By Brad Reagan

The practice of no-till planting has a firm foothold among American farmers. But many of them aren't using it full time—and there are big obstacles that may limit how far it spreads.

Introduced in the early 1960s, no-till didn't hit the mainstream until about 1980, after gas prices spiked. By 2009—the latest figures available—about 35.5% of the country's cropland had no-tillage operations, according to the Department of Agriculture.

Now the agency estimates the practice is growing by 1.5% a year, says John Horowitz, an economist with the USDA's Resource and Rural Economics Division. But those numbers don't tell the whole story.

For one thing, most American farmers—unlike their peers in countries such as Brazil—use no-tilling methods only part of the time. Less than 10% of American farmers are considered "continuous no-till" practitioners, says Tony Vyn, a professor of agronomy at Purdue University.

The rest employ no-till on a selective basis, or use hybrid techniques such as "strip tillage," in which they loosen only those zones of soil where seeds will be planted and leave the areas between them untouched. "That is the route more and more operations are taking," Dr. Vyn says.

Why? Conventional tilling offers one big advantage to farmers: the potential for earlier—and thus longer—planting seasons in certain circumstances.

When there's a lot of rain in late spring, no-till farmers have to wait until the fields dry naturally before they can start planting. But plowing dries out fields, so farmers who use traditional methods can start planting a lot sooner.

Another obstacle to no-till is a bit of a paradox: While the practice is generally perceived as environmentally friendly, it also requires more herbicide use. After all, disrupting the weed cycle is one of the primary reasons farmers plow their fields.

Not only does heavy use of herbicides make some farmers and consumers uneasy, some farmers have reported that weeds are getting increasingly resistant to herbicides. That forces them to find new combinations of weed killers or, in some cases, return to plowing.

Looking forward, researchers are watching closely to see how farmers react to the effects of this year's calamitous drought, which Mr. Horowitz calls "a curve ball" for the adoption of no-till.

No-till farmers typically benefit when droughts hit in July and August, when their fields are able to supply moisture better than fields that have been plowed. This year, though, the drought hit much earlier, landing in full force in May through some major corn-producing states like Indiana. That hurt many no-till farmers, because the roots of their crops hadn't yet been established when the heat wave hit.

But Mr. Horowitz says the long, dry summer will also likely draw attention to no-till's abilities to lessen soil erosion and retain moisture. Meanwhile, if gas prices continue to creep higher, he says, that also would attract more farmers.

"We expect, if anything, [the drought] will accelerate the adoption of no-till," he says.