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Soil texture

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Photo: Jardin botanique de Montréal (Lise Servant)  

Soil texture refers to the size and proportion of the mineral particles in the soil. Specifically, it refers to the relative percentages of sand, silt and clay.

Sand is the largest of these three particles. It is easily visible with the naked eye. Clay, on the other hand, is much finer (you need an electron microscope to see the particles). Silt falls between the two extremes.

Depending on the proportion of each type of mineral, soils can be divided into four groups: sandy soils, silty soils, clay soils and loams. Each group has distinct features.

Sandy soils (light soils, yellow soils)

Sandy soils consist mainly of coarse sand. Soils of this type are easy to work and warm up quickly in spring. They are well aerated and have good drainage, but are subject to leaching (of water and minerals). They are usually lacking in nutrients and tend to be acidic.

Silty soils

Silty soils consist mainly of fine sand and silt. Rain and watering tend to form a crust on the surface of this type of soils, making it impossible for water and air to penetrate. They also compact very easily, suffocating the plants’ roots and the organisms in the soil.

Clay soils (heavy soils, clayey soils)

Clay soils contain over 25% clay. These are usually rich soils with good water- and nutrient-retention properties. However, they are poorly aerated and drained and tend to be alkaline. In addition, they are difficult to work, slow to warm up in spring and easily compacted.

Loams (loam, loam soils, average soils)

Loam soils contain about 40 to 60% sand, 30 to 50% silt and 15 to 25% clay. These are excellent soils for growing plants, because they are well balanced in terms of aeration, drainage and water and nutrient retention. They are also highly fertile. These soils are suited to growing most plants.

Most soils in Quebec are clay or sandy; silty or loam soils are fairly rare.

The defects in sandy, clay and silty soils can be corrected by improving the soil structure and adjusting the pH, as necessary. If you have loam, it is important to maintain or improve your soil by regularly adding organic matter.

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