Effect of seed-placed urea fertilizer and N-(n-butyl)thiophosphoric triamide (NBPT) on emergence and grain yield of barley

Seedling damage from excess seed-placed urea fertilizer can be a major problem in one-pass seeding and fertilizing systems. Field studies were conducted on a clay loam and a fine sandy loam soil over 3 yr to evaluate the impact of seed-placed urea N, with and without the addition of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) on stand density and growth of barley. Seedling damage, as indicated by reduction in stand density, occurred on both soil types at rates of seed-placed N as low as 40 kg N ha−1. Addition of NBPT to the urea fertilizer increased stand density at N levels where damage occurred with the untreated urea. Dry matter yield at heading generally was unaffected by N application or use of NBPT; however, final yield was increased by use of NBPT in four of five site-years. Use of NBPT appears promising as a method of reducing the risk of seedling damage from seed-placed urea fertilizer, thus increasing the rate of urea-N that can be safely placed with the seed. Key words: Urea...