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.

中文翻译：

---

苜蓿后第一年小粒氮素需求

在犹他州和西部山区，小谷物通常在苜蓿 ( Medicago sativa L.)之后轮作种植，尤其是在干旱年份，因为它们比玉米 ( Zea mays L.)需要的灌溉更少。多项研究表明，继苜蓿后玉米很少需要施氮肥，但很少有人评估小谷物对氮的需求。本研究的目的是确定是否需要施氮肥以经济地优化第一年软白冬小麦（Triticum aestivumL.) 跟踪苜蓿以及是否可以预测响应。2018-2019 年期间，在犹他州的 12 个第一年小麦种植地进行了肥料试验（四次重复，最高 13 N 率）。2018 年春季土壤硝酸盐浓度≥17 mg kg ^{–1 的}三个地点不需要氮来提高产量。2019 年剩余的 9 个土壤硝酸盐含量≤13 mg kg ^{–1 的}站点都对肥料 N 具有产量、测试重量和蛋白质响应。 2019 年这九个站点的最佳产量、蛋白质和测试重量的经济最优 N 比率为 22公斤 N 公顷^–1(18%) 在不同的小麦/N 价格比率中，与单一春季 N 相比，分批施用（秋季和春季）更高。推迟施氮直到 2019 年旗叶产量下降，并没有提供经济蛋白质或测试重量优势。结果表明，只有当春季土壤硝酸盐<17 mg kg ^–1时，96–147 kg N ha ^–1（取决于价格比）应在春季单次施用至苜蓿之后的第一年软白冬小麦。