Floating weed harvesters have opened passages through Dane County Wisconsin’s dense tangles of underwater plants for about 50 years. The barges wield rotating cutting bars like those on farm combines to cut a submerged crop that is fertilized too well by runoff of nutrients like dairy manure. Each spring, the county launches a flotilla of
An estimated 9 to 10 percent of Wisconsin wells have tested over safe limits for nitrate. Studies have estimated that 90% of nitrate in groundwater comes from spreading of synthetic fertilizers and dairy manure on farm fields, with most of the remainder from septic systems. Nitrate behaves differently. Relatively little lingers near roots where it