Organic matter and screens

A set of OM246 total organic material samples inadvertently got a grinding and sieving process just like normal soil samples.¹ As you probably know, a key distinction of OM246 testing is that soil samples are tested at the lab as is, with no subsampling or screening of the sample.

That grinding process was unfortunate. We couldn’t get normal OM246 values because an unknown quantity of living and dead undecomposed plant material (organic material) had been removed. But we could still use these samples to learn something.

Another set of samples were collected from the same greens. I asked the lab to do the OM246 test on the second set of samples, and also to test the sieved material from the original sample submission so we could measure the amount of material removed by sieving.

For this set of samples, it was a 45% reduction in total organic material at the 0–2 cm depth. At the 2–4 and 4–6 cm depths, there were a 16% and 12% reduction caused by grinding and sieving. There’s a lot more undecomposed living and dead plant material at the 0–2 cm depth.

I’ve written previously about the separation of organic material from samples, or inclusion of that material, but I hadn’t measured it directly quite like this before. I encourage all professional turfgrass managers to be familiar with the information in these posts:

• Organic matter separation from turfgrass soil samples
• Organic matter terminology in turfgrass soils
• A Tale of Two Tests: Why I like to know both humus (a standard soil organic matter test) and total organic material (the #OM246 test), and how I use that information
• All the organic material

For a look at the grinding machine and screens used to process soil samples (this process is not performed on OM246 samples), watch the process in this video.