Overview
Phosphorus is an important requirement of many plant compounds that are essential for growth.
Most soils in the UK have adequate phosphate, although soil indices have declined in recent years. However, not all is in ‘pools’ that are available to the plant. Potentially up to 90% of phosphate applied is not utilised. Movement of phosphate is very slow (0.02 mm/day). Plant roots take up phosphorus from soil solution mainly as the HPO - and HPO2- ions. 2 4 4 Phosphate (-ve charge) can be ‘locked up’ in soils with high levels of cations (+ve charge, eg. calcium, magnesium or iron).
Availability is reduced in heavy clays or other soils with high fixing capacity and in very acidic soils (eg. peats or heathland) or very alkaline soils, (eg. calcareous soils) where calcium phosphate precipitation occurs.
Sources of phosphate for use in inorganic fertiliser will become limiting in the next 30 years and more will need to be utilised from organic manures and improvements in availability from soil reserves by increasing plant growth promoting rhizobacteria (PGPRb) levels (eg. Bacillus and Rhizobacter).
Key functions in the plant
Key component of ATP (adenosine tri-phosphate) which is used in the energy transfer process within the plant
Involved in nucleic acid formation, protein synthesis and carbohydrate metabolism
Formation of cell membranes, phospholipids
Important role in stimulating early growth and development
Factors affecting availability to plant
Deficiencies can occur during periods of rapid growth or during cold/wet conditions.
Deficiency can also occur in soils with low organic matter
Compacted or waterlogged soils limit root growth and the ability of the plant to absorb phosphate