Providing residual fertilizer to containerized floriculture products to improve postproduction (consumer) performance is a means to add value and differentiate product quality. Water-soluble and controlled-release fertilizers are widely used for production of container crops. Using CRF instead of WSF is recommended to the landscape service industry as a best management practice to provide nutrients for an extended period (Andiru et al., 2013; Chen et al., 2011). CRF include urea, ammonium nitrate, potassium nitrate, or other soluble fertilizer materials coated with a polymer, resin, sulfur, or a hybrid of sulfur-coated urea coated with a polymer or resin. Polymer-coated materials release nutrients primarily based on the temperature and moisture status of the substrate (Sonneveld and Voogt, 2009). Many studies have demonstrated that CRF have potential to reduce N and phosphorus runoff as compared with fertigation (Wilson and Albano, 2011; Wu et al., 2008). The use of CRF alone does not provide a complete solution to the problem of nutrient leaching; however, appropriate fertilizer application methods, CRF types, and irrigation strategies must be calibrated to match crop needs and the local environment (Broschat and Moore, 2007).
Both growth chamber and greenhouse methods have been used to compare how CRF will act in a particular controlled environment (Broschat and Moore, 2007; Carson and Ozores-Hampton, 2012). Field methods are also used to measure N release in commercial vegetable soil conditions (Birrenkott et al., 2005; Simonne and Hutchinson, 2005). The CRF response profile under controlled laboratory conditions can be combined with substrate extraction methods in the field to quantify release characteristics of CRF for different crops and locations (Birrenkott et al., 2005).
A range of fertilizer strategies are available to provide nutrients during production and consumer phases. Containers may be produced with WSF and then top-dressed with CRF before sale. A CRF may alternatively be incorporated into the substrate or top-dressed at planting with a longevity that exceeds the production time, so that residual nutrient reserves remain for the consumer. In a commercially available technology [DCT (Protect™; Everris, Geldermalsen, The Netherlands)], a second outer coating is present over a conventional single-coated CRF prill (Osmocote Exact™; Everris), which according to the manufacturer delays the initial nutrient release for 1.5 to 2 months depending on temperature. For the purposes of clarity in this article, we will use OSM to refer to single-coated CRF technology (Osmocote™; Everris), to differentiate from DCT. A blended product of OSM and DCT (Osmocote Hi-End™; Everris) will be referred to as OSM + DCT, and both OSM and DCT will be referred to as types of CRF.
The objective of this study was to compare nutrient release, plant performance, and cost for strategies that potentially provide adequate nutrition during both the production and consumer phases for container-grown floricultural plants. Unless indicated as top-dressed, all CRF treatments were incorporated into the growing substrate before planting. Fertilizer strategies included WSF only, a combination of low rates of WSF during production plus OSM (WSF + OSM), WSF during production with DCT (WSF + DCT), and OSM or OSM + DCT without WSF. These strategies were used to encompass most approaches in use by floriculture producers. A greenhouse experiment was conducted with petunia grown in a peat/perlite substrate in containers for 42 d with WSF or CRF treatments to simulate the production phase. Plant growth and nutrient level were evaluated under simulated consumer conditions in a landscape planting and in containers for an additional 98 d. A simple financial budget for each fertilizer strategy was calculated. An additional experiment was conducted to generate nutrient release curves in growth chambers at 10, 21, and 32 °C with sand-filled columns, using a protocol based on Carson and Ozores-Hampton (2012).
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