Pedologist

This is the most challenging question. "Most important" is always answered from the perspective of values.

☛ To many farmers, the most important thing about soil is that it produces crops that provide their livelihood.

☛ To environmental engineers, the most important thing about soil is its ability to purify itself.

☛ To engineers who build things, the most important thing about soil is its ability to support weight or loads. (The leaning Tower of Pisa leans because it was built on soil that could not support its weight.)

☛ To people concerned about wildlife, the most important thing about soil is its role in providing habitat (food and shelter) for many wild animals and several endangered species.

Soil scientists agree that soils form over time as the climate (temperature, rain, wind, etc.), topography (shape of the landscape), parent material (weathered rocks or stuff deposited by wind, water, ice, or gravity), and living organisms (plants and animals that live in the soil) interact. So, when soil scientists want to know how old a soil is, they look for clues. Though the climate affects how fast weathering and erosion occur, it is usually does not give many clues about how long a soil has been in a given spot. The landscape, parent materials and trees provide better clues. A soil cannot be younger than the oldest trees growing on it. It cannot be older than the materials in which it forms or the landscape on which it is found. Soil scientists work with geologists to determine how old the landscape is, and how long the parent materials have been there. Since most deposition of parent materials occurred before written history began, geologists make educated guesses, estimating the age of the landscape (and materials in it) relative to periods of known glaciation, volcanic activity, floods, and similar events. Soil scientists know that certain positions on the landscape tend to form more rapidly than others. More soil formation occurs on flat landscapes in upland positions than on slopes. Erosion on the slopes limits the rate of soil formation. Soil formation in lowland positions may be slowed by deposition of new materials on the surface by floods or gravity.

There are many animals that make homes or dens in the soil, starting with many too small to see with your eye. Many worms and insects spend part or all of their lives in the soil. Many rodents (mice, rats, gophers, prairie dogs, groundhogs, rabbits and hares) live in the soil, as do many reptiles (snakes, lizards, toads and tortoises). Several predators dig dens in the soil (foxes, badgers ...) and some live under rocks or in caves (bobcats, coyotes, cougars, wolverines, and even bears, to name a few). Worms are probably the largest animal that spend their entire life in the soil - there are some earthworms in Australia that are 2 m long! Most of the larger animals sleep in a den in the soil, but spend much of their time roaming around looking for food.

My daily routine is varied. As a professor, during the semesters when I am teaching 3 classes and 2 or 3 labs, most of my time is consumed in preparing for lectures or labs, and conducting the lectures and labs. Often about 16 to 20 hours a week is spent with students in classes or labs. Another 10 hours a week is usually spent preparing for them. Additional work is involved in preparing assignments and exams and grading them. I also have work that I do for the university, serving on committees and things that takes an hour or two a week. I a few hours each week with undergraduate students answering questions and helping them understand things they did not grasp during the lectures, and with graduate students, providing guidance on their research projects. I probably average 50 to 60 hours a week when all those things are combined. Sometimes I take work home, usually it is grading papers, or reviewing a manuscript (the scientific report of a research project). In addition to working with schools occasionally (usually about 500 plus students per year), I also give presentations on soil for local meetings, usually for farmers or for Master Gardeners groups.

The first soils began to form as soon as parent material was available, either through deposition of particles by wind, water, ice, or gravity, or through weathering of rocks. One of the most important processes in topsoil formation is the accumulation of humus (organic matter) that occurs as plants grow, die, and are decomposed, and as earthworms, termites, ants, and other organisms rework the material. A by-product of this process is that individual particles are joined together to form aggregates. Aggregates are groups of individual soil particles held together by organic matter or other forces, and are the foundation of soil structure. At first, these changes may be rapid, but they tend to slow as time progresses. Soil scientists would expect more dramatic differences in the first 10 years after deposition, than in the next 10 years, than in the last ten years of the first century after the deposition, etc.

Soil particles are defined as less than 2 millimeters in diameter. Particles larger than that are called gravel or rocks.

Soil particles come in three sizes:

☛ Sands are the largest, and are coarse and gritty. They allow water and air to move into and through the soil because there are large pores (holes) between them.

☛ Silts are the middle-sized soil particles, and are smooth. They feel much like flour or baby powder. They hold water that plants can use.

☛ Clays are the smallest soil particles, and are fine and sticky. They hold a lot of water, but do not give as much to the plants as silts. They also hold nutrients. They help hold soil together in clods which scientists call aggregates. Clays can be molded and shaped, much like modelling clay or Play-Dough.

☛ An ideal soil would have equal amounts of sand, silt, and clay particles. But most soils are not ideal. Some are mostly sand, others are mostly clay or silt, depending on where they are found. The about equal mixtures of soil particles are called loams.

I have a bachelor's degree (B.S.) in agriculture and a master's (M.S.) degree in Plant Science from West Texas University (now known as West Texas University, where I now teach). My degree is in soils and is from Iowa State University. As you might imagine, it took quite a while to get all those degrees (almost 13 years).

Soils degrees are usually only available at land grant universities that have agriculture programs, though universities with environmental science programs are developing soils programs now, too.

A recent job announcement with the USDA Natural Resources Conservation Service had the following definition of a soil scientist: a degree in soil science or closely related discipline that included 30 semester hours or equivalent in biological, physical, or earth science, with a minimum of 15 semester hours in such subjects as soil genesis, pedology, soil chemistry, soil physics, and soil fertility.

A soil horizon is a layer generally parallel to the soil crust, whose physical characteristics differ from the layers above and beneath. Each soil type usually has three or four horizons. Horizons are defined in most cases by obvious physical features, chiefly colour and texture. These may be described both in absolute terms particle size distribution for texture, for instance and in terms relative to the surrounding material (i.e., "coarser" or "sandier" than the horizons above and below). The differentiation of the soil into distinct horizons is largely the result of influences, such as air, water, solar radiation and plant material, originating at the soil-atmosphere interface. Since the weathering of the soil occurs first at the surface and works its way down, the uppermost layers have been changed the most, while the deepest layers are most similar to the original parent material.