T. Powell Gaines
Tifton Physical Soil Testing Laboratory, Inc.
Published in Carolinas Newsletter May/June 1992

The USGA elected not to list recommendations for laboratory water permeability rates for a putting green root zone mixture (greensmix) in their last publication. "Specifications for a Method of Putting Green Construction, 1969, USGA". Their reason was that the laboratory infiltration value changes markedly in the field as the green matures.

The previous USGA publication, "Refining the Green Section Specifications for Putting Green Construction, 1983, USGA'., stated that minimum laboratory water infiltration rates for topsoil mixtures should be 2 in./hr. for bermudagrass greens and 3 in/hr. for bentgrass greens, maximum laboratory rates should not exceed 10 in./hr., and rates of 4 to 6 in./hr. are ideal.

As more greensmixes have been developed and analyzed in the laboratory in recent years than ever before, the trend has been for developers of new courses to want higher and higher initial water permeability rates for greensmixes. The initial water permeability rate is the rate of a greensmix before grass is established. Once grass is established the rate should decrease and slowly decline over the years as the green becomes more compacted and organic matter accumulates in the topsoil mixture due to root and thatch decomposition. The initial water permeability rate should be as high as the rate will ever be. The laboratory infiltration rate of a greensmix attempts to simulate the initial water permeability rate of a greensmix on the course before grass is established.

Suggested guidelines our laboratory has used in recent years for maintaining optimum water permeability rates of established greens have been 4 to 8 in./hr. for bermudagrass greens and 8 to 12 in./hr. for bent-grass greens based on previous USGA recommendations and laboratory analysis of existing greens with reference to comments from golf course superintendents on the physical quality of their greens. As pointed out, the initial rate has to be higher than the rate of established greens.

Based on our interpretation of the data that is available to us at the present time, our lab will continue to recommend an initial water permeability rate of approximately 10 to 14 in./hr. for bermudagrass greens and approximately 10 to 14 in./hr. for bentgrass greens. Allowing for a 25 to 50% reduction in water permeability rates due to grassing, organic matter accumulation, and severe compaction, these initial rates should decrease to approximately 4 to 8 in./hr. for established bermudagrass greens and approximately 8 to 12 in./hr. for bentgrass greens. If research in the future determines that these recommended initial rates need to be modified, then they can be adjusted accordingly.

The alternative of determining a water permeability rate of a greensmix without offering any recommendation or guideline pertaining to the results found offers little benefit to those in golf green construction and maintenance. Why run the test if no interpretation can be made of the results?