ues). Soil management of pH with such techniques is an important tool in preventing the onset of black layer.

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soaked filter paper at the neck of the container and measuring the time necessary for the paper to turn black. Blackening within 10 seconds indicates severe reducing conditions and persistent anaerobic soil conditions. If nothing happens within 2 minutes, reducing conditions are not present and the black layer is most probably not authentic.

In one instance, this test was slightly misleading because it detected iron sulfide deep in the root-zone profile, where the iron sulfide was not caused by soil sulfur-reducing bacteria. At the same depth in the root-zone profile, the organic matter content and the proportion of iron in the reduced form Fe²⁺ was very low. Further investigation showed that the drainage layer was a slag material that was releasing hydrogen sulfide gas (H₂S) below the root-zone profile. The gas was diffusing into the soil pores and reacting with iron oxide to produce FeS precipitate.

Ferrous sulfate is often used to improve turf color. This may increase or decrease the potential for black layer development depending on the redox status of the soil at time of application. If conditions are anaerobic when applied, FeSO₄ provides SO₄^2-, which may be reduced to sulfide, and Fe²⁺ will most likely stay in the reduced state and react with the bacterially produced hydrogen sulfide.

Sulfur-reducing bacteria have an optimal pH of about 7.0, but many golf greens have pH values below 5.0. Sulfide production at or below this value is very unlikely. If conditions are aerobic and oxidizing at the time of ferrous sulfate application, Fe²⁺ will be oxidized to Fe³⁺ and precipitate as iron oxide, releasing H⁺ ions, and SO₄^2- will remain unchanged. The consequence of this reaction is one of soil acidification and a reduction in pH value. (Increased H⁺ ion concentration results in reduced pH val