Confined animal feeding dairy operations have generated excess amounts of manure, creating a need to identify alternative uses for this plant nutrient source. The objectives in this study were to (i) study the effect of composted dairy manure on Windthorst soil (fine, mixed, active, thermic Udic Paleustalfs), (ii) evaluate two soil testing methods for measuring P when composted dairy manure is applied, and (iii) determine tall wheatgrass [Thinopyrum ponticum (Podp.) Barkworth & Dewey Jose] yield response to six rates of composted dairy manure and two rates of inorganic N fertilizer. A randomized complete block design experiment arranged in a splitplot with four replications was initiated in 2001. Main plots received a single application of composted dairy manure at rates of 0, 11.2, 22.4, 44.8, 89.6, and 179.2 Mg ha1, which were incorporated before planting tall wheatgrass at the rate of 17 kg ha1. Subplots received annual split applications of inorganic N at 224 or 336 kg ha1. Composted dairy manure averaged across the 20022003 and 20032004 growing seasons increased soil organic matter (OM) 54%, pH 55%, infiltration rate 550%, P 480%, and K 84% in this soil. The improved soil properties increased dry matter (DM) yields each growing season (20022003 and 20032004) up to 96 and 58%, respectively. Tall wheatgrass had similar crude protein (CP) (158231 g kg1), DM yields (38589536 kg ha1), P concentrations (1.42.8 g P kg1), and P removal rates (5.426.7 kg ha1) compared to other coolseason perennial grasses.
