Let's talk about soil
We want soil to work for us, says soil scientist Ray Weil. We want it to hold water, recycle nutrients and keep diseases at bay. But we pulverize it with plows and expose it to evaporation and erosion. Now, does that make sense?

By Pat Michalak

Ray Weil at a field day last summer, picking apart the secrets of healthy soil with a hunting knife and his wit. Ray is a professor of soil science at the University of Maryland and co-author of The Nature and Properties of Soils.

January, 2003: Dr. Ray Weil (pronounced “Let’s talk about soil quality for a WHILE”) is a professor of soil fertility and ecology at the University of Maryland, and an internationally recognized leader in research on soil quality and in soil science education. Attend one of Weil’s lectures, and you’ll wonder, “How valuable is my soil? What am I doing to improve it?”

Land has a known economic value, but ponder for a minute the value that you add to your soil. Has its condition improved or deteriorated? Are you killing your soil? Unfortunately, soil quality is difficult to measure.

We want soil to work for us. It has to absorb and hold water; it must breathe; soil should recycle nutrients; and, it should help to keep diseases at bay. Below, Dr. Weil tells farmers, especially those in the Northeastern United States, how to put their soil to work and build soil quality at the same time.

“A farmer thinks, ‘I’ve only got 10 acres or 20 acres and I’m growing strawberries and other high value crops like sweet corn. How can I take some of my land out of production and plant wheat or cover crops that aren’t worth much?’”

Take a small part of your farm out of production, says Weil. Find a little slice of land that you can start to improve, then add more slices each year. That way, some of your land is on the road to recovery. When you finally get a high value crop on it, you’ll notice that your soil is much more productive. Over time, proper soil management helps to improve soil quality. Follow these guidelines when managing your slice:

• Reduce or eliminate tillage. In a five-year rotation, include at least three years without tillage.
• Smooth the tillage transition by including cover crops and legumes in your rotation, and leave plenty of residues.
• Select crop varieties that produce plenty of growth above- and belowground. As with building muscle, you won’t wear soil out by growing big plants on it. You’ll improve it!
• Apply animal manure, and other organic materials. But if the organic material is not homegrown, be sure to avoid applying excessive nitrogen or phosphorus in the process.
• Use lime, if needed, to adjust soil pH and raise calcium levels.
• Limit or eliminate herbicides and pesticides in order to encourage natural cycles of pest control.

“Tillage is usually a few steps forward and a few steps back. Natural processes, and not tillage, will make your soil loose.”

Stop stirring up your soil. Don’t break up the soil aggregates. Tillage stimulates both erosion, and the loss of organic matter. If you feel you must till, be sure to use an implement that makes cracks in the soils, but doesn't turn it over. Better yet, try a system that doesn't use tillage at all. Once you stop tilling, it may take several years for natural processes to take affect. It’s usually around the third or fourth year that you’ll see things turn around. Organic no-till is a greater challenge, and may require several more years. The worst thing you can do is keep a soil bare by tilling several times each year. Surprisingly, most crops can be grown under no-tillage—very small seeded crops like lettuce may be exceptions.

“Put roots first. Roots are the way to go. You want to plant cover crops with a lot of roots, and then leave the roots underground.”

Cover crops and organic matter at work: Root channels and worm channels facilitate plant growth.

When is it easiest to push through a soil? Answer: When it’s wet in early spring. That’s when cover crops are growing —those are the plants that break through soil compaction. Cereal rye has a good root system that is active in the early spring. Cover crops with taproots are good, too. Try to add oilseed radish, dandelions or mustards to your crop rotation in order to increase root biomass.

“In the forest, 90% of this years roots are growing down channels where roots have already been. It’s just like hiking in a thicket—it requires too much energy to bushwhack, so you follow a deer trail.”

