Abstract: The characteristics of potassium release dynamics of multi-longevity controlled release fertilizers (CRFs) were investigated by using ion exchange resin membrane (IERM) adsorption method in a soil-column leaching experiment. The results showed that the accumulated net K2O adsorbed by IERM was in the order of FT1>FT4>FT2=FT7>FT5>FT6=FT3 among the treatments. There wasa significant correlation between the net amounts of K2O adsorbed and the amount of K2O in leaching solution every week during early stages of the experiment. However, there was no significant correlation between the net amount of K2O adsorbed and K2O in leaching solution of every fortnight in late stage of the experiment. The accumulated net amount of K2O adsorbed by IERM was greater at the third and the seventh times of extraction. Results also indicated that the value of M in Richards equation was no significant difference among treatments and bigger than that measured. The value of k was in a larger range of 0.1130 to 0.2722 which was able to reflect the difference of K2O release from the CRFs accurately. Nevertheless, the value of M in Logistic equation varied among treatments and smaller than that measured. The value of k was in a narrow range of 0.5066 to 0.6006 which could hardly to reflect the difference of K2O release from the CRFs accurately. It is concluded that Richards equation is better than Logistic one to describe and forecast nutrient release dynamic properties of the multi-longevity CRFs by using ion exchange resin membrane.

Key words: Ion exchange resin membrane, Controlled release fertilizer, Adsorption, Dynamics