ARS | Publication request: Changes in yield and nitrate losses from using drainage water management in Central Iowa, USA

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2012
Publication Date: November 1, 2012
Citation: Jaynes, D.B. 2012. Changes in yield and nitrate losses from using drainage water management in Central Iowa, USA. Journal of Soil and Water Conservation. 67:485-494.

Interpretive Summary: The upper Midwest is the dominant source of nitrate to the Mississippi River and most of this nitrate enters surface waters through the extensive network of agricultural, subsurface drain pipes underlying the region. Drainage water management (DWM) is a potentially valuable drainage management practice for reducing nitrate losses from artificial drainage. But the practice is essentially untested in Midwest conditions and its water quality and crop yield benefits unknown. This paper reports results from applying DWM to a 54 acre production field in central Iowa as part of a 5-state Conservation Innovative Grant effort to document the impact of DWM across the Midwest. We showed that over the 4-yr of the study there was a significant 18% decrease in tile flow, no significant decrease in nitrate concentration, and a significant 21% reduction in nitrate in tile drainage when using DWM compared to conventional drainage. No yield benefits from DWM were measured for 2 yr of corn, but a significant yield increase of 7% was measured for 2 yr of soybean. This study along with studies in other Midwest states will help the United States Department of Agriculture - Natural Resources Conservation Service (USDA-NRCS) and state action agencies determine to what extent the practice of DWM can impact local and regional water quality and to what extent the practice should be emphasized in cost share programs such as the Environmental Quality Incentives Program (EQIP).

Technical Abstract: Drainage water management (DWM) is a potentially valuable management practