Slow-release Fertilizers Optimize Mycorrhizal Development in Container-grown Pine Seedlings Inoculated with Pisolithus tinctorius1

Abstract

Abstract Seedlings of pitch pine (Pinus rigida mill.) and Virginia pine (P. virginiana mill.) were grown with and without inoculum of the ectomycorrhizal fungus Pisolithus tinctorius [(Pers.) Coker & Couch] in a sphagnum peatmossperlite medium supplemented with various rates of the slow-release fertilizer (18N–2.5P–10K Osmocote or single rates of 14N–6P–11.6K Osmocote and 19N–3P–8.3K Sierrablen plus ON–19.8P–OK superphosphate) or a soluble 20N–8.6P–16.4K fertilizer treatment. Mycorrhizal development was evaluated after 5 months of growth and then after a 3-month cold storage period. Seedlings heavily mycorrhizal with P. tinctorius and of acceptable planting size were produced with 2.3 to 4.5 kg 18N–2.5P–10K Osmocote/m3 medium. Higher fertilizer rates reduced or eliminated mycorrhizal development and reduced plant growth. Seedlings grown with soluble fertilizer were comparable in size to those produced with slow-release fertilizers, but mycorrhizal development was eliminated. The 3 slow-release fertilizer formulations produced seedlings of comparable size and mycorrhizal development. Superphosphate with or without slow-release or soluble fertilizer did not influence seedling growth or mycorrhizal development. Mycorrhizae continued to develop while plants were in cold storage. The ITW One-Way tube produced seedlings equal in size to those produced in the Leach Pine Cell, but mycorrhizal development appeared to be more sensitive to high fertilizer rates with the ITW tube. Mycorrhizal development did not affect seedling size.