The problem is agricultural practices that lead to increased runoff, not the amount of nitrogen naturally occurring in the soil or the amount applied. https://

The problem is agricultural practices that lead to increased runoff, not the amount of nitrogen naturally occurring in the soil or the amount applied. https://www.desmoinesregister.com/story/money/agriculture/2015/04/11/data-shows-nitrates-higher-improving-iowa-rivers/25606321/ https://www.desmoinesregister.com/story/money/agriculture/20... "Nitrate levels in Iowa's major rivers have increased more than threefold since the 1950s, but have stabilized — and even slightly declined — in recent decades, according to an in-depth review of available research."