June 1994 - Volume I, Issue 6

Root Zone Mixtures:
USGA Guidelines for Greens

David M. Kopec, Extension Turfgrass Specialist

The April Newsletter contained guidelines for the revised USGA greens specifications for GRAVEL and the INTERMEDIATE (choker) layer, which lies between the gravel and the rootzone. Remember: the intermediate layer can be eliminated if and only if the gravel meets specific size requirements and is used with the appropriate rootzone sand mix.

In this issue, the new revised SAND ROOTZONE specifications are listed, along with physical properties that are set within limits for good rootzone performance.

Revised Particle Size Distribution for USGA Rootzone Mix

Material Size Recommendation
Fine Gravel 2.0 - 3.4mm Preferably none. Not more than 3% of the total particles in this range.

Very Coarse Sand 1.0 - 2.0mm Not more than 10% of total particles, which would include up to the 3% max fine gravel.

Coarse Sand 0.5 - 1.0mm Minimum of 60% of total

Medium Sand 0.25 - 0.50mm particles fall in this range.

Fine Sand 0.15 - 0.25mm Not more than 20% of the particles may fall in this range.

Very Fine Sand 0.05 - 0.15mm Not more than 5%.

Silt 0.002 - 0.05mm Not more than 5%.

Clay less than 0.002 Not more than 3%.

(All three of these should not exceed 10%)

Organic Amendments:
For organic amendments, the material (most often used is peat) must have an organic matter content of 85% by weight as determined by loss on ignition (ASTM D 2974-87-Method D).

Other organic sources like rice hulls and finely ground bark are acceptable if composted through a thermophilic stage (composted and rotated with moisture for natural heat generation), followed by a mesophyllic stabilization phase, and the approval of a soil testing laboratory. Composts should be aged for 1 year. I say, stick with the peat -- it's to easy to get in trouble using other materials.

Furthermore, the rootzone mix with the compost as the organic amendment must meet the physical properties as defined in the revised recommendations.

Other Inorganic or Additional Amendments:
Polyacrylamide or starch gels and most reinforcement materials are not recommended at this time for USGA rootzone mixes.

Lastly, the physical properties (which are performance related measures) for the revised rootzone mix are listed below.

Physical Characters of Revised USGA Rootzone Mix

Property Recommended Range
Total porosity 35% - 55%

Air filled porosity (40cm tension) 15% - 30%

Capillary porosity (40cm tension) 15% - 25%

Saturated Conductivity

Normal: 6-12 inches/hr (15-30cm/hr)

*Accelerated: 12-24 inches/hr (30-60cm/hr)

O.M. content by weight 1% - 5% (ideally 2% - 4%)

* Accelerated range= Extreme use conditions where water quality is poor (leaching fractions are high due to salts in the water), or a cool season turfgrass species is grown out of it's range of adaptation.

This concludes the series on the revised USGA specifications. If you would like more detailed guidelines which include information on drainage, lab testing guidelines, top mix placement and smoothing, seed bed preparation, as well as information provided in this and the April Newsletter, contact David Kopec at the University of Arizona, Room 303, Bldg. 36, Tucson, AZ, 85721. Phone: 321-7785.

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