Controlling aquifer nitrogen levels when fertilizing crops: A study of groundwater contamination and denitrification

Nitrogen levels in groundwater are a safety concern because many of the aquifers are below intensive agricultural production areas. This paper uses a dynamic model of groundwater flow and denitrification to determine if cropping practices with heavy nitrogen use, such as continuous corn, cause the aquifer nitrogen level to exceed the EPA limit. In many instances, high nitrogen use by farmers does not lead to excessive nitrogen levels in the aquifer. However, in those situations where aquifer levels are too high, a reduction in fertilizer can lower aquifer nitrogen without a similar loss in profitability. A key point for aquifer nitrogen levels is the rate of denitrification. If this rate is too low, then nitrogen will likely be a problem no matter what farmers do. The effects of a nitrogen standard versus a nitrogen tax are also addressed and results show that information about the aquifer is needed for either to be effective. In addition, an input tax would have to be relatively large to be effective.