Aglime Facts & Figures
Effect of pHCa on the availability of plant elements.
The relative availability of 12 essential plant nutrients in well-drained mineral soils in temperate regions in relation to soil pH. A pHCa range between 5.0 and 6.0 (between heavy lines) is considered ideal for most plants.
Effect of aluminium on phalaris
The problem
As the pH declines, concentrations of aluminium and manganese, which are toxic to plants, increase and availability of nutrients such as calcium, magnesium and potassium decrease. When the soil clay minerals degrade, aluminium is released into solution. Aluminium concentrations increase below pH 4.8, and any small decrease in pH can result in a big increase in aluminium concentration in some soils. The problem with aluminium in soil solution is that it stunts root growth and plant nutrient availability is reduced. Plant water use is also reduced and perennials fail to persist because of reduced root access to subsoil moisture.
The effects of soil pH on aluminium.
The Cost
Acidification is costing the national agricultural economy around $300 million each year. Beyond farm-gate impacts triple this cost to the community.
The impacts of soil acidification are potentially enormous and include:
- increasing dryland salinity
- increasing nitrate pollution of groundwater and reduced water quality
- reduced plant yields, farm income and domestic/export earnings
- reduced options for agriculture
- reduced vegetative cover and accelerated water runoff and erosion
- irreversible degradation of the clay content of soil, hence reduced fertility
- declining pH of waterways and aquatic environment
- increased infrastructure cost
- decreased land values.
The acid attack
Acidity itself is not responsible for restricting plant growth. The associated chemical changes in the soil can restrict the availability of essential plant nutrients (for example, phosphorus, molybdenum) and increase the availability of toxic elements (for example, aluminium, manganese).
Essential plant nutrients can also be leached below the rooting zone. Biological processes favourable to plant growth may be affected adversely by acidity. Acid soils have a major effect on plant productivity once the soil pHCa falls below 5
pHCa 6.5 Optimum for most plant growth. Neutral soil. Trace elements may become unavailable.
pHCa 5.5 Balance of major nutrients and trace elements available.
pHCa 5 Below pH5 aluminium may become soluble in the soil depending on soil type. Phosphorus combines with aluminium and may be less available to plants.
pHCa 4.5 Manganese becomes soluble and toxic to plants in some soils. Molybdenum is less available. Soil bacterial activity slows down. Aluminium becomes soluble in toxic quantities.
pHCa 4 Soil structural damage.[/vc_column_text][/vc_column][/vc_row]