Boron (B) is an essential micronutrient for plants, involved in controlling metabolic processes via the regulation of cell membranes. Additionally, boron is an important structural component of cell walls, where it controls porosity and tensile strength. Boron has secondary roles in sugar translocation, protein synthesis and auxin metabolism. Boron deficiency leads to abnormal cell division, which affects growing points causing tissues to become distorted and eventually die. Symptoms of B deficiency include dieback of the apical growing point on the main stem, followed by subsequent growth and dieback of side shoots. Other symptoms may include brittle leaves, stunting and poor seed set. Oilseed rape has a much higher requirement for B than cereals, and B deficiencies occur worldwide.
Boron is of interest in crop production because of potentially adverse effects arising both from deficiency and toxicity, when present in excess. Deficiency is most likely to occur on soils derived from acid igneous rocks and, especially sandy soils which inherently contain little B. Boron availability varies seasonally; deficiency is observed more frequently in a dry summer following a cool, wet spring, especially if growing conditions improve rapidly after a dry period.
