05.08.2024
Challenges in management of black layer in turfgrass
Formation and Properties of undesired Black Layer in Turfgrass Systems and the challenges it poses to groundskeepers
Formation of Black Layer
- Anaerobic Conditions: The black layer usually forms in soils where oxygen availability is severely limited. This anaerobic environment is caused by a variety of causes, including inadequate soil drainage, compaction, and high thatch formation. The lack of oxygen hinders aerobic microbial activity while promoting the growth of anaerobic microbes.
- Microbial Activity: Under anaerobic conditions, facultative and obligate anaerobic bacteria are the primary decomposers of organic materials. In the absence of oxygen, these bacteria use other electron acceptors, such as sulfate (SO₄²⁻). Microbial reduction of sulfate produces hydrogen sulfide (H₂S), a gas with a distinct rotten egg stench and contributes to the soil's black layer.
- Sulfide Accumulation: Hydrogen sulfide reacts with divalent iron (Fe²⁺) in soil to generate insoluble iron sulfide (FeS), which causes the black color in this layer. This reaction is represented by the following chemical equation:
Fe2++H2S→FeS+2H+Fe2++H2S→FeS+2H+ - Organic Matter Dynamics: The constant accumulation of organic matter from degraded plant leftovers, roots, and microbial biomass serves as a substrate for anaerobic microbes. The high organic content, along with little oxygen transport, maintains the anaerobic conditions required for black layer growth.
Implications for turfgrass health
- Root Health: The black layer is harmful to root health because it accumulates hazardous metabolites including hydrogen sulfide and organic acids. These chemicals can harm root cells, reducing root function and nutrient intake. The ensuing phytotoxicity can cause root necrosis and a reduction in turfgrass vitality.
- Gas Exchange: Anaerobic conditions reduce the soil's ability to enable gas exchange. Oxygen is essential for root respiration and the microbial actions that improve soil health. Impaired gas exchange causes hypoxic conditions for plant roots, resulting in metabolic stress and decreased physiological activities, including reduced energy production via aerobic respiration.
- Water Movement: The existence of a black coating can interfere with the soil's hydraulic capabilities. The buildup of tiny organic particles and the development of iron sulfide compounds can affect soil structure, resulting in reduced pore space and permeability. This might create waterlogging in the root zone or inhibit water infiltration, resulting in an adverse environment for turfgrass growth.
Management Strategies
- Aeration: Mechanical aeration treatments, such as core aerification, can reduce soil compaction and improve oxygen transfer to the root zone. Regular aeration prevents the formation of the black layer by increasing aerobic microbial activity and improving soil structure.
- Drainage Improvement: Improving both surface and subsurface drainage systems can help to reduce waterlogging and keep the root zone oxygenated. Installing drainage tiles and grading can assist manage surplus water and prevent anaerobic situations.
- Thatch Control: Managing thatch accumulation with procedures like as verticutting, topdressing, and the application of biological thatch degraders can help to reduce the organic debris that contributes to black layer formation. Thatch management improves air and water flow across the soil profile.
- Soil additives: Adding soil additives like sand can improve soil texture and porosity, increasing air and water circulation. Amendments can also help to dilute organic matter concentrations, lowering the risk of anaerobic conditions.
- Irrigation Management: Proper irrigation methods that avoid overwatering can help prevent the formation of anaerobic zones. Using soil moisture sensors like TDR and timing irrigation based on turfgrass water requirements can help to optimize water use and maintain proper soil moisture levels.
- Products like #OxyTurf: OxyTurf is a patented liquid blend of naturally occurring plant extracts, using enzymatic biocatalysis, that stimulates positive microbial activity, kick-starts decompaction of the soil and improves its percolation capability, allowing for improved aeration and control of excessive organic matter and black layer.
Conclusion
The black layer is a significant soil condition that develops in anaerobic conditions and poses a threat to turfgrass health because it affects root function, gas exchange, and water flow. Understanding the science behind its creation and employing focused management methods can help limit its negative impacts, maintaining a healthy and resilient turfgrass system.
