VOLATILIZATION LOSSES OF SURFACE-APPLIED UREA NITROGEN FROM VERTISOLSIN THE INDIAN SEMIARID TROPICS

The N loss from Vertisols was estimated by measuring the loss of N-15- labelled urea N under conditions that promote NH3 volatilization. Urea granules were placed on the top of 150-mm deep soil columns (Vertisol s) collected from three sites with a range in pH, electrical conductiv ity, and cation exchange capacity. There were two contrasting moisture treatments, one near field capacity (wet) and another with intermitte nt wetting of the soil surface before allowing the columns to dry (moi st-dry). The results indicated that losses were influenced markedly by pH and moisture treatment, being 29.5, 33.5, and 33% from the wet soi ls and 37, 42, and 40.5% from the moist-dry soils with pH values of 7. 7, 8.2, and 9.3, respectively. These observations clearly indicate tha t broadcasting of urea on the surface of Vertisols may cause substanti al N losses.