Effects Of Irrigation And Nitrogen Management On Summer Maize Growth And Water–nitrogen Use Efficiency Under Micro–sprinkling Irrigation

The Huang-Huai-Hai Plain is one of the most important maize production area in China.The irrigation water resources do not match the cultivable land in this area.However,the excessive use of irrigation water and nitrogen fertilizer and low utilization efficiency in summer maize production in this area not only cause waste of resources,but also lead to the expansion of groundwater funnel area and deterioration of soil quality.Therefore,there is an urgent need to optimize water and fertilizer application appropriate arrangements for maize.In order to achieve high yield and efficient utilization of water and nitrogen resources,an experimental study on water and nitrogen operation effect of maize under micro-sprinkling irrigation was carried out in Tai’an,Shandong during 2018 and 2019 growing season.The experiment used a split-plot design with wetting soil layer depth as the main plot and nitrogen application rate as the sub plot,and three replicates were performed.The main plot was set up with four wetting soil layers were set as 0¹0(W₁₀),0²0(W₂₀),0³0(W₃₀)and 0⁴0(W₄₀)cm,respectively.The supplemental irrigation was applied at sowing,jointing and tasseling stages of summer maize and the measurement position was below the micro-sprinkling hose and the relative soil moisture content at the corresponding soil depth after irrigation was 100%of field water capacity.The sub factor consisted of nitrogen rates 0,120,180,240 and 300 kg·hm^-2,which were successively denoted as N₀,N₁₂₀,N₁₈₀,N₂₄₀ and N₃₀₀.The nitrogen application period was consistent with the irrigation period.Nitrogen fertilizer was divided into three equal parts,base fertilizer is applied before sowing and other two parts are applied with irrigation water at jointing and tasseling stages.The effects of different irrigation and nitrogen application combinations were discussed on soil water and nitrogen distribution,maize growth and development,evapotranspiration（ET）,yield composition and water and nitrogen use efficiency under micro-sprinkling irrigation.The main results are as follows:（1）At the same growth stage of summer maize,the distribution characteristics of soil moisture and nitrate nitrogen in the 0¹00 cm soil layer were similar,but there were significant differences in soil water and nitrogen content between different treatments.Under different water and nitrogen levels,the soil moisture content decreased with the increase of nitrogen level and decreased first and then increased with the increase of irrigation water,especially in the soil moisture at 0⁴0 cm soil layer.The soil nitrate content decreased with the increase of irrigation water and increased with the increase of nitrogen application,and gradually moved to the deep soil with development of growth stage.Meanwhile,micro-sprinkling irrigation has better soil water and nitrogen distribution uniformity of summer maize field,and the Christianson uniform coefficients of soil water and nitrate nitrogen were greater than 0.8 and0.9,respectively.（2）Increasing the irrigation amount and nitrogen application rate had certain promoting effects on summer maize plant height,stem diameter,leaf area index,nitrogen accumulation and transportation,and aboveground dry mass.Overall,the indicators showed a trend of increasing with the increase of irrigation amount and nitrogen application rate in 2018.In 2019,the indicators showed a trend of increasing with the increase of irrigation amount and nitrogen application rate,but decreased when nitrogen application rate reach higher.When the irrigation amount and nitrogen application rate reached at a certain level,the promoting effect of increasing water and nitrogen on the growth of maize plants would be weakened and even have a negative effect.The results of the two-year test showed that when the amount of nitrogen application was 180²40 kg·hm^-2 under W₂₀ micro-sprinkling supplemental irrigation treatment,all growth indexes of summer maize had higher values.（3）At silking stage,chlorophyll index,photosynthetically active radiation capture ratio and transmittance ratio,net photosynthetic rate and transpiration rate of summer maize firstly increased and then decreased with the increase of nitrogen application rate under W₂₀ irrigation treatment.There is no significant difference among N₁₈₀,N₂₄₀ and N₃₀₀ treatments.（4）Increasing irrigation amount and nitrogen application rate can increase grain yield of summer maize,but when water and nitrogen application reaches at a certain level,the effect of increasing yield weakens.Only nitrogen application had a significant effect on the grain yield of summer maize in 2018,and irrigation and water-nitrogen interaction had no significant effect on it.In 2019,irrigation and nitrogen application had a significant effect on the grain yield of summer maize,both water-nitrogen interactions had no significant effect on it.Compared with the high water and nitrogen treatment(W₄₀N₃₀₀),the grain yield of W₂₀N₂₄₀ treatment（2018）and W₂₀N₁₈₀ treatment（2019）did not decrease significantly,but the irrigation amount decreased by 47.15%and 52.33%,and the nitrogen application amount decreased by 20%and40%.Compared with the traditional irrigation and nitrogen application modes（CK₁）,the grain yield of W₂₀N₂₄₀ treatment（2018）and W₂₀N₁₈₀ treatment（2019）has increased to a certain extent,and the irrigation water consumption has decreased by 50.49%and 47.11%,respectively.（5）Properly reducing water and nitrogen rate can effectively reduce ET and improve water and nitrogen utilization efficiency while ensuring the grain yield of summer maize,under micro-sprinkling irrigation with water-fertilizer integration condition.Compared with high water and nitrogen treatment(W₄₀N₃₀₀)and traditional irrigation and nitrogen application modes（CK₁）,W₂₀N₂₄₀ treatment（2018）and W₂₀N₁₈₀ treatment（2019）significantly reduced ET,but increased water use efficiency,nitrogen partial factor productivity and agronomic efficiency of nitrogen fertilizer by 7.75%¹9.26%,22.76%⁷0.32%and 43.67%,respectively.（6）Comprehensive consideration the irrigation amount,nitrogen application rate,grain yield,ET and water and nitrogen utilization efficiency,it is suggested that the water and nitrogen application scheme under the micro-sprinkling irrigation in the test area as follow:the target soil layer was 0²0 cm,and the nitrogen application rate was 180²40 kg·hm^-2.The supplemental irrigation and nitrogen fertilizer was applied at the sowing and the beginning of jointing and tassel stage.The target water content of supplemental irrigation was 100%of the field capacity,and the nitrogen application ratio was 1:1:1.Base nitrogen applied before sowing,and the remaining fertilizer applied along with irrigation water at the beginning of jointing and tassel stage.