At Steve Groff’s farm in Pennsylvania (see farmer profile at left), Dr. Weil found a plow pan between 6-20” deep. However, Groff had stopped tilling his soil, and mulch formed on the soil surface. The mulch attracted earthworms that created channels deep within the soil. The channels allow for drainage, while the organic-rich channels walls are known to be good at absorbing pesticides and nutrients that might otherwise wash from the soil. Steve’s vegetable roots grew right down the earthworm channels, right through the compaction zone. With earthworms working for you, you don’t need a subsoiler. By leaving the soil untilled, root channels remain open and new roots will follow the same channels. Earthworm numbers will increase in most parts of the USA.

“Think of an acre of land and picture a full-size pickup truck overloaded with this huge pile of fungal hyphae and bacterial slime. A good heaping pickup load would be 1 – 1 ½ tons. That’s the living biomass you’re aiming for.”

Although you won't see them on most soil test reports, there’s more than just one kind of organic matter. Organic matter is actually a diverse bunch of compounds, many which haven’t been identified. Active organic matter (less than 1/5 of total organic matter) contains a myriad of living organisms and materials they use as food. When these organism "eat" the organic matter (and each other) they release plant nutrients such as N, S and P as well as micronutrients.

When you clear land in native vegetation and start plowing it, within a few years you’ll lose most of the active organic matter and that’s when the soil quality goes down. Fortunately, you can increase the active fraction since that’s the part that accumulates first. When farmers have a problem field that just doesn’t yield as well, low active organic matter is often the culprit.

Passive organic matter is protected from microorganisms because it is chemically too hard to "digest' or because it is tucked away inside soil aggregates where even tiny bacteria cannot get at it. Much of the passive organic matter in soil has been there for centuries, even millennia. It turns over very, very slowly, so it does little to release nutrients or increase microbial activity.

However, passive organic matter acts much like a sponge, holding a lot of water. It provides much of the soil's cation exchange capacity that makes calcium, magnesium, potassium and other nutrients available to plants and prevents them from washing away. It’s a kind of long-term storage or “capital” of nutrients decades and centuries.

Passive organic matter also plays a role in global climate change. Most agricultural soils have about one-half the carbon as they had under natural vegetation. That’s mainly because tillage speeds the decomposition of organic matter. During this process microorganisms turn the carbon in organic matter back into carbon dioxide gas that adds to the amount of this greenhouse gas in the atmosphere.

If we can build up passive organic matter in soils, we can undo some of the past losses. Crops take carbon dioxide out of the atmosphere and turn it into compounds like sugars and cellulose. Eventually some of this carbon is returned to the soil in plant residues, and transformed into soil organic matter, thus lowering the amount of this gas that can contribute to global warming.

When you’re trying to improve your soil, it takes much longer to increase the passive organic matter than the active. However, the passive organic matter sequesters the carbon in the soil for a much longer time than the active, and therefore it is most important in combating global warming.

“If your soil clods can't pass the water test, change your management practices. It will help your bottom line as well as the soil.”

Simple clod test: Healthy soil, at left, holds together in water, while poor soil falls apart.

You can perform a simple soil aggregate stability test at home with a soil sample, a small glass jar and some tap water. Several days before, collect the soil. Include soil from a “problem” field, as well as soil from a fence row or field you feel is in excellent condition, such as one coming out of sod. Allow the samples to
dry at room temperature. Fill two glass jars half way with water, then place a dry clod of soil from each sample into its jar. Stir the water gently. Watch closely to see whether the clod remains intact or falls apart (as in the photo).

Soil that falls apart and gives off few air bubbles has poor aggregate stability. Soil clods that hold together, that absorb water easily, and that emit air bubbles indicates soil with good aggregate stability and a good portion of active organic matter. According to Dr. Weil, “Good soil should be at least 50% air space (that’s where the bubbles come from). If your soil clods hold together, and the water stays clear, even when you stir, you’re probably on the right track with soil management. Keep doing what you’re doing.” Farm fields managed without tillage have the greatest aggregate stability, because as the active organic matter increases, microorganism numbers increase. Microorganisms are the critters that produce the glues that hold the soil together. You can improve soil quality and aggregate stability by adding amendments like manure, but if you follow with a plow, you may do more harm than good.