What's Left to Eat?

Soil: Treating It Like Dirt

Soil isn't just dirt. Healthy soil is a complex community of living things. These organisms make farming possible. Yet current agricultural practices often treat soil like dirt. That can affect our food—and our health.

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The first U.S. President was also an innovative farmer. He grew more than 60 crops on his 3,000-acre plantation, Mount Vernon. Washington's pioneering methods made him part of the sustainable-agriculture movement of his day, known as the "new husbandry."

E03_side1_100x146 George Washington by Gilbert Stuart. This is the famous portrait that Dolley Madison saved from the burned White House in 1814. Source: The White House

Many farmers would deplete a parcel of land, then move west to new acres. Not Washington. He found ways to keep Mount Vernon's soil in good health. These included a seven-year crop rotation and plantings of grasses, clover, and buckwheat (which enrich soil). He experimented with various fertilizers such as fish heads, mud from the creek, and made fertilizers from manure, ashes, and even plaster of paris for its calcium and sulfur content. Washington thought that he was improving upon the customary method of plowing only a few inches. But we now know that his method of plowing 8 to 10 inches deep was harmful. Farming is a continual learning process.


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A few of Washington's crops.
Source: Mount Vernon

Concern for his soil spurred Washington to make an unusual decision for a Virginia planter: He stopped growing tobacco. It depleted the soil, and the market for it was unpredictable. Instead, Washington used wheat as his cash crop.

The Mount Vernon website can tell you all about how Washington was "first in farming."

 

"Wow! Look at that beautiful soil." That's not something you hear very often. Most people take soil for granted and few give it much thought. Yet we benefit from it many times each day—whenever we eat. Soil plays a crucial role in our ability to grow food.

 

Montgomery County, Iowa. Source: USDA
Montgomery County, Iowa.
Source: USDA

 

Healthy soil is a living entity, a rich mixture of organic matter (also called humus) and sand, silt, and clay. The layer closest to the surface is called topsoil. Beneath the topsoil are subsoils, layers of unweathered soil that are lower in organic matter. Below all that lies bedrock.

click to enlarge image
Source: Birdlife South Africa
Source: Birdlife South Africa

For farming, topsoil is the key layer. It's home to a host of living things: ants, mites, nematodes, slugs, snails, spiders, worms, and much more, including tiny dirt dwellers, known as microorganisms. Topsoil also includes the nutrient-rich remains of organisms that have died. You can learn about one prominent resident—the earthworm—at the University of Wisconsin's Urban Horticulture website.

SOIL CITY

The microbe population in a single teaspoon of topsoil can be larger than the human population on the entire planet!

Making themselves at home in their crowded world, these soil residents create a 3-D maze of minute tunnels called pores. These channels allow water and air to penetrate and move through the soil. As you can imagine, water's ability to reach plant roots is very important for raising crops.

 

Source: Natural Resources Conservation Service
Source: Natural Resources Conservation Service

 

Microorganisms also benefit soil in several other ways:

  • keeping nutrients in the soil,
  • killing pests that attack plants,
  • binding with soil in ways that make it less likely to wash away, and
  • making pollutants less harmful to the soil, sometimes even removing them completely.

THE SOIL FOOD WEB

Like computers connected to the World Wide Web, the jam-packed residents of the topsoil constantly interact with one another. But the action doesn't stop there. Plants growing in the soil also interact with those underground inhabitants. Add all those relationships together, and you get the soil food web.

click to enlargeSource: Bureau of Land Management
Source: Bureau of Land Management

The plant-soil relationship, scientists say, is one of the most extraordinary interactions in all of nature. For instance, most plant roots have cells that act as sensors. They can actually detect vital nutrients in the soil and direct the roots to grow toward them.

As plants grow, they remove some nutrients from the soil and return others. Different plants take and return different nutrients. These exchanges help soil renew itself over and over again. Understanding the importance of this process, farmers practiced crop rotation for thousands of years. They planted each crop in a different place every year, allowing these plants time to enrich the soil. Sometimes, farmers also let a field lie fallow, or empty. That gave the soil a chance to regenerate itself.

