Beyond fertilizer management for reducing nitrogen losses to surface waters in the corn belt of United States

Background/Question/Methods

The United States is the leading producer of corn and soybean in the world.  Most corn and soybean is grown in the Midwest – a region dominated by seasonally wet soils requiring artificial subsurface drainage for crop production.  Row crop production on these soils has been identified as the major source of nitrate within the Mississippi River basin and nitrate is the primary cause of hypoxia in the northern Gulf of Mexico.  As a consequence, much attention has been focused on nitrogen management to reduce the reactive N entering the Nation’s waters from row crop production.  However N fertilizer management alone cannot reduce nitrate losses from artificially drained fields sufficiently to meet water quality goals, thus additional methods for reducing nitrate losses are needed.  These methods include the incorporation of fall-planted cover crops into the corn-soybean rotation to extend the growing season.  Other practices focus on the subsurface drainage that transports most of the nitrate to surface waters.  These practices include denitrification wetlands, drainage water management, and denitrifying bioreactors.  A newly emerging practice, re-saturating riparian buffers, focuses on reconnecting the artificial drainage with riparian buffers and using the buffers to remove nitrogen before entering streams. 

Results/Conclusions

Adopting these practices on all suitable locations, would have the potential of reducing nitrate loads to Midwestern streams from 20 – 25% and would do so at a cost ranging from US$1.90 – $13.75 per kg N removed.  So what are the current impediments to wide scale adoption of these practices?  Currently there are no economic incentives for farmers to adopt these practices, thus the costs need to be borne by the public sector and conservation practices need to compete with other uses of these funds.  In the near term, additional sources of monies for conservation practices do not appear likely.  How about by the turn of the century?  Certainly it is hazardous to predict this far into the future, but some trends appear to be well established.  Corn and soybean production will need to increase to provide food for an increasing world population and the increasing desire for meat protein by newly affluent countries.  Conversely, fuel will become much more expensive which will increase the cost of farming and make conservation of on-farm resources more economically attractive.  An agricultural production system less dependent on inputs from outside the farm represents a unique opportunity for the increased adoption of conservation practices for water quality.