Soil Erosion: The Silent Killer

Published on: 09:16AM Dec 08, 2009
"The nation that destroys its soil destroys itself", President Franklin D. Roosevelt

The value of soil is something that is taken for granted. Soil is the foundation for all living things and without it, life on earth is not sustainable. Soil is a complex mixture of rock, organic matter, water, air, and living organisms that produces our food, cleans our water, and sequesters carbon. Despite this importance to the human population, soil is eroding faster than it is being replaced. In the last 30 years, roughly 30% of the Earth's arable land has eroded according to a David Pimentel, professor at Cornell University.

"Soil erosion is second only to population growth as the biggest environmental problem the world faces," said Pimentel.
Over half of America's best cropland is experiencing an erosion rate 27 times the natural rate or 11,000 pounds per acre according to the Department of Agriculture. The natural, geological erosion rate is about 400 pounds of soil per acre per year.
Iowa, which has some of the best topsoil is the world, has seen its topsoil erode from a depth of 18 inches down to 10 inches according to the Department of Agriculture. Productivity drops off sharply when topsoil reaches 6 inches or less, the average crop root zone depth, notes the Soil and Water Conservation Society.
According to Andres Arnalds of the Icelandic Soil Conservation Service, roughly 38,000 square miles of land (100,000 square kilometers) each year becomes severely degraded or turns into desert due to erosion.
"We are overlooking soil as the foundation of all life on Earth," said Arnalds. "Soil and vegetation is being lost at an alarming rate around the globe, which in turn has devastating effects on food production and accelerates climate change."
The primary cause of rapid soil erosion is modern farming techniques. Tilling and the removal of crop residues after harvest are the key culprits of erosion. The tracks left by tractors in the soil are the erosion route for half of the soil that washes or blows away. Row crops, such as corn and soybeans, result in roughly 50 times more soil erosion than sod crops, such as redtop and clover.
The economic impact of soil erosion in the United States costs the nation approximately $37.6 billion each year in productivity losses and damage from soil erosion. Worldwide it is estimated to be $400 billion per year, according to Cornell University.
One way to reduce soil erosion is to use no-till farming methods, which leaves crop residue (corn stalks) in the ground. The crop residues provide soil nutrition, water retention, and soil carbon. Currently, only 20% of corn in the U.S. is grown using no-till.
Iceland is a prime example of the dangers of soil erosion. Since the country was settled in the ninth century, over half of the vegetative cover has been destroyed and 40% of its soil has eroded according to a national survey completed in 1997. Now desert covers 45,000 square kilometers, or 40% of the country.
Despite spending the last 100 years trying to improve its soil, Iceland needs to import a large portion of its food supply and is continually battling climate change. Arnalds noted that Iceland should serve as a warning to other countries. "It is far better to preserve than restore," he said.
Carbon Storage
Soil stores carbon as it is one of the key ingredients for plant growth. The amount of carbon stored in soil is roughly twice the amount of carbon found in the atmosphere and three times the amount in vegetation. Across the US, agricultural methods have removed approximately 20% to 50% of the Earth's original soil carbon, and up to 70% in some regions according to the USDA.
Land degradation may account for up to 30% of the world's green house gas releases according to Ohio State University. While tillage of crop residue still locks carbon into the ground for a short period of time before it is released into the atmosphere, no-till methods lock carbon into the crop residue for a longer period of time, delaying the release into the atmosphere.
In many areas of the US, there becomes a problem when there is not enough moisture in the soil. Often times, irrigation is a last step for solving the low moisture dilemma, but no-till farming can be the first step. No-till farming locks in moisture throughout the entire year. Since the top portion of soil is not broken, moisture stays in the soil and will naturally work out any compaction layers within the soil through freezing and thawing.
On the other hand, some farmland experiences too much soil moisture. In these areas, typically in river valleys or other often flooded areas, soil must be tilled so the dark soil can be exposed to the sun and heat up in early spring, drying it out. If tillage is not done to moisture rich soils, the entire planting season is at risk because farmers cannot get into the fields.
Soil acts as one of the best natural water filters. For example, a substance will be absorbed into the ground by topsoil. Topsoil filters out many of the impurities and harmful makeup of the substance. After draining through the topsoil, the substance travels through a sandy gravel layer which will further filter the substance before it enters an aquifer, according to the University of Missouri. Surface water sifts through soil and by the time it reaches an aquifer, it is some of the purest, cleanest water on Earth.
Value of Farmland
No two parcels of farmland are identical when it comes to soil content. Soil classes have a direct correlation to the productivity of land. Farmland values differ due to variations of soil content. Soils are rated by class. Within each class, soils can be noted with a problem, such as erodible, or wetland. Farmland appraisers take soil contents into great consideration when valuing land.
Soil erosion is a growing concern across the globe. The demand for farmland is growing with the increasing population and food demand. Farmland is being lost to development at a rate of two acres per minute in the US according to the American Farmland Trust, while erosion is thinning the fertile topsoil of some of the most productive farmland in the world. It is very important that erosion is kept to a minimum because without a strong top soil, food production will decrease significantly.

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