Feeding Healthy Soil

How to meet your soil's nutritional needs so it meets yours.

April 8, 2011

In the organic system, soil is a living organism that provides nutritional support for people but also has nutritional needs of its own. For those who think of soil as nothing more than dirt, it may take an attitude adjustment to view soil as a living collection of creatures, along with minerals and bits of living material: iron oxides, unicellular bacteria, actinomycete filaments, flagellated protozoans, ciliated protozoans, amoebae, nematodes, root hairs, fine roots, elongate springtails, and mites. 

All of these substances have an essential role in organic soil health and the quantity and quality of an organic garden's glory. They break down the huge, unwieldy proteins and lignins in straw, leaves, and the wastes and remains of living creatures into simple, accessible compounds, like nitrate and ammonium, that plants transform back into spicy peppers and mellow watermelons. One organic tomato grower summed it up like this: "The soil is like a farmer's bank. You've got to keep making deposits into it all the time. If you withdraw from it until it's empty, you'll be out of business." 
When it comes to firing up a garden's resident soil microbes, the organic shed is filled with practical, adoptable soil-building tools, which for ease can be grouped by the benefits they provide. 
Soil Fertility and Regeneration
Key tools in organic soil fertility and regeneration include cover crops, crop rotation, compost, soil aeration, and mulch. Legume cover crops, such as winter peas or clovers, and edible legumes, such as beans, have the ability to transform nitrogen from the air into nitrogen in the soil. Legumes can provide the main serving of nitrogen for heavy-feeding crops like corn, melons, and tomatoes. After the crops are harvested, buckwheat or cereal rye cover crops can be sown to capture leftover nitrogen, saving it in a stable form to make it available for the next rotation. 
Microbes require certain working conditions to furnish the nutrients necessary for healthy harvests. Fresh air and a steady supply of food and water, plus protection from temperature extremes, will ensure productive soil. Covering the soil with biodegradable mulches, regularly incorporating fluffy composts, and minimizing compaction with good bed design are great ways to make sure the microbes stay munching and the plants producing. 
Keeping the beds planted with crops or cover crops or piled with mulch encourages roots and earthworms that will work to make the soil airy and loose. If the soil already suffers from compaction problems, try growing a cover crop with a big taproot, such as the tillage radish (also known as oilseed or daikon radish), to break up the hard subsurface soil layers. These crops are also great at bringing up minerals and micronutrients from the subsoil that shallow-rooted crops have a harder time reaching. 
Pest Management
Minimizing soil disturbance also helps control weeds. A soil can have all the nutrients in the world, but weeds can destroy its productive capacity by outcompeting tender crop plants for nutrients and other resources. Frequent disturbance by digging or hoeing perpetuates the problem by dragging weed seed reservoirs from the deeper soil layers to repopulate the surface. By reducing or eliminating surface disturbance, organic growers can exhaust the seed bank in the surface layer and create a more productive soil environment. Mulch, key to reducing temperature and moisture extremes in the soil, can also improve soil quality by shading the soil surface and putting surface seeds into dormancy until they can be decomposed by the well-fed soil fauna. 
Crop rotation is the practice of growing a sequence of different types of crops on the same field or garden bed over several years. While the prime reason to follow broccoli with bell peppers might be to control cabbage moths, crop rotation also helps maintain an appropriate balance of nutrients. The result is healthy plants that can better resist disease. For example, too much soil nitrogen makes tomatoes more vulnerable to late blight than those growing with more appropriate nitrogen levels. Rotation also aids in cleaning out diseases like fusarium wilt, which can live in soil for up to 7 years. To reduce pathogens in the soil and maintain optimum soil health, Cornell University plant pathologist Margaret Tuttle McGrath, Ph.D., recommends a rotation that is longer than 7 years. 
Organic soil health is complex, but the tools used to implement or restore it are simple. 
Alison M. Grantham is the Research Manager at the Rodale Institute