A Rapid Test for Prediction of Nutrient Release From Controlled Release Fertilizers.

Nutrient release from soluble granular fertilizers can be modified by polymer coating. The coating technology can be fine-tuned to change the duration (3 to 9 months) and rate of nutrient release, hence these products are termed as controlled release fertilizers (CRF). There is a need to develop a rapid technique to verify the release duration of the long-term release CRF. In this study, nutrient release from polymer-coated CRF products at 100¢ª C in water was evaluated to predict nutrient release at 25¢ª C. Polymer-coated urea (43% N) and polymer-coated N, P, K (14-14-14) fertilizer products with designated release of 3 to 6 months were used in the study. Weighed amounts of CRF products were placed in sealed mesh bags and incubated in water at 25¢ª C and release was evaluated over 220-days period. Controlled release fertilizers constant temperature extractor was used to study the release of the above CRF products at 100¢ª C over a 7-day period. Regression equations were developed for cumulative nutrient release rate as a function of release time separately at 25¢ª C and 100¢ª C. Using the above regressions, the release duration for a given percent nutrient release from each of the CRF products at each temperature were calculated to establish a relationship between the release duration at 25¢ª C as a function of that at 100¢ª C for a given percent release. This relationship is useful to predict the release duration at 25¢ª C by conducting a rapid release test at 100¢ª C. This study demonstrated that the rapid release test at 100¢ªC successfully predicted nutrient release rate and duration at 25¢ª C.