Boosted by increasing commodity prices, farmers in the Bay watershed have begun planting more land in row crops, reversing a long-running decline in cropland acreage.

The change is a boon to farmers, who have sharply increased planting corn, wheat and soybeans as prices for each set records this year.

But the change also carries a price for the Chesapeake-and Bay cleanup efforts. The transition of hay, pasture or idle land to corn and soybean production can dramatically increase the amount of nutrients and sediment washing into local streams.

It also means that Bay cleanup plans, know as tributary strategies, likely underestimated the level of effort needed to reduce pollution from agricultural lands.

Food prices are soaring, in part because of increased demand for ethanol, but also because of global food shortages, which has led the United Nations to urge increased production.

"What is driving it is world prices," said Doug Parker, a professor of agricultural economics at the University of Maryland. "Farmers are business people. They are responding to the price and the market."

But it's also a stark reminder that efforts to clean up the Bay can be seriously sidetracked by factors that originate from changes far outside the watershed.

"If we don't understand that, people may have false expectations about what we can achieve," said Mark Dubin, an agricultural specialist with the University of Maryland who is stationed at the Bay Program Office in Annapolis. Outside market forces, he said, "probably have more impact than anything else we do."

The impact on the Bay could be significant. Calculations by Dubin suggest that the increased amount of crop land, coupled with the more intensive use of crop land, may be coming close to offsetting other nutrient reduction efforts from agriculture.

A year ago, some experts had worried that increasing demand for corn-driven in part by increasing demand for ethanol- would cause farmers to grow more corn instead of other crops.

But the emerging picture is more complicated. Even though they did not switch from growing other crops to grow corn, farmers across the watershed are still growing significantly more corn, soybeans and wheat than they did just two years ago, according to figures from the U.S. Department of Agriculture.

Because other crop plantings have not decreased-such as oats, barley, cotton and peanuts-the increase appears to have come from other land, such as hay, pastures or previously idle farm land.

Watershedwide, an analysis of USDA figures by the Bay Journal indicate that about 65,000 additional acres were plowed for crops this year than in 2006.

Overall, the watershed has about 3 million acres of corn and soybeans, and the additional plantings since 2006 represent an increase of about 2 percent.

While that change may seem small, the impact on the Bay can be significant. A hay field, for instance, may lose only about 6 pounds of nitrogen per acre each year. Idle lands and pastures similarly produce small nitrogen "loads" to streams, and ultimately, the Bay.

When converted to more intensive row crop production, those numbers can increase dramatically. Soybeans lose about 22.5 pounds of nitrogen per acre and corn, 30 pounds. So a switch from soybeans to corn has less of a nutrient impact than a switch of hay or idle land to corn or soybeans.

And that change is only part of the story. High commodity prices have also triggered a sharp increase in wheat plantings, USDA figures show.

The amount of wheat in the watershed- which typically is planted on fields after other crops are harvested-surged by 135,000 acres from 2006.

That has some benefits: Wheat plantings can help stabilize soil and reduce erosion during the winter, and if planted as a cover crop and not fertilized in the fall, can absorb some excess nitrogen left in the ground after soybeans or corn is harvested.

When fertilized to maximize production, though, it results in more nitrogen seeping into streams.

"If it is a cover crop, it's a positive change," Dubin said. "If it's not, it's more of a negative change."

Dubin said it was a "shot in the dark" to estimate the impact of increased wheat production. But a vast majority of winter wheat grown in the watershed is not enrolled in cover crop programs. With wheat hitting record prices, both Dubin and Parker said the temptation would be great to maximize production on other acreage.

Calculations made by Dubin suggest the increased crop acreage, coupled with more intensive production from those fields, had the potential to increase runoff from row crops by 8 million to 9 million pounds of nitrogen per year since 2005, an average of nearly 3 million pounds a year.

In comparison, nitrogen reductions from all sources in the watershed have averaged about 3.5 million pounds per year. "The combination of land use change and intensification will start canceling out nutrient reductions," Dubin said.

For the Bay Program, the change presents another problem. From 1985 through 2005, the total amount of row crop land in the watershed had declined by more than 600,000 acres, from 4.85 million acres to 4.23 million acres.

That trend was expected to continue into the future. Figures from the Bay Program show an expected loss of another 124,000 acres of crop land between 2005 and 2010. So tributary strategies anticipated a loss of high runoff from crop land, not an increase.

Further, the Bay Program expected the amount of low-runoff hay land to increase, not decrease. That means the amount of actions needed to control agricultural runoff were almost certainly underestimated in the strategies.

The upside is that increased profitability provides an incentive to keep farmland in production in areas under development pressure. "There's a positive in staying in agricultural land use," Dubin said.

Increased farmland production can help bolster the economies of struggling rural communities.

"It is providing an economic base to the farm community that it hasn't had for 100 years, so I really can't complain about it," said Bill Matuszeski, former director of the Bay Program Office, who has recently worked on reports exploring the potential of biofuels to boost farm income. "The major decisions are being made by the farmers and not the state programs which are underfunded."