DIFFERENTIAL LEACHING OF NUTRIENTS FROM SOLUBLE VS CONTROLLED-RELEASE FERTILIZERS

Extremely sandy soils and poorly distributed high annual rainfall in the state of Florida contribute to significant leaching losses ot nutrients from routine fertilization practices. A leaching column experiment was conducted to evaluate the leaching losses ot nutrients when using currently available N, P, K blend fertilizers tor young citrus tree fertilization. Fertilizer blends included NH4NO3, Ca(NO3)2, IBDU, IBDU plus Escote, Nutralene, Osmocote, and Meister. Following leaching of 1000 ml of water through soil columns, which simulates leaching conditions with 26 cm of rainfall, the amount of NO3 and NH4 recovered in the leachate from soil columns amended with an NH4NO3 blend accounted for 37% and 88% of the respective nutrients contained in the quantity of blend per column. The corresponding values for soil columns amended with a Ca(NO3)2 blend were 48% and 100%. Leaching losses of both NO3 (<3%) and NH4 (<4%) were drastically decreased when using controlled-release fertilizers. The recoveries of P and K in 1000 ml of leachate were 1.3% and 8%, respectively, of the nutrients added as Osmocote, which contained coated P and K sources. In the case of the rest of fertilizer blends, the recoveries of P and K in 1000 ml of leachate were as high as 52%-100% and 28%-100%, respectively. Therefore, controlled-release technology offers an important capability for minimizing leaching losses of nutrients.