Step 4 - The Root Zone Mixture

The sand used in a USGA root zone mix shall be selected so that the particle size distribution of the final root zone mixture is as described in Table 3.

Table 3

PARTICLE SIZE DISTRIBUTION OF USGA ROOT ZONE MIX

Soil Selection:

If soil is used in the root zone mix, it shall have a minimum sand content of 60%, and a clay content of 5% to 20%. The final particle size distribution of the sand/soil/peat mix shall conform to that outlined in these recommendations, and meet the physical properties described herein.

Organic Matter Selection:

Peats - The most commonly used organic component is a peat. If selected, it shall have a minimum organic matter content of 85% by weight as determined by loss on ignition (ASTM D 2974 Method D).

Other organic sources - Organic sources such as rice hulls, finely ground bark, sawdust, or other organic waste products are acceptable if composted through a thermophilic stage, to a mesophilic stabilization phase, and with the approval of the soil physical testing laboratory. Composts shall be aged for at least one year. Furthermore, the root zone mix with compost as the organic amendment must meet the physical properties as defined in these recommendations. Composts can vary not only with source, but also from batch to batch within a source. Extreme caution must be exercised when selecting a compost material. Unproven composts must be shown to be nonphytotoxic using a bentgrass or bermudagrass bioassay on the compost extract.

Inorganic and Other Amendments: Porous inorganic amendments such as calcined clays (porous ceramics), calcined diatomites, and zeolites may be used in place of or in conjunction with peat in root zone mixes, provided that the particle size and performance criteria of the mix are met. Users of these products should be aware that there are considerable differences between products, and long term experience with some of these materials is lacking. It should also be noted that the USGA requires any such amendment to be incorporated throughout the full 12-inch (300 mm) depth of the root zone mixture. Polyacrylamides and reinforcement materials are not recommended.

Physical Properties of the Root Zone Mix: The root zone mix shall have the properties summarized in Table 4, as tested by USGA protocol (proposed ASTM Standards).

Table 4

PHYSICAL PROPERTIES OF THE ROOT ZONE MIX

Related Concerns

IT IS ABSOLUTELY ESSENTIAL TO MIX ALL ROOT ZONE COMPONENTS OFF-SITE. No valid justification can be made for on-site mixing, since a homogeneous mixture is essential to success.

A QUALITY CONTROL PROGRAM DURING CONSTRUCTION IS STRONGLY RECOMMENDED. Arrangements should be made with a competent laboratory to routinely check gravel and root zone mixtures during production and blending. It is imperative that these materials conform to the recommendations approved by the laboratory in all respects.

Care should be taken to avoid overshredding the peat, since it may influence performance of the mix in the field. Peat should be moist during the mixing stage to ensure uniform mixing and to minimize peat and sand separation.

Step 5 - Top Mix Covering, Placement, Smoothing, and Firming

The thoroughly mixed root zone material shall be placed on the green site and firmed to a uniform depth of 12 inches (300 mm), with a tolerance of ± 1 inch (25 mm). Be sure that the mix is moist when spread to discourage migration into the gravel and to assist in firming.

Step 6 - Seed Bed Preparation

Sterilization: Sterilization of the root zone mix by fumigation should be decided on a case by case basis, depending on regional factors. Fumigation always should be performed:

• In areas prone to severe nematode problems.
• In areas with severe weedy grass or nutsedge problems.
• When root zone mixes contain unsterilized soil.

• Check with your regional office of the USGA Green Section for more information and advice specific to your area. (USGA Green Section Staff)

  Step 7 - Fertilization

  Contact your regional USGA Green Section office for establishment fertilizer recommendations and grow-in procedures. (USGA Green Section Staff)

  This document details the recommendations of the USGA Green Section for the construction of golf greens. A great deal more information regarding various construction techniques used to build the USGA green can be obtained from the regional Green Section offices and the Green Section's Construction Education Program.

  The Construction Education Program can be reached at the following address: