Rootzone Amendments

The 2004 USGA recommendations for putting green construction allow for a wide variety of potential amendments for sand-based rootzones. Specifically mentioned as acceptable rootzone amendments are peat, compost, and porous inorganics. The recommendations also include guidelines for determining acceptability of these amendments.1

This newsletter is the first of a two part series on rootzone amendments. This first part will discuss organic amendments and the second part will cover inorganic amendments.

With these newsletters, we hope to provide some general insight into how the various amendments affect the performance of rootzone mixes. We will not be directly comparing the various amendments. We also will not discuss cost of the various amendments. Most importantly, we are not trying to show favoritism towards any particular type or brand of product. We are trying to present some information on what might be expected when adding the various amendments to sand-based rootzones.

Sand based rootzones have properties that are advantageous for high performance turf. These rootzones resist compaction and most often provide desirable internal drainage characteristics.

Amendments are added to sand based rootzones to improve other physical performance characteristics of the rootzone. This “improvement” in performance will mean something different depending upon the project goals. However, it is generally true that amendments provide increased water and nutrient retention. This is critical because straight sand is characteristically deficient in these areas.

Peat is probably the amendment that has been most frequently used in golf and sports turf rootzones. Peat for rootzones is roughly divided into two types: Reed Sedge and Sphagnum. Reed sedge peat comes from bogs that are composed of herbaceous peat plant materials (reeds, sedges, grasses). Sphagnum peat is harvested from bogs that contain decomposed sphagnum moss.

After peat is harvested from the bogs, it is screened, graded, and prepared for storage or shipment. It is important to use peat that has been specially graded for turfgrass rootzones. Rootzone grade peat is typically finer than horticultural grade. Finer peat blends more uniformly with sand and helps to fill pore spaces.

There are four or five different peat suppliers that are most often used for golf and sports rootzone mixes. While these suppliers may have different types of peat, they are all graded for turf grass rootzone use.

For most sands, either sphagnum or reed sedge peat can be used to prepare quality rootzone mixes. Blending peat in to the rootzone will typically lower the infiltration rate and increase the water holding versus straight sand. Peat also functions as a binder to help the stability of the rootzone. The amount of peat blended into the rootzone will vary depending upon the gradation of the sand, the peat used, and the project needs. Most blends range from 5% to 20% peat by volume. In general, higher peat contents will result in lower perc rates and higher capillary porosities.

Compost arises from decaying organic matter. Sources of compost that we have used in mixes vary from municipal waste to pine bark to earthworm castings, and several others.

Only mature composts (fully decomposed) should be used in rootzone mixes. Raw compost or actively decomposing compost should be avoided due to the potential for burning the turf. Composts that vary in composition from lot to lot should also be avoided.

Different types of compost can have drastically different performance characteristics. Mixes with finer composts, such as worm castings, will typically decrease infiltration rates and increase capillary porosity (similar to peat mixes). Mixes with coarser composts may raise infiltration rates and lower capillary porosity.

Prior to selecting an amendment, it should be tested by a qualified, independent laboratory. Organic amendment qualification testing usually involves determining the organic content and moisture content. Additional testing can include particle size determination, pH, and conductivity. Composts are also tested for maturity.

Preparation and testing of lab mixes prior to rootzone blending is recommended. Lab mixes, using potential sands and amendments, provide support for rootzone material selection, and guidelines for determining optimum sand -amendment mix ratios.

In the lab the organic content of rootzone mixes is determined on a dry weight basis. In the field the organic content of these same mixes is usually expressed on a volume basis. To properly convert from % organic matter (dry wt.) to % organic matter (vol.) several parameters must be known, including, % moisture of sand & peat, bulk weight and organic content of peat, and a few others. In lieu of giving a convoluted calculation, the tables below provide some estimates that can be used for converting between dry weight and volume.

Sand/Peat Ratio (V/V)	% Organic Matter (dry wt.)	Sand/Peat Ratio (V/V)	%Organic Matter (dry wt.)
95/5	0.3 - 0.7	95/5	0.15 - 0.3
90/10	0.7 - 1.2	90/10	0.3 - 0.6
85/15	1.2 - 1.7	85/15	0.6 - 0.9
85/15	1.2 - 1.7	80/20	0.8 - 1.2

In 2004 the USGA Recommendations For a Method of Greens Construction were revised to include porous inorganics as an acceptable amendment for rootzone mixes. ”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.”1

Although inorganic amendments were only recently approved by the USGA, these products have been used for golf & sports turf rootzone mixes for many years. Inorganic amendments are typically used to reduce rootzone compaction (lower bulk density), increase infiltration rate, and/or increase the water and nutrient holding of rootzone materials.

In general, sand and inorganic amendment mixes are prepared by volume additions. As with organic amendments, inorganics are not one size fits all. Typical rootzone mix ratios range from 95/5 to 80/20 Sand/Amendment. The proper volume ratios for any particular project will be dependent upon the sand and amendment being utilized, the desired usage, and the project specifications or desired outcome. We strongly recommend lab testing to determine optimum mix ratios.

Calcined Clays are mined from porous clay deposits. The material is crushed and screened into various particle sizes. The clay is then calcined (rotary kiln fired at very high temperatures). Various grades (based on particle size distribution) of calcined clays are available for use in rootzone mixes.

Calcined clays are the inorganic amendment that our lab has most often been asked to use in rootzone mixes. In our experiences the addition of porous ceramics typically results in an increase in infiltration rate, total porosity, capillary porosity, and nutrient retention. Due to the high infiltration rates, these type of amendments are often used when it is desired to remove excess salts from a soil.

A diatom is a unicellular organism that is surrounded by a porous silica shell. When diatoms die the remaining shell becomes diatomaceous earth. Calcined diatoms are kiln fired to create a stable porous material. Adding calcined diatomaceous earth to sand-based rootzones typically results in increased porosities, infiltration rates and nutrient retention (similar to calcined clays).

Zeolites are naturally occurring, porous materials. There are many different zeolites with diverse physical performance characteristics. When added to sand-based rootzone mixes, some zeolites increase infiltration rate and porosities. Other zeolites decrease infiltration rate but increase capillary porosity (similar to some organic amendments).

When selecting inorganic amendments, it is important to select an amendment grade (size of particles) that complements the sand. Coarser grades of inorganics will usually result in higher infiltration rates and lower capillary porosities than finer grades. Thus coarser amendments are often used with fine sands, and finer amendments with coarse sands.

Testing to determine performance of any given sand and amendment mix should be an integral part of the amendment selection process. Lab mixes, using potential sands and amendments, provide support for rootzone material selection and guidelines for determining optimum sand and amendment ratios. Determination of optimum mix ratios can provide information needed to properly compare the costs of different amendments.

Turf Diagnostics & Design has the analytical tools and the expertise to evaluate rootzone amendments and mixes. We can also help you to create mixes that meet your specific project needs. Please contact us if we can help.

Send mail to turfdiag@turfdiag.com with questions or comments about this web site. Copyright © 2005

Send mail to turfdiag@turfdiag.com with questions or comments about this web site.
Copyright © 2005