Boron (B) is essential for crop growth and development but in very small quantities. While the precise role of boron in plants is not fully known there is evidence to shown that boron is important for cell division, the production of nucleic acids, the movement of sugars across membranes and the development of reproductive structures. For most crops, 1- 4 mg B/kg soil is sufficient to prevent nutrient deficiencies. Less than 1.0 mg B/kg is rated as marginal to deficient. Deficiencies are more likely to occur where high biomass crops encounter low soil moisture conditions. Boron toxicity in Australia is mainly confined to the low rainfall (<550 mm/yr) Mallee vegetation communities of Western Australia, South Australia and Victoria. The soils typically contain highly alkaline (pH>8) and sodic clay subsoils which are poorly leached.