The physical properties of soil, in order of decreasing importance for ecosystem services such as crop production, are texture, structure, bulk density, porosity, consistency, temperature, colour and resistivity.[1] Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand, silt, and clay. At the next larger scale, soil structures called peds or more commonly soil aggregates are created from the soil separates when iron oxides, carbonates, clay, silica and humus, coat particles and cause them to adhere into larger, relatively stable secondary structures.[2] Soil bulk density, when determined at standardized moisture conditions, is an estimate of soil compaction.[3] Soil porosity consists of the void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining. Resistivity refers to the resistance to conduction of electric currents and affects the rate of corrosion of metal and concrete structures which are buried in soil.[4] These properties vary through the depth of a soil profile, i.e. through soil horizons. Most of these properties determine the aeration of the soil and the ability of water to infiltrate and to be held within the soil.[5]
| Property/behavior | Sand | Silt | Clay |
|---|---|---|---|
| Water-holding capacity | Low | Medium to high | High |
| Aeration | Good | Medium | Poor |
| Drainage rate | High | Slow to medium | Very slow |
| Soil organic matter level | Low | Medium to high | High to medium |
| Decomposition of organic matter | Rapid | Medium | Slow |
| Warm-up in spring | Rapid | Moderate | Slow |
| Compactability | Low | Medium | High |
| Susceptibility to wind erosion | Moderate (High if fine sand) | High | Low |
| Susceptibility to water erosion | Low (unless fine sand) | High | Low if aggregated, otherwise high |
| Shrink/Swell Potential | Very Low | Low | Moderate to very high |
| Sealing of ponds, dams, and landfills | Poor | Poor | Good |
| Suitability for tillage after rain | Good | Medium | Poor |
| Pollutant leaching potential | High | Medium | Low (unless cracked) |
| Ability to store plant nutrients | Poor | Medium to High | High |
| Resistance to pH change | Low | Medium | High |
- ^ Gardner, Catriona M.K.; Laryea, Kofi Buna; Unger, Paul W. (1999). Soil physical constraints to plant growth and crop production (1st ed.). Rome, Italy: Food and Agriculture Organization of the United Nations. CiteSeerX 10.1.1.466.9332. Archived (PDF) from the original on 8 August 2017. Retrieved 1 May 2022.
- ^ Six, Johan; Paustian, Keith; Elliott, Edward T.; Combrink, Clay (2000). "Soil structure and organic matter. I. Distribution of aggregate-size classes and aggregate-associated carbon". Soil Science Society of America Journal. 64 (2): 681–89. Bibcode:2000SSASJ..64..681S. doi:10.2136/sssaj2000.642681x. Retrieved 1 May 2022.
- ^ Håkansson, Inge; Lipiec, Jerzy (2000). "A review of the usefulness of relative bulk density values in studies of soil structure and compaction" (PDF). Soil and Tillage Research. 53 (2): 71–85. Bibcode:2000STilR..53...71H. doi:10.1016/S0167-1987(99)00095-1. S2CID 30045538. Archived (PDF) from the original on 22 October 2017. Retrieved 1 May 2022.
- ^ Schwerdtfeger, William J. (1965). "Soil resistivity as related to underground corrosion and cathodic protection" (PDF). Journal of Research of the National Bureau of Standards. 69C (1): 71–77. doi:10.6028/jres.069c.012. Retrieved 1 May 2022.
- ^ Tamboli, Prabhakar Mahadeo (1961). The influence of bulk density and aggregate size on soil moisture retention. Ames, Iowa: Iowa State University. Retrieved 1 May 2022.
- ^ Brady, Nyle C. (1984). The nature and properties of soils (9th ed.). New York, New York: Collier Macmillan. ISBN 978-0-02-313340-4. Retrieved 8 May 2022.