Suitable split nitrogen application increases grain yield and photosynthetic capacity in drip-irrigated winter wheat (Triticum aestivum L.) under different water regimes in the North China Plain

Abstract

Chemical fertilizer overuse is a major environmental threat, critically polluting soil and water resources. An optimization of nitrogen (N) fertilizer application in winter wheat (<i>Triticum aestivum</i> L.) in association with various irrigation scheduling is a potential approach in this regard. A 2-year field experiment was carried out to assess the growth, yield and photosynthetic capacity of drip-irrigated winter wheat subjected to various split applications of urea (240 kg ha^-1, 46% N). The eight treatments were, two irrigation scheduling and six N application modes in which, one slow-release fertilizer (SRF). Irrigation scheduling was based on the difference between actual crop evapotranspiration and precipitation (ETa-P). The two irrigation scheduling were I₄₅ (Irrigation scheduling when ETa-P reaches 45 mm) and I₃₀ (Irrigation scheduling when ETa-P reaches 30 mm). The six N levels were N_0-100 (100% from jointing to booting), N_25-75 (25% during sowing and 75% from jointing to booting), N_50-50 (50% during sowing and 50% from jointing to booting), N_75-25 (75% during sowing and 25% from jointing to booting), N_100-0 (100% during sowing), and SRF₁₀₀ (240_kg ha^-1, 43% N during sowing). N top-dressing application significantly (<i>P<</i>0.05) influenced wheat growth, aboveground biomass (ABM), grain yield (GY) 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 I₄₅SRF₁₀₀ treatments, respectively had the highest GY (9.83 and 9.5 t ha^-1), ABM (19.91 and 19.79 t ha^-1), net photosynthetic rate (35.92 and 34.59 µmol m^-2s^-1), stomatal conductance (1.387 and 1.223 mol m^-2s^-1), <i>SPAD</i> (69.33 and 64.03), and chlorophyll fluorescence <i>F_V/F_M</i> (8.901 and 8.922). 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. The I₄₅N_50-50 treatment offers to farmers an option to sustain wheat production in the NCP.