Coupled Effects Of Irrigation Scheduling And Split Nitrogen Application Modes On Growth,Yield,Grain Quality And Water-Nitrogen Productivity Of Drip-Irrigated Winter Wheat In The North China Plan

The North China Plain（NCP）has progressively implemented drip irrigation in winter wheat（Triticum aestivum L.）production,because of its substantial irrigation water saving and improved water-nitrogen use efficiency.Irrigation methods and nitrogen（N）fertilization modes have been critical in maintaining wheat as a major food crop worldwide,and they are becoming increasingly important as a climate change adaptation response.Both irrigation methods and N fertilization modes have complex impacts on wheat physiology,growth and development,leading to a regulation of wheat grain yield and grain quality.However,the optimal water-N utilization regime for drip-irrigated winter wheat is still unclear.An optimization of N fertilizer application in winter wheat in association with various irrigation scheduling is a potential approach in this regard.A 2-year（2020-2021 and 2021-2022）field experiment was carried out to assess the physiological growth,yield,water-N productivity,grain quality of drip-irrigated winter wheat subjected to different irrigation scheduling and split applications modes of fixed amount of urea(240 kg ha^-1,46%N).The two irrigation scheduling levels and six N application modes levels are settled.Irrigation scheduling levels was set according to the difference between actual crop evapotranspiration（ETa）and precipitation（P）,and the two irrigation scheduling levels were expressed as I₄₅（taking an irrigation when ETa-P reaches 45 mm）and I₃₀（taking an irrigation when ETa-P reaches 30 mm）,respectively.Split application mode levels was set according to the ratio of base applied N fertilizer amount to top dressed N fertilizer amount,and the six N application mode levels were expressed as 100%top dressed in jointing to booting(N_0-100),25%base applied during sowing and 75%top dressed in jointing to booting(N_25-75),50%during sowing and 50%from jointing to booting(N_50-50),75%during sowing and 25%from jointing to booting(N_75-25),100%during sowing(N_100-0),and 100%240 kg ha^-1 slow release fertilizer（SRF,43%N）was base applied during sowing.The two factorial field experiment was conducted adopting a randomized complete block design with a total of twelve（2*6）treatments,including the two irrigation regimes and the six N application modes,which involves a single level of slow-release N-fertilizer（SRF）.The main findings were as follows:1.N application modes and irrigation scheduling significantly（p<0.05）influenced wheat growth, aboveground biomass,yield and its components,photosynthetic and chlorophyll parameters,and plant nutrient content.According to the averages of the two winter wheat-growing seasons,the I₄₅N_50-50 and I₄₅SRF₁₀₀treatments,respectively had the highest grain yield(9.83 and 9.5 t ha^-1),aboveground biomass(19.91 and 19.79 t ha^-1),net photosynthetic rate(35.92 and 34.59μmol m^-2s^-1),stomatal conductance(1.387and 1.223 mol m^-2s^-1),SPAD（69.33 and 64.03）,and chlorophyll fluorescence F_V/F_M（8.901 and 8.922）.Based on the physiological responses of winter wheat to different irrigation scheduling and N application modes,the present study provided convincing confirmation that N applied equally in splits at basal-top-dressing rates could be a desirable N application mode under drip irrigation system and could economically compete with the costly SRF for winter wheat fertilization.Considering growth and yield formation,the I₄₅N_50-50 treatment offers to farmers an option to sustain wheat production in the NCP.2.Experimental results demonstrated that optimizing irrigation and N application regimes positively influenced wheat grain yield,ETc,and water-N productivity.The maximum grain yield achieved in I₄₅N_50-50 had ETc of 376.67 and 378.67（mm）,in 2020-2021 and 2021-2022,respectively.The optimization procedure TOPIS designated I₄₅N_50-50as the best treatment based on high grain yield and minimized ETc.Based on the two years average,the I₄₅N_50-50treatment also resulted in the highest water use efficiency(2.61kg m^-3),irrigation water use efficiency(3.74 kg m^-3),and partial factor productivity of N(40.99 kg kg^-1).Considering comprehensively grain yield,ETc,and water-N productivity,the combination of split N application as 50%of basal and 50%of topdressing and 45 mm irrigation quota was an optional choice for winter wheat production under drip irrigation system.3.The experimental findings revealed that grain-filling,grain yield,grain nutrient content and grain quality were markedly affected by the different irrigation scheduling and N-fertigation rates.The N_50-50,N_75-25,N_25-75 and SRF₁₀₀ treatment were more beneficial for winter wheat grain-filling when compared to the N_100-0 and N_0-100 treatments under both irrigation regimes and during both seasons.The I₄₅N_100-0 treatment significantly（p<0.05）increased the grain total starch content by 7.30%and 8.23%in comparison with the I₄₅N_0-100 and I₃₀N_0-100 treatments,respectively during the 2021-2021 season.The I₄₅N_100-0 treatment significantly（p<0.05）increased the grain total starch content by 7.77%,7.62%and 7.88%in comparison with the I₄₅N_0-100,I₃₀N_0-100 and I₃₀N_25-75 treatments,respectively during the 2021-2022 growing season.Considering the principal component analysis,the N_50-50 split N-fertigation mode could be an optional choice for farmers during drip-irrigated winter wheat production.These findings could serve as a scientific foundation for water-N management of drip-irrigated wheat in the NCP.