Black layer only occurs in anaerobic soil conditions. It is caused by a physical condition of the soil. If the soil does not drain quickly enough or impenetrable layers are present which restrict downwards water movement, it is likely that Black Layer will occur.
· When a root zone has excess water present, the water will push air out of the soil pore spaces. A root zone in this condition can be described as anaerobic.
· In an anaerobic soil, aerobic bacteria are replaced by anaerobic bacteria.
· Anaerobic bacteria produce Hydrogen sulphide gas, which has a characteristic 'rotten egg' smell. It is poisonous to grass plant roots.
· Hydrogen sulphide reacts chemically with metal elements such as Iron (Fe), creating black deposits, which form layers within the soil.
Possible causes of Black Layer:
· Poor rootzone mixture.
· Layering in the soil profile
· Buried thatch layers
· Soil panning.
· Incompatible top dressing
· Black layer only occurs in soils with excess water present.
· Black layer can be cured by improving drainage or increasing aeration.
· Sulphur does not cause Black Layer.
· Sulphur is an essential grass nutrient.
· Potassium nitrate does not prevent 'Black Layer'
· Continued use of Potassium nitrate may cause soil de flocculation, which could increase the risk of 'Black Layer'.