Economic and Environmental Considerations for Drainage Design

Abstract

<p>Water table management through the use of artificial subsurface drainage systems is of primary importance in humid areas with poorly or somewhat poorly drained soils to maximize agricultural productivity Excess precipitation in Iowa and many other Mississippi/Ohio River watershed agricultural production states is removed artificially via subsurface drainage systems that intercept and usually divert it to surface waters. Subsurface drainage systems have been installed to allow timely seedbed preparation, planting and harvesting and to protect crops from extended periods of flooded soil conditions. The tradeoff of improved subsurface drainage is a significant increase in the losses of nitrate-nitrogen (Gilliam, et al. ,1999). Nitrogen, either applied as fertilizer, or manure or derived from soil organic matter, can be carried as nitrate with the excess water in quantities that can cause deleterious effects downstream. The movement of nitrogen from agricultural fields via drainage waters is a major factor in nonpoint source pollution of surface waters and ultimately the Gulf of Mexico where it has been implicated as a cause of the Hypoxic Zone (Mitsch et al., 2001; Rabalais, et al., 1996). As a result there is a need to investigate methods that can be used to minimize the loss of nitrates via subsurface drainage. One method to do this is to design the drainage system to drain the minimum amount of water required to maximize crop production or net production benefits. Skaggs et al. (2003) have demonstrated that as drains are spaced closer together the volume of subsurface drainage increases and subsequently the nitrate loss increases. Also, as the drains are spaced closer together the cost per acre for the drainage system increases. However, as drains are spaced further apart there can be a decrease in crop production which would have a negative economic impact. So, in designing and installing a subsurface drainage system the environmental implications and economics of the system should be considered. The purpose of this paper is to discuss how economics and the environment can both be considered in drainage design.</p>