Nitrogen Fertilizer Needs of Small Grains After Alfalfa

Small grains are commonly grown following alfalfa in Utah and the Intermountain West, especially during drought years as small grains require less irrigation than corn. Several studies across the country have shown that corn following alfalfa rarely needs N fertilizer, yet relatively few have evaluated the N needs of small grains. Furthermore, research on the N needs of small grains grown as forage vs. grain are even more sparse. The objectives of this research are to quantify the N contributions of alfalfa to small grains and develop N guidelines for the first and second year following alfalfa termination, to determine the economics of alfalfa-corn vs. alfalfa-small grain rotations and whether early spring soil nitrate tests or plant chlorophyll content at flag leaf or boot stage could predict N response. Experiments were conducted on 18 field sites in Utah and Colorado in 2018. Four sites had direct comparisons of small grains harvested as grain vs. forage, while another five and nine sites were harvested as grain or forage only, respectively. At each site, four replications of six N rates ranging from 0 to 168 kg N ha-1 were applied in the early spring as ammonium nitrate. Early results indicate that N fertilizer was not needed to increase small grain yield at most sites, unless small grains followed old stands (\u3e 9 yrs). These results will help growers better utilize N credits from alfalfa, improve their small grain yield and profit, and reduce negative implications of excessive N fertilizer applications