The heavy snowpack covering Iowa's farm fields hides many secrets, including a future this spring that could mean flooding and significant, damaging runoff of Iowa's topsoil and its crucial nutrients.

Iowa lost up to $1 billion worth of nitrogen 2 years ago as floods cut through the eastern third of the state. Mahdi Al-Kaisi, associate professor and extension soil scientist at Iowa State University, described the spring 2 years ago as "a significant loss of both topsoil and nitrogen."

The spring runoffs are just the latest chapter in what has been a longstanding worry in Iowa: the loss of the state's valuable topsoil and its nutrients, which have either blown away or been washed downstream.

"In the 150 or so years since soil cultivation began in Iowa, we've lost about half of the organic nutrients originally in the soil," Al-Kaisi says.

Environmentalists worry about nitrates — the soluble particles that can't be held in the soil under wet conditions — running into rivers and lakes, expanding the environmental degradation of Iowa's waters. Iowa farmers are no less concerned about the problem.

"I worry a lot about my nitrogen, but then I worry about it every year," says Roger Doehrmann, who farms near Williamsburg, Iowa.

Tim Burrack, a veteran farmer in the Arlington area of northeast Iowa that was hit hard by flooding 2 years ago, says: "You're always nervous as you look forward to spring. I know people are worried about snow, and they should be, but usually it's the spring rains that do the damage."

Snow has been on the ground for a record 2 months already, which is a mixed bag for farmers, Al-Kaisi says. As long as the snow is on the ground, it performs several valuable functions.

"The snow holds down the topsoil, so you don't have wind erosion," Al-Kaisi says.

The snow also keeps the soil warmer.

"If there is snowpack, then the temperature of the ground and subsoil below stay more constant than if the ground is bare under severely cold conditions," he says.

That extra-hard ground, exposed and frozen in winter, will thaw more slowly and thus be more prone to runoff in the spring.

"It really is better to have snow all winter long, because it keeps the soil temperature stable and allows better absorption of the water when the snow beings to melt," Al-Kaisi says.

It's when the melting begins that things get dicey. Ideally, a midwinter thaw will spread the melt over a longer period. But many know the state can seldom count on such good fortune.

Iowa farmers will face more risk this spring because the water tables already are high, thanks to two consecutive years of above-average moisture. October had the most rainfall in Iowa since 1881.

"The ability of the soil to absorb moisture will be more limited than usual," Al-Kaisi says.

Another complicating factor this spring will be how much tilling and nitrogen application still needs to be done on fields that may have missed the usual postharvest fall work because of the weather-delayed harvest.

Farmers typically like to do their tilling and fertilizer application in the fall, which usually is drier and offers better conditions and a longer window of opportunity for work than Iowa's typically wet springs.

But the wet 2009 was not a usual fall. Burrack considers himself among the fortunate.

"I was able to get most of my dry fertilizer on and about half of my ammonia," Burrack says.

Al-Kaisi says many farmers couldn't get their fertilizer on in the fall, and the spring applications are more vulnerable to snow and rain runoffs.

"Management is really the key," Al-Kaisi says. "People don't realize the stress farmers face in the spring getting everything timed correctly."

Beyond the matter of timing of tilling is the question of whether to till at all.

Farmers traditionally have tilled soils for the benefits of aeration, plus the belief that tillage reduced the growth of micro-organisms. Motorists on Iowa highways annually see the black, overturned earth that signals the end of harvest.

The no-till faction has long decried the practice because the loose soil is more vulnerable to wind erosion if it doesn't get winter snow cover.

While city dwellers might think that tillage enhances the ability of the soil to absorb moisture, Al-Kaisi says that is not so.

"Tillage actually creates a layer of compaction in the soil about 18 to 20 inches below the surface, which interferes with the absorption of moisture," Al-Kaisi says. "If you don't till, then the soil can more naturally absorb moisture."

Al-Kaisi counts himself among the no-till advocates. Where fall or spring tillage was once almost universal in Iowa, today as much as 20% of corn acres and 30% of soybean acres are left untilled.

No-till advocates say the preserved cornstalks in untilled fields act as a brake for snow and ice, which reduces the drifting that, come spring, can lead to flood problems.

"No-till definitely is a way to reduce the dangers of spring flooding," Al-Kaisi says.

But he says no-till doesn't work everywhere.

"No-till works just fine for soybean acres," Al-Kaisi says. "But it presents challenges for corn."

A particular hurdle for no-till is in the poorly drained Des Moines Lobe, a geological formation. The Des Moines Lobe extends from its namesake city northward to the Minnesota border between Dickinson and Howard counties. It was left behind by Iowa's last glacier about 12,000 years ago.

While the soil in the lobe is rich, it drains poorly. Al-Kaisi says.

"This is the area where no-till farming is most difficult," he adds.