During a recent USGA Course Consulting Service visit, we looked at a few greens that were struggling. Chlorotic and thin turf was prevalent in the low areas. When we pulled soil samples, the distinctive sulfur smell gave it away – they had black layer.
Black layer is almost always associated with waterlogged soils. The lack of oxygen encourages sulfur-reducing bacteria to go to work. When they respirate, they produce hydrogen sulfide. In anaerobic soils, hydrogen sulfide reacts with metals in the soil to create metal sulfides. When those metal sulfides accumulate, they create a black layer. It is believed that during this black layer formation process, the hydrogen sulfides are toxic to turfgrass plants (Berndt, 2016). Roots become stunted and eventually the turf dies.
So, how do we get rid of black layer? The simple answer is to get more oxygen into the rootzone and pay attention to your fertilizer sources. Here are some steps to take:
Check your irrigation coverage. I often see black layer in areas where sprinklers are hitting the green that shouldn’t be. During the irrigation season, this extra watering does not allow the soil to dry properly.
Irrigate wisely. Use moisture meters and irrigate only when the turf needs it. Turf in areas with black layer will have a compromised root system. Monitor soil moisture in those areas and irrigate only when drought symptoms begin to show.
Aerate more. Introducing physical channels for oxygen to reach the black layer will immediately improve conditions. Black layer does not like abundant oxygen.
Consider removing liners in low spots. Many courses have liners that separate the greens mix from the soil outside. These liners can act as drainage dams in low areas. Removing sections of liner can allow the greens mix to drain better.
Add drainage. In some cases, you may need to add drainage to low spots.
Check your fertilizer sources. Organic nitrogen sources require oxygen to become usable food for the plant. This nitrification process reduces available oxygen in the soil. Reduced oxygen levels lower the redox potential of soils, and a low redox potential is a precursor to black layer development. A better source of nitrogen would be a nitrate source. Studies have shown that nitrate sources of nitrogen actually increase redox potential and prevent hydrogen sulfide production (Berndt, 2016).
The good news on black layer is that it can be pretty easy to fix. As soon as you get more oxygen into the soil profile, the black layer begins to go away. It may take a few years to completely knock it out, but it is possible with good cultural, irrigation and fertilizing practices.
