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Here's a fascinating trend in U.S. agriculture that's been going on for the past few decades. It's the dramatic rise ... of no-till farming:

(U.S. Department of Agriculture)

"No-till farming" sounds pretty dull at first. The term basically describes ways to grow crops each year without disturbing the soil through tillage or plowing.

But it's an important idea. Plowing and tillage are major sources of soil erosion around the world — they were key factors behind the Dust Bowl in the 1930s. What's more, churning up all that soil can release a significant amount of carbon dioxide into the atmosphere, helping to warm the planet. So, since the 1980s, more and more American farmers (and policymakers) have started taking no-till farming seriously.

In the United States, no-till farming is now growing at a pace of about 1.5 percent per year, according to the Department of Agriculture. In 2009, about 35.5 percent of the country's cropland had at least some no-tillage operations — though only 10 percentwere full-time no-till operations. (The rest involve a selective use of no-till or a mix of techniques.)

Why did no-till farming spread? This 2008 report (pdf) in Scientific American tells the broader back story. For most of human history, farmers plowed their soil to plant crops. The advent of tractors in the 20th century made it even easier to churn up fields. But as soil erosion became a massive environmental problem around the globe, that slowly changed.

Soybeans grown into corn stalks in a no-till field in Union County, Iowa (USDA)

The advent of new herbicides such as atrazine and paraquat in the 1940s and 1950s allowed farmers to kill weeds without plowing up more soil. And the invention of specialized seeding equipment in the 1960s allowed farmers to plant while barely disturbing the soil. Various federal government subsidies for soil conservation also gave farmers incentives to switch practices — particularly after the 1985 farm bill. So did higher oil prices.

The pros and cons of no-till: As the technique became more widely used, U.S. farmers found that they could conserve water, reduce erosion and use less fossil fuel and labor to grow crops. Cropland erosion in the United States dropped nearly 40 percent between 1982 and 1997.

But the practice can have downsides too: For one, it often leads to heavier use of chemical herbicides to kill weeds, which makes many farmers and consumers uneasy. (It's worth noting, however, that heavy herbicide use may not be inevitable; here's a look at ongoing research on how to reduce it through the use of cover crops and other techniques). The specialized equipment can also cost more upfront, even if it eventually saves time and fuel.

In addition, the transition in farming methods can often be difficult. And there are still some clear advantages to conventional tilling, which can, for instance, allow farmers to start planting earlier in the year after heavy rains, since plowing helps dry out the soil sooner.

Will no-till farming keep spreading? Based on survey data, the Department of Agriculture expects no-till operations to keep spreading in the United States in the years ahead, "albeit at a much reduced pace among corn producers."

(Scientific American)

But what about the rest of the world? That's a trickier question. In 2004, farmers were practicing no-till operations on less than 7 percent of cropland worldwide — and most of that was in the United States, Brazil, Australia, Canada and Argentina. The practice has barely caught on in Europe, Africa or Asia. China has only recently begun taking an interest in the concept (see chart).

A recent report (pdf) from the U.N. Environment Program (UNEP) argued that, historically, governments have had to step in to encourage the practice to get it to spread — either by offering research and training or providing financial support to help ease the transition. Australia, for instance, has offered tax credits to farmers to pay for the climate-change benefits from no-till farming.

If that trend caught on, it could have a few big climate benefits. It would lock more carbon in the soil and curtail fossil-fuel use in farm operations. The UNEP estimates that no-tillage operations in the United States have helped avoid 241 million metric tons of carbon-dioxide since the 1970s. That's equivalent to the annual emissions of about 50 million cars. What's more, the practice could help farmers deal with drought, which may become more prevalent in parts of the world if the planet keeps heating up.

Further reading:

-- This 2008 Scientific American essay on no-till farming (titled "No-Till: The Quiet Revolution") is a nice little introduction to the subject.

-- Page 24 of this UNEP report on climate change has a helpful discussion of no-till practices around the world — including both the benefits and why the transition is often so difficult.

-- Tom Philpott has a good profile in Mother Jones of no-till/cover-crop evangelist David Brandt.