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Soil Building and Soil Quality (Part II)
by David Podoll

Loss of soil quality most often happens so slowly that the additional horsepower it took to pull the digger through the ground this year isn't noticed. Some farmers may never notice. Others might wax nostalgic about how the ground used to hold more of a hard rain, or how many earthworms there used to be, or how the ground use to smell different, or how it didn't take near as much fertilizer to get the same yield.

Soil quality, or what we often call tilth, is a sensory measure of the soil's ability to be worked easily, to hold water, to smell sweet, to crumble easily into large aggregates, and to resist wind and water erosion. Other indicators may be a dark color, the presence of much soil fauna and fungi, and the ability to grow healthy, abundant crops without fertilizer.

With heavy machinery and fast tillage, we have the ability to destroy soil tilth rather rapidly. And it is much easier to destroy tilth than to build tilth. Organic farmers rely on building inherent fertility to produce quality crops. So, paying attention to preserving tilth as well as building tilth is critical to the long-term productive ability of the soil. We may be tempted to withdraw from our tilth savings in lean years or in difficult situations. If we don't work to replenish these savings, lean years will be every year.

I recall one field that I undersowed to sweetclover in 1977, shortly after I started farming organically. This field hadn't had a legume or perennial grass since it was broken up about 70 years before. It also lost considerable soil during the thirties. It was hard to work. Canada thistle was a big problem and inherent fertility was low. The earth seemed to rejoice with the sweetclover. Rain was plentiful the next year, and the clover grew up to 9 feet tall in some places. Incorporating all that biomass made the earth sing. It ate it up. I had never seen such vigorous decay. The next year the ground yielded 50-bushel rye and 40-bushel wheat. Most thistle patches disappeared. It was my first big learning experience about soil building and the earth's ability to regenerate itself. It might be that the worst field is the best teacher. It presents the toughest challenge and the greatest opportunity for creativity.

After more than twenty years and six green manure rotation cycles, I've learned some things about soil building on this field:
1. Don't work the soil when it is too wet. Oh, how easy it is to do with big tires on tractors and a shortage of time. This field is low and I've relied on frost too much to break up packed soil. Even then it is hard for earthworms and clover roots to burrow and push.

2. A substantial green manure at least every third year is necessary to build soil. Actually, I incorporate two: a mix of legumes in the summer and a solid barley or oats cover in the fall for winter protection.

3. Choice of crops has a significant bearing on soil building. Perennial grasses and deep-rooted legumes are the best for soil building. Shallow rooted legumes and annual grasses are next in line. Row crops like corn, solid seeded broadleafs like buckwheat, and broadleaf row crops like sunflowers are more destructive. Grain legumes like soybeans and dry beans along with vegetable crops are the most destructive of soil tilth. Of the varieties of crops I raise, I choose those which produce the most biomass. Additionally, I like to let the biomass grow as "old or ripe" as possible. For instance, a cover crop that is incorporated lush and green decays fast, losing most of its mass as C02, having little or no long term soil building effects. On the other hand, a well into bloom sweetclover crop, straw, or fodder from ripe oats or corn, decays much more slowly. Left are substantial lignified materials that helps build stable soil humus.

4. Practice less and slower tillage. Till for a definite reason and do a good job so it doesn't have to be done over again. And the faster you go, the more you "fine" the soil. I have incorporated into my rotation plan periods of one year or more without tillage. Earthworms do best without disruption.

5. Soil quality was helped a lot when I began to use animal manure. Scientifically it has not yet been identified why, but it is certainly one of those things we "just know".

6. Keep the ground covered. The sun and raindrops falling at terminal velocity are hard on any bare soil particles. Have something growing all the time if possible or till to keep residues on the surface.

7. This should probably be number one. I have no doubt that the most beneficial and economical practice on an organic farm is the growing and capturing of your own carbon in the biomass as much as you can for cycling through the soil's biological engine. The more carbon you can cycle through the soil, the better. No off farm input will come close to having the same benefits.

This field is still a struggle. Soil building can have dramatic spurts when conditions are right, like 1977. But some years the clover didn't catch well. Sometimes I worked the ground when it was too wet. Sometimes I tilled too often to control weeds. Sometimes the ground wasn't covered enough when it rained hard. The one thing most beneficial to soil quality I have not yet accomplished is rotating into a perennial grass and grazing it appropriately. The earth heals with grass.

These basic principles of soil building are unchangeable and unchanging. They work everywhere. How they are applied changes from farm to farm and region to region. Generally, soils build slower and degrade slower as the climate becomes dryer and colder. Soils regenerate faster and degrade faster as the climate becomes wetter and warmer.

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