Use of boron in conifer and hardwood nurseries

Abstract

Nursery seedlings with visual boron (B) deficiencies are rare, especially for broadleaf species but they may have occurred in conifer nurseries in Florida, Oregon and the UK. Factors favoring a deficiency include high soil pH, high soil calcium and low soil moisture (i.e. withholding irrigation). Symptoms of a boron deficiency in pine include dead terminals, resin exudation from buds, dark green foliage, and terminal needles with less than 3 μg g-1 B. Chlorosis is an iron deficiency symptom but is not a boron deficiency symptom. At some nurseries (with more than 2% organic matter and more than 0.05 μg g-1 B in irrigation water), seedlings do not have a hidden hunger for B. As a result, there are no published trials that demonstrate a positive growth response from adding boron to managed nursery soils (when seedbed density is not reduced by boron). This review highlights some of the past and current uses of B in nurseries with a focus on deficiency and toxicity effects.