David M. Kopec, Extension Turfgrass Specialist
The USGA putting green specifications have been revised, after careful research by Dr. Norm Hummell and the USGA. One of the changes relates to one of the most argumentative issues about USGA greens in general. This issue centers around the intermediate sand layer (choker layer), which acts as an intermediate barrier between the rootzone and gravel drainage layer. The whole idea of a USGA green is to provide the turf with a large and deep enough "pot" to regulate moisture holding capacity, drainage and infiltration... all at the same time.
The changes and relative sizes of particles (of both the sand and the gravel) affect the moisture holding capacity and drainage, as a function of pore space. The changes in pore space at the interface layers determines largely the properties the rootzone sand has.
These relationships have been now been defined for construction of new greens both WITH or WITHOUT the intermediate (choker) layer.
CONSTRUCTION INCLUDING GRAVEL
DRAINAGE LAYER PLUS INTERMEDIATE LAYER
1. The intermediate level should be uniformally installed to a thickness of between 2 - 4 inches.
2. Make sure the surface of each layer conforms to the contours of the proposed finish grade. In otherwords, don't change the depth of materials to make them "level", if the playing surface of the green itself will not be level.
When both the intermediate layer and gravel are used, the guidelines are as follows for recommended particle size(s).
REVISED USGA PARTICLE SIZE DESCRIPTION OF GRAVEL
AND INTERMEDIATE (CHOKER) LAYER MATERIALS
(using intermediate layer) Particles are not more than 10% greater than 1/2" (10 mm)
At least 65% of the particles should be between 1/4" (6 mm) and 3/8" (9 mm)
Not more than 10% of the particles less than 2 mm
Intermediate Layer: At least 90% of the particles between 1 mm and 4 mm
There are about 25 mm in one inch. Next months issue will contain the revised updates on size recommendations for gravel when an intermediate (choker) layer is not used.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.