10 09 09 Green Manure ER

Those of us interested in growing food, whether we are gardeners or farmers, are always working with two challenges. The first is how to get our plants the nutrients they need, and the second is weed control. Conventional agriculture and organic agriculture approach these problems in two very different ways. Last week we looked at the approach taken by conventional agriculture and suggested that given the finite resources of this planet, this chemically dependant approach is unsustainable on the long run.

Prior to the advent of chemical fertilizer and chemical weed control, farmers in this area had two tools: alfalfa and summer fallow. Most farmers had a three or four year rotation, with summer fallow appearing once in that rotation. The summer fallow field would not be seeded that year, and would be tilled whenever it showed significant weed growth. In this way weeds would be brought under control, and, remarkably, the fertility of the field would be enhanced. The year after summer fallow the yield would always be significantly better. Many farmers would also seed a field into alfalfa knowing that this reduced the weed population in that field, and significantly increased subsequent yield.

Green manuring is another way of increasing fertility and suppressing weed populations. A green manure crop is a crop that is planted specifically in order to increase soil fertility. Farmers and agricultural researchers have known about green manure for hundreds of years. Extension bulletins circulating prior to the widespread use of agricultural chemicals spoke of green manure, but my recollection is that farmers in this area taking green manure seriously at that time. The Natural Systems Agriculture team at the University of Manitoba have been advancing the science of green manuring. As I have said earlier in these columns, I had an eye opening experience as I visited their plots near Carman this summer.

Many of us learned about humus, that component of the topsoil layer abuzz with microbial activity, way back in grade school, but a subsequent focus on chemical farming has diverted attention away from that element of the soil. Now, farming with green manure suggests that the farmer's task is to feed those microbes, and they in turn feed the crop. Tilling the soil and keeping the soil bare destroys microbes and organic matter. Growing and incorporating plant vegetation feeds the microbes and contributes to soil structure.

At the risk of over-simplifying a complex aspect of agriculture, I am suggesting that a farmer (or gardener) planting a green manure crop is striving for two things simultaneously: covering his soil with vigorously growing vegetation, and reducing the weed population simultaneously. This means that they seek out vigorously growing crop species (which will obviously compete well with weeds), but they work this crop down as soon as the crop reaches the flowering stage. That is when the plants stop growing and begin to form seed. When that crop is worked down, any weeds growing in that crop are also destroyed. Immediately a new crop is planted. Some crops, such as buckwheat and chickling vetch reach their plow-down stage in six or seven weeks, so there can be as many as four plow-downs in a single summer.

The South Eastman Transition Initiative is interested in fostering dialogue about agriculture less dependant on non-renewable resource inputs. But we are also interested in addressing many other aspects of non-sustainable lifestyles. Join us September 21 for a planning meeting. More information at our website southeasttransition.com, or phone 326-9621

Eric Rempel