What Can Dissolve the Minerals in Soil?

Minerals Defined

• In the context of soil science, "mineral" refers to any plant nutrient that comes from the soil rather than from the atmosphere. In gardening discussions, though, "mineral" is sometimes used in reference to the nutrients typically supplied by rock-based amendments such as greensand, rock phosphate and granite dust. This informal usage might exclude nutrients like potassium, which is abundant in most soils, and nitrogen, which can be obtained from the atmosphere by leguminous cover crops.

Weathering

• The minerals within rock particles are not readily available to plants. The process of weathering slowly dissolves these rock particles; as a result, the mineral nutrients are transformed into soluble substances that can be absorbed by plant roots. This process occurs very slowly when soil is first being created from parent rock materials, but it can occur much more quickly in fertile, biologically active soil. There are two general types of weathering: chemical and physical.

Physical Weathering

• Only certain types of physical weathering are relevant to the soil in an established garden. Abrasion refers to any physical process that grinds up rock particles. Gardeners can benefit from this type of weathering by choosing mineral amendments ground into very small particles. Heat also contributes to weathering, so you should maintain good drainage and aeration in garden soil because these qualities help soil warm up more quickly in the spring.

Chemical Weathering

• Chemical weathering is the primary way to make minerals biologically available. Acidic substances in the soil can actually dissolve rock materials, so acids are essential to obtaining the nutrients from existing soil minerals and from mineral amendments. For example, carbonic acid and humic acid are produced through the decomposition of organic matter, and these substances help make mineral nutrients more soluble. Earthworms can also be considered a form of chemical weathering, because they leave behind castings that contain more available minerals than ordinary soil.