What is the difference between slow-release fertilizer and controlled-release fertilizer?
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When it comes to fertilizing succulents, slow-release fertilizer is certainly one of the fertilizers that will be mentioned. Although by habit it is called slow-release fertilizer, strictly speaking, what everyone calls slow-release fertilizer is actually controlled-release fertilizer. However, in terms of effect, the two are more or less the same in meaning. Below is an explanation found online about slow-release fertilizer and controlled-release fertilizer.
Slow-release fertilizer and controlled-release fertilizer release nutrients slowly and have a long fertilizer effect. In this sense, there is no strict distinction between slow-release fertilizer and controlled-release fertilizer. However, from the perspective of the mechanisms and effects that control the rate of nutrient release, slow-release fertilizer and controlled-release fertilizer are different. Slow-release fertilizer slows the release rate of nutrients in the fertilizer through chemical and biological factors, and during release it is affected by many external factors such as soil pH, microbial activity, soil moisture content, soil type and irrigation volume; while controlled-release fertilizer wraps water-soluble fertilizer inside a membrane through an external coating so that nutrients are released slowly. When the coated fertilizer granules contact moist soil, the moisture in the soil penetrates through the coating into the interior, causing part of the fertilizer to dissolve, and this part of the water-soluble nutrients then slowly and continuously diffuses outward through the micropores in the coating. The higher the soil temperature, the faster the fertilizer dissolves and the faster it passes through the membrane; the thinner the membrane, the faster the penetration.
Second, from the perspective of the types of nutrients, the two are also different. Slow-release fertilizer is mostly a single-nutrient fertilizer, with the main variety being slow-acting nitrogen fertilizer, also called long-acting nitrogen fertilizer, which has very low solubility in water. After being applied to the soil, under the action of chemical and biological factors, the fertilizer gradually decomposes, and nitrogen is released slowly, meeting the crop's nitrogen demand throughout the growing period. Controlled-release fertilizer is mostly an N-P-K compound fertilizer or a complete-nutrition fertilizer with trace elements added. After being applied to the soil, its release rate is affected only by soil temperature. But soil temperature also has a great influence on plant growth rate. Within a certain temperature range, as soil temperature rises, the release rate of controlled-release fertilizer accelerates, and at the same time the plant growth rate accelerates, and the demand for fertilizer also increases.
Third, whether the nutrient release rate is consistent with the plant's nutrient demand at each stage. Slow-release fertilizer releases nutrients unevenly, and the nutrient release rate is not necessarily fully synchronized with the crop's nutritional needs; the nutrient release rate of controlled-release fertilizer is relatively consistent with the plant's nutrient demand rate, thereby meeting the crop's nutrient needs at different growth stages.
But in practice, for succulents, deciding how much fertilizer is released based on temperature seems not very scientific. After all, the hottest time in summer is when succulents are at their weakest, and they do not really need fertilizer that much (the most precise approach is probably to decide when to apply slow-release fertilizer based on the duration of the fertilizer effect. For example, the commonly used Osmocote A2 has a fertilizer effect of 5-6 months, so burying fertilizer in January and having it end in July is also perfect). Perhaps deciding fertilizer release based on temperature really is not that scientific, so there is also the third-generation Osmocote precision-controlled fertilizer, whose characteristic is balanced release throughout the entire release period (the release amount is completely consistent across different release periods). Unfortunately, the nitrogen-phosphorus-potassium ratio is 15-9-11, which clearly was not prepared for succulents either...
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