Nitrogen Application in Sainfoin under Rain‐Fed Conditions in Wyoming: Productivity and Cost Implications

Leguminous crops such as sainfoin ( Onobrychis viciifolia Scop.) have low N 2 fixation; hence, supplementary N is usually provided to realize maximum yield. Nonetheless, N application should be justified by economic benefit to the cropping system. This study evaluated the productivity, nutritive value, and cost implications of N application in sainfoin under rainfed conditions at high elevations in Wyoming. The study was a 2‐factorial experiment set in a randomized complete block design with four replications, where four cultivars (Delaney, Remont, Rocky Mountain, and Shoshone) and four N rates (0, 40, 80, and 120 kg ha −1 ) were the treatments. Sainfoin was established in 2012, and N was broadcast‐applied in May 2013 and 2014 using urea as the N source. The profitability of the N application was assessed using a benefit–cost ratio analysis. Sainfoin yield and nutritive value was affected by cultivar and N application. Remont (1.08 Mg ha −1 ), Rocky Mountain (1.17 Mg ha −1 ), and Shoshone (1.16 Mg ha −1 ) produced higher forage dry matter (DM) than Delaney (0.84 Mg ha −1 ). The effect of N application on the forage DM was linear, but applying >80 kg N ha −1 did not result in significant increase in the forage DM. The benefit–cost ratios for the three N rates were less than one in both years, which indicated a net loss in revenue. In general, sainfoin DM and crude protein (CP) increased with N; however, the increase in forage DM with N application was not economical due to higher production costs.