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Edaphology and Our Soil

Most conscientious gardeners and others who grow plants must be good edaphologist in that they are people who need to be concerned about the relationship of soil to the plants that grow in it. Vegetable and flower gardeners, as well as people involved in growing orchards of fruit trees, or stands of pine check the quality of the soil where they want to plant their tomatoes, peas, kale, potatoes, roses, peach, maple, pine trees, or whatever is needed at the time, and make sure the soil in whatever environment they happen to be in is in good enough condition to grow what they wish to plant.

Like a lot of scientific terms, the word edaphology has its roots in ancient Greek: edaphos means ground, and logy, implies the study of something. So, since edaphology is defined as the study of the way soils influence the growth and wellbeing of plants, that make millions of growers of vegetables and flowers, shrubs and trees edaphological in that they get involved in the important ecological relationship between soil fertility and plant cultivation.

It all starts with soil, which is composed from a variety of ingredients such as inorganic minerals weathered from Earth’s crust or lithosphere that are blended together with organisms such as bacteria, fungi, worms, insects, plus decayed organic matter created by a plethora of microorganisms that break down dead plants and animals. And no soil is complete without water and air. This blend of inorganic and organic materials makes good soil one of the most nutrient rich compounds on Earth.

When Earth formed from cosmic dust and debris floating around in the nascent solar system, there was no soil as we think of it now. The early Earth was basically just rock formed from hardened magma spewed out from volcanos, and water, some of it in the cosmic debris that formed the Earth and some of it brought in by icy comets and meteors. It took millions of years of weathering from wind, rain, tides, freezing and thawing, and plate tectonics, to turn Earth’s crust into regolith made of small rocks and dust, and then many more years for the decomposing work of living organisms to break down the regolith into the fertile soil that grows the crops we humans must have to survive.

Weathered rock, the basis for all soil, becomes sand and some of the grains can be relatively large, such as the sand we see at the seashore or at the bottom of a river or creek. Smaller particles of sand are called silt, and the finest-grained mineral particles make up clay. Generally speaking, the most fertile soil, called loam, is about 20% clay, 40% sand, and is topped by a layer of organic matter called humus. Most of our crops around the world are grown in loam that has a high amount of humus.

Soil marks the mid-point between the layers of our environment that give us the sustenance we need to live. Above our soil is the atmosphere — the oxygen we breathe and the carbon dioxide plants use in photosynthesis. At the surface of the Earth is the biosphere — which is all living things on Earth from bacteria to humans. Also on Earth’s surface is the hydrosphere –all of the water in the oceans and fresh water lakes and rivers, as well as the water locked up as ice in glaciers. Around us and under us is the lithosphere – the layer of rock that makes up Earth’s crust and upper mantle. And in the middle of these layers are the humans whose long evolution gave them time to successfully adapt to this complex environment of rocks, soil, water, and air. Our bodies and brains are made of the atoms and molecules we get from these elements through the food we eat, the water we drink, and the air we breathe.

Not only does soil grow our food, which is the edaphological function of soil. It is also good for the human immune system. Soil happens to be the habitat for the most diverse group of microbes on Earth, and in the millions of years humans have coevolved with these microorganisms, our bodies have learned to use them to our advantage, especially in the use of the anti-inflammatory proteins found in soil. Like any system in the body, the immune system does better if it is occasionally activated and exercised, just as muscles do in physical exercise, or as a vaccination builds up the immune system in the body. So, occasionally getting soil on you is actually good for you. Just ask any three-year-old.

It is believed that the first agriculture, and consequently, the first edaphology, was carried out in what we today call the ‘fertile crescent’, a stretch of arable land running from upper Egypt to the land around and between the Tigris and Euphrates rivers in modern day Iraq. Archaeologist believe it was here that humans first cultivated crops sometime around 11,000 years ago. Other areas, such as meso-America, also show signs of early agriculture. Once established, the practice of growing crops and domesticating animals spread quickly around the world.

One of the first people to write about agriculture was Cato the Elder born in Tusculum, Italy in 234 BCE. Among his many writings is one called De Argi Cultura in which he wrote about such things as crop rotation and the use of legumes to enhance soil fertility. He probably did not realize the science behind it, but he had discovered that legumes, such as peas and beans, are able to take in in nitrogen from the atmosphere as well as from pockets of air in the soil and increase the amount of nitrogen in the soil, or as edaphologists say, ‘fix” nitrogen in the soil that benefits other plants when crops are rotated. He must have followed his own good advice for growing healthy crops because he lived to be 85 years old, which was a very old age in his day.

