By John Hibma – What makes good soil? Virtually every person on this planet sooner or later comes in contact with earth and soil. Whether they are a farmer, a gardener sharing gardening tips related to soil, or a homeowner with a big or small yard, people have some interaction with the ground that’s yielding a plant intended to be either food or an ornament. Even a city dweller who is surrounded by canyons of concrete and steel probably has a couple of potted plants to take care of. Except for those limited examples of hydroponics or an algae that’s growing in a lake or pond, everything we grow is grown in soil. Soil is essential to plant productivity. Healthy soil is the foundation of successful agriculture and, on a different level, the existence and stability of productive societies.
But it’s also very easy to take soil for granted or to abuse soils. There’s so much of it around that it’s easy to fall into the trap of thinking that we’ll never run out of good soil. Such is not the case. We have to know what makes good soil in order to keep the ground healthy and productive.
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What is soil? Soil is an aggregate of four basic components: mineral solids, water, air and organic matter. Depending on how much of each is present in soil determines what makes good soil for growing crops for human and animal consumption, or for flowers that will adorn the dining room table.
Soil health (also referred to as soil quality) can then be defined as “the capacity of a soil to function within ecosystems and land use applications that can sustain productivity, maintain environmental quality and promote plant and animal health.” Characteristics of healthy soil include:
• Good soil tilth
• Sufficient depth
• Proper levels of nutrients
• Good drainage
• Large populations of beneficial organisms
• Resistance to weeds and degradation
• Resilient when unfavorable conditions occur
Many of us don’t have to look any farther than our home yards and lawns to be able to understand basic soil health. The flower beds have soil that is dark in color and crumbly and loaded with earthworms. (As a matter of fact, using worms for composting is an excellent way to improve the quality of soil.) The soil drains very quickly after a summer thunderstorm and the plants that grow there are vigorous. The lawn has sections that never seem to need water, but then there’s that patch right in the middle that always turns brown in the summer no matter how much water it gets. Grass is difficult to grow there, but weeds love it. Over the years you’ve learned that a couple of bags of manure or topsoil have improved those areas. You’ve learned that certain plants grow better in a more acidic soil and others do well in an alkaline soil.
Achieving and maintaining a healthy soil involves the integration of physical, chemical and biological components that result in improved productivity and environmental quality.
Probably a better way to learn what constitutes good soil health and what makes good soil is to study what constitutes unhealthy soils. The most obvious clue to an unhealthy soil is the fact that nothing will grow in it or, if it does, it grows poorly. Poor quality soils are the result of soil compaction, surface crusting, low organic matter and minerals, increased pressure from diseases, weeds, and insects as well as the lack of beneficial organisms.
Several methods that are commonly used in the field to evaluate soil health are: a) a penetrometer to measure the compaction of the soil at different soil depths, b) digging a spade full of soil and examining the structure and texture of the soil as well as the roots and other organic matter present in the soil, c) using a soil core probe that takes a profile of the soil that can be analyzed in a soil testing laboratory, and d) a rain simulation sprinkler steadily raining on a measured sample contained in a sieve below and the soil that is not washed away is used to compute the aggregate stability of the soil. The sprinkler can be adjusted to simulate varying intensities of rainfall.
Soil degradation can result from the overuse of heavy farming equipment that compacts soils and makes it impossible for roots to grow. The lack of rotating crops over time will eventually deplete the soil of essential nutrients. Poor drainage will drown out root systems. There must be enough organic matter to facilitate chemical transfer of carbon as an energy source for the soil microbes. Microbes are necessary to decompose organic matter to make available chemical ions that must by taken up into the plant.
Managing soils to maintain health and quality is as much a science as it is an art. Good soil aggregation—the minerals, air, water and organic matter—is essential for maintaining good soil structure that enables adequate air exchange and water drainage. The texture of a soil is a good indication of its health. Soil texture is usually classified as clay, clay loam, loam, sandy loam, or sand. Any of the three loams are generally the most desirable types and most productive soils. Loams tend to have the best soil characteristics that allow for good drainage, aggregate stability, organic matter and active carbon.
Testing of soils for chemical, biological and physical attributes is a useful tool that will help determine the health of soils. Check with your local ag extension agent or local soil conservation district for more information about soil testing. Basic tests include using a penetrometer to measure soil compaction and taking soil samples to determine soil type and structure as well as biological activity. Knowing how to till soil can help you determine the pH of your soil, which is a good indicator of soil health and what makes good soil.
Once you know what makes good soil, improving the health of a soil will take time and patience. Often, there will be more than one problem with a poorly productive soil and a management plan can be developed to restore functionality to the soil. Several of the main categories of action for soil management are listed below:
• Reducing or modifying tillage
• Crop rotation
• Growing cover crops
• Adding organic amendments
• Adding chemical amendments
Soil management practices are very dependent upon farm-specific conditions such as soil type and the kind of crop to be grown. Each situation must be considered independently.
For most of mankind’s history the land on which we grow crops must have appeared to be inexhaustible. But no longer is that the case. As the world’s population continues to grow, estimated to be at nine billion by mid-century, healthy and productive soil is rapidly becoming a scarce resource. Recognizing the vital importance of healthy soils, and what makes good soil for growing, is key to the sustainability of agriculture and should make us realize that healthy soil is a resource that we cannot afford to squander.
Originally published in the January / February 2013 issue of Countryside & Small Stock Journal and regularly vetted for accuracy.