Nitrogen recovery from controlled-release fertilizers under intermittent leaching and dry cycles

The efficiency of nitrogen (N) use by crop plants depends, in part, on the leaching losses below the rooting depth in soils. A leaching column study was conducted to evaluate N transformation and leaching from three urea- based Controlled Release Fertilizers (CRF) and uncoated urea applied to a sandy soil. Each leaching was followed by 6 days of incubation at 33-35 degrees C. After 18 leaching and dry cycles (3960 mt of water leached, equivalent to 90-cm rainfall), recovery of total N (sum of all forms in the leachate, residual soil N, and residual fertilizer N) accounted for 89, 85, 84, and 45% of the total N applied as Poly-S, Meister, Osmocote, and Urea, respectively. Cumulative N forms in 3960 mL leachate accounted for 59, 44, 33, and 28% of total N applied as Poly-S, Urea, Osmocote, and Meister, respectively. Leachate N accounted for 98% of total N recovery from uncoated urea, and 60% of leachate N was in Urea-N form. Cumulative NO3--N in 3960 mL leachate accounted for 80, 98, 97, and 24% of the total N leached from Poly-S, Meister, Osmocote, and Urea amended soil columns, respectively. Soil residual N, (sum of NH4+-N and NO3--N) after completion of 18 leaching and dry cycles, accounted for 11, 9, 3 and 0.9% of total N applied as Meister, Poly-S, Osmocote, and Urea, respectively. No fertilizer residue was recovered in the urea treatment. In the case of the CRF sources, the residual fertilizer N accounted for 48, 45, and 22% of total N applied as Osmocote, Meister, and Poly-S, respectively. Among the CRF products, longevity of release was significantly greater for the Meister and Osmocote compared with Poly-S.