|(a) No fertilizer label shall bear a statement that connotes or implies that certain plant nutrients contained in a fertilizer are released slowly over a period of time, unless the slow release components are identified and guaranteed at a level of at least 15% of the total guarantee for that nutrient(s). (b) The terms, "water insoluble," "coated slow release," "slow release," "controlled release," "slowly available water soluble," and "occluded slow release" are accepted as descriptive. However, the Service may require the manufacturer to provide data substantiating the claim (from tests carried out under guidance of a recognized reputable researcher acceptable to the Service). A laboratory procedure, acceptable to the Service for evaluating the release characteristics of the product(s), may also be required. (c) If an amount of nitrogen is designated as slow release "nitrogen-containing organic" or "organic nitrogen," then:
(1) 60% of that amount must be water-insoluble and coated urea may not be included in meeting the 60% requirement; (2) at least 15% of total nitrogen guaranteed--not just that designated "nitrogen-containing organic" or "organic nitrogen"--must be water-insoluble.