Fact Sheet 6: Root Facts

Size

For most plants, there is as much growth above the soil surface as there is below as roots.
Dryland crops grow 90 percent of their roots in the top 10 cm of soil.
The remaining 10 percent of roots may grow as deep as 2m to tap deep water for 'survival and insurance'.
In ideal conditions, roots can grow up to 1cm/day.

Roots grow easily where the soil strength is less than 3 Mega Pascals (3 MPa).
Fibrous rooted plants e.g. grass and cereals can penetrate 5 MPa soil strength with difficulty.
Plants with large diameter roots including those with tap roots are more sensitive to soil strength than those with fine fibrous roots.

Roots grow randomly but grow faster and branch more where conditions are good - i.e. adequate moisture and fertiliser, low soil strength.
Roots do not grow towards water or fertiliser but cluster around these areas as they promote growth.
Roots grow randomly with a slight tendency to go grow down, shoots grow up, drawn towards the sun.
As soil clay content increases, less roots are required to fully explore soil water. This is because clay can conduct water to the roots.

Roots absorb the majority of their water and fertiliser a few millimetres behind the growing tip.
Older roots act as pipes to transfer the water and nutrient to the plant.
Where root growth is restricted or disease attacks the root tip uptake will be restricted.

Plentiful early season rainfall will lead to rapid and prolific root growth of dryland crops and pastures.
If there is no follow-up rainfall, the lush growth will rapidly remove soil moisture leaving a moisture shortage later in the season. This may affect seed set and grain fill and result in 'haying off' in cereals.
A plant can survive with only a fraction of its root system if rain falls regularly through the growing system. In this situation root disease may not affect yield.

Fact Sheet 6: Root Facts

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