PREVENTING BLACK LAYER
The lack of air circulation in the soil reduces oxygen, which can be very detrimental to the soil profile and consequently affect negatively the turf health.
The black layer is often a symptom of anaerobic soil conditions, usually appearing in high sand content soil, and just as the name implies, it is a horizontal black stratum formed in rootzone at a depth of 1.3 to 10 cm. It causes a reduction in several elements that are essential to the survival of plants. The colour black is the result of a reduction of iron, and the hydrogen sulphide that occurs on the black layer is responsible for an unpleasant smell that helps on the identification of the problem.
There are several factors that may result in the lack of oxygen and poor infiltration rate in the soil such as compaction, excessive organic content layer, excessive sulphur and high sodium additions or any layering that occurs in the rootzone that impedes water movement. Problems characterized as abiotic are not caused by living organisms, but by other factors such as edaphoclimatic conditions, intensity of traffic, inadequate use of chemicals and improper use of the maintenance machinery.
When the soil becomes anaerobic the solubility and chemistries of the nutrients modifies, certain elements are more available for the plant and others become toxic. The lack of O2 promotes the development of anaerobic microorganisms that produce metabolites that can be unfavourable to the development of the plants, such as sulphide (H2S) and iron sulphide (FeS). The black layer may become most evident during prolonged periods of hot humid weather and usually algae is also observed in conjunction with the layer, aggravating the surface sealing that may occur.
The lack of oxygen in the rootzone causes the reduction of the capacity of absorption of nutrients and water causing severe root decline, weakening the plant and diminishing its resistance to disease, wear, heat and cold tolerance.
To prevent Black Layer, it is important to apply topdressing material with similar physical characteristics to the existing on the rootzone and to use only slow release fertilizers or to fertilize lightly and frequently, but the best way to manage the black layer is preventing anaerobic conditions by improving water drainage and coring. The SubAir system is a good option to prevent the problem as it is designed to improve aeration, providing fresh air direct to plant roots and stimulating microbial activity. Also, it stabilises water delivery to the root system and removes harmful gases such as Carbon Dioxide, Methane and Hydrogen Sulphide.