Week of 9/23/07

Dear EarthTalk: The soil beneath our feet is a critical resource we often take for granted. But I have heard that there are many threats to soil. What are they and how do we make things right?

—J. Lyons, Andover, MA

Even among the ecology-minded, soil falls well below the radar of important causes. But the relationship between soil quality and both environmental and human health is intricately entwined. From the food we eat and the clothes we wear, to the air we breathe and water we need to drink, we depend upon the dirt beneath our feet. Soil nurtures and feeds all life on Earth, while it under girds our cities, forests, waterways and crucial agricultural activities. Further, healthy soil and the plant matter it holds steady act as important "carbon sinks" that lock vast amounts of carbon up that would otherwise contribute to global warming.

Throughout history, great civilizations prospered where soils were fertile and fell when soils could no longer sustain rough treatment. In Mesopotamia, poor land management caused soils to become degraded, leading to loss of agricultural productivity, migrations—and ultimately, civilization collapse. Ancient Greece suffered a similar fate. Many experts also blame the fall of the great Mayan civilization on soil exhaustion and erosion, resulting from agricultural practices and clear-cutting of forests.

Today, we face many of the same issues: forest loss, over-consumption, overpopulation and over-worked soils nearing collapse. While factors such as logging, construction, off-road vehicles, floods and droughts threaten soil, high use of agricultural pesticides, fertilizers and other chemicals, as well as livestock grazing and the "factory farming" of food animals, are primary culprits.

Chief among threats to soils is damage to or loss of fertile topsoil. According to the American Society of Agricultural and Biological Engineers (ASABE), topsoil erosion today reduces productivity on 29 percent of U.S. cropland and negatively affects 39 percent of rangeland. In West Africa, fertilizer overuse is causing already acidic soils to become even more so, making the farming of even native crops difficult. In Sub-Saharan Africa, declining soil fertility from intensive farming is a main cause of poverty and hunger.

Urban erosion is equally significant and is becoming more serious as population growth fuels urban development. Housing and building projects gouge the soil and strip its vegetation. Rain then washes the soil away into sewers and then waterways. This leads not only to water pollution, but the glut of nutrients the soil carries with it causes "algae blooms" that use up oxygen and choke out the aquatic life.

Educating farmers in the U.S. and abroad about the damaging effects of intensive agriculture and over-application of synthetic fertilizers and pesticides is a good place to start to try to make things right. Converting more farming over to organic methods that eschew chemicals altogether is an even better solution. Supporting local farms also promotes better land stewardship, as mega farms make heavy use of synthetic fertilizers, and factory animal farms generate huge amounts of animal waste, which pollutes surrounding land and soil. And cities and towns can do their part by supporting low-impact development and mandating greener design standards.

CONTACTS: ASABE; The Scoop on Dirt: Why We Should all Worship the Ground We Walk On

Dear EarthTalk: I was surprised to learn recently that some cities, including New York, have outlawed kitchen-sink garbage disposals, at least in homes. I would have thought these machines were Earth-friendly. What’s the deal?

—Maggie Mangan, St. Louis, MO

Kitchen sink garbage disposals are not necessarily Earth-friendly in and of themselves, but they do play a valuable role in grinding up food scraps into small enough bits for local sewer or on-site septic systems to handle. In the U.S. overall, about half of all homes have a garbage disposal in the kitchen. New York did outlaw the devices for many years, thinking a ban would alleviate the strain on the city’s aging sewer system. But a study later conducted in the mid-1990s found benefits to lifting the ban, including a likely reduction in rat and cockroach problems and a reduced flow of solid waste to landfills already bursting at the seams. So in 1997 the Big Apple began allowing the devices again.

But garbage disposals are not the greenest way to dispose of food waste. According to Mark Jeantheau of the popular eco-website Grinning Planet, conscientious consumers interested in returning food-based nutrients back to the Earth should bypass the garbage disposal in favor of composting.

"The ground-up waste [in a garbage disposal] does not go back to nature’s water supply to be gobbled up by fish and other life forms," he says. Sewage-treatment and septic systems remove "any food value the waste might have had." Indeed, most modern-day sewer filtration systems utilize chemicals to rid the outflow of any life forms, beneficial or otherwise. Plus, grinding food in a garbage disposal uses a lot of freshwater, which is becoming a more and more precious commodity.

Those on their own septic systems also might want to minimize their use of the garbage disposal. According to the U.S. Environmental Protection Agency (EPA), regular use of garbage disposals leads to a "more rapid buildup of scum and sludge layers in the septic tank and increased risk of clogging in the soil adsorption field due to higher concentrations of suspended solids in the effluent." Jeantheau adds that even if a given septic system is designed to handle heavier, food-based loads, it still might not be worth the risk: "There are few homeowner nightmares worse than having your septic system go belly up."

While composting may sound like a messy proposition, it doesn’t have to be. For starters, those doing the dishes should make sure to dump any and all food waste items into a kitchen-based composting bin with a lid that seals tight. Many municipalities now make such bins available to interested residents. A mesh strainer in the hole in the sink can catch smaller food scraps and be dumped into the composting bin when the dishes are done.

When the kitchen-based compost bin fills up, it can be dumped into a larger composting bin outside. After four to six months, you should have some nice compost to add to your garden and jumpstart the health of your soil. Companies such as The Compost Bin and Clean Air Gardening offer online sales of a wide variety of quality compost bins of different shapes and sizes, and provide a wealth of comparative information for the interested consumer.

CONTACTS: Grinning Planet; The Compost Bin; Clean Air Gardening