WHAT IS IT? Particulate organic matter (POM) consists of very small bits of plant and animal residues that have not yet decomposed.
as seen in the picture of POM magnified under a microscope.
WHY IS IT IMPORTANT: Our goal is to identify practices that can help farmers increase POM over the short and longer terms. POM is the active (quick release) soil carbon. Left over from previous seasons, It releases nutrients within the cropping season, as it decomposes. It also contributes to the enhancement of other key indicators of soil health, such as the reduction in soilborne pests and diseases, due to increased microbial diversity, and aggregate stability, which in turn influences a soil’s capacity for rainwater infiltration and storage.
POM is one of the most useful measures for our research since the POM test enable us to clearly visualize differences between healthy (high POM) and unhealthy (low POM) soils. ALSO, POM is readily influenced by farmers soil management practice over the short term. Thus, we expect farmers to see an increase in POM when they grow high biomass legumes, such as lablab or pigeon peas, and other crops that produce a lot of residues that can be recycled back to the soil.
Generally, the larger the amount of POM recovered from a soil, the healthier that soil is going to be. But it is important to understand that soils differ in their ability to accumulate POM. Under the same environmental conditions and management practices, soils with a higher clay content will always accumulate more POM than sandy soils, which lack the small size soil particles (clays) that help protect POM. Factors that increase microbial activity also affect POM build-up. Less POM build up occurs in warmer than cooler environments. Aerating the soil via cultivation reduces POM build up, which is why no-till systems will have higher POM levels than cultivated soils.
Quick Guide: Particulate Organic Matter (POM) TEST – Steve Vanek
Brief Materials:
- Small drink bottle with 2mm holes drilled/ melted
- Sieve bag made of 0.25mm mesh (a small sieve made with a piece of women’s stocking may work)
- Two buckets or deep basins
- Small piece of cloth, 15×15 cm, to catch POM
- Cut cylinder from water or drink bottle and rubber bands, to catch POM
Brief procedure:
- Use a 100g container of dry soil. Remove small stones and larger roots from the sample before filling the container.
- Place bottle with 2mm holes inside mesh ag
- Put soil inside the bottle
- Wash the the bag and bottle combination vigourously in the first bucket of water
- Check that all aggregates or clumps of soil are broken down inside bottle. Use a small stick to break open any aggregates or you will underestimate POM.
- IMPORTANT: Rinse the bag+bottle combination in a second bucket. There should not be much additional clays washed out now.
- Using a wash bottle, transfer the contents of mesh bag to a decanting cup
- You can do a final check in the decanting cup that you are seeing mostly or only sand and organic matter (POM) and not a lot of small aggregates.
- Pouring into a cloth mounted on the end of a plastic cylinder from a small bottle, decant off the floating organic matter.
- Refill as many times as needed to decant off all but the last few grains of POM (shake the decanting cup slightly to enhance separation).
- Remove cloth from end of cylinder. Scrape POM into center of cloth in a single layer.
- Estimate the diameter of circle, in cm, that you can make with the POM and compare to rating chart (below).
Above is the qualitative rating scheme for the POM test.
Amount of POM build up possible varies by soil texture with coarser textured soils having less. Therefore, you may also be able to develop a more local scheme by comparing to local high benchmarks, using amount of POM recovered for local areas of uncultivated land– a hedgerow, perennial grassland, or forest site– for a high level.
If you let it dry, you can keep it as a record to compare to after using soil management practices that increase POM
Materials needed
