Despite soil being the foundation of our yards and gardens, most people know little-to-nothing about it.
Soil is a dynamic, living system that enables plants to function properly. Soil does not necessarily equate to ‘dirt’ which usually implies a state or quality of uncleanliness.
Soil performs at least four functions in relation to plants. The first is it physically supports a plant.
The root system of most plants extends into the upper layers of the garden’s soil. Depending on the plant species and the type of root system inherent to that plant, roots extend downward to about 8 to 12 inches in the soil. The roots provide structural anchorage for the plant.
Whether growing turf, ornamentals or trees, local soils are the basis of life in panhandle Florida. These gardenias deliver profuse blooms when the soil under them meets their needs. The only way to know for sure is to soil test.
The second is the water intake required for the plant’s survival. Most herbaceous plants are greater than 95% water. All of that water entered the plant through the root system.
Water enters through the terminal half-inch or so of each root tip. The loss of water from the leaves by transpiration provides the force that drives water uptake into the root system.
As water leaves the leaf surface, more water is taken into the root. An extensive root system allows sufficient water uptake to supply the needs of the entire plant.
The third is nutrient uptake. Soil acts as a repository for the mineral nutrients that plants need. The nutrients are in solution in the soil water and are taken up by the plant as it takes up needed water.
The fourth is delivery of oxygen. Roots are part of a living and respiring organism. As such, they have an absolute requirement for oxygen.
The porous nature of soils allows oxygen uptake. One of the factors limiting how deep roots penetrate the soil is oxygen availability. Soil compaction can seriously limit oxygen supply.
Soil is comprised of a mineral (inorganic, non-living) component and an organic (living or formerly living) component. The ratio and composition of these elements vary from site to site.
The mineral component of soil typically is broken down into subcategories based on the particle size of the inorganic matter rather than chemical composition. All come from the parent rock underlying the top layers of the soil.
There are three general categories: sand, silt, and clay. The most common in many areas are sand particles which are the largest and range in size from 0.05 to 2.0 mm.
Silt particles range from 0.002 to 0.05 mm and clay particles are those less than 0.002 mm (less than 7.8 hundred-thousandths of an inch).
Sand and many silt particles are easily visible with the naked eye, but clay particles are best seen through a microscope. For perspective, consider that smooth-feeling talcum powder is a clay.
The percentage of sand, silt, and clay in a soil greatly impacts the water-holding capacity and air-holding capacity of a soil. A greater percentage of larger particles, i.e. sand, results in greater pore space because the particles cannot fit as tightly together.
These soils can, at times, hold more water and allow more air penetration. They drain well, but also can dry out quickly.
The organic component in the soil is comprised of the living or formerly living matter. A teaspoon of soil may contain billions of individual organisms.
The majority of these are bacteria and fungi. However other living organisms may include insects, worms, and even plant roots. The organic matter is a rich repository of nutrients which the plant will utilize for growth.
Most Florida soils contain less than 0.5% organic matter. The high sand content results in elevated aeration and a higher oxygen content.
The plentiful rains keep the soil relatively moist and the mild climate leads to high microorganism levels which increase the rate of organic matter decomposition.
So, while soil is underfoot, its effects on everyday life are never far away. Without it, life in north Florida (and everywhere else) would not exist.
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