Prediction of Controlled-release Fertilizer Nitrogen Release Using the Pouch Field and Accelerated Temperature-controlled Incubation Methods in Sand Soils

Controlled-release fertilizers (CRFs), a vegetable production best management practice in Florida, are soluble fertilizers (SFs) coated with a polymer, resin, or a hybrid of polymer coating sulfur-coated urea. In 1994, a Controlled Release Fertilizer Taskforce developed an accelerated temperature-controlled incubation method (ATCIM) to predict column-incubated CRF nitrogen (N) release for regulatory purposes. Determination of CRF field N release uses a field method such as a pouch field study, which requires multiple samples and high costs for laboratory N analysis. If the ATCIM may be used to predict CRF N release in the field, then vegetables growers will have a faster and lower-cost method to determine N release compared with the pouch field method. Therefore, the objective of this study was to evaluate the correlation of the ATCIM and the pouch field method as a predictor of N release from CRFs in tomato production in Florida. In 2011 and 2013, 12 and 14 CRFs, respectively, were incubated in pouches placed in polyethylene mulched raised beds in Immokalee, FL, and extracted in the ATCIM during 2013. The ATOM CRF results were used individually and grouped by release duration to create predicted N release curves in a two-step correlation process. The two-step processes predicted the percentage N release of individual CRF with R-2 of 0.95 to 0.99 and 0.61 to 0.99 and CRFs grouped by release duration with R-2 of 0.64 to 0.99 and 0.38 to 0.95 in 2011 and 2013, respectively. Modeling CRF N release grouped by release duration would not be recommended for CRF 180-d release (DR), because coating technologies behaviors differ in response to high fall soil temperature in polyethylene mulched beds. However, with further model calibration, grouping CRFs of 90 to 140 DR to simulate the CRF N release profile may allow the ATOM to predict CRF N release without performing the pouch field method, which currently negated the usefulness of the ATCIM in a tomato production system.