Volatilization losses of surface-applied urea nitrogen from Vertisols in the Indian semi-arid 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 (Vertisols) collected from three sites with a range in pH, electrical conductivity, and cation exchange capacity. There were two contrasting moisture treatments, one near field capacity (wet) and another with intermittent wetting of the soil surface before allowing the columns to dry (moist-dry). The results indicated that losses were influenced markedly by pH and moisture treatment, being 29.5, 33.5, and 33% from the wet soils 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 that broadcasting of urea on the surface of Vertisols may cause substantial N losses.