Nitrogen requirements of first‐year small grains after alfalfa

Abstract

AbstractSmall grains are commonly grown in rotation following alfalfa (Medicago sativa L.) in Utah and the Intermountain West, especially during drought years, as they require less irrigation than corn (Zea mays L.). Several studies have shown that corn following alfalfa rarely needs N fertilizer, yet few have evaluated the N needs of small grains. Objectives of this research were to determine whether N fertilizer is needed to economically optimize the yield and quality of first‐year soft white winter wheat (Triticum aestivum L.) following alfalfa and whether the response could be predicted. Fertilizer trials (four replications of up to 13 N rates) were conducted on 12 first‐year wheat sites in Utah during 2018–2019. Three sites in 2018 with spring soil nitrate concentrations ≥17 mg kg–1 required no N to improve yield. The remaining nine sites in 2019 with soil nitrate ≤13 mg kg–1 all had yield, test weight, and protein responses to fertilizer N. Economic optimum N rates for optimal yield, protein, and test weight across the nine sites in 2019 were 22 kg N ha–1 (18%) greater for split applications (fall and spring) compared with single spring N across various wheat/N price ratios. Delaying N applications until flag leaf decreased yield in 2019 provided no economic protein or test weight advantages. Results indicate that 96–147 kg N ha–1 (depending on price ratio) should be applied as a single application in the spring to first‐year soft white winter wheat following alfalfa only when spring soil nitrate is <17 mg kg–1.