Leaching of Nitrogen from Slow‐Release Urea Sources in Sandy Soils

Application of readily soluble forms of N fertilizers to sandy soils may cause leaching of NO 3 ‐N resulting in contamination of groundwater. The leaching loss of N may be reduced to some extent by using slow‐release forms of N. An intermittent leaching and incubation technique, to mimic natural occurrence of rainfall and dry conditions, was used to examine the leaching of N from readily soluble (NH 4 NO 3 ) and slow‐release fertilizers [isobutylidene diurea (IBDU) and a polyolefin resin‐coated urea, Meister] in Wabasso (sandy, siliceous, hyperthermic Alfic Haplaquod) and Candler (hyperthermic, uncoated Typic Quartzipsamment) soils. After 29 d, the cumulative recovery of the applied fertilizer N in the leachate for the treatments decreased in the following order: NH 4 NO 3 (88‐100%) > IBDU (27–32%) > Meister (11.5–11.7%). A significant portion (19.5–35.5%) of the total N leached from IBDU and Meister was in the urea form in the initial leaching; however, after 9 d, NO 3 and NH 4 forms represented the major portion of leachate total N. Although N from NH 4 NO 3 was leached completely from the Candler sand, 12% of the applied N (as NH 4 NO 3 ) was not recovered in the leachate from the Wabasso sand. Cumulative NH 4 ‐N leached from the Wabasso sand was only 58% of that from the Candler sand. The results demonstrate that the amounts and forms of fertilizer N leached from the sandy soils depend on the solubility of the fertilizer, the soil type, and the duration of intermittent leaching.