Science Assessment to Support an Illinois Nutrient Loss Reduction Strategy.

Illinois developed a strategy to reduce both nitrate-N and total P stream loads by 45%. This was required by USEPA to improve local water quality and reduce the hypoxic zone in the Gulf of Mexico. To support the strategy development, we conducted a science assessment of nutrient loads in the state, identified and estimated both point and non-point sources, and then estimated how effective various practices would be in reducing nutrient losses along with the costs. We combined the various reduction methods into scenarios that would reduce nutrient loads by 20 or 45%. Annualized twenty-year total costs for 45% reductions in nitrate-N and total P were estimated at about $800 million per year, with substantial upfront costs depending on the practice. Of that total, $114 million was for point source reductions, with the remainder for agriculture. Reductions in nutrients from the various practices varied from 7 to 90% per acre; only perennials were > 50%.  Practices such as cover crops would reduce both nitrate-N and total P losses, but were expensive per lb of nutrient reduced. For nitrate-N, tile bioreactors were cheapest, but were not well accepted by the stakeholder group. For P, reduced tillage and P fertilizer reductions would both save dollars and reduce nutrient losses. No one practice could make major reductions individually, and most of the 22 million corn and soybean acres in the state would need to employ one of the practices listed. Initial efforts might first be directed towards point source P reductions and nitrate-N losses from tile-drained agricultural fields, as this would be the most cost effective approach.