Phosphorus has a
negative charge; however it sticks strongly to aluminium and iron.
It does this particularly well if the soil pH is below 7, if you
raise the pH with calcium it stick to the calcium ions.
The plant cannot
remove Phosphorus from either, therefore Phosphorus is most readily
available at a pH of 6.5 .
Phosphorus is very
immobile in soils, it doesn't move to the roots, therefore it is
essential to create the best conditions to promote good root
activity so that the comprehensive root system comes in contact with
enough P. Soil porosity is important to ensure sufficient oxygen is
present for respiration soils with organic matter present are more
likely to have a strong mycorrhiza population, mycorrhiza live off
sugars in the plants roots but help to pull in phosphates in return,
this symbiotic relationship with plants is beneficial to both.
As mentioned in the
nitrogen report, phosphorus is needed to synthesise important
molecules such as proteins and DNA which are responsible in cell
The picture above
shows the smaller plant deficient in phosphorus, exhibiting
yellowing and eventual death of lower leaves.
In mild deficiency
cases growth is checked and spindly, new leaves are dark green and
reduced in size, lower leaves may become orange/green in colour.
Severe deficiency will
cause stunted plants with young leaves dark green and reduced in
size. Lower leaves become orange with browning at the margins
resulting in death of affected leaves. Flowering is delayed, bloom
size reduced and fewer blooms on sprays. Petals may suffer some loss
Where there is an
excess of phosphate certain micro-nutrient deficiencies may be
result e.g. iron, copper, manganese.
For deficiency feed with mono ammonium phosphate dissolved in
water, or apply super phosphate directly to the soil and water in.
For excess water heavily in an
attempt to leach excess, be aware of possible micro-nutrient