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Table 1

Plant Available Water Capacities (AWC) for Textural Classes in Montana

Soluble salts and gravel will decrease plant available water capacity. Organic matter and good soil structure will increase it. Capacity increases about 0.1 inches per foot for each 1% organic matter. Soils with water restricting layers like compacted subsoil, shallow bedrock or stratification can increase plant available water capacity of the overlying layers. Soils that are deep, medium textured and uniform can have decreased plant available water but allow for deeper rooting.

Approved by Soils Committee, Montana State University (MSU), Plant and Soil Science Planning Conference, January 31, 1984.

Table 1
Soil Texture Soil Textural Class Estimated Average Plant AWC (inches per foot)
Sandy Soils Course Texture Sands 0.5
Loamy Soils 1.0
Loamy fine sands
Loamy very fine sands
Fine sands
Very fine sands		 1.25
Loamy Soils Moderate Coarse Texture Sandy loam
Fine sandy loam		 1.5
Medium Texture Very fine sandy Loam
Loam
Silt loam
Silt		 2.0
Moderately Fine Texture Clay loam
Sandy clay loam
Silty clay loam		 2.2
Clayey Soils Fine Texture Sandy clay
Silty clay
Clay		 2.0

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