Soil is defined as the top layer of Earth that allows the growth of plants. All areas have a different soil horizon, and that profile will change over time, and can contain all of the different types of soil discussed in this article. You can find out what your soil horizon is by digging a hole in the ground and then observer the cross sections in that hole.
Permaculture is not about changing one type of soil to another type of soil, but is about creating a top layer of soil, in your soil horizon, that plants will thrive in without having to change the underlying soil profile. BUT, it is very important to know what the soil type is that you are building your permaculture soil on. The underlying soil type will effect the temperature, water drainage, water retention, and the depth of your plants roots. Typing your soil can be very complicated. You will hear people classify soil by color, weight, and other measurements. I hope that this article helps in clarifying some of the different types of soil, and terminology used. Over time as you build your permaculture top layer, the underlying soil horizon will change. It will take years, but eventually the changes you make on the top layer will percolate down to the lower layers of the soil horizon. That is a great side effect of doing permaculture gardening, but it is not the ultimate goal.
According to the Unified Soil Classification system (USCS) there are 5 different types of soils. They include Gravel, Sand, Silt, Clay and Organic. But I would like to add an additional type, and that is of Peat. There are different grades of those types (poorly graded, well-graded, high plasticity, and low plasticity), but I will leave that for another post.
Gravel is composed of rock fragments. These fragments can be in a lot of different sizes. It is pretty easy to identify gravel. There is really not a good test to verify it is gravel besides the look and texture. Because gravel has an inferior ability to retain moisture, nutrients, plant life in gravel soil is more sparse. One advantage to a gravel soil is that it does have a very high water drainage rate, so it can be good for plants that need a dryer root system. But it also does not retain nutrients.
Sand is more granular than gravel is, and is comprised of finely divided rock particles. It is finer than gravel, but is coarser than silt. Water drains rapidly, and also does not store nutrients for plants very efficiently. The nutrients are carried away usually to quickly for plants to be able to use them. You can test to see if your soil is sand by picking some slightly wet sand up. If you try to create a ball with it, it will not form one, will leave particles on your hands, and crumbles easily in your fingers.
Silt is finer than sand, but not as fine as clay. Silt is fine enough that it may also be found in suspension in bodies of water. Silt is usually what makes rivers, and lakes have a dirty look to them. When silt is wet, it will have a slippery feel, but when it dries, it will have a floury feel. Silt drains poorly, and is usually cooler than sand.
Clay has the smallest particles. Clay can be easily molded in your fingers when wet, but when it dries, it becomes hard or brittle. If clay is wet, it forms into balls easily if rolled in your fingers, and feels sticky. Clay soil is cold, and takes time to warm, because it does hold moisture well. Clay also stores nutrients well. The downside is that when clay becomes dry, it becomes very hard and plants have a hard time growing in dry clay.
Organic soil is soil that is primarily made up of matter composed of organic compounds. It usually contains the remains of plans, animals, and their waste products. Organic soil is usually created by the organic matter being broken down by bacterial or fungal action. Soil holds water, and nutrients, giving plants the capacity for growth.
Some people classify peat with organic soil, but I feel it is in a class all of its own, because of how unique it is in its formation. It only forms in peatlands, bogs, and mires. Peat if rolled will not form a ball. It is spongy to touch and will release water if squeezed. Peat can be added to the other types of soil to increase its ability to retain water and nutrients.
So, which soil is the best?
The answer to this question is all of them in a mix. When you have some of all of the soil types mixed, you get what is called Loam. usually the composition is 40%-40%-20% (sand-silt-clay). The best type of soil to plant in is loam with the inclusion of organic matter. This way you get the best combination of draining, nutrients and moisture. But because it is almost impossible to create loam, permaculture may be the answer. It is impractical to create loam on a large scale in most environments. Loam is ideal for starting plants that then can be moved to your permaculture garden.
Loam is considered ideal for gardening and agricultural uses because it retains nutrients well and retains water while still allowing excess water to drain away. A soil dominated by one or two of the three particle size groups can behave like loam if it has a strong granular structure, promoted by a high content of organic matter. However, a soil that meets the textural definition of loam can lose its characteristic desirable qualities when it is compacted, depleted of organic matter, or has clay dispersed throughout its fine-earth fraction.
Loam is found in a majority of successful farms in regions around the world known for their fertile land. Loam soil feels soft and crumbly and is easy to work over a wide range of moisture conditions. [Source]
Besides doing the ball test, as motioned in the different soil types, you can do jar test. The jar test is explained at the end of this document: Soil Types and Testing. It will help you find where your soil fits, if it is sandy, clay, or loam soil.
Below is a video that explains loam a little better, with details on how to mix it.
Soil color can also tell you a lot about the soil, dark soils have high organic matter, aeration, available nitrogen, fertility, and a low erosion factor. Moderately dark soils have medium organic matter, erosion factor, aeration, available nitrogen and fertility. Light soils have low organic matter, aeration, available nitrogen, fertility and a high erosion factor. [Source]
Soil Temperature also has a lot to do with growing plants, and the type of soil you have under your permaculture can effect that as well. For the fastest growth, you want to try to keep your soil temperature at 65-70 degrees F. Above or 85 degrees and below 40 degrees you have no growth, and little to no bacteria or fungi activity.