Introduction
This is the name given to a layer or zone, which can be either continuous or discontinuous, and is formed in the soil profile under wet and anaerobic conditions, with the formation of the black colour of the layer/zone being mainly due to the production of iron sulphide.
Effect on Turf
Turf growing on soil which contains a Black Layer, that is typically 25- 40mm in thickness, is very shallow rooted and has a poor ability to withstand wear and has leaves which are yellowish in colour.
Surface formation of Black Layer may also occur in some circumstances.
Factors which contribute to Black Layer
- A waterlogged or saturated rootzone;
- Insufficient oxygen for adequate root growth and development;
- Soil compaction;
- Alkaline pH.
- Poor drainage of the layer beneath the rootzone, effectively producing a perched water table.
- Incorrect top-dressing with excessive amounts of fine particles.
- Using rollers for cosmetic purposes prior to football matches, increasing compaction.
- Bentgrass and annual meadow grass swards can be particularly affected.
- Possibility of seepage through joins in pitch covers on football pitches, used during winter months. Water accumulates in low spots.
Control and prevention of Black Layer
- Aeration - to maintain the oxygen supply to grass roots, decompose organic matter and maintain adequate drainage potential within the rootzone;
- Acidifying fertilisers (sulphate of ammonia, sulphate of iron) - to help reduce surface pH. Black layer is not generally found below pH 5.5.
- Acidic rootzones - be careful when choosing the rootzone used in constructions and ensure it is not at the extremes for suitable grass growth;
- Reduce thatch build-up - by scarification, verticutting and aeration;
- Top-dressing - ensure a narrow particle size range, which reduces interpacking and maintains porosity;
- Slow release and organic fertilisers - try not to apply these in the latter part of the growing season, as low nutrient uptake by the grass, as well as the nutrient being applied close to the surface layer can encourage surface rooting and thatch build up. Do not apply these fertilisers on compacted soils.
- Improve subsurface drainage.
References
1. (1988) "The Black Layer", The Journal of the Sports Turf Research Institute, Vol.64, pp190-191
2. (1993) "Science in aid of turf management", Horticulture Week, February 5, pp29-31
3. (1993) "How to cope with BLACK LAYER", Turf Management, February, p.15
4. (1995) "Bolton: Black Layer Blues II", The Groundsman, May, p.46
5. (1995) "Our green suffers the black layer blues", Turf Answers, Turf Management, June, pp11-12