Verdure: Thatch, mat and coring

University of Maryland researchers analyzed the effects of three different coring regimes on the quality and thatch-mat content of a creeping bentgrass green.


Organic matter accumulation has long been a concern for turfgrass managers, who have adopted many strategies to combat it, including aerification or the application of topdressing or other materials, such as wetting agents or microbial degraders. Still, organic matter management is often first addressed through cultivation practices, including aerification.

With that in mind, turfgrass researchers at the University of Maryland (and one author at Rutgers University) examined the practice of coring on the quality and thatch-mat (thatch-mat is the term for the organic layer consisting of thatch and the intermixed topdressing sand) content of a Providence creeping bentgrass putting green.

The researchers at Maryland studied the effects of three different coring regimes: (1) spring-only (late April) with cores removed, followed by sand topdressing to fill the holes; (2) spring + summer coring (three times in early and late June and late July), with the cores ground and reincorporated into the holes as topdressing; and (3) no coring, no topdressing.

For spring coring, removed cores were 0.5 inch (1.27 cm) in diameter, penetrated to a depth of 3.5 inch (9.0 cm), and were removed at equidistant 2-inch (5.0-cm) spacing. For the summer coring treatment, cores were 0.25 inch (0.64 cm) in diameter, penetrated to a depth of 2 inches (5.0 cm), and had a hole spacing of 1.5 × 2 inches (3.8 × 5.0 cm). The location was a sand-based (97% sand) putting green mowed at 0.156 inch (4 mm), and the study was performed for two years.

Collected data included turfgrass quality, turfgrass color and thatch-mat depth. To further study the effect of accumulated topdressing sand, the researchers also collected loss-on-ignition (LOI) data, where thatch-mat samples were combusted in an oven to ignite organic matter. This allowed for two different calculations: total organic matter content, which was LOI divided by the surface area of the samples; and organic matter concentration, which was the organic matter (weight of the LOI) divided by the dry weight of the cores.

In general, plots that had spring coring or spring + summer coring had better spring color (through May) than the plots that were not cored. Summer coring did reduce color in June and July, and it also reduced turfgrass quality (in year 1, especially), with recovery within two weeks. By the second year of the study, turfgrass quality was typically similar among all treatments.

Plots that were aerified and received topdressing sand or reincorporated cores had thicker thatch-mat layers. Over two years, thatch-mat depth was deepest in the spring + summer treatment (89% increase compared with non-cored), followed by the spring-only coring (66% increase), followed by the non-cored bentgrass. Much of this accumulation occurred between late summer and the following spring. Total organic matter (amount of organic matter per unit area) was less affected by the various treatments and was the same among treatments after two years. However, the concentration (amount of organic matter in a gram of soil) of the organic matter in the non-cored bentgrass was substantially greater than that measured in aerified treatments (211% and 298% greater than in the spring-only and spring + summer treatments).

So why was total organic matter unaffected, but the organic matter concentration substantially changed? Well, when coring was combined with topdressing, the organic matter was diluted by the topdressing sand/reincorporated cores, and concentration was reduced within the thatch layer.

The takeaway message from this work was threefold: (1) measuring only thatch-mat depth can present a misleading picture of organic matter accumulation; (2) spring and spring + summer coring reduced organic matter concentrations; and (3) summer coring created injury, and it should be used with care or avoided, especially on newer stands of bentgrass.

Source: Fu, J., P.H. Dernoeden and J.A. Murphy. 2009. Creeping bentgrass color and quality, chlorophyll content, and thatch-mat accumulation responses to summer coring. Crop Science 49:1079-1087.

Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and president-elect of the Crop Science Society of America. She is a 20-year member of GCSAA.