Abstract
Managing nutrients in wheat (Triticum aestivum L.) to produce both high yields and acceptable quality has been a challenge for growers in the Pacific Northwest (PNW). The 4R’s i.e., right source, right rate, right time, and right placement of fertilizer application can significantly improve crop yield and environmental stewardship. The 4R’s of nutrient management take into consideration the agronomic, socio-economic, and environmental benefits. This study aimed to pinpoint the most appropriate nitrogen (N) fertilizer management strategies for growers in the PNW to improve wheat production. Field trials were established at four locations in Southern Idaho: Rexburg and Grace in 2020, and Rexburg, Kimberly, and Parma in 2021 resulting in five site-years of data. Single and combinations of all 4R practices including rates (YG = yield goal: 50, 75, 100%), sources (ESN = Environmentally Smart N, Urea, UAN = urea ammonium nitrate), time (pre-plant = PP, at-planting = AP, flag leaf = FL), and placements (BRCST = broadcast, BA = banded, S = sprayed) of N fertilizers were evaluated to determine their impacts on the yield and quality of wheat. The experimental plots were arranged in a randomized complete block design with eighteen treatments and four replications. Grain yield and protein content were recorded at maturity. Except for Grace, all site-years were responsive to N fertilizer treatments. In 2020, Treatment 6 (N applied at 100%YG, split applied as urea broadcasted pre-plant followed by UAN sprayed at flag leaf) produced the highest (8,755 kg/ha) grain yield at Rexburg, and Treatment 1 (unfertilized check) produced the lowest (5,517 kg/ha) grain yield. In 2021, the highest yield was recorded for Treatment 17 (N applied at 100%YG rate, split applied as ESN broadcasted pre-plant followed by banding ESN at planting and UAN sprayed at flag leaf) for Rexburg (8,507 kg/ha), Treatment 11 (N applied at 100%YG rate, split applied as ESN broadcasted pre-plant followed by UAN sprayed at flowering) for Kimberly (3,197 kg/ha), and Treatment 3 (N applied at 100%YG rate, single application as urea by broadcasting and spraying at pre-plant) for Parma (6,239 kg/ha). Grain protein was higher for Treatment 11 (N applied at 100%YG rate, split applied as ESN broadcasted pre-plant followed by UAN sprayed at flag leaf) for Rexburg in 2020. In 2021, the highest grain protein was recorded at Treatment 18 (N applied at 75% YG rate, split applied as ESN broadcasted pre-plant followed by banding ESN at planting and UAN sprayed at flag leaf) for Kimberly, Treatment 13 (N applied at 100%YG rate, split applied as urea broadcasted at pre-plant followed by banding urea at planting and UAN sprayed at flag leaf) for Rexburg, and Treatment 7 (N applied at 100%YG rate, split applied as urea broadcasted at pre-plant followed by banding urea at planting) for Parma. For effective timing and placement of N fertilizers, split applications with split placements are recommended to help crops utilize nutrients throughout the entire season. In general, the recommended appropriate N fertilizer management strategy to increase grain yield and grain protein content is Treatment 6 (N applied at 100%YG, split applied as urea broadcasted pre-plant followed by UAN sprayed at flag leaf).