Turf talk -- 'California' vs. USGA greens

We're in the planning stage of a new course, and we're strongly considering building the greens in "California style" What are the differences between the USGA profile and the California profile?

Ongoing research at Ohio State University (OSU) is beginning to reverse several myths about the differences between these two subsurface profiles. "There's a lot of things that we found from that research that surprised me," says Ed McCoy, Ph.D., an OSU soil scientist.

McCoy found that water drains much faster and more completely from the USGA profile than from the single-layer California-style green when identical materials were used in the single-layer green and in the upper layer of a USGA-style green.

Both styles of greens have drainage pipes beneath them. But in the USGA-style green, a layer of fine gravel is sandwiched between the drain works and the overlying layer of growing media (sand mixed with organic matter).

This layer of gravel has long been credited with creating a "perched water table" in the overlying growth media. In fact, the overlying root zone layer merely holds moisture for plant use after excess water has drained away through the gravel.

The belief in a "perched water table" has persuaded many experts to suspect that USGA-style greens drain less completely than single-layer greens. But McCoy's research says otherwise. Forty-eight hours after water was applied to experimental greens, the California-style root zone contained substantially more water than the USGA root zone and would have required at least another 48 hours to drain as thoroughly, McCoy says.

"Water has to follow a much longer pathway to leave the root zone of a California green than it does in the USGA green," he explains. Water only needs to move downward to the gravel layer to drain from a USGA green. It must move sideways toward a drainage tile to leave a California-style root zone.

Ironically, this water movement in a California-style green profile is more representative of what happens in perched water tables occurring in nature. Geologists define a perched water table as water-saturated soil or sand overlying a less-permeable layer of clay or bedrock above the main water table, according to Nathan Myers, a U.S. Geological Survey hydrologist in Lawrence, Kan. By flowing sideways to get past the less-permeable layer, water from a natural perched aquifer drains to the main aquifer deeper underground, he says.

When moist or wet soil overlies a drained gravel layer (as in a subsurface USGA green profile), "it would be difficult to develop a water-table condition," Myers explains.

McCoy's work continues, funded by GCSAA and the USGA. Meanwhile, the question of which green profile to use remains a judgment call.

"You could build a California green that would drain as well as a USGA green," McCoy says, but the California green would need a more permeable root zone mix, which would probably require the builder to use little or no organic matter in the root-zone mix. On the other hand, the USGA's gravel layer can add substantial costs to greens construction.

-- Mark Kind, GCM technical editor

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