Feb 08 2010
To review, we know that soil is a complex mixture of inorganic material (sand, silt, clay), macronutrients (N, P, K), air, water, organic material (humus) and a dazzling multitude of critters like decomposers and detritovores. Soil’s also critical to humanity’s survival; the 15-20 cm of topsoil keeps the world from mass starvation by growing our food supply. What complicates the matter? It takes a very long time for soil to renew itself; in fact, it takes centuries to replenish just one inch (2.5 cm) of topsoil because of the slow, gradual cycles of weathering and decomposition.
- Soil is incredibly complex.
- We desperately need good-quality soil to survive.
- Soil is a renewable resource, but it takes a LONG time to regenerate.
The issue we face? Degradation. More specifically, we’re going to focus on erosion, the movement of particles by water (#1) and wind (#2). Now, this definition sounds pretty harmless, but there are some devastating consequences that come with these moving particles of soil:
- If the rate of erosion is greater than the soil formation rate, soil becomes a nonrenewable resource. Soil in the USA is currently eroding about seventeen times faster than it is being produced. (Maine Bureau of Land and Water Quality)
- Washed-away sediment is the number-one water pollutant. Sediment clouds water, preventing light from entering the water, thus decreasing the water’s overall productivity.
- Soil becomes less fertile. As we’ve already established, starvation isn’t fun.
Currently, we’re facing a huge worldwide problem with soil erosion, and it shows:
The above picture was taken in Madagascar, which has a huge problem with soil erosion due to deforestation. (Destruction of root systems + lack of soil cover + precipitation = severe water erosion of soil)
In the 1930s, the United States had its own problems with erosion: the Dust Bowl. (A sweet video below.)
So, what can we do about erosion? Well, farmers can plant crops without disturbing soil (low-till, no-till) and can leave crop residue and its stabilizing root systems; furthermore, they can plant cover crops and trees to protect soil in non-harvest times. On the government level, soil conservation programs (National Resources Conservations Services) can educate farmers on soil conservation principles, and subsidies for taking erodible land out of production (The Food Security Act of 1985) can help restore eroded areas.
Here are some additional erosion-reducing farming techniques:
- Terracing - cutting hillsides into earthen dams to slow water
- Contour farming – plant in strips on hillsides perpendicular to slope to slow flow of water
- Strip cropping – plant different types of crops in strips
- Alley cropping (agroforestry) - plant fruit-bearing trees in alternating rows with low-lying crops to block wind
- Windbreaks – plant trees around crops to block wind
I hope you enjoyed the scribe post, and I promise I’ll be kind in selecting the next scribe. Oh, some other links:
Carleton College Geoscience: An excellent collection of erosion-related videos.