The Authority in Potassium and Magnesium
The boron content of soils in humid climates ranges between 5-80 mg kg-1. Soils rich in sand typically contain a lower boron content (5-20 mg kg-1) than soils rich in clay and organic matter (typically 30-80 mg kg-1). In saline soils, boron concentration may be so high that it can reach levels that are toxic to plants. Boron is present in the soil solution in the form of boric acid (H3BO3) which is produced during weathering of mica and tourmaline. Boric acid dissociates above pH 6.3 and the negative charge of the anion produced,is attracted to the positive surfaces of iron and aluminium oxide, clay minerals and organic substances thus limiting availability to the plant. Since boron is taken up with the soil water, boron deficiency mainly occurs during dry periods.
Boron belongs to the group of essential micro-nutrients and affects many processes in the plant metabolism. The requirement of the various crops for boron is very different. For example, monocotyledonous plants such as cereals generally have a lower requirement for boron than dicotyledonous crops. This is thought to be due to key differences in the cell wall structures of the two groups. Boron is taken up by plants mainly in the form of boric acid.