Nutrient Guide And Turf Disease Management (P3)

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Phosphorus (P)

Overview

Phosphorus is an important requirement of many plant compounds that are essential for growth.

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 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). Plants roots take up phosphorus from soil solution mainly as the H2PO4- and HPO42- ions.

Phosphate (-ve charge) can be ‘locked up’ in soils with high levels of cations (+ve charge, eg. calcium, magnesium or iron). So availability is reduced in heavy clays or other soils with high fi xing 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 by improving the availability from soil reserves by increasing soil plant growth promoting rhizobacteria (PGPRb) levels (eg. Bacillus and Rhizobacter).

Factors aff ecting availability to plant

  • Defi ciencies can occur during periods of rapid growth or during cold/wet conditions.
  • Defi ciency can also occur in low organic matter soils
  • Compacted or waterlogged soils limit root growth and the ability of the plant to absorb phosphate

Factors aff ecting availability to plantPotassium (K)

Overview

Potassium is an essential component of plant nutrition. Potassium defi cient plants are known to be less resistant to plant diseases.

Key functions in the plant

  • Maintenance of water balance in the plant, and helps regulate cell water content and plant turgor, maintaining stem strength.
  • Important role in transpiration by controlling stomatal pore opening and closing
  • Involved in transport of sugars from ‘sources’ to ‘sinks’
  • Good mobility in the plant There are 4 pools of potassium in the soil, most is in soil minerals, these weather to release slowly available potassium embedded in clays (slowly exchangeable K), readily available potassium held on the surface of clays or organic matter (exchangeable K) and potassium in soil solution.

Factors aff ecting availability to plant

  • Low pH soils
  • Defi ciency can be common at the end of the growing season, especially on light, sandy soils.
  • Soils with low clay reserves where little K is released, and on sandy or light soils where K can be leached
  • Drought and high levels of magnesium reduce uptake

Factors aff ecting availability to plant

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