A person considered the ‘father of soil science’ in the United States was a Virginia planter named Edmund Ruffin who lived from 1794 to 1865. One of his papers, for example, explained how to use marl – a mixture of clay, sand, and lime which is rich in calcium carbonate — to reduce acidity in soil.

Of some interest to Charlestonians is that when South Carolina seceded from the United States in December 1860, Edmund Ruffin, a slave owner and staunch secessionist, came to Charleston to help form the new Confederate government. He was with the group of soldiers at Fort Johnson who fired on Union troops at Fort Sumter, and he claimed to have fired one of the first shots of the war. After Lee surrendered in April 1865, Ruffin was so despondent he committed suicide. He might have gone on to make other useful discoveries in agriculture if his politics and racial prejudices had not overcome him.   

We in the low country of South Carolina both love and hate our salt marsh soil, which most of us affectionally call pluff mud. It is a blend of organic material such as decayed spartina grass, the remains of a myriad of crabs, worms, diatoms, dinoflagellates, and other mud-dwelling creatures, as well as inorganic minerals from eroded rocks, and dissolved salt.

Some folks tend to deride pluff mud as smelly and difficult to walk in, which it is, but it is also one of the most chemically rich soils to be found anywhere. As early as the 1700s gardeners began to use it as a fertilizer to ameliorate overused soil that had lost its fertility. In fact, it was used extensively by the growers of some of the finest cotton ever grown, the famous sea island cotton that was the mainstay of the low country economy for many decades. It does, however, contain more salt than some plants can tolerate and for that reason, never became a commonly used fertilizer for vegetables.

Our planet’s good soil is one of the main reasons we humans successfully evolved here. Earth is the only place in our solar system that we know of where fertile soil exists. Perhaps Mars had fertile soil at one time, but the dry regolith there now lacks sufficient organic content to grow much of anything. And in the next few years when space travel becomes more prevalent, the lack of good soil on the moon and Mars could someday be a problem we would need to rectify.

There is some speculation that if enough organic matter is added to the lunar or Martian regolith, they could become fertile enough to possibly produce edible fruits and vegetables. It would be similar to trying to make dry desert sand fertile by adding abundant amounts of organic material and water. We have seen this happen to some extent in some desert areas of the western US, so it could possibly work on the moon and Mars as well. Biologists and chemists are working on the problem now.

Mars, though, has another challenge. The regolith there contains a substance called calcium perchlorate, which in high doses can be toxic to humans by reducing hormone production in the thyroid gland. It can be leached out of the soil with large amounts of water, but so far, our Martian probes have not found enough water on Mars to do the leaching.

Some of us tend to take our soil for granted, but like our water and air, soil is an important resource that should be conserved and cared for. It can be polluted by chemicals or industrial waste to the point where it will not grow crops or it can be eroded by rain or wind if the plant root base is not adequate to hold it in place. It takes many years for the effects of rain, wind, and countless microbes to make good loam that, unfortunately, can be spoiled or eroded in a very short time.

As our world population tops 8 billion people, taking care of our soil becomes more critical. Through a variety of methods, such as organic farming, genetically modified plants, and elaborate irrigation systems, we are trying to squeeze as much nutrition and productivity out of our soil as possible. Today’s farmers — whether it is mom, dad, and the kids on a few acres or corporate farmers shipping tons of wheat, corn and soybeans around the world –have a lots mouths to feed and the number is growing daily. We cannot afford to let our good soil become contaminated.

So, whether you are growing beautiful flowers, lettuce and tomatoes for a salad, or genetically modified rice in India, it is important to take good care of your soil. We humans are creatures of the soil just like the microorganisms that keep the soil healthy. And like the many other organic creatures that depend on soil, our relationship must be symbiotic. If we want soil to nurture us, we must nurture it by not polluting it or treating good soil as little more than a garbage dump. If we are good to our soil, it will continue to be good to us.   And in closing, a word on dirt…There has always been some question as to the difference between soil and dirt. We tend to lump them together at times, but the perspicacious edaphologist knows that they are not the same. Dirt is the stuff you get on your clothes when you have been doing work from cleaning a dirty floor to fixing a flat tire. People and things get dirty when exposed to garbage, greasy dishes, or other dirty stuff. Dirt is also the unpleasant and often false information a politician spreads on twitter or Facebook about a political rival. Our social media is full of dirt these days. Soil, on the other hand, is the nutritious and mineral-laden crust of our Earth that plants grow in and that keeps us alive. So, conscientious edaphologists know to plant their crops in fertile soil, not dirt.

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