Nitrogen fertilizer needs of first‐year small grain forages following alfalfa

Abstract

AbstractSmall 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.