Nutrient and Biomass Accumulation of Container-grown Landscape Trees with Controlled Release and Organic Fertilizer

Nutrition management is one of the most critical elements of container nursery production.  In particular, understanding crop nutrient demand is essential to developing optimal fertilization programs that provide adequate nutrients for tree growth and health but reduce the potential for nutrient leaching or run-off.  In this project we developed water and nutrient budgets for two nursery tree crops; shade trees (Platanus × acerifolia ‘Bloodgood’) grown in #25 containers and conifers (Picea pungens and Abies fraseri) grown in #7 containers.  All trees were grown in a soilless substrate consisting of 80% composted pine bark and 20% peat moss.  Trees were irrigated once daily with an automated miscrosprinkler system.  Irrigation was adjusted periodically to provide 10-20% leaching fraction.   Within each nursery section, trees were fertilized with either controlled release fertilizer (Osmocote 15-9-12, N–P₂O₅–K₂O, Everris, Inc.) or an OMRI-listed organic source (blend of NatureSafe 8-5-5 and NatureSafe 10-2-8).  A third group of trees in each section was not fertilized.  We measured height and caliper on all trees at the beginning and end of the season.  A subsample of trees was destructive sampled at the end of the season to develop allometric equations of stem, foliage and root biomass as a function of trunk caliper and height.  Nutrient concentrations were also determined for stems, foliage, roots, and remaining substrate of subsampled trees. Biomass accumulation of stems, roots, and foliage was estimated for all trees based on the allometric equations.  The total nitrogen accumulation was calculated from biomass estimates and stem, foliage, and root nutrient concentrations.  For shade trees and conifers, the biomass accumulation was similar between fertilizer sources and greater for fertilized trees than unfertilized trees.  Nutrient accumulation in trees and nitrogen leaching were lower with the organic fertilizer source than with the controlled release fertilizer.  Our results indicate that organic fertilizer can produce acceptable growth and quality but understanding nutrient release will be critical to ensure adequate nutrition in container culture.