Black Layer in USGA Specification Constructed Putting Greens: What is it, and how do I get rid of it?
By Colin Mumford
United States Golf Association (USGA) specification putting greens are a design of golf green that creates a perched water table within a high sand content rootzone that overlays a gravel raft drainage system (Adams and Gibbs, 1994). This type of construction is very popular because it enables year round playability (ground weather conditions permitting) due to its free draining nature. However, high sand content greens can be prone to black layer (Hodges and Campbell, 1992; Nilson and Denford, 1998; Emmons, 2000).
Black layer is the formation of a layer of metal sulphide (Adams and Smith, 1994; Perris and Evans, 1996) within the rootzone, which develops through a combination of hydrogen sulphide (H2S) gas that is produced from sulphur reducing bacteria (SRB), and the reaction of the H2S with available minerals to form metal sulphide precipitate. This can lead to a decline in grass plant quality (Berndt and Vargas, 1992), as H2S will reduce root respiration, and ultimately the death of the grass plant, which will affect the playability of the putting green surface, although some grasses, such as Agrostis palustris have been observed growing through and clear of black layer (Hodges and Campbell, 1992).
When the rootzone lacks oxygen (O2) its redox potential declines, allowing SRB to thrive, as they require anaerobic sites, the presence of organic matter, and moisture to remain hydrated and active (Berndt, 1996). Due to the very nature of the USGA specifications, the greens have a zone of saturation (therefore anaerobic) with the retention of a water table, which keeps the rootzone moist through capillarity. Anaerobic conditions in the rootzone can also occur through waterlogging from heavy rainfall, the overuse of irrigation, or where the aerobic respiration exceeds the rootzones oxygen supply (Forrester, 1999).
Compaction of the rootzone will also assist SRB as the rootzone will have reduced pore spaces and therefore impeded drainage (Adams and Gibbs, 1994), which in turn will result in the accumulation of thatch. Thatch will further impede drainage as well as provide an additional source of organic matter for the SRB to feed upon.
The overuse of inorganic fertilizer additions to the rootzone such as ferrous sulphate and sulphate of ammonia as part of the maintenance regime can also depress the redox potential and stimulate the production of H2S (Berndt, 1992). Although organic fertilizers will also reduce soil oxygen as they stimulate microbial activity, which uses more oxygen.
Potential Solutions to Black layer
Black layer is difficult to eliminate when it has formed (Nilson and Denford, 1998). Management practices may be exacerbating the problem through inappropriate applications of fertilizer, or the overuse of irrigation. However, black layer can be reduced and/or eliminated through correct cultural practices. The use of bio-stimulents and microbial inoculants is also claimed to reduce black layer.
The principle aims of cultural practices to reduce black layer are to improve aeration and airflow through the rootzone and to reduce thatch. Improved aeration of the rootzone can be achieved through spiking, coring and slitting, and through high pressure water and air injection methods, as well as air suction systems that draw excess moisture out of the rootzone via the drainage system (Emmons, 2000). The use of aeration will relieve compaction and therefore improve the volume of macropores in the rootzone, which will aid drainage, reduce thatch and the anaerobic conditions. Topdressing, verti-cutting and scarification are also methods that can be used to reduce thatch (Emmons, 2000).
Correct management of the amount of irrigation applied to the turf is vital. Irrigation is required when the demand for water by the grass plants exceeds the amount of natural rainfall. Excessive irrigation will fill the majority of pore spaces in the rootzone and reduce O2 levels. To reduce black layer, light frequent applications of irrigation are preferable to avoid saturating the rootzone (Forrester, 1999).
A redox potential that is high enough to avoid the release of H2S can be achieved with the use of nitrate based fertilizers (Berndt, 1996). Although, the benefits are short lived because of the process of denitrification, however this can be overcome by small frequent applications of fertilizer (spoon-feeding) instead of larger infrequent applications. The use of reducible iron (Fe3+) compounds have also been shown to act as a redox buffer that delays sulphide production (Adams and Smith, 1994).
There are many bio-stimulant and microbial inoculant products on the market that claim to reduce black layer. These products range from activated carbon to absorb H2S (Rigby Taylor, 2002), to liquid or powder based microbial inoculants (Green-Releaf, 2002) that are claimed to break down and degrade the black layer. Although these products do not work by themselves, as cultural practices - defined earlier in this article - have to be carried out in conjunction with the bio-stimulant / microbial inoculant. The use of wetting agents is also thought to aid drainage and reduce black layer.
Black layer can affect turfgrass health and quality, which in turn affects playability. USGA specifications are prone to black layer because of their high sand content however, by carrying out the appropriate cultural methods the production of H2S, which causes black layer, can be prevented.
The use of bio-stimulants and microbial inoculants are claimed to work by their manufacturer, but only if the cultural practises are carried out in tandem with their application. Therefore it may be the cultural practices and not the product that relieves black layer.
Adams, W.A. and Gibbs, R.J. (1994) Natural Turf for Sport and Amenity: Science and Practice. Wallingford: CAB International.
Adams, W.A. and Smith, J.N.G. (1994) 'Experimental Studies on Black layer', in A.J. Cochran and M.R. Farrally (eds.). Science and Golf II: Proceedings of the World Scientific Congress of Golf. London: E. and F.N. Spon. 447-454.
Berndt, W.L. and Vargas, J.M. (1992) 'Elemental Sulphur Lowers Redox Potential and Produces Sulphide in Putting Green Sand', HortScience, 27 (11). 1188-1190.
Berndt, W.L. (1996) 'Blacklayer and Applications of Nitrate', Golf Course Management, 64 (10). 57-58.
Emmons, R. (2000) Turfgrass Science and Management (3rd edition). New York: Delmar Thomson Learning.
Green-Relief. (2002) Green-Relief. [www Document].
(accessed 28th January 2002)
Forrester, M. (1999) Black Layer in Golf Greens. Unpublished HNC Thesis, Writtle: Writtle Agricultural College.
Hodges, C.F. and Campbell, D.A. (1992) Nutrient Salts and Toxicity of Black-layer [www document]. (accessed 28th January 2002).
Nilson, S.M. and Denford, K.E. (1998). 'Anticipating Black layer', Golf Course Management, 66 (12). 62-63.
Perris, J. and Evans, R.D.C. (1996) The Care of the Golf Course (2nd edition). Bingley: Sports Turf Research Institute.
Rigby Taylor. (2002) Blockade G1000 [www document]. (accessed 30th January 2002).