Irrigation at an Early Growth Stage in Water‐Limited Conditions Improves Wheat Nitrogen Use

ABSTRACT Water and nitrogen (N) limitations are major abiotic stress factors constraining cereal productivity, particularly when they coincide with critical growth stages. In boreal‐nemoral environments, limited spring precipitation and high evaporative demand often lead to water scarcity, which in turn limits N uptake and assimilation. This study investigated the effects of early growth stage irrigation on wheat ( Triticum aestivum L. emend. Thell) performance under conditions of insufficient available N. Experiments were conducted in controlled conditions in a greenhouse with either irrigated or nonirrigated spring wheat that were either N fertilised (150 kg N ha −1 ) or unfertilised (0 kg N ha −1 ). Wheat grown under combined irrigation and N supply exhibited significantly greater water and N uptake, photosynthetic rate and stomatal conductance, compared to treatments with limited water and/or N. Irrigation improved agronomic N use efficiency by 75%, fertiliser N recovery by 44%, and both N translocation and remobilisation efficiency by 16% compared with nonirrigated wheat. Nitrogen deficiency stress reduced fertile florets per spike, grain number, grain weight and final grain yield, but early‐stage irrigation mitigated these effects. Key parameters for optimising N use efficiency included N uptake efficiency ( R 2 = 0.78), utilisation efficiency ( R 2 = 0.84) and grain N yield ( R 2 = 0.79). In conclusion, early growth stage irrigation markedly improved N utilisation in conditions where limited water availability restricts spring wheat growth and yield formation.