Irrigation and nitrogen effects on tall wheatgrass yield in the Southern High Plains

Winter months in the Southern High Plains of the USA have the lowest precipitation. As a result, producers using tall wheatgrass [Agropyron elongatum (Host) Beauv.] may get higher production in the spring and possibly throughout the growing season with additional irrigation: Also, growers need information about interactions between soil moisture and N fertilizer to maximize productivity. In a split-plot study conducted at the New Mexico State University Agricultural Science Center at Tucumcari from 1997 to 1999, tall wheatgrass furrow-irrigated monthly from April to September was irrigated once, twice, or not irrigated during winter as the whole-plot treatment. For subplot treatments, tall wheatgrass annually received 168 kg N ha(-1) split into two; three, or four equal applications. Tall wheatgrass irrigated in the winter yielded more dry matter (DM) over the 3 yr than unirrigated tall wheatgrass (11.72, 12.10, and 13.55 Mg ha(-1) for tall wheatgrass not irrigated, irrigated once, or irrigated twice, respectively). Tall wheatgrass fertilized three or four times outyielded tall wheatgrass fertilized twice (11.08, 12.85, and 13.44 Mg ha(-1) for two, three, and four N applications, respectively). No interaction occurred between the irrigation and N treatments. A year X harvest X N effect existed in which a mid-December N application, preceded and followed by precipitation, produced approximately 1 Mg ha(-1) more DM than unfertilized tall wheatgrass in the first harvest the following year. Both supplemental winter irrigation and N application scheduling offer opportunities for tall wheatgrass producers to increase production in the Southern High Plains of the USA.