Problems in the use of urea as a nitrogen fertilizer

Abstract. N ‐( n ‐butyl) thiophosphoric triamide (NBPT) is the most effective compound currently available for retarding hydrolysis of urea fertilizer in soil and for decreasing ammonia volatilization and nitrite e accumulation in soils treated with urea. It is a poor inhibitor of plant or microbial urease, but decomposes quite rapidly in soil with formation of N ‐( n ‐butyl) phosphoric triamide, which is a potent inhibitor of urease activity. The adverse effects of urea fertilizers on seed germination and seedling growth in soil are due to ammonia produced through hydrolysis of urea by soil urease. They can be eliminated by addition of a urease inhibitor to these fertilizers. The leaf‐burn commonly observed after foliar fertilization of soybeans with urea results from accumulation of toxic amounts of urea in the soybean leaves rather than formation of toxic amounts of ammonia through urea hydrolysis by leaf urease. Leaf‐burn is accordingly increased rather than decreased by addition of a urease inhibitor to the urea fertilizer applied.