Managing Surface Organic Matter in Bentgrass Putting Greens – Turfgrass Science at Purdue University

Managing Surface Organic Matter in Bentgrass Putting Greens

As you begin planning for spring core cultivation, consider the following as some food for thought. Turf research has shown that excessive organic matter, and/or thatch (> ½ inch), in the upper (1-2 inches) rootzone profile can lead to rapid turf decline during stressful summer months. Excessive organic matter results in low soil oxygen, poor/shallow rooting, high moisture, decreased percolation, increased disease and pest activity, softer surfaces prone to scalping, and localized dry spots.

Frequent sand topdressing and hollow tine aerification are the primary cultural practices most effective for putting green thatch management. However, some greens may require more topdressing or aerification than others. This is due to differences in age, growing environments, fertility programs, traffic, compaction, etc. Organic matter production of cool-season grasses is highest during periods of cool temperatures (32-55 F) and in areas with low air circulation. Greens in shaded areas with restricted air movement, high moisture, and low light often exhibit higher organic matter in the upper profile than those in sunny environments. These microenvironments are often great design features, but create tough growing conditions.

Prior to seasonal aerification, identify any greens that have been troublesome in the past and determine if they are located in a microenvironment conducive to organic matter accumulation. You could also determine the exact percent by weight of organic matter with a simple loss on ignition lab test at an accredited soils testing laboratory (Information on accredited soils testing laboratories can be found at the following website: ). Adjustments in management practices such as supplemental topdressing or more frequent aggressive core cultivation practices will improve the rootzone profile and help produce a better quality playing surface. Additionally, solid tine aerification or water injection during the summer may help improve the anaerobic soil conditions detrimental to root health. (Note: The turf should be actively growing and healthy prior to doing any of these cultural practices previously mentioned to prevent causing further stress on an already weakened plant.) Remember, some organic matter is good (<¼ inch) as it provides a cushion from traffic and absorbs the impact of a golf ball. However, high organic matter buildup (> 3% by weight) may cause the turf to be more prone to diseases, mechanical injury, and summer decline.

Factors Increasing Organic Matter Accumulation in Cool Season Turf

•  Extended temperatures of 32-55 F are when organic matter decomposition and microbial activity and breakdown are low.

•  Poor air circulation yields high moisture on the surface which leads to anaerobic conditions and delays canopy drying.

•  Aggressive growing turfgrasses, resulting from excessive fertilization, newer cultivars with rapid organic matter accumulation, high mowing heights, or frequent irrigation.

•  Infrequent turf cultivation and topdressing which are key cultural practices involved with organic matter management.

•  Acidic conditions (<6 pH) in the soil limit microbial populations growth and reproduction.

•  Unrestricted use of pesticide formulations which reduce microbial populations.

In : Carrow, R. N. 2003. Surface organic matter in bentgrass greens. [Online] USGA Turfgrass and Environmental Research Online. September 1. 2(17):1-12.

Stresses Associated with Excessive Organic Matter

•  Anaerobic conditions are produced from the blockage of macropore space in the upper profile, which ultimately causes a decline in microbial populations responsible for degrading organic material.

•  Poor rooting results from the depleted soil oxygen available for root initiation. Additionally, roots prefer growing in thatch because it is easier to penetrate compared to soil.

•  Increased pathogen activity is observed due to high moisture at the surface. The thatch layer is also a perfect environment for many turf pathogens.

•  Pest damage is associated with high levels of organic matter because it offers ideal growing conditions for many of the turf insects.

•  Excessive drying results because of the hydrophobic organic coating forming on surrounding sand particles as a result of organic matter breakdown, producing hydrophobic conditions.

•  The turf is more prone to scalping and other mechanical injury because of softer, wetter surfaces produced from excessive water holding capabilities of the thatch layer.

•  Increased algae populations are observed because of higher moisture at the surface.

Keys to a Successful Aerification

•  Prior to any aerification, it is important to make an accurate assessment of turf health. If turf is severely weakened, increased stress from aerification will lead to slower than average recovery time.

•  Avoid using high PGR rates 2-3 weeks prior aerification to avoid slow recovery.

•  Apply ½ lb quick release N/1000 ft 2 about a week BEFORE you aerify to encourage a healthy, fast recovery.

•  Hollow tines are best for relieving compaction and organic matter removal and are most commonly used by turf managers assuming adequate turf health. Solid tines are less aggressive and result in less tearing and should be used if turf is not healthy enough.

•  Tine size and spacing effect the amount of surface area impacted from aerification. USGA agronomists recommend that aerification should impact at least 20% of the putting green surface area each year.

•  After core removal and clean-up, back fill aerification holes with a DRY sand that matches or is slightly coarser than the underlying rootzone. (Note: Select sands that contain > 60% in the medium-coarse size, avoid sands that have < 20% fines)

•  Be sure to keep turf well hydrated to promote recovery. Additionally, roll prior to first mowing to smooth out the bumpiness which is prone to scalping.

•A healthy, actively growing putting green should return to normal in 5-14 days depending on tine size and spacing

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