Nitrogen requirements of first‐year small grains after alfalfa

Small 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 .