Are you healthy? It is easier to identify an unhealthy person or animal than it is to identify one that is healthy. So it is with soil. Who decides what healthy soil is, and how can you tell how healthy your soil is?
The definition I use for a healthy agricultural soil is this: a healthy soil is a soil that is managed efficiently for crop production, and it consistently yields at or near its potential yield.
Soils differ from place to place. No matter where they are, or what kind of soils they are, healthy agricultural soils will:
- Efficiently cycle plant nutrients.
- Maintain or increase water-holding capacity, aggregate (particle) stability, and soil organic matter.
- Maintain or decrease compaction and root penetration resistance.
- Fine-textured soils will maintain or increase water infiltration rates.
If you are seeing some unhealthy symptoms, what could they be and what should you do? This week, we’ll discuss the chemistry and biology for healthy soils, and next week, we’ll go through soil water, and how to get just the right amount.
It’s Chemistry, Dear Watson: pH, Aluminum, and Root-Health
Crop roots will only thrive to the degree that their environment allows. Overall, soil pH is one of the first areas to tackle in soils. When soil pH is too low or too high, nutrients are less available. The goal is to reach the soil pH sweet spot of about 6.5-7.
So here’s a chicken-and-egg problem. Some say that healthy plants make soils healthy. Others say that soil fertility has to come first if plant roots are to proliferate. The data and the experiences of many farmers and agricultural researchers support the second view. Plants need nutrients to grow up or down, and nutrients are more available when the pH is at the sweet spot.
Some soils have a lot of aluminum in them, which, if floating around, will keep roots from growing, leaving them short and stubby, without much branching. There is more “free aluminum” when the pH is low. For example, if free aluminum levels are high in a particular soil (Al3+, which is toxic to the roots of many plant species), many crops will not thrive. Their roots will be stubby without much branching or fine structure. By adding lime to such acidic soils, much of the free aluminum is converted to a less soluble form and the soil can become very hospitable to crop roots.
Soil Workers Require Good Working Conditions
Soil biology is getting a lot of press these days, even though historically, it has been under-emphasized.
The vast majority (90%+) of microbial life in the soil exists within a fraction of a millimeter from root tissue. Parts of plant roots are continuously being sloughed off, parts of roots are dying, new cells are replacing dead ones, and organic compounds are continuously secreted. All those bits feed soil microbes.
In return, the microbes break down dead plant material, re-releasing nutrients in plant-available forms. Microbial secretions cause soil aggregates to form, which allows air to move in and out of the soil, providing oxygen for both roots and microbes, in addition to improving water infiltration and reducing root penetration resistance.
To live and work, soil microbes need food, water, and oxygen. Without microbial “workers”, plant material would pile up and nutrients would never be released. The soil microbes working in the soil are critical for plant growth, and the community of workers present is dramatically influenced by management.
In our infinite wisdom, we have found ways to partially, temporarily, and artificially accomplish some things without microbes. If nutrient cycling is poor, or if manure is not going back on the field, we can compensate with synthetic fertilizer. Equipment, agricultural chemicals, pesticides, and fertilizers are all amazingly helpful tools, but the soil is teeming with organisms and micro-organisms that provide amazing services.
If the microbes don’t want to work, we are still good to grow. Right? Sort of. We can grow crops hydroponically, but it obviously makes more sense to harness the power of microbes. The good news is that soil microbes are abundant: there are up to ten billion (10,000,000,000) bacteria in one GRAM of dry soil. That is about 2.3 billion billion (that is, 2,300,000,000,000,000,000) bacteria in the top 3.5 inches of soil of one acre of land. There are also MANY other soil micro and macro organisms. The bad news is that the land manager is responsible for their work environment. If their needs are not understood, acknowledged and ultimately met, morale goes down, and a ‘slowdown strike’ is sure to follow.
Healthy Soil Is Solar-powered + pH
Sunshine falls on every square inch of your land whether a leaf is there to make use of it or not. When we take advantage of the sun, we feed the workers that improve soil by their very act of living. A vigorous cover crop or perennial pasture for the biological solar panels (leaves) will end up feeding the soil microbes. Busy, well-fed microbes do a better job nutrient cycling, yielding more organic matter, improved soil structure, better water infiltration, and increased water-holding capacity. To have healthy soil and happy microbes, we need to make sure our soil chemistry isn’t out of whack. Start with a soil test for pH needs at the very least, and keep soil covered year round for the healthiest soil you can have.
Thanks to Rachel Gilker for helping with this article.