Variation in Nutrient Release of Polymer-Coated Fertilizers
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Polymer-coated fertilizers (PCF) are used primarily in horticultural plant production. However, interest in using these fertilizers in forest tree nurseries has increased over the last decade. Compared to immediately-available forms of fertilizer and other controlled-release fertilizer types, PCF tend to release nutrients in a relatively consistent flow over time. This helps to improve efficiency of fertilizer use. Nutrient release from PCF is primarily dependent on media temperature; an estimated timeframe for nutrient release at a specific temperature is provided by the manufacturer. Although many different products fall into the general category of PCF, the actual polymer material used varies among products. This affects the degree to which nutrients are released over time. Additionally, timeframes for nutrient release are simply estimates provided by the manufacturer based on lab results, and actual release under operational conditions may deviate considerably from these estimates. There is also considerable variation in release of individual nutrient ions over time from PCF. For instance, many products release a large percentage of available nitrogen soon after application, while release of phosphorus is delayed. Because timing of nutrient release can be critical to successfully using PCF in forest tree nurseries, differences among products should be understood by nursery growers when incorporating various types of PCF into production.
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