Tuesday, November 14, 2006
206-7

Nitrogen Recovery from a Controlled-Release Fertilizer Applied on Surface and Sub-Surface of a Sandy Soil.

Shinjiro Sato and Kelly Morgan. Univ of Florida, SWFREC, 2686 SR 29 N, Immokalee, FL 34142

Controlled-release fertilizers (CRF) are used to reduce leaching of nutrients, especially NO3–-N to groundwater, which have been caused mainly by application of soluble N fertilizers to sandy soils in Florida. A leaching column study was conducted to evaluate N leaching and transformation from a CRF (CitriBlen) over a 16–wk period when it was applied on the soil surface or incorporated into the soil. When one pore volume of water (457 mL) was applied to column weekly or biweekly, CRF released urea-N slowly over time with two distinct peaks of release on 3–4 and 7–8 wk after application. Also, NH4+-N and NO3–-N were leached in large amounts on adjacent wk as for urea-N peaks. Cumulatively, the most leached N at the end of study was in NH4+ form, followed by NO3– form. Sum of all N forms leached and volatilized accounted for 53% to 69% of total N applied. At the end of the study, 17% to 23% of total N applied remained in fertilizer pellets and in the soil, with NH4+ being the form most often found in soil. Total N recovery from CRF was 70% and 93% of total N applied for surface and sub-surface application, respectively. It was indicated that the better recovery rate with sub-surface application may have been due to minimized N loss by NH3 volatilization, which would have otherwise remained in soil as NH4+-N (sub-surface application of fertilizer resulted in more than three times NH4+-N remained in soil, as compared to surface application). On average of both application treatments throughout 16–wk period, it required 5.8 h for ammonification and 4.5 d for nitrification to occur after N release. It is important to characterize CRFs for specific soil type, leaching volume and cycle, and application manner for the best management practice of these fertilizers.

Handout (.pdf format, 216.0 kb)

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