Delay in the release from the sigmoid-type HCRF-S70 is due to its larger amount of water requirement to start the nutrient release as compared to the exponential type HCRF-E50.
To initiate the release nutrients, a certain amount of water needs to permeate into the film-coated controlled release fertilizer, HCRF-S70 needs more water to permeate than HCRF-E50.