Thursday, June 17, 2010
Humans use up soil. It is a sad fact, but it is true. The very basis of our food system is a substance that gets depleted but rarely replenished. Part of the problem is in how we think and how we view soil. Most people think of soil as a reserve of nutrients for plants to take from as they grow. In return, we put nitrogen, phosphorus and potassium back, thinking that it replenishes what we took out. It doesn’t. Soil is a living organism that is fed by a continuous input of organic material, mostly in the form of dead plant material and animal waste. When nutrients, including organic material, are removed from the soil without properly returning it, the organisms in the soil starve and eventually die. Healthy soil has several inches of organic matter that act like a sponge when it rains, soaking up moisture quickly when it rains and reducing runoff. As the soil dies, it also loses the ability to store water, eventually leading to a process called desertification. By some estimates, 38,000 square kilometers of arable land are lost per year to desertification.
Biologist Allan Savory, who won this year’s Buckminster Fuller Challenge, set about tackling the problem of desertification decades ago. In his native country of Zimbabwe, this process has been turning grasslands and savannahs into deserts. In addition to poor farming practices, desertification is achieved by overgrazing the land to the point that it cannot recover and is left a dry, parched landscape. The new landscape is no longer productive from a human standpoint, but is also detrimental from a climate change standpoint, as it is much more prone to fire and no longer sequesters carbon in the soil. He began with a holistic approach, studying how natural grasslands support vast herds of ungulates. He assumed that the grasslands evolved with their herd animals as part of the same ecosystem. Then he looked at the difference between how natural herd animals graze the land and how domesticated animals graze the land. What he found was counter-intuitive.
In the wild, animals used to travel in vast herds, much like the wildebeests do today in Africa. The bison herds in America were equally massive. What the wild herds DON’T do, though, is stay in one place and continually graze the same grasses over and over. The grasses need time to recover between grazings. He also found that huge herds of ungulates till up the ground as they walk on it, distributing and trampling in the organic material they are depositing. He set out to emulate this method of grazing by increasing herd sizes and more closely managing how they migrate across the land as they feed. Grass keeps a reserve of energy in its roots. When it is grazed to the ground, it uses those reserves to put up more leaves. When the large wild herds graze, they eat the old vegetation until it is depleted and then move on to find more food. The grass puts up new leaves a few days later, after the herd has left. When a cow grazes in one area, it prefers to eat the tender young leaves. By doing so, it hinders the ability of the plant to recover fully.
Savory started helping cattle ranchers increase the size of their herds, a process that nearly no one thought would work. Then he helped them manage how the herds roamed across the land, fully grazing one area out and then not returning to the same area until it was fully recovered. The grasslands recovered and the grasses started growing back in, creating a healthy ecosystem. Eventually, the water retention of the soil increased and springs started to develop. Stream flows increased and the whole desertification process was reversed.