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 rooting 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 inhibitor coated urea (Agrotain: N-(-n butyl) thiophosphoric triamide (NBPT)) applied to a Candler fine sand (hyperthermic, uncoated Typic Quartzipsamments) during six cycles of intermittent leaching with 220 mL each of water (total 1320 mL) through the soil columns (equivalent to 30 cm rainfall). The amount of NO3-N recovered in the leachate from calcium nitrate treated soil accounted for 43% of the total N applied. Leaching of N from urea and Agrotain 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 applied as urea and Agrotain, respectively. The cumulative amounts of NO3-N and NH4-N recovered in six leachate fractions from urea treated soil accounted 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%, respectively. Soil analysis after the completion of leaching showed no urea throughout 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.