Incorporating Controlled - Release Fertilizer Technology into Outplanting

The application of controlled-release fertilizers (CRF) at the time of planting offers a means to improve the establishment of forest tree seedlings. As compared to conventional fertilizers, the gradual pattern of nutrient release from CRF may better coincide with plant needs, minimize leaching, and improve fertilizer use efficiency. Many different CRF types are available and products differ in both the technology by which nutrients are contained and the environmental stimulus for nutrient release. Coated CRF use a polymer or sulfur coating to encapsulate water-soluble nutrients; coating thickness and media temperature primarily control the rate of nutrient release. Uncoated nitrogen reaction products are relatively insoluble in water and nutrient release is generally controlled by water availability and/ or microbial decomposition. Results from field trials in the Pacific Northwest (USA) indicate that attaining a positive response at outplanting with polymer-coated CRF is largely dependent on soil moisture availability. Continued release of fertilizer nutrients under hot and dry conditions may cause root damage and increase seedling susceptibility to drought. In the southeastern US, rainfall during summer may reduce the potential for this problem. On drought-prone sites, however, a conservative polymer-coated CRF application rate or the use of CRF with moisture-dependent forms of nutrient release is recommended.