Coupling Effects Of Water And Fertilizer On Growth Of Drip-Fertigated Spring Maize In Arid Northwest China

An abundance of light and heat resources in the arid regions of northwestern China is conducive to high yields of the crops.However,due to water shortages and low use efficiency of water and fertilizer in this region,modern agriculture that develops efficient use of water and fertilizer was constrained.In recent years,with the advancement of agricultural intensification,maize production in the northwest region has developed rapidly,and the application of drip irrigation has gradually increased.In the northwestern region of China,where water resources are scarce.Thus,how to use drip fertigation technology to improve maize yield and water and fertilizer use efficiency is of great significance for the development of efficient and green modern agriculture.In this study,spring maize?Qiangsheng 51?was tested.A field experiment was conducted during 2015 and 2016growing seasons at Wuwei Experimental Station for Efficient Use of Crop Water,Ministry of Agriculture,northwest China.In order to explore drip irrigation and fertilization modes for improving water and fertilizer use efficiency of maize.Using 'Qiangsheng 51' as the test cultivar,the field experiment was subjected to four water supply levels,I₆₀,I₇₅,I₉₀and I₁₀₅ in 2015,and I₆₀,I₈₀,I₁₀₀ and I₁₂₀ in 2016,were in interaction with four fertilization levels that based on different ratios of N-P₂O₅-K₂O,i.e60-30-30,120-60-60,180-90-90 and 240-120-120 kg/hm²,ET_c is the average annual crop evapotranspiration.This resulted in 16 treatments.The effects of different drip irrigation and fertilization levels on the growth,yield and components,root indicators,water use efficiency,NPK use efficiency,NPK accumulation,soil moisture and soil temperature were analyzed.The growth characteristics,dry matter accumulation,root distribution,soil water and heat distribution,and water and fertilizer consumption mechanisms of spring maize under different levels of drip irrigation were studied.Moreover,the relative root length density distribution model of spring maize was established.The HYDRUS-2D was used to simulate and verify the soil moisture and heat transfer patterns of different drip irrigation fertilization spring maize.Following are the main achievements of this thesis:?1?The effects of different water and fertilizer supplies on spring maize growth and dry matter accumulation under drip fertigation conditions were investigated.And each parameter was comprehensively evaluated using the Principal Component Analysis method.The plant height and stem diameter of spring maize with different water and fertilizer treatments increased with the increase of irrigation and fertilization levels,and the maximum values were found in I₁₀₅F₂₄₀ and I₁₂₀F₂₄₀40 treatments in 2015 and 2016,respectively.In the two years,LAI showed the law of "increasing-platform-lowering".The quality of root dry matter decreased with the increase of fertilizer application rates,and reached the maximum at F₁₈₀.The excessive application of fertilizer was not conducive to root growth.From the ratio of root to shoot,the ratio of root to shoot decreased with the increase of irrigation amount,and increased first and then decreased with the increase of fertilizer application,and the maximum value was obtained in I₆₀F₁₂₀ treatment.As a harvest index that directly reflects the "source-library" relationship of crop groups,the effects of irrigation and fertilization on spring maize harvest index were extremely significant?P<0.01?The net assimilation rate?NAR?of spring maize showed an "M"-shaped double-peak curve change during the whole growth period.The dry matter quality of the above-ground part was consistent with the Logistic growth model,and the fitting result was superior?R²=0.996,P<0.01?.Plant growth status is closely related to the formation of crop yield.Principal component analysis was used to comprehensively evaluate the correlation between spring maize yield and growth index,water use efficiency,harvest index and net assimilation rate.It was found that the above-ground dry matter,net assimilation rate and yield were most closely related.The highest score of irrigation and fertilization were achieved by100%¹05%ET_c and F₁₈₀ fertilization,respectively.?2?Optimized water and fertilizer management achieved a synergistic improvement in spring maize yield,as well as water and fertilizer use efficiency.Moreover,it significantly reduced fertilizer losses.Optimized water and fertilizer management achieved a synergistic improvement in spring maize yield and water and fertilizer use efficiency,and significantly reduced fertilizer losses.The utilization efficiency of different nutrient