Longevities and nitrogen, phosphorus, and potassium release patterns of polymer-coated controlled-release fertilizers at 30°C and 40°C

The weekly nitrogen (N), phosphorus (P), and potassium (K) release from 17 polymer-coated controlled-release fertilizer (CRF) formulations of Nutricote, Apex Gold, Osmocote, and a g-month Macrocote were measured at 30.6 +/- 0.8 degrees C and 40.0 +/- 1.5 degrees C. Five grams of each CRF were placed at a depth of 50 mm in 280 x 50 mm acid washed then rinsed silica sand columns which were leached with deionized water three times each week until nutrient recovery ceased. The volume of leachate was recorded each week and subsampled for ammonium-N, nitrate-N, phosphate-P, and K analyses. Each CRF treatment was replicated three times at each temperature. Nutrient release profiles were determined. Longevities, measured as weeks to 90% nutrient recovery, were considerably shorter than the nominated release periods for all formulations. Within each CRF product group, the longevity of 9 and 12 month formulations were similar with Apex Gold 12-14 month high nitrate having the longest (38 weeks for N at 30 degrees C) and Osmocote 8-9 month the shortest (23 weeks for N at 30 degrees C). There were consistent trends in the nutrient release periods across all CRFs with P>K>N and with differences of around 10% in duration between nutrients. The P:N release ratio exceeded 0.10 for most CRFs during the early release period indicating an adequate P supply for most plant species. The mean reduction in longevity for Nutricote, Apex Gold, and Osmocote formulations for an increase in incubation temperature from 30 degrees C to 40 degrees C was 19-21% for N, 13-14% for P, and 14-15% for K. All CRFs released nutrients unevenly with the highest rate occurring during the early part of the release period. This pattern was accentuated at 40 degrees C and by the shorter term release formulations. The nutrient release rates of all CRFs declined steadily after their maxima.