This study was conducted to determine the effects of temperature on nutrient release patterns of three polymer-coated fertilizers (PCFs), each using a different coating technology: Osmocote Plus 15N-3.93P-9.96K, Polyon 18N-2.62P-9.96K, and Nutricote 18N-2.62P-6.64K. Each fertilizer was placed in a sand-filled column and leached with distilled water at ≈100 mL·h-1, while being subjected to a simulated diurnal container temperature change from 20 to 40 °C and back to 20 °C over a period of 20 hours. Column leachate was collected hourly and measured for soluble salts and NO3-N and NH4-N content. For all fertilizers, nutrient release increased and decreased with the respective increase and decrease in temperature. Nutrient release patterns of the three fertilizers differed, with Osmocote Plus showing the greatest overall change in nutrient release between 20 and 40 °C, and Nutricote the least.

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Seedlings of 30-, 35, 40-, -45, and 50-day-old marigold (Tagetes erecta Big. `Inca Gold') in 500-ml plastic pots containing a 1 peat: 1 perlite (v/v) medium were treated with several fertilizer levels (N at 20, 50, 80, and 110 mg·liter-1); solution nutrient levels in the medium were determined 6 hours later. Older/larger container-grown plants absorbed more N, P, and K from the medium solution than younger/smaller plants. Also, older plants (>40 days) absorbed at least 88% of the solution N regardless of N treatment. Nitrogen absorption, regardless of plant age, increased as N application rates increased. The latter result implies that even though total N absorption increases with plant age/size, nutrient levels in the medium solution for optimal growth and nutrient uptake may be similar regardless of plant size.

In containerized nursery-crop production, conventional phosphorus (P) fertilization amounts are reported to be in excess of plant needs which has resulted in poor P use efficiency (PUE) and subsequent P leaching from containers. Phosphorus leaching can be reduced and PUE improved without affecting plant growth by reducing P fertilization. The objective of this study was to identify the lowest controlled-release fertilizer (CRF)-P content and subsequent pour-through-extracted substrate pore-water P (PWP) concentration that produces maximal shoot growth of two common container-grown nursery crop species, Hydrangea macrophylla 'PIIHM-II' (hydrangea) and Ilex crenata 'Helleri' (holly), in a pine bark substrate. Hydrangea and holly liners were potted into 3.8-L containers containing a pine bark substrate and grown simultaneously in two different Virginia ecoregions, Middle Atlantic Coastal Plain (MACP) and Ridge and Valley (RV). Plants were fertilized with one of five CRF formulations, each containing equal nitrogen (N) and potassium (K) and 0.4%, 0.9%, 1.3%, 1.7% or 2.6% (control) P to supply containers with 0.1, 0.2, 0.3, 0.4 or 0.6 g P, respectively. In both ecoregions, hydrangea shoot dry weight (SDW) and growth index [i.e., (widest width + perpendicular width + height) ÷ 3, GI] values were maximal in plants fertilized with 0.3 to 0.4 g P or the control. The lowest CRF-P rate needed for maximal SDW and GI of holly was 0.2 g P at the RV site and 0.4 g P at the MACP site. Mean PWP concentrations that corresponded with highest SDW were as low as 0.8 and 1.2 mg L −1 for hydrangea and holly, respectively. Results from this research suggest hydrangea requires approximately half the P rate supplied by recommended rates of conventional CRFs. Since the growth response of holly to CRF-P rate at the MACP site was inconsistent with results observed at the RV site and findings in scientific literature, further research is needed to determine the minimum required CRF-P rate for this taxon.

Sulfur (S) is essential to the growth of higher plants; however, research on S fertilizer requirements for container-grown nursery tree species has not been established. The purpose of this study was to determine the substrate solution S concentration that maximizes the growth of container-grown pin oak (Quercus palustris Münchh) (pin oak–K2SO4 experiment) and japanese maple (Acer palmatum Thunb.) (japanese maple–K2SO4 experiment) in a pine bark (PB) substrate. Both species were fertilized with solutions supplying a range of S concentrations (0, 1, 2, 5, 10, 20, 40, or 80 mg·L–1) using K2SO4. Regression analysis revealed that dry weights of both species were near maximum at the predicted application concentration of 30 mg·L–1 S, which corresponded to about 15 and 7 mg·L–1 S in substrate solution for pin oak and japanese maple, respectively. In a Micromax, FeSO4, lime experiment, S was supplied to pin oak via a preplant micronutrient sulfate fertilizer or FeSO4 in limed or unlimed PB. When the PB pH was relatively low (4.5, unlimed), FeSO4 and the preplant micronutrient fertilizer were effective in supplying ample S. However, when the PB pH was relatively high (6.1, limed), the preplant micronutrient fertilizer with micronutrients in a sulfate form was more effective in supplying S and micronutrients than FeSO4.