Boron (B) availability in soil and its function in plant metabolism
Boron can be applied directly to soil through fertigation or via a foliar spray. Because application rates are quite low, the optimal option is to combine B with other fertilizers. During periods of high precipitation or heavy irrigation, boron can leach out of the soil quickly.
KEY FACTS
- Boron (B) is a member of the metalloid group of elements, which also includes silicon (Si) and germanium (Ge), characterized by intermediate properties between metals and non-metals.
- Although B is not an enzyme constituent, it plays a crucial role in cell wall formation and stability, sugar metabolism and effective pollination.
FUNCTIONS
- Cell wall (lignification processes) and membrane integrity
- Carbohydrate translocation and metabolism
- Maintaining water status and ion uptake
- Effect on plant respiration and photosynthesis
- Stimulation of phytohormone synthesis
- Role in reproduction — essential for pollen tube growth
- Improves calcium mobility in the plant and prevents its deficiencies
- Required for effective nitrogen fixation and nodulation in legume crops
AVAILABILITY
- At the pH typical for the cytoplasm (pH 7.5), > 98 percent of B is in the form of free B(OH)3.
- Boric acid and borate salts can readily react with many types of soil organic matter and are prone to be removed from soils by leaching.
- B availability is strongly affected by soil water content and becomes limiting in dry conditions where mass flow to roots is reduced.
- Rate of B uptake decreases strongly when the pH of the external solution is increased.
- Boron deficiencies reduce calcium motility in the soil.
