Proper plant nutrition remains one of the most important topics for growers of nursery container stock. While some substrates have a starter charge of fertilizer incorporated, the pine (Pinus sp.) bark-based substrates commonly used by nursery growers contain little nutrient value. With the investment in plants, substrate, containers, water, and labor, growers need to be sure that they are using the correct fertilizer regimen for their production system.
CRFs are part of common fertilization strategies in container production systems. These products are usually applied to the substrate surface after potting, or are incorporated into the substrate before potting. These CRFs are resin or polymer coated to slowly release their nutrients over the course of a growing season. The composition and thickness of the coating dictate release rate and longevity, typically measured in months (Goertz, 1993; Yeager and Cashion, 1993). However, these longevities are subject to change based on temperature. As substrate temperature in containers vary significantly with location, so do these longevities which differ with local climate (Cabrera, 1997). A commonly used CRF (Osmocote® Plus 15N–3.9P–10K; ICL Specialty Fertilizers, Dublin, OH), may be rated at 5- to 6-month longevity at 70 °F, but is only rated 4–5 months at an average 80 °F temperature. At a cooler 60 °F average, this product is rated for 6–7 months of release. Research has shown that, while product labels often reflect a change in longevity with temperature variation, CRF longevity is often shorter than what is listed on the label (Meadows and Fuller, 1983). One study indicated that release rates vary for many CRFs on the market, including Nutricote® (Arysta LifeScience America, New York, NY), Apex Gold® (JR Simplot Co., Bosie, ID), Osmocote®, and Macracote® (Fetrool, Dandenong South, Victoria, Australia) (Huett and Gogel, 2000). Some formulations were observed to reach maximum release rate after 2–3 weeks, while others reached maximum release between 7 and 13 weeks. Blends of release patterns have been customized for specific applications based on release patterns (Medina et al., 2008). New polymer technologies for coating the fertilizers are resulting in CRF with a wider range of release rate. The objective of this study was to determine the effects of four formulations of CRF, including two with new polymer coating technology, on leachate pH and electrical conductivity (EC), and plant growth of two species of woody plants, across three application rates.
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