Putting Green Organic Matter Calculator

This putting green organic matter calculator projects how organic matter in the top 100 mm of a sand-based green will change over 30 years. Organic matter in the top 20 mm decides how firm a green plays and how much water it holds. Knowing where it is heading lets you set a sand and coring program on numbers rather than habit.

What you need

First, you need loss-on-ignition (LOI) results for each 20 mm band to 100 mm. You also need the month you took the cores, your topdressing depth and months, and your coring details. For climate, the calculator uses long-term Bureau of Meteorology averages for seven Australian capitals. Alternatively, you can enter your own monthly temperatures.

What it tells you

The calculator shows organic matter by depth today and in future years. It also plots a monthly projection for each band and totals the sand your program applies each year. Finally, it works out the topdressing needed to bring the top 20 mm to your target. You can name your club, add each green you tested and compare them side by side. Then print one green or every green as a PDF report.

Screened or whole-sample LOI

A standard soil test sieves the sample to 2 mm before ignition, which removes most roots, thatch and mat. In contrast, whole-sample testing ignites everything, so it reads higher from the same core. For this reason, tell the calculator which method your lab used. Then calibrate only against an earlier test that your lab ran the same way.

Where the model comes from

Dr Ed McCoy (The Ohio State University) and Jeff Broadbelt (DryJect) developed the original organic matter management tool. Gilba Solutions adapted it for 20 mm sampling bands to build this putting green organic matter calculator. However, its default rates come from Ohio. So treat an uncalibrated projection as a direction of travel, and calibrate it against an earlier test from the same green.

Want a test and a program that fits your own greens? Gilba Solutions offers independent soil testing and agronomy services for golf and bowling greens. Talk to Jerry Spencer, principal agronomist, or read more on greens management in the Gilba turf blog.