Recovery of Grain Yield and Protein with Fertilizer Application Post Nitrogen Stress in Winter Wheat (Triticum aestivum L.)

Abstract

Unfavorable weather conditions and lack of appropriate farm machinery often delay N application. This results in nitrogen (N) deficiency during the vegetative and early reproductive growth stages of winter wheat. The objective of this study was to evaluate the impact of N application timings (from tillering to flag leaf growth stages) on winter wheat grain yield and protein. The study was conducted across 12 site–years in Oklahoma, US. The treatments included a non-fertilized check, a pre-plant application of 100 kg N ha−1, and ten in-season application timings at 100 kg of N ha−1. The in-season treatment applications were initiated at the point when an N deficiency was visually identified by comparing the pre-plant treatment to the non-fertilized check. The treatments were applied in a progressive order every seven growing degree days (GDD > 0 °C) until a cumulative GDD of 63 was reached after visual deficiency (DAVD). All in-season treatments increased grain yield and protein as compared to the non-fertilized check, showing that N was a yield-limiting factor. The nitrogen applications made post Feekes 8 decreased grain yield when compared to pre-plant applications. Across this data set, that timing corresponded to a range of 21 to 63DAVD. The results suggested that forgoing N application until the growth stage Feekes 7, even when the visual N deficiency was highly apparent before that stage, had no negative impact on the yield, and it even increased the yield as compared to the pre-plant application in some cases. The plant developmental stage at which the N application takes place is more critical than the level of N deficiency. Our results show that N fertilizer applications should be made posteriorly to the crop dormancy to maximize both yield and protein, and that plants can recover from N deficiency when applications are made until the late-vegetative phase (Feekes 7). This document shows that winter wheat producers have a much wider N application window than traditionally believed.