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

The weekly nitrogen (N), phosphorus (P), and potassium (K) release from 17 polymer-coated controlled-release fertilizer (CRF) formulations of Nutricot e, 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 col umns which were leached with deionized water three times each week until nu trient recovery ceased. The volume of leachate was recorded each week and s ubsampled 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 re covery, were considerably shorter than the nominated release periods for al l formulations. Within each CRF product group, the longevity of 9 and 12 mo nth formulations were similar with Apex Gold 12-14 month high nitrate havin g the longest (38 weeks for N at 30 degrees C) and Osmocote 8-9 month the s hortest (23 weeks for N at 30 degrees C). There were consistent trends in t he 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 exceede d 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 Nutri cote, Apex Gold, and Osmocote formulations for an increase in incubation te mperature 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 ra te occurring during the early part of the release period. This pattern was accentuated at 40 degrees C and by the shorter term release formulations. T he nutrient release rates of all CRFs declined steadily after their maxima.