A Rapid Technique for Prediction of Nutrient Release from Polymer Coated Controlled Release Fertilizers

Controlled release fertilizers (CRF) are produced with different rates and durations of nutrient release to cater to different crops with wide ranges of nutrient requirements. A rapid technique is needed to verify the label specifications of nutrient release rate and duration. Polymer-coated urea (PCU) (43% nitrogen [N]) and polymer-coated N, phosphorus (P), potassium (K) (PC_NPK; 14-14-14) fertilizer products were used in this study. Soil incubation of the above CRF products at 25 ̊C showed that 63.6% to 70.8% of total N was released over 220 days (d). At 100 ̊C in water 100% of N release occurred in about 168 to 216 hours (h). Regression equations were developed for cumulative nutrient release as a function of release time separately at 25 ̊C and 100 ̊C. Using the above regressions, the release duration for a given percent nutrient release at each temperature was calculated. These values were then used to establish a relationship between the release duration at 25 ̊C as a function of that at 100 ̊C. This relationship is useful to predict the release duration at 25 ̊C of an unknown CRF product by conducting a rapid release test in water at 100 ̊C. This study demonstrated that a rapid nutrient release test at 100 ̊C successfully predicted nutrient release rate and duration at 25 ̊C, for polymer coated fertilizers. Therefore, this rapid test can be used to verify the label release rate and duration of most CRF products.