Sometimes in passing some citified slicker will claim to be working the dirt in his/her garden. I usually smile politely and edge away. Gardens don’t have dirt in them, they have soil. The difference lies not only in the connotation of “dirt” and “soil,” but in what they denote. In a piece in Science News from 2008, Pat Megonigal, a soil scientist, says that dirt is displaced soil. That sounds glib, but really gets to the heart of the matter.
Soil is a complex mixture of small broken up minerals (rocks), water, air and organic matter. The plurality ~45% is mineral. Water and air take up about a quarter each and the remainder is organic matter. Of course this varies tremendously. Some soils are almost entirely air and mineral (desert sands). Some, mucky soils are almost entirely organic matter: like the peaty soils of the Scottish highlands.
The soil texture is determined by the ratio of the various sizes of minerals. The largest pieces are called sand. When put into water this part of the soil will settle out quite quickly. The second largest is silt which will take a little while to settle down. Finally the clays which are small enough that most light microscopes can’t resolve them. Some of these will stay suspended in the water column. The percentages of these various sizes determines a great deal about your soil. How much water can your soil hold on to? Will it retain lots of nutrients?
It is very difficult to change the texture of your soil without adding tremendous amounts of clay, silt or sand. In small scale gardening it is possible, but for farmers it is not feasible. We can add minerals in the form of rock phosphate, green sand and some other amendments. These will add nutrients, but they will not change the soil texture.
The organic matter includes all manner of whatnot. There’re the living microorganisms, the decomposing organisms and the stable humus. Humus is the smallest part of the organic matter and is not readily identifiable as former plant matter with the naked eye. It holds onto nutrients and it is one thing that we can really build in the soil by adding compost.
So a soil actually emerges from many different constituents. It’s affected by the rain, the larger organisms, the climate, and even the slope. This complex beast hosts not just the plants and the charismatic megafauna (that’s not meant to be a slur against Mitt Romney), but the soil bacteria. A recent paper in PLoS Computational Biology claims that there are 5000 or so species in just a half gram of soil from Minnesota. Each of these would be represented by thousands of individuals.
When a bit of soil is removed from its milieu it is dirt. Even if a shirt can become soiled, it does not have soil on it: it is covered in dirt.
Sometimes some citified slicker will claim to be working the dirt in his/her garden. I usually smile politely and edge away. Gardens don’t have dirt in them, they have soil. The difference lies not only in the connotation of “dirt” and “soil,” but in what they denote. In a piece in Science News from 2008, Pat Megonigal, a soil scientist, says that dirt is displaced soil. That sounds glib, but really gets to the heart of the matter.
Soil is a complex mixture of small broken up minerals (rocks), water, air and organic matter. The plurality ~45% is mineral. Water and air take up about a quarter each and the remainder is organic matter. Of course this varies tremendously. Some soils are almost entirely air and mineral (desert sands). Some, mucky soils are almost entirely organic matter: like the peaty soils of the Scottish highlands.
The soil’s texture is determined by the ratio of the various sizes of minerals. The largest pieces are called sand. When put into a water-filled beaker this part of the soil will settle out quite quickly. The second largest is silt which will take a little while to settle down. Finally the clays which are small enough that most light microscopes can’t resolve them. Some clay will stay suspended in the water column indefinitely (it’s colloidal!). The percentages of these various sizes determines a great deal about your soil. How much water can your soil hold on to? Will it retain lots of nutrients? Sandy soils are droughtier and hold fewer nutrients. Clay soils hold water and nutrients, but tend to be quite dense.
It is very difficult to change the texture of your soil without adding tremendous amounts of clay, silt or sand. In small scale gardening it is possible, but for farmers it is not feasible. We can add minerals in the form of rock phosphate, green sand and some other amendments. These will add nutrients, but they will not change the soil texture.
The soil’s organic matter includes all manner of whatnot. There’re the living microorganisms, the decomposing organisms and the stable humus. Humus is the smallest part of the organic matter and is not readily identifiable as former plant matter with the naked eye. It holds onto nutrients and it is one thing that we can really build in the soil by adding compost.
So a soil actually emerges from many different constituents. It’s affected by the rain, the larger organisms, the climate, and even the slope. This complex beast hosts not just the plants and the charismatic megafauna (that’s not meant to be a slur against Mitt Romney), but the soil bacteria. A recent paper in PLoS Computational Biology claims that there are 5000 or so species in just a half gram of soil from Minnesota (just imagine what soil from a warmer climate would be like). Each of these would be represented by thousands of individuals.
When a bit of soil is removed from its milieu it is dirt. Even if a shirt can become soiled, it does not have soil on it: it is covered in dirt. Don’t treat your soil like dirt and it’ll reward you.