WHEN SOIL GOES "MONO"

Nowadays, however, many farmers do things differently. They practice monoculture, planting the same crop year after year. Doing so may help the farmer survive economically, but it takes a heavy toll on the soil. Soil degradation may result.

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Source: Journey to Planet Earth

Without natural ways of replenishing soil nutrients, farmers grow increasingly dependent on chemical fertilizers. These fertilizers can increase crop yields, but they affect the soil food web. Over time, the microorganisms become depleted and soil loses its vitality and is no longer full of life.

Something else happens too. Lacking microbes to create tiny waterways and organic matter that binds soil together, the soil becomes less porous, and more water runs off the surface. So some farmers need to use more irrigation water for their crops.

Problem is, irrigated land is often prone to salinization. Unlike rainwater, irrigation water contains salts and leaves salt deposits behind when it evaporates. The amount of salt that is left on the soil may be modest at first, but it builds. Once the land becomes too salty, growing anything on it is almost impossible. Ancient civilizations such as Mesopotamia disappeared in large part because their farmland contained too much salt.

RUNAWAY SOIL

What could be worse than damaging one's valuable topsoil? How about losing it altogether? Erosion is a major problem in many agricultural areas. The United Nations estimates that one percent of Earth's topsoil is lost to wind and water erosion each year.

Water can also carry off nutrients and other soluble matter that are vital to crop plants. This is called leaching.

 

Source: Natural Resources Conserva<span>tion</span> Service
Source: Natural Resources Conservation Service

 

Erosion happens for a variety of reasons:

  • Degraded soil is less porous, so water from irrigation or rain sometimes races over the land, into streams or rivers. As the water moves, it carries bits of precious topsoil along with it.
  • Grazing too many animals in a field can strip away plants that help hold soil together. And the animals' hooves pack down the soil, making it less porous.
  • Without the root systems of living plants to help hold dirt in place, air movements can easily sweep topsoil away. Countless acres of topsoil have truly gone with the wind.
  • Population growth has forced subsistence farmers in developing nations to try to raise crops on steep hillsides and in other areas prone to erosion. This makes erosion worse.
  • Clearing rainforests, primarily to grow commerical crops for export, has led to massive erosion.
  • Deforestation and poor farming practices in some places have caused an increase in desertification, the spread of deserts into surrounding areas. Scientists are still trying to determine whether that process can be reversed.

FIGHTING FOR HEALTHY SOIL

Soil degradation and erosion have serious consequences. Topsoil loss, particularly in developing countries, can lead to food shortages and even famines. The UN calculates that soil degradation afflicts 25 percent of farmland in the developing world, and the percentage is rising. Studies show that poverty and health problems are most prevalent in places with the worst soil.

To combat erosion, more and more farmers are turning to conservation tillage. That's a broad name for a variety of planting techniques designed to minimize erosion. One technique is to reduce the amount of plowing, or not plow at all (no-till farming). Another is drip irrigation, in which small plastic tubes slowly bring water to the base of each plant. This method cuts down on water usage, salinization, and erosion.

Soybeans. Source: Natural Resources Conservation Service
Soybeans grow amid "stubble" from earlier crops. Leaving old plants in place and not plowing them underground is an example of conservationtillage.
Source: Natural Resources Conservation Service

The Core 4 Conservation site offers pictures and diagrams that explain conservation.

Farmers are also creating set-asides. Set-asides are pieces of highly erodible land on which people no longer grow food. Instead, they plant cover crops, whose sole purpose is to help hold soil in place and build soil fertility. In some areas, laws force farmers to take such erodible land out of farm use completely.

Do these anti-erosion methods work? Yes! To take one awesome example, erosion has dropped by 90 percent in some parts of Latin America. If we're determined, we really can stop treating our soil like dirt.



 

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