Effects Of Nitrogen Amounts On Maize Growth And Soil Organic Carbon/nitrogen Under Supplement Irrigation And Rainfed Conditions

The field experiment was conducted from March to December in 2018 at Guangxi University Farm(22°50'N,108°17'E),Nanning,Guangxi,China.With maize(var.Wanchuan 1306)as a test material,planting pattern viz.30,60 cm row spacing,and the planting density was 52500 plant/ha.Two factors in the test design were nitrogen fertilizer and water,respectively.The maize field experiment was established as a split-plot design of three replications with water as the main plot and nitrogen as the subplot.The main results are as follows:1 Effects of different water conditions and nitrogen amounts on CCI,LAI,dry matter weight of maizeSupplement irrigation and nitrogen amounts could effectively slow down the decrease of CCI and LAI at late growth stages,and accelerate dry matter accumulation.The dry matter weight of supplement irrigation was 1.7%higher than that of rainfed(P>0.05).The dry matter weight increased with the increase of nitrogen amounts;compared with NO,the dry matter weight of N1,N2,N3 and N4 increased by 23.5%,44.7%,54.8%and 71.0%,respectively.2 Effects of different water conditions and nitrogen amounts on carbon and nitrogen metabolism after anthesisGS activity and PEPC activity of rainfed condition were higher that of supplement irrigation(P<0.05);SPS activity of supplement irrigation condition was 11.6%higher that of rainfed(P<0.05).The GS activity,NR activity,PEPC activity and SPS activity increased with the increase of nitrogen amounts.Compared with NO treatment,the average PEPC activity values of N1,N2,N3 and N4 treatments increased by 19.3%,44.5%,38.0%and 46.9%,respectively.3 Effects of different water conditions and nitrogen amounts on dry matter transfer amounts,nitrogen accumulation and distribution after anthesisAt R6,the dry matter transfer amounts of stem and leaf and the contribution rate to grain under supplement irrigation condition were significantly higher than that of rainfed(P<0.05).From R0 to R6,the nitrogen accumulation and the proportion of nitrogen accumulation of stem+sheath and leaf showed a decreasing trend,the nitrogen accumulation and the proportion of nitrogen accumulation of grain were increased significantly(P<0.05).4 Effects of different water conditions and nitrogen amounts on soil organic carbon fractions and soil nitrogenThe main fractions of soil organic nitrogen were amino acid N and NH3-N.Soil organic nitrogen fractions of supplement irrigation condition were significantly higher than that of rainfed.However,the soil organic carbon fractions under supplement irrigation condition was significantly lower than that of rainfed.Compared with NO,amino sugar N,amino acid,NH3-N,hydrolysable unknown organic N,SOC and MBC of N3 was increased by 50.8%,15.7%,0.8%,8.6%,9.1%and 50.0%,respectively.5 Effects of different water conditions and nitrogen amounts on nitrogen use efficiencyWater and nitrogen amounts significantly affected NBI,NUE,PNUE,NAE and NPFP(P<0.05).With the increase nitrogen amounts,NBI,NUE,PNUE,NAE and NPFP decreased instead of increasing.The NAE and NPFP values of N4 decreased by 4.3%and 37.4%(P<0.05).6 Effects of different water conditions and nitrogen amounts on yield and yield composition of maizeThe supplement irrigation condition had no effects on the plant height,stem diameter,ear height,ear height/plant height(P>0.05).Compared with rainfed,grain yield,ear weight,thousand gain weight and harvest index of supplement irrigation condition was increased by 15.7%,11.0%,1.8%and 17.6%,respectively.Nitrogen application is beneficial to increase harvest index,whereas,when N>250 kg/ha(N3 and N4),harvest index increased;Compared with NO,grain yield,ear weight,thousand gain weight and harvest index of N3 was increased by 68.2%,57.1%,30.2%and 8.8%,respectively.7 Relationship of plant with soil carbon and nitrogen under different water conditions and nitrogen amountsThe nitrogen accumulation and yield were directly related to nitrogen application and soil organic carbon/nitrogen fractions.The nitrogen accumulation and yield were positively correlated with N,MBC,amino sugar N,amino acid N and total hydrolysable organic N.In addition,there was negative correlation between nitrogen accumulation and yield with total soil N.The annual maize yield of double-cropped maize in Guangxi could be effectively increased by nitrogen application 250 kg/ha combined with proper irrigation under the phased drought condition,and which were conducive to improve soil carbon and nitrogen supply potentials.