Boron is an essential micro-nutrient for both plants and animals. The role or roles of boron in plant metabolism are not fully understood but include maintenance of cell membranes and transport of other nutrients through them (Shorrocks 1990). Where boron is deficient, cell division does not proceed normally so there are effects in growing points where tissues become distorted and eventually die. This can lead to loss of apical dominance, development of side shoots and a bushy appearance to the plant. Deficiency also affects pollination and seed set. A large proportion of hollow hulls in sunflower is a typical symptom of boron deficiency. Damage to cell walls is responsible for the brown flecks, stripes and zones associated with boron deficiency in sugar beet (‘heartrot’), swedes (‘brown rot’), carrots (‘five o’clock shadow’) and celery (stripes along stems).

Most boron is taken up by the plant passively as boric acid (H3BO3). Once taken up into leaves, boron tends to be immobile in most plant species and is not translocated from older to younger leaves to any great extent. Deficiency symptoms therefore appear first in younger tissues.

Typical concentration of boron in plant tissue is 20 – 200 mg B/kg dry-matter depending on crop species. For most broad leaved crops, a concentration less than 20 mgB/kg dry-matter indicates probable deficiency. The concentration indicating deficiency is lower in grasses and cereals:

Boron Deficiency Examples

	Sugar Beet Heart-rot is the classical exhibition of Boron deficiency in Sugar Beet. The 'crown' of leaves is poorly attached to the root and severe harvesting-loss can occur if belt-lifting harvesters are used.
	Apples Internal corking, premature drop, highly coloured fruit.
	Oil Seed Rape The centre of the stem turns brown.