Growth response of Hydrangea macrophylla and Ilex crenata cultivars to low-phosphorus controlled-release fertilizers ; Scientia Horticulturae

Abstract

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) divided by 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. ; Virginia Agricultural Experiment Station; Clean Water3 of the National Institute of Food and Agriculture, U.S. Department of Agriculture [SCRI 2014-51181-22372]; Virginia Nursery and Landscape Association; Horticultural Research Institute, Virginia Agricultural Council; Hatch Program ; The authors thank Julie Brindley, Velva Groover, and Anna Birnbaum for technical assistance, as well as Saunders Brothers Nursery and Bailey Nursery for donating plants for this research. Funding was provided by the Virginia Agricultural Experiment Station, the Hatch Program and Clean Water3(SCRI 2014-51181-22372) of the National Institute of Food and Agriculture, U.S. Department of Agriculture, the Horticultural Research Institute, Virginia Agricultural Council, and the Virginia Nursery and Landscape Association. ; Public domain authored by a U.S. government employee