Changes in yield and nitrate losses from using drainage water management in central Iowa, United States

Abstract

Drainage water management (DWM) is a potentially valuable management practice for reducing NO₃ losses to surface waters in areas of artificial drainage. But the practice is essentially untested in Midwest United States conditions and its water quality and crop yield benefits uncertain. This paper reports results from applying DWM to a 22 ha (54 ac) production field in central Iowa as part of a five-state Conservation Innovative Grant effort to document the impact of DWM across the Midwest. Three of nine plots in an existing tile drainage research site were retrofitted with control structures so that the drainage level could be controlled. Water flow from the tile in each plot, NO₃ concentration in the drainage, and crop yield were measured over a four year period from 2006 to 2009. The field was in a two year corn (Zea mays L.)–soybean (Glycine max [L.] Merr.) rotation with nitrogen (N) fertilizer applied before the corn crop only. During four years of monitoring tile flow, there was a significant (p = 0.05) 21% decrease in tile flow, no significant decrease in NO₃ concentration, and a significant 29% reduction in NO₃ load leaching from the DWM treatment compared to conventional drainage. No yield benefits from DWM were observed for the two year average for corn (2006 and 2008), but a significant yield increase of 8% was observed for the two year average for soybean (2007 and 2009). For the four years monitored in this study, it is unclear if the yield increase for soybean versus no increase for corn was due to weather patterns or because corn and soybean responded differently to the raised water table caused by DWM.