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 prob lem in one-pass seeding and fertilizing systems. Field studies were conduct ed on a clay loam and a fine sandy loam soil over 3 yr to evaluate the impa ct of seed-placed urea N, with and without the addition of the urease inhib itor N-(n-butyl) thiophosphoric triamide (NBPT) on stand density and growth of barley. Seedling damage, as indicated by reduction in stand density, oc curred 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 lev els where damage occurred with the untreated urea. Dry matter yield at head ing generally was unaffected by N application or use of NBPT; however, fina l yield was increased by use of NBPT in four of five site-years. Use of NBP T appears promising as a method of reducing the risk of seedling damage fro m seed-placed urea fertilizer, thus increasing the rate of urea-N that can be safely placed with the seed.