogen fertilizer and biological humic acid can increase soil nutrient content and reduce soil p H so that it tends to be neutral.In wheat maturation stage,soil alkalihydrolyzed nitrogen,available phosphorus and available potassium contents increased by 6.9%,8.0%and 4.5%,respectively,compared with 70%N+FA,and 4.9%,5.8% and 6.0%,respectively,compared with 100%N+FA.At maize maturity stage,soil alkali-hydrolyzed nitrogen,available phosphorus and available potassium contents increased by 4.8%,8.0% and 6.1%,respectively,compared with 70%N+FA,and 6.9%,5.3% and 5.4%,respectively,compared with 100%N+FA.The effect of nitrogen reduction combined with biological humic acid(70%N+FA)was better than that of 100%N+FA treatment. |
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