This illustration from the Soil Science Society of America clearly shows the major differences in soil structure. As gardeners, we can learn from this and begin to understand what challenges or benefits these soil structures might offer us.
Because particles of soil are so small or they seem small, it is hard for most of us to visualize, let alone understand, the importance of soil structure. Those structural elements in our everyday lives don't quite work to explain soil structure.
Soil structure is not quite a skeleton, upon which other elements are hung or attached.
Soil structure is not quite a framework that we would recognize in a building under construction.
Soil structure is not truly fixed or unchangeable. In fact it can change in response to some forces. Natural forces are the action of soil insects and other life forms and plant roots, erosion, water action and gravity. Other forces are compaction by vehicles, foot traffic and similar activities.
Granular texture (think cookie crumbs) is found in the first several inches of soil. This is the root zone, the rhizosphere, the zone of greatest bacterial and micro-organism activity. The cookie crumb configuration is paradise for fine plant roots and bacterial and other microscopic life forms. Water film can coat the 'crumbs'; roots can wander through the 'crumbs'; air and other gases can move through this soil with ease.
As gardeners, we love this soil structure. We know that soil with good structure can be enhanced with regular additions of compost (worked into the soil) and mulch (on the surface of the soil).
Blocky or angular blocky soil structure has faces (or sides) that intersect at sharp angles. There is space between particles for water film and the movement of gases. This photo (left) should be frighteningly familiar to many of us.
As gardeners, we know this soil structure could be improved by some compost to help the soil retain moisture and provide a more robust environment for soil micro-organisms.
Prismatic soils are those that are vertically elongated and usually have flat tops. Soils with this sort of structure are normally found at depths and are not usually associated with surface soil structures.
Columnar structure (photo left), even though it is a feature of arid soils, is not one that most home gardeners in this are would have to deal with.
As Black Hills gardeners, we would have little chance of facing the challenge of these soils.
Platy soil structure is one we know well, for this flat and laminated form is the structure of our clays. The platy (or plate-like) structure makes the movement of water, air, plant roots, and soil organisms very difficult. Additionally clays can be very complex chemical and electrical substances.
An ion is a particle that is electrically charged (positive or negative) and a cation (pronounced cat - ion) is a positively charged ion.
Clay soils are often nutrient-rich, holding those nutrients in a tight, electrical embrace and releasing them very slowly.
As gardeners we appreciate the nutrient giving potential of our clays and know that the method for encouraging this to happen is to amend the clay soils with humus-rich compost and keep the soil covered with mulch. Rain water, percolating through the organic mulch and compost creates a dilute humic acid which in turn relaxes the electrical bonds between the clay plates. Once there is organic material in and on the soils, the soil micro-organisms become active, further improving the soil.
Single grained or sandy soil is described as each grain by itself. Lacking organic material and form, this sort of soil could not support plants or any degree of soil micro-organisms.
As gardeners, we know that even though these discrete grains of sand give the illusion of "loosening" another soil - for example, clay, this is the worst sort of application. Clay plus sand is concrete. This is not a good choice for a gardener to make when trying to "improve" the soil.
In this area, the first and best response to challenged soil is the addition, by digging in, of well-aged compost and the regular applications of surface mulch.
SOIL IS A LIVING, BREATHING ENTITY. SOIL IS A PROCESS, NOT A PRODUCT. SOIL CREATION TAKES TIME. SOIL MAINTENANCE AND NURTURE IS A CONTINUOUS PROCESS.