Small grain forages are commonly grown following alfalfa (Medicago sativa L.) in Utah and the Intermountain West, especially during drought years as small grains require less irrigation than corn (Zea mays L.). Several studies have shown that corn following alfalfa rarely needs nitrogen (N) fertilizer, yet few have evaluated N needs of small grains grown for forage. Objectives of this research were to determine whether N fertilizer is needed to economically optimize the yield and quality of first‐year small grain forages following alfalfa, and whether spring soil nitrate tests can predict N responsiveness. Fertilizer trials (four replications of six N rates) were conducted on 11 first‐year small grain forage sites in Utah during 2018 and 2019. Results indicated that N fertilizer was not needed to economically increase small grain forage yield at most (91%) site‐years. The one responsive site‐year followed an old and thinning alfalfa stand (9‐yr old) and required only 67 kg N ha⁻¹. In contrast, forage quality improved with average N fertilizer applications ranging from 101 to 142 kg N ha⁻¹ at all but one site‐year. Soil nitrate concentration was able to separate yield and forage quality response to N in 73 and 53% of the cases, respectively, suggesting it may be a viable prediction test for yield and some aspects of quality response in this rotation. Results indicate that growers often do not need to apply fertilizer N to first‐year small grain forages unless compensation for forage quality improvement outweighs fertilizer costs.

中文翻译：

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苜蓿后第一年小粒草料的氮肥需求

小颗粒饲料的情况普遍种植的紫花苜蓿以下（苜蓿L.）在犹他州和山间西方，特别是在干旱年份为小杂粮需要比玉米少灌溉（玉米L.）。几项研究表明，苜蓿后的玉米很少需要氮肥，但很少有人评估过用于饲草的小谷物的氮需求。这项研究的目的是确定是否需要氮肥以经济地优化苜蓿后第一年小谷物饲草的产量和质量，以及春季土壤硝酸盐试验是否可以预测氮响应。在2018年和2019年期间，在犹他州的11个第一年小谷物饲草场进行了肥料试验（四次重复，每6次施氮）。结果表明，不需要氮肥即可最多（91％）地经济增加小谷物饲草的产量-年。一个响应站点年遵循一个古老且变薄的苜蓿林（9岁），仅需要67 kg N ha ^-1。相比之下，除一个站址年外，其他所有肥料的平均氮肥施用量在101至142 kg N ha ^-1之间，从而改善了草料质量。土壤硝酸盐浓度能够分别在73％和53％的情况下分离出对N的产量和牧草质量响应，这表明这可能是该轮作中产量和质量响应某些方面的可行预测测试。结果表明，除非提高草料质量的补偿超过化肥成本，否则种植者通常不需要在第一年的小谷物饲草上施用氮肥。