In my last article, I talked about the variety of products available to help organic farmers address nutrient deficiencies or imbalances on their farms. I also stressed the importance of designing a farming system that built and maintained soil fertility with a minimum of purchased inputs.
In the broadest sense, farmers need to view their farm as an ecosystem that draws in energy from the sun and stores, transforms, and recycles that energy in the form of plants and animals on the farm. Purchased inputs add energy in one form or another, while crop and livestock sales are "energy" exports. The health of the farmer’s bank account in measured by the difference between the costs of inputs and operations and the quantity and value of the products sold. The health of the farm’s "fertility" account is determined by the difference between the nutrients captured and stored on the farm and the nutrients lost through products that are sold off the farm, and through processes like erosion and leaching. True sustainability, then, is the ability to maintain and even increase the positive balance in both of these accounts!
If the sun is the primary source of energy, plants are the obvious means of capturing that energy. Growing plants transform the sun’s energy into sugars, which are then combined with air, water, and minerals from the soil to create more complex molecules. When the plant dies, all this material is returned to the soil. Not only is this organic matter rich in nutrients, it only improves soil structure, making it less prone to erosion and nutrient leaching.
Plants, in turn, feed animals. Animal manure is an excellent source of fertility, and the inclusion of pasture and forage crops in the crop rotation provide many benefits to the soil. As well, feeding livestock can be seen as a "value-added" enterprise because their products have a higher economic value and lower nutrient density than the crops they eat. For example, because hay is harvested as a green, growing crop, it contains a lot of nutrients. Those nutrients are gone forever when the hay is sold off the farm, but when it is fed to livestock, most of the nutrients end up in the manure.
Often overlooked, however, are the immense herds of "livestock" at work beneath the soil’s surface, busily digesting and transforming plant wastes and soil minerals into soil fertility. Biological activity makes the soil’s vast reserves of phosphorus and potash available to plants, and as such, is absolutely essential to the soil fertility of an organic farm. Three-quarters of the nitrogen, two-thirds of the phosphorus, and 80 per cent of the sulfur in the soil is made available by the bacteria, fungi, mites, nematodes, and earthworms in the soil. Earthworm castings are 3 to 11 times higher in essential nutrients than the material that the earthworm consumes; the castings can add up to 33 tonnes per acre. Bacteria also play a key role in the nitrogen cycle. Mycorrhizal fungi form beneficial partnerships with plant roots to provide access to phosphorus, ammonium, potassium, calcium, iron, copper, manganese, zinc, and nickel. The life of the soil is a highly valuable but rarely considered component of soil fertility.
Thinking this way and being aware of these processes leads to a few simple concepts that go a long way toward building and maintaining soil fertility:
1) Maximize solar gain - keep plants growing on the soil as much as possible. Use underseeding, cover crops, and winter cereals in your crop rotation. (This also cuts down on nutrient losses through erosion and leaching).
2) Use crops to increase available nutrients - legumes fix nitrogen; oats, barley, and buckwheat help make phosphate available, and residues like straw build potash.
3) Feed the soil’s "livestock" - leave crop residues and wastes in the field. Leave straw and stubble on the field, or return it in the form of used livestock bedding or mulch. Minimize tillage and compaction to avoid killing soil life. Crop rotation, especially including legumes and oilseeds, boost soil life.
4) Minimize nutrient losses - Avoid soil erosion. Compost livestock manure in order to stabilize nutrients (composting needs to be done right in order to avoid nutrient leaching, too).
5) Consider livestock - many experienced organic farmers report that livestock manure has an unmatched ability to improve soil in ways that cannot always be explained. Livestock products are also "value-added".
As always, I welcome feedback and suggestions. You can contact me by emailing wallbridge@ontarbio.com or call 613-724-9287.
Upcoming events:
The 24th Annual Guelph Organic Conference runs from January 20 to 23. This is the largest organic conference in Canada. For more info go to www.guelphorganicconf.ca or call 519-824-4120 x56205.
For upcoming meetings, events, and training courses from the Ecological Farmers Association of Ontario, visit www.efao.ca or call 519-335-6566.
From the Archives:
News, January 2005
