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Have you ever wondered what dirt is made of? The simple answer is that dirt is mixture of a whole lot of “stuff” such as rocks, sand, clay, and organic matter. The characteristics of the dirt in your area depend on the weather, the combinations of rocks, sands and clays, your geographic location, and what kind of organic matters are in the soil.
You might ask how in the world does this happen. Well, the climate has a major effect on the breakdown of solid materials. Alternate freezing and thawing cycles as well as wet and dry phases will accelerate the breakup of rocks and over time smaller and smaller particles are formed. Rocks are responsible for soil texture and, sometimes, alkalinity. Soils produced from limestone are often finely textured, neutral to alkaline and fertile. Soft shale rock can develop into a heavy clay soil; sandstone becomes a coarse sandy soil. Granite usually turns into a sandy loam, slightly acidic soil.
The topography, or shape of the land surface, also plays a role in soil development. Soils are often deeper in low areas and flat geographic surfaces and shallower on slopes and rims. Dirt in drier regions can often turn salty where as low areas in wet climates can become peat bogs.
Organic matter is another important component of diet; as a matter of fact it is the source of most nutrients found in the soil. The nutrients are released during the decaying process of organic matter. Living creatures play another essential role in the development of soil. Animals like moles and earthworms help aerate the dirt, while humans rearrange the landscape by moving large amounts of dirt or turning over the soil in their gardens and yards. Over the span of thousands of years, all these factors work together to create the soil we see today.
Did you know that only about half of the dirt or soil on Earth is made up of solid material like rock, organic matter and living soil creatures (worms, ants, fungi and bacteria)? The other half consists of air and water. If you’re lucky these will be present in approximate equal amounts in your yard. Air is essential because it supplies oxygen to soil creatures and plant roots, without it both would suffocate. Aerated soil also makes good drainage possible.
Soil with a good percentage of water is crucial because nutrients and other chemicals vital for healthy plants are dissolved in it. This nutrient filled water is held on the surface of the soil particles. Clay soils hold more water because the soil particles are smaller and there is more surface area. Sand particles are larger, yet more porous so they have less surface area and therefore do not hold water very well. This is why clay soils stay wet longer and sandy soils dry out quickly, requiring more irrigation and fertilization. A good soil mix should include 50% solid material, 25% air and 25% water and it would possess soil particles of various sizes.
Soil Composition:
Rock fragments: of varying sizes, from stones down to sand and silt granules.
Clay: made up of sticky mineral particles that tend to hold water.
Humus: decomposed plant and animal matter.
Living creatures: such as worms, insects, fungi, and microbes—that consume and contribute to soil makeup.
Water: from rain along with dissolved nutrients.
Air: mostly nitrogen and oxygen.
The ideal soil composition is 50% solid matter, 25% air, and 25% water. The makeup of the solid matter depends on the region, which is why some areas have:
Clay soil, which holds water and can drown some plants. It also hardens to a bricklike consistency during drought.
Sandy soil, found near the coast, which drains water rapidly and is best suited for drought-tolerant plants.
Loamy soil, which is crumbly, humus-rich, and considered to have the ideal proportion of ingredients for planting.