Many books about gardens, crops, and pastures refer to soil and soil types. After all, soil type is a key piece of the farming equation, one that will affect many of your practices.
So perhaps a few definitions are in order.
Of course, we could get really scientific about this and delve into the nuances of soil composition, detailing every slight variation. But since an understanding of all the fine distinctions isn’t absolutely crucial to success in stewarding the soil, we’ll just cover the basics: sand, silt, clay, and loam. The first three of these are classified by particle size.
Of the various soil types, sand is the coarsest, the individual particles ranging in size from about 0.05 mm all the way up to 2 mm. Consequently, if you pick up a pinch of sand between your fingers, it will feel gritty.
Because sand particles are so large, there is a lot of space between them, which allows water to pass through easily. Sandy soils, therefore, drain well—sometimes a little too well. To help retain some moisture in the soil, gardening experts often recommend adding organic matter, such as compost or mulch, to the soil. Organic matter acts like tiny sponges wedged between the particles of sand, capturing and holding water as it flows through.
Silt ranks between sand and clay in particle size, the particles ranging from 0.002 to 0.05 mm. A pinch of silt rubbed between the fingers often feels like flour.
Silt tends to be fertile and generally makes a better soil for most garden and field crops than either sand or clay. However, because the particles in silt are smaller than those in sand, they are more prone to compaction. When the particles are pressed tightly together, water cannot drain out of the soil easily and may drown the roots of the plants. Organic matter is the cure for this situation because it will separate the particles and allow better drainage.
Clay particles are even finer than silt particles, measuring less than 0.002 mm in size. One of the key characteristics of clay is the ease with which it compacts. This is the soil a toddler would have the best luck with if he had a mind to make mud pies.
Since clay compacts so easily, water has a very difficult time passing through and draining out of the soil. This can result in a very waterlogged garden or field after a heavy rain. Once again, organic matter helps by separating the particles.
Ah, now we come to the soil that every farmer and gardener wants—loam. Loam is a mixture of sand, silt, and clay in various proportions, and it usually contains enough organic matter to provide fertility and an ideal texture for growing plants, as well. A handful of loam feels soft and crumbly.
Loam generally has all of the strengths of its constituent parts without their weaknesses. It holds water better than sand, but drains better than silt and clay. Loam also tends to be very fertile. Its main requirement is wise stewardship. Compaction should be avoided, and the organic matter should be replenished frequently as it is used up by plants.
Some Final Thoughts
Obviously, then, loam is the easiest soil to care for, but don’t worry if your spadeful of dirt turns out to be one of the other three. Sand, silt, and clay can all be improved with time and organic matter. Organic matter is the key to creating and maintaining a good soil, no matter what category the particles fall into.