Use of the urease inhibitor N-(n-BUTYL)-thiophosphoric triamide decreased nitrogen leaching from urea in a fine sandy soil

Application of soluble forms of nitrogen (N) fertilizers to citrus trees in sandy soils of central Florida may cause leaching of NO3- below the rootin g depth. A leaching column study was conducted to evaluate the leaching of urea, NH4+ and NO3- forms of N from calcium nitrate, urea, and urease inhib itor coated urea (Agrotain: N-(-n butyl) thiophosphoric triamide (NBPT)) ap plied to a Candler fine sand (hyperthermic, uncoated Typic Quartzipsamments ) during six cycles of intermittent leaching with 220 mL each of water (tot al 1320 mL) through the soil columns (equivalent to 30 cm rainfall). The am ount of NO3-N recovered in the leachate from calcium nitrate treated soil a ccounted for 43% of the total N applied. Leaching of N from urea and Agrota in treated soil was pronounced during the second and third leaching events. Cumulative leaching of urea form of N accounted for 12 and 8% of total N a pplied as urea and Agrotain, respectively. The cumulative amounts of NO3-N and NH4-N recovered in six leachate fractions from urea treated soil accoun ted for 14 and 21%, respectively, of the total N applied to the column. The corresponding values for the Agrotain treated soil were 8 and 17%, respect ively. Soil analysis after the completion of leaching showed no urea throug hout the entire depth of column in either urea or Agrotain treatments. The total recovery of N (leachate plus soil) was 48.1, 40.4, and 49.7% of total N applied as urea, Agrotain, and calcium nitrate, respectively. This study demonstrated a significant reduction in leaching of N forms from Agrotain as compared with that from urea.