Decades of adding fertilisers and manure to drive Iowas crop production has loaded the land with nutrients that are ending up in the water supply
Brent Bierbaum climbs into the ditch running alongside one of his corn fields and dips a nitrate testing strip into the water. He checks the strip: the reading is somewhere between 10 and 20 parts per million. It confirms the water running off this field contains nitrates at levels that would be unsafe, and illegal, in drinking water.
Brent, whose family have been farming in this part of south-west Iowa for five generations, never used to worry about the runoff from his fields. On a hot day, cutting thistles in the corn fields, hed go down to the creek and drink straight from the tile line the water coming off the fields. Cold, clean its the best water around, he says.
Things changed when his local town, Griswold, started having problems with their drinking water. Nitrates are a soluble form of nitrogen that is added to fields as synthetic fertiliser and animal manure; nitrates from Brents fields, and other neighbouring farms, were making their way into the towns wells. Nitrate from farmland in Iowa is already a major contributor to the chemicals making their way to the Gulf of Mexico via the Mississippi river, suffocating marine life in the dead zone. Suddenly what had been a distant problem, more than a thousand miles away, was on the doorstep, threatening the health of friends and neighbours.
Oh my gosh, he says. We all have friends who drink the water in town; we drink the water in town, so we all had an interest in it.
Like most small towns in rural Iowa, Griswold is surrounded by vast fields of corn and soya bean. Giant grain silos glinting in the spring sunshine are all that punctuate the landscape for miles around.
Iowas world-famous soils are packed with nitrogen a gift from nature that allowed commercial agriculture to take root here but decades of adding synthetic fertilisers and animal manure to drive production has loaded the land with nutrients it cant hold on to. Crop production in Iowa is still the main source, but animal manure from the states 20 million pigs has contributed to the problem.