Heitor Cantarella1, Johnny R. Soares1, Rafael M. Sousa1, Rafael Otto2, Cleiton Sequeira3
1 Agronomic Institute of Campinas, Av. Barão de Itapura 1487, Campinas, SP, 13020-902 Brazil, Email: cantarella@iac.sp.gov.br
2 ESALQ-University of São Paulo, Av. Padua Dias, 11, Piracicaba, SP, 13418-900 Brazil.
3 Koch Agronomic Services, 4111 E. 37th St. N, Wichita, KS 67220, USA.
Abstract
The urease inhibitor N-(n-butyl thiophosphoric acid triamide) (NBPT) is being used to reduce ammonia (NH3) volatilization losses of surface-applied urea but its shelf life is an issue. Urea treated with NBPT was stored for up to one year at two locations in Brazil: Paranaguá, PR (25°30’S and 48°30’W) and Rondonópolis, MT (16°26’ S and 54°49’ W). Treated urea samples were collected for the determination of NBPT concentration and for NH3 volatilization from a Latosol under laboratory conditions. Ammonia losses from untreated urea varied from 32 to 48% of applied nitrogen (N); the corresponding values for freshly NBPT-treated urea varied from 8 to 26% of applied N. For fertilizer stored up to 6 months, NH3 losses from untreated urea were significantly higher than those of urea containing NBPT, with no difference found among NBPT treated urea samples regardless of storage site and bag size. After 6 months, volatilization losses of NBPT treated samples stored in Rondonópolis were higher than those from Paranaguá. When samples were stored for 9 months, NH3 losses for Paranaguá samples and freshly NBPT-treated urea were about 15% of applied N, while for Rondonópolis samples, losses were about 30% of applied N. Losses for untreated urea were about 45% of applied N. After 1 year, Paranaguá samples were still performing the same as freshly NBPT-treated urea. The degree of degradation of NBPT on urea stored under conditions similar to those of Paranaguá grants a shelf-life longer than those stored under hotter conditions similar to Rondonópolis.