HYDROLYSIS OF UREA IN 2 SANDY SOILS UNDER CITRUS PRODUCTION AS INFLUENCED BY RATE AND DEPTH OF PLACEMENT

The use of urea as a nitrogen (N) source is increasing in citrus production on sandy soils in Florida. Entisol and Spodosol are the two major soil orders used for citrus production. This study was conducted to examine the difference in rate of urea hydrolysis as influenced by depth of placement in a Candler fine sand (Typic Quartzipsamment) and a Wabasso sand (Alfic Haplaquod). These two soils represent the contrasting soils typically found in the citrus growing region of central, southern, and east coast regions of Florida. The rate of urea hydrolysis was faster in a Candler fine sand than that in a Wabasso sand and was greater for the low (0.25 g N/kg) than that for the increased (0.50 or 1.00 g/kg) rates of urea applications in both soils. In a parallel experiment, the rate of urea hydrolysis was examined at various depths (0 to 15-, 15 to 30-, 30 to 45-, and 45 to 60-cm) in the Candler fine sand using in situ and laboratory incubation studies. The rate of urea hydrolysis decreased with an increase in depth of placement of urea. Increased content of organic matter and higher soil temperature in the surface soil may contribute to increase in urease activity thus resulting in increased rate of urea hydrolysis than that in the lower depth soil.