by spring maize varies with the amount and nature of fertilizers and it follows the order:P>K>N.In terms of nitrogen fertilizer,the nitrogen utilization efficiency of spring maize was the highest when the dosage was 120 kg N ha^-1.When the nitrogen fertilizer dosage increased to 240 kg N ha^-1,the nitrogen use efficiency decreased by 13.1%.When the application range of phosphate fertilizer is 30-60 kg P₂O₅ ha^-1,it was more conducive to the improvement of phosphorus utilization efficiency.Excessive application of potassium fertilizer will caused absorb the luxury of potassium in plant,reduced the yield and the utilization efficiency of potassium.When the application rate of potassium fertilizer increased from 30 kg to 120 kg K₂O ha^-1,the utilization efficiency of potassium decreased by 25.2.%.Spring maize kernels responded to different nutrient intakes indicated the proportion of nutrients required by the plants.The average absorptions of N,P and K by 100 kg grains treated under different irrigation and fertilization conditions were 1.00,0.21,and 0.39,respectively.?3?The distribution of roots of spring maize at different growth stages was studied under different drip fertigation conditions.The relative root length density distribution model of spring maize under water and fertilizer coupling was developed.There were significant correlations between root characteristics parameters and yield and total dry matter quality of spring maize at different growth stages.The correlation coefficients followed the order:filling stage>12 collars stage>maturity stage>6 collars stage.The effects of root distribution on maize yield and dry matter mass were maximized during the grain filling period,followed by 12 collars.A normalized root length density?NRLD?distribution model of spring maize was established to describe NRLD distribution under different water supply and fertilization levels under drip irrigation.Overall,the length of root from ground to the upper 1/3 of the underground part accounted for 73.6%of the overall root length,and the length of root from ground to the upper 1/2 of the underground part accounted for82.8%of the overall root length.?4?The temporal and spatial distribution of soil moisture and soil temperature in spring maize root zone with different water and fertilizer supplies was revealed.The water-heat migration pattern of maize farmland under drip fertigation conditions was simulated and validated based on HYDRUS-2D model.The irrigation conditions had a significant effect on the daily average temperature of 5cm below the surface from the 6 collars to maturity stage of spring maize.The temperature difference in all soil layers by one specific irrigation treatment was maximized at the seedling stage,followed by the 12 collars.The discrepancy of soil temperature was maximized at point T1,while the median soil temperature decreased as the soil depth increased.In a specific soil layer,the median soil temperature decreased as the irrigation volume increased.The water and heat transfer in soil for spring maize under drip irrigations was simulated using the HYDRUS-2D model and the results indicated good consistence of the simulated soil water content and soil temperature and the measured values.The n-RMSE of simulated and measured water content in the 0-60 cm soil layer by I₆₀,I₇₅,I₉₀and I₁₀₅ treatments were between 11.9%and 21.3%,while those in other soil layers were below 20%.The RMSE of temperature in surface soil?0-5 cm?decreased as the irrigation volume increased,while that in other layers decreased and then increased as the irrigation volume increased.The RMSE of temperature was minimized by I₉₀ treatment in all layers.The n-RMSE of soil temperature were less than 10%in all layers by all treatments,except for the 5 cm of surface soil by I₆₀ treatment?14.0?,indicating excellentsimulation performance.?5?The water-fertilizer coupling effect on spring maize yield,dry mass,water use efficiency,fertilizer partial factor productivity,and economic benefit indicator was analyzed under drip fertigation conditions.In terms of coupling of water and fertilizers,the binary quadratic regression equations of spring maize yield,ground dry matter mass,WUE,PFP,and net income with irrigation volume and fertilizer amount as independent variables reached extremely significant levels?P<0.01?and the coefficient of determination was above 0.8 in 2015 and 2016.Using the binary quadratic regression method and normalization,it was demonstrated that the overall benefits of spring maize yield,WUE,and net income were maximized at irrigation volumes of 452?110%ET_c?mm in 2015 and 449?98%ET_c?mm in 2016 and fertilization of190-95-95?N-P₂O₅-K₂O?kg/ha in 2015 and 178-89-89?N-P₂O₅-K₂O?kg/ha in 2016.