Effects Of Water And Nitrogen Fertilizer Synergistic On Nitrogen Transformation And Water And Fertilizer Utilization In Summer Maize Farmland Soil

Corn is the first grain crop sown area and total yield.Irrigation and fertilization play an important role in ensuring corn yield.At present,irrational irrigation amount and excessive fertilization are common in maize planting,which leads to low water use efficiency and nitrogen use efficiency and environmental pollution.Nitrogen synergists can inhibit part of the conversion process of nitrogen fertilizer in soil so as to reduce nitrogen loss and improve fertilizer use efficiency.However,the application effect of nitrogen synergists is affected by soil water status and other environmental factors.The field experiment of summer maize was conducted in Guanzhong Plain,Shaanxi Province from2021 to 2022.The two experimental factors were irrigation level,four urea types combined with nitrogen synergists,and irrigation level was 40 mm(W1)and 60 mm(W2),respectively.Urea combined with nitrogen fertilizer synergists included pure urea(U),urea combined with nitrification inhibitor(U+DCD),urea combined with urease inhibitor(U+NBPT)and double-action inhibitor(NBPT+DCD).The experiment was a complete combination design,that is,urea(U),urea + nitrification inhibitor(U+DCD),urea + urease inhibitor(U+NBPT),urea + double action inhibitor(U+NBPT +DCD)were set at two irrigation levels,and another treatment without urea was set up(N0).This study focused on analyzing the effects of irrigation level and nitrogen synergists on the accumulation and distribution of maize dry matter mass,nitrogen accumulation and distribution of various organs,yield and water and fertilizer utilization efficiency,soil nitrogen transformation,soil ammonia volatilization,and economic benefits of maize production.The main research results are as follows:(1)Effects of irrigation level and nitrogen fertilizer synergist on soil mineral nitrogen of summer maizeUnder the same fertilization conditions,urea combined with nitrogen fertilizer synergists could significantly reduce the nitrate nitrogen content in summer maize seedling stage in soil,especially the U+DCD treatment was the most significant,urea combined with nitrogen fertilizer synergists could significantly increase the ammonium nitrogen content in summer maize seedling stage in surface soil.The nitrate nitrogen content of summer maize surface soil decreased with the increase of irrigation amount.Compared with U treatment,U+DCD and U+NBPT treatment could significantly reduce the residual nitrate nitrogen in soil,and the residual nitrate nitrogen decreased with the increase of irrigation amount.(2)Effects of irrigation level and nitrogen synergist on ammonia volatilization in summer maize soilUrea and nitrogen synergist had significant effects on ammonia volatilization rate and accumulation.U+DCD treatment increased the ammonia volatilization rate and increased the accumulation amount,while U+NBPT and U+NBPT+DCD treatment could significantly reduce the ammonia volatilization rate,reduce the accumulation amount of ammonia volatilization,and delay the peak time of ammonia volatilization rate.In 2021,the cumulative amount of ammonia volatilization increased with the increase of irrigation amount,and in 2022,the cumulative amount of ammonia volatilization decreased with the increase of irrigation amount.(3)Effects of irrigation level and nitrogen synergist on yield and economic benefit of summer maizeIrrigation level and type of nitrogen synergist had significant effects on summer maize yield.Compared with U treatment,the yield of urea combined with nitrogen synergist increased by 5.91-19.27%,and the yield of U+NBPT+DCD treatment under W2 condition was the highest.The effect of N synergist on yield was more reflected in the effect on grain number per ear.The number of grain per ear increased in the treatment of N synergist.Under the same fertilization condition,the yield of summer maize increased with the increase of irrigation amount.Urea combined with nitrogen synergist and increased irrigation amount could improve the economic benefit of maize planting.In the two years of experiments,the net benefit of summer maize planting under U+NBPT+DCD treatment was the highest under W2 irrigation level.(4)Effects of irrigation level and nitrogen synergist on dry matter and nitrogen accumulation in summer maizeIrrigation level and nitrogen synergist had significant effects on dry matter accumulation.Compared with treatment U,the dry matter mass of the treatment with N synergist increased significantly,and the dry matter proportion of the grain was also increased by N synergist application.Compared with U treatment,total nitrogen accumulation in plants treated with nitrogen synergist was significantly increased.The improvement effect of nitrification inhibitor U+DCD treatment at W1 level was the most significant,and that of double-effect inhibitor U+N+D treatment at W2 level was the most significant.Both dry matter accumulation and plant nitrogen accumulation increased with the increase of irrigation amount.(5)Effects of irrigation level and nitrogen synergist on water and fertilizer use efficiency of summer maizeIrrigation level and type of N synergist had significant effects on water use efficiency.Compared with U treatment,the water use efficiency of N synergist treatment increased by7.07%～41.83%,and water use efficiency increased with the increase of irrigation amount.Nitrogen partial productivity,nitrogen agronomic use efficiency and nitrogen use efficiency were significantly increased under the treatment of N synergist.Nitrogen partial productivity and N use efficiency increased by 3.36%-13.46% and 0.46%-29.78% with the increase of irrigation amount.(6)Comprehensive evaluation of irrigation level and nitrogen synergistFour factors including economic benefit index,growth index,environmental benefit index and water and fertilizer utilization index were considered,and yield,economic benefit,dry matter accumulation,ammonia volatilization accumulation,residual nitrate nitrogen,water use efficiency and partial productivity of nitrogen fertilizer were selected as indexes.A fuzzy comprehensive evaluation system was established to evaluate the irrigation level and the application effects of nitrogen synergist types.In the two summer maize experiments,the score of U+NBPT+DCD treatment under W2 irrigation level was the highest.