Leaching of Nitrogen from Slow-Release Urea Sources in Sandy Soils
- F. L. Wang and
- A. K. Alva
Application of readily soluble forms of N fertilizers to sandy soils may cause leaching of NO3-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 (NH4NO3) 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: NH4NO3 (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, NO3 and NH4 forms represented the major portion of leachate total N. Although N from NH4NO3 was leached completely from the Candler sand, 12% of the applied N (as NH4NO3) was not recovered in the leachate from the Wabasso sand. Cumulative NH4-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.
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