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Measured nutrient uptake (from fertilizers) by plants can be achieved through modification of fertilizer products—either chemically to reduce their solubility or physically, for instance, by coating encapsulation. These types of fertilizers are known as slow- and controlled-release fertilizers. The slow-release (SRF) and controlled-release (CRF) fertilizers belong to the larger group of enhanced efficiency fertilizers, which also include nitrogen stabilizers, nitrification inhibitors, urease inhibitors and stabilized fertilizers. Controlled-release fertilizers are generally coated products (either with polymer or sulfur or a combination of both). Slow-release fertilizers are noncoated products that release the nutrient uncontrolled but slowly. These are mainly urea-aldehyde reaction products but also other slowly soluble products such as fertilizer spikes and ion exchange resin fertilizers. Whereas the bulk of the fertilizer market belongs to the stabilizers and inhibitors categories, SRFs and CRFs are used at much smaller volumes and therefore might be considered specialties.
The following pie chart shows consumption of controlled- and slow-release fertilizers by application in the United States, Western Europe and Japan:
Demand for CRFs and SRFs has increased over time because of the following advantages relative to readily soluble nitrogen fertilizers:
- Reduction of nutrient losses that occur between application and uptake by the plant
- Reduction of nitrogen toxicity (reduced salt index), particularly to seedlings, caused by high ionic concentrations associated with rapid dissolution of soluble fertilizers or from evolution of ammonia by hydrolysis of certain salts (e.g., urea)
- Reduction in the number of fertilizer applications, resulting in convenience and cost savings in labor and energy
- Reduction of topical growth (flush growth) and clippings
- Improved agronomic yields
- Improved rooting
- Improved cell wall strength
- Improved soil microorganism health/populations
- Retention of desirable color
The trend toward increasing use of coated controlled-release fertilizers is expected to continue. Coated fertilizers, particularly polymer-coated products, have been the fastest growing segment of the SRF and CRF market and will continue to grow at a faster rate than other SRF and CRF types. Overall, global demand for SRFs and CRFs will continue to increase at a moderate rate over the next several years.
Demand for controlled- and slow-release fertilizers will experience continued growth as they prove to be an efficient alternative to conventional fertilizers because of their environmentally friendly, resource-saving, and labor-saving characteristics. However, because of the high price of SRFs and CRFs relative to conventional fertilizers, their application thus far has been limited to ornamental, horticultural, and turf applications. As larger production scales of these materials are achieved, the costs are expected to decline from current values, and will make SRFs and CRFs more attractive for commodity/open-field/broad-acre crops such as corn, wheat, and potatoes. Another factor that will drive SRF and CRF demand in the future is the regulations and penalties that encourage growers to minimize fertilizer runoff in water streams.
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