As a farmer perhaps I can add some insight into this issue.  Corn is the crop that generates the most income on my operation and while it is possible for some operators to produce alternative crops like hay or vegetables, the economies of production demand that corn be grown in Iowa.  There are three primary methods of applying nitrogen in Iowa.  Anhydrous ammonia can be applied in the fall and with the use of some “preservative” additives this can be a pretty good method.  Anhydrous ammonia can be spring applied before planting as can either ammonium nitrate which is a white salt like solid or a urea liquid solution which is a combination of ammonium nitrate and urea.  All three forms of nitrogen can also be applied after the crop is growing.  The application of these products before planting in the spring is probably the most common method in Iowa.  If the soil does not become over saturated after application the majority of the nitrate stays put and is used by the corn crop.

Perhaps the best management practice for nitrogen application is to apply some before the corn is planted and the rest after the corn is growing.  The split application minimizes the chances of nitrates leaving the field but this can be challenging as adverse weather can prevent later applications not to mention the fact that additional applications cost money. 

This spring we had extremely wet weather which has resulted in very high nitrate levels in the rivers.  As to answering Tom’s question as to where the nitrates are coming from I would suggest that if you could find a graph of nitrate levels in the river water over time you would get a pretty good idea of where it is coming from.  Being that most of the fertilizer is in place by late spring or early summer one would expect that the portion of the contribution would fall off through the rest of the year.  I did a little searching and was unable to find any good charts documenting nitrate levels on a short enough time scale to implicate agriculture although I am sure that data of that time scale is available.

My gut instinct is that the majority of the problem we are seeing in Iowa this year is due to corn production.

What can be done?  Later applications of nitrogen would surely help but these also add expense that the farmer has to incur in extra passes and equipment.  My personal fantasy would be some kind of encapsulated form of nitrogen that could be applied before planting but would release on a time schedule regardless of moisture conditions so that the crop could be fed as needed.  I have not heard of any such research happening but who knows?  I once asked an agronomist if he thought that a corn plant would ever be created that could fix its own nitrogen but he replied that the energy demands of nitrogen fixation would ensure that such a plant was not competitive with more traditional types of corn.

Perhaps the simplest short term solution would be to have waterworks increase their treatment capacity.

Corn production is not perfect by any means, but it does work well in Iowa and it does contribute greatly to the state’s economy.  The ultimate answer is probably a combination of all factors contributing a little to hopefully get things to a manageable level.

Steve Swan

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