The 2012 ASHS Annual Conference

Controlled-release fertilizers (CRFs) are soluble nutrient sources coated with a polymer, resin, sulfur or a hybrid of sulfur and a polymer.  These coated materials release nutrients in water at a predictable rate when used at the manufacturer specified temperature (e.g., 25 °C). Controlled-release fertilizers are dried when stored prior to nitrogen (N) analysis. However, no studies have evaluated the influence of drying methods on N analysis.  Nitrogen may be subject to volatilization at high temperature and lower moisture content.  The purpose of the study was to evaluate the effects of CRF drying method on N recovery rate compared to a non-dried control. Controlled-release fertilizers [PolyS 37N–0P–0K, (Everris; Marysville, OH); ESN 44N–0P–0K (Agrium AT; Loveland, CO); Multicote 40–0–0, (Haifa; Haifa, Israel)]  equivalent to 1 g N were incubated in plastic zipper bags with 100 g of sand at 80% field capacity for 21 and 42 days before the drying treatments that consisted of oven drying (60 °C for 72 h), air drying in a greenhouse (21and 17 days), desiccators drying (21and 17 days), and a control (no drying).  Nitrogen was analyzed by combustion [Antek 9000 N analyzer (Pac. Co., Houston, TX)].  A randomized complete block design consisting of three CRFs, four drying treatments, two durations of incubation replicated four times was employed.  Crystals accumulated on the CRFs during drying, thus CRF continued to release nutrients that must be conserved until analysis.  All CRF drying methods had similar N recovery rates with a mean ± sd, for the 21 day incubation, of 68.7 ± 2.6, 42.2 ± 1.4, and 59.9 ± 1.4 for PolyS, ESN, and Multicote, respectively, and for 42 day incubations of 47.2 ± 2.2, 41.5 ± 2.4, and 27.3 ±1.8 for PolyS ESN and Multicote, respectively.  The drying treatments were not different from the non-dried control, therefore volatilization did not influence N recovery rate.