found in natural soils where a programof sand topdressing has been employedto control thatch or modify poor physi-cal conditions. In the latter case theblack layer generally occurs at or nearthe surface

The turf growing on the affected ar-eas dies in a relatively nondescript pat-tern. The grass may die rapidly byturning a straw to reddish-straw orbronze colour; or occasionally, the af-fected turf may become chlorotic be-fore dying.

A parallel phenomenon is know tooccur in water wells and in drain lines.In water wells slime producing micro-organisms proliferate on the screens ofsand points and out into the surround-ing aquifer. This brown to black slimygrowth gradually becomes sufficientlydense enough to plug the screen andreduce the water flow. When tile linesare placed in high iron content soils andbackfilled with high organic contenttop soils a reddish brown slime depositoccurs within the tile which eventuallyplugs the tiles. In the first case thecolour is associated with reduced man-ganese whereas with the tile lines thematerial is precipitates of reduced iron

,compounds.

Black Layer Formation in Turf

Characteristics, Causesand Cures

R. W. Sheard, P.Ay.

What are the causes?Many theories have been promoted

for the formation of the black layer butthey all accept the basic cause is ananaerobic condition; that is, a lack ofoxygen in the soil atmosphere. Work atMichigan State has provided rather de-finitive data that the anaerobic condi-tion results in the reduction of sulphatesulphur by sulphur reducing bacteria tosulphides. The reducing conditions

The occurrence of black layer in turf, for sports facilities has been a con-

tinuing problem over the past twodecades. Generally the condition hasbeen associated with construction ofthe fields using U.S.G.A. Green Sectionspecifications or variations thereof.The condition is recognized by chloro-sis and die back of the turf which cannot be identified as a nutritional orpathogenic problem but which appearsassociated with it certain characteristicsof the root zone.

What are thesecharacteristics?

As the name suggests the condition isblack discolorations on the soil parti-cles and slime materials in the root zonewhich occur as continuous horizontalplates of varying thickness or verticalcolumns of black, often slimy, rootzone material. Associated with theblack layer are unpleasant swampy orsewer like odours; even that of rotteneggs which is the aroma of hydrogensulphide.

The black layers may be from 0 - 10em below the surface. The layers mayrange from 2 to 7.5 ern thick wherethey occur at or near the surface to 1 to3 ern thick where they are deeper in theprofile. The affected areas may be asso-ciated, but not necessarily, with minordepression in the playing surface. Theaffected areas have a reduced infiltra-tion rate, combined with a reduced hy-draulic conductivity. Due to the blackslime of bacteria - metal complexes thecondition is often referred to as a"black plug layer".

While generally a condition that oc-curs on sand based root zones, it is also

created by the responsible bacteria in turnresults in the formation of iron and man-ganese suphides, the latter causing theblack colour. Also associated with the re-duction of sulphur compounds is the for-mation of hydrogen sulphide which givesrise to the "rotten egg" odour. Further-more, hydrogen sulphide is a weak acidwhich can be very toxic and damaging tothe turf root system

There are four prerequisites necessaryfor the formation of the black layer: 1) ananaerobic (oxygen deprived) atmospherein the soil, 2) an organic material availablefor microbial decomposition, 3) a sourceof sulphur compounds, and 4) the occur-rence of sulphur reducing bacteria. With-out anyone of these conditions the blacklayer will not form.

The first condition is satisfied any timeyou have a poorly drained or waterloggedcondition. The waterlogged conditionmay result from a perched water table ora permanent water table caused by a num-ber of factors. With regard to the secondprerequisite decomposable organic mate-rial is always present in soils where theroot system is in a continuing process ofregeneration. Sulphur compounds occurin all soils and are constantly being addedas a product of acid rain and in fertilizers.Sulphur reducing bacteria are found in allsoils and can soon be spread by dust topure sand root zones and rapidly prolifer-ate when the conditions are right.

What are the cures?It is obvious from the four prerequisite

noted above that one, the occurrence ofsulphur reducing bacteria, cannot beeliminated. Likewise the occurrence ofdecomposable organic material cannot beavoided. Steps, however, can be taken toreduce the impact of the other two.

The ultimate cure is in the beginning,during construction of the facility. At thisstage the design and construction shouldbe to insure adequate drainage to avoidpotential anaerobic situations. Prudencerequires that the final contouring be doneon the subgrade, not the final surface.Thus the depth of the root zone will beuniform and the water content will re-main constant across the field with nolocalized wet spots.

Table 1: The formation of black layer and turf quality resulting from the snitrogen used for turf production under poorly drained conditions.

•Nitrogen Source Turf QualityBlack Layer Rating*

*On a scale 0 -4, where 0 was no peg discoloration

** On a scale 0 -5, where 0 was no injury and 4 was death of the turf.

Ammonium sulphate

Urea

Ammonium nitrate

(ave. 25 labels)

3.36

3.080.76

The ultimate cure is in thebeginning, during

construction of the fa,ci/ity.

As part of the system to remove excesswater is the system used to provide water- the irrigation system. Excess irrigationthrough reliance on electronic gadgetsand not through thoughtful use ofweather data adds to the drainage prob-lem.

At the construction stage uniform, off-site mixing of the sand, organic sourceand any soil materials is essential to avoidlocalized interruption in drainage flow.When a cross section of the root zone hasthe "marble cake" appearance one may besuspicious of poor mixing being the causeof the black layer. Some designers of fieldswill place 20 ern of pure sand below a final10 em of sand:soil:organic mix - "the twolayer cake." Again a condition for aperched water table is created, which incombination with the other three prereq-uisite conditions may lead to black layer.

Since the black layer condition reflects alack of oxygen in the root zone and as itoccurs in the top 10 ern of the profile,

(rating**)

1.963.44

0.68

deep coring, with hollow tines, and re-moval of the cores will give temporaryrelief. Observa. tions by sr~rts turf manag-ers have found the black layer to disap-pear in the area of the c are hole and inthe core itself as it is exposed to theatmosphere.

Where topdressing is practiced it is im- II I

perative that the material used conformsas closely as possible to the existing ma-terial to avoid layering. Changing top-dressing materials from year to year resultin the "multi-layered cake."

The use of nitrate fertilizers can affordsome relief. Work by Drew Smith atSaskatoon demonstrated that a nitratesource of nitrogen could alleviate the con-dition. The nitrate ion acts as a substitute'for oxygen under the waterlogged condi-'tionsassociated with the black layer. Us-ing wooden plant labels whichdiscoloured according to the degree ofblack layer formation, he assessed i theeffect of sources of nitrogen applied toturf growing in pots of course sand whichwere kept in an waterlogged conditionfor approximately six weeks (Table 1).The data: clearly show nitrate forms ofnitrogen were superior to urea and am-monium sulphate in deterring black layerformation.

When black layer' is a problem avoidingsulphur containing fertilizers by substitut-ing nitrate carriers for the nitrogen sourcewill provide some degree of relief.

My thanks to Pam Charbonneau forher extensive file on the Black Layer.