Farmers in the Upper Mississippi River basin have made significant progress in reducing sediment, fertilizer and pesticide runoff but need to do more to cut pollution to acceptable levels, a major U.S. Department of Agriculture study says.

Agriculture Secretary Tom Vilsack said Tuesday that the study establishes that good conservation practices do indeed work. It’s the first among several studies the USDA plans to release evaluating the effectiveness of conservation practices on major watersheds.

“First and foremost we found that farmers in this area are stepping up in a significant way to embrace conservation,” Vilsack said in a phone interview with The Associated Press before the report’s release on Wednesday.

The region’s most critical conservation concern is excessive runoff of nitrogen fertilizer, the report said. The region’s corn crop, in particular, uses large amounts of nitrogen.

About 51 percent of crop acres in the region require more aggressive steps to reduce nitrogen loss, and about 62 percent of the region’s cropland overall requires better management to reduce losses of nitrogen and phosphorous, which leaches out of manure and other sources.

The solution, the report and Vilsack said, is better attention to the proper rate, forms, timing and methods of fertilizer application.

On the positive side, the study found use of soil-erosion controls are widespread, and only about 15 percent of cultivated acres still have excessive sediment loss. And it said conservation practices in the region have been highly effective in reducing pesticide runoff.

“When you see the pesticide risk to human health reduced by 48 percent, and only 1 to 2 percent of pesticide actually leaves the field, we know that with more precise application, more rotations and scouting, we can do an even better job of reducing risks associated with pesticides and reassure people about the safety of the food that they’re eating,” Vilsack said.

The Upper Mississippi basin covers about 190,000 square miles, including large swaths of Minnesota, Wisconsin, Iowa, Illinois and Missouri, as well as smaller parts of South Dakota, Michigan and Indiana. It accounts for more than 40 percent of the U.S. corn harvest and more than a third of the U.S. soybean crop.

“This kind of study allows us to reaffirm to taxpayers that investment in conservation are wise and appropriate uses of their dollars,” he said.

Vilsack said the findings give the USDA reason to be more confident of the value of its other upcoming reports, including its study on Chesapeake Bay.