Soil Mineralogy

Soil mineralogy is closely related to soil fertility. Differences in soil mineralogy cause great differences in soil fertility. For instance, moderately weathered clays attract and retain greater amounts of nutrients than highly weathered clays and oxides. Though volcanic ash inherently has a low ability to hold nutrients, it interacts with organic matter to produce very fertile soils. Knowledge of mineralogy helps to determine the appropriate nutrient management strategy for your soil.

In our discussion on soil texture and structure, we mentioned that the very small particles form aggregates. On Maui, the major groups of small particles include silicate clays, organic matter, volcanic ash minerals, and oxides. In fact, this grouping of small particles is also used to describe the distinct categories of soil mineralogy (types of clay minerals).

Soil mineralogy:

• Layered silicate clays
• High activity
• Low activity
• Organic matter
• Volcanic ash material
• Oxides

Soil behavior is greatly influenced by these types of clay minerals and/or the amount of organic matter that a particular soil type contains.

Before discussing differences in soil mineralogy, it is very helpful to understand the concepts of cation and anion exchange capacities (CEC and AEC). CEC and AEC are properties that can help differentiate soil minerals.