Fast measurement of nutrient release rate of coated controlled-release fertilizers

The fast extraction measurement of nutrient release rate of coated controlled-release fertilizer was the key for quality determination and criterion establishment.The nutrient release rate and release longevity could be estimated or evaluated in short period of time by using fast extraction measurement method.The nutrient release longevity of four kinds of coated controlled-release fertilizers was mensurated in water at 25℃,and the results matched the results of the fast extraction and chemical measurement at 100℃.The fitted equations of release time of coated controlled-release fertilizers at the same nutrient release rate were established,validated and evaluated.The fast extracted solution of coated controlled-release fertilizers at 100℃ could be mensurated by using electrical conductivity method(convenient measurement method).The results indicated that the fitted equations of release time of four kinds of coated controlled-release fertilizers at the same nutrient release rate were significantly correlated.The nutrient release rate of coated controlled-release fertilizers could be mensurated accurately in short period of time by the fast extraction measurement at 100℃.By using fast extraction measurement method at 100℃,the release longevity of 36 months of coated controlled-release fertilizers could be estimaed in 1048 hours,and the maximum forecasting error was only 10 days(5.6%) for mensurating 6 months of release longevity at 25℃.The electrical conductivity measurement method at 100℃ could also be used for mensurating the nutrient release rate of coated controlled-release fertilizers.This method was more convenient compared with the chemical measurement at 100℃,and the maximum forecasting error was only 15 days(8.3%) for mensurating the release longevity of 6 months of coated controlled-release fertilizers at 25℃.