Forage Yield and Fertilizer Recovery by Three Irrigated Perennial Grasses as Affected by N Fertilization1

Abstract In many locations in the United States the livestock industry uses irrigated grasses for hay production. The purpose of this study, conducted in western South Dakota on heavy clay soils (Ustertic camborthids), was to determine forage yield responses and N recovery of three irrigated grasses‐reed canarygrass (Phalaris arundinacea), garrison creeping foxtail (Alopecurus arundinaceus), and smooth brome (Bromus inermis)—to single and split N applications. Single N treatments consisted of 0, 56, 112, 224, or 448 kg N/ha applied in March. For the split N applications, these same rates were applied both in March and again after the first hay cutting. Forage yields were maximum when the grasses were fertilized with 224 kg N/ha in the split applications. Maximum forage yields ranged between 8,899 kg/ha (air‐dried) for garrison creeping foxtail and 11,802 kg/ha for smooth brome. Split applications did not benefit total production at the 56 kg N/ha rate. First cutting forage N percentages varied between 0.8 and 1.3 for N rates of 56 to 224 kg N/ha and between 1.3 and 2.3 for N rates of 224 and above. The percentage of N was highest, frequently over 3%, in second cutting forage from treatments receiving split fertilizer applications. Percent total N recovered increased as fertilizer rate increased when all N was applied in March, but recovery was highest for the split application of 224 kg N/ha. Recovery by smooth brome forage was highest with split applications (up to 50% recovery), but was highest for the other grass species for single annual (March) applications.