Page 114 - Nutrient Management Planning Guide

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Chapter 3.4

The CEC of a soil is primarily influenced by soil texture and organic matter content. Among the mineral components of soil, clay particles generally have the highest cation exchange capacity followed by silt and sand (Table 3.4.7).

Table 3.4.7 General Relationship Between Soil Texture and Cation Exchange Capacity

Soil Texture

CEC, Normal Ranges (cmol/kg of soil)

Sand 1–5 Fine sandy loam 5–10 Loams and silt loam 5–15 Clay loam 15–30 Clay 30+

Source: Hausenbuiller 1985

Consequently, CEC increases with increased clay content of soils. The type of clay in soil also has an important impact (Table 3.4.8).

Table 3.4.8 Range of Cation Exchange Capacities of Different Types of Clay

Type of Clay

CEC, Normal Ranges (cmol/kg of soil)

Allophane 100–150 Montmorillonite 60–100 Chlorite 20–40 Illite 20–40 Kaolinite 2–16

Source: Hausenbuiller 1985

Organic matter content of soils also has an important influence on the CEC of soils since it has a CEC range of 100 to 300 cmol/kg of soil. There is potential to increase soil CEC by adopting practices and crop rotations that focus on building soil organic matter content.

Estimating CEC from Soil Texture

Direct measurement of CEC is time consuming and is not part of most basic commercial soil analysis packages. Clay and organic matter are the major soil components that contribute to cation exchange; therefore, it is possible to estimate total CEC of a given soil sample based on the percentage of organic matter and clay content and the CEC estimates of each.

Most soils in Alberta have clays similar to montmorillonite. The contribution of the clay fraction of soils towards CEC would be in the 60 to 100 cmol/kg range.

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