Particulate organic matter

Particulate organic matter (POM, macroorganic matter, or coarse fraction organic matter) is defined as soil organic matter between 0.053 mm and 2 mm in size.[1][2] Isolated by sieving, this fraction includes partially decomposed soil detritus and plant material, pollen, and other materials.[3][4] Consistent sieving is important when determining POM content because isolated size fractions will depend on the force of agitation [2]

POM is readily decomposable and serves many soil functions. It is a source of food or energy for soil organisms and nutrients for plants. POM also enhances soil structure leading to increased water infiltration, aeration and resistance to erosion [3][5] Soil management practices, such as tillage and compost/manure application, alter the POM content of soil and water.[3][4]

Role in soil function

The decomposition of POM provides energy and nutrients. Nutrients not taken up by soil organisms may be available for plant uptake.[4] The amount of nutrients released (mineralized) during decomposition depends on the biological and chemical characteristics of the POM, such as the C:N ratio.[4] In addition to nutrient release, decomposers colonizing POM play a role in improving soil structure.[6] Fungal mycelium entangle soil particles and release sticky, cement-like, polysaccharides into the soil; ultimately forming soil aggregates [6]

Effect of soil management

Soil POM content is affected by organic inputs and the activity of soil decomposers. The addition of organic materials, such as manure or crop residues, typically results in an increase in POM.[4] Alternatively, repeated tillage or soil disturbance increases the rate of decomposition by exposing soil organisms to oxygen and organic substrates; ultimately, depleting POM. Reduction in POM content is observed when native grasslands are converted to agricultural land.[3] Soil temperature and moisture also affect the rate of POM decomposition.[4] Because POM is a readily available (labile) source of soil nutrients, is a contributor to soil structure, and is highly sensitive to soil management, it is frequently used as an indicator to measure soil quality.[5]

Surface water contamination

In poorly-managed soils, particularly on sloped ground, erosion and transport of soil sediment rich in POM can contaminate water bodies.[5] Because POM provides a source of energy and nutrients, rapid build-up of organic matter in water can result in eutrophication.[6] Suspended organic materials can also serve as a potential vector for the pollution of water with fecal bacteria, toxic metals or organic compounds.

References

  1. ↑ Cambardella, C. A.; Elliott, E. T. (1991). "Particulate soil organic-matter changes across a grassland cultivation sequence.". Soil Science Society of America Journal. 56 (3): 777–783. doi:10.2136/sssaj1992.03615995005600030017x.
  2. 1 2 Carter, M. R. (1993). Soil Sampling and Methods of Analysis. CRC Press.
  3. 1 2 3 4 Brady, N. C.; Weil, R. R. (2007). The nature and properties of soils (11th ed.). Upper Saddle River, NJ: Prentice-Hall Inc.
  4. 1 2 3 4 5 6 Gregorich, E. G.; Beare, M. H.; McKim, U. F.; Skjemstad, J. O. (2006). "Chemical and biological characteristics of physically uncomplexed organic matter". Soil Science Society of America Journal. 70 (3): 975–985. doi:10.2136/sssaj2005.0116.
  5. 1 2 3 "Particulate Organic Matter". Soil quality for environmental health. NRCS.
  6. 1 2 3 Six, J.; Bossuyt, H.; Degryze, S; Denef, K (2004). "A history of research on the link between (micro) aggregates, soil biota, and soil organic matter dynamics". Soil and Tillage Research. 79 (1): 7–31. doi:10.1016/j.still.2004.03.008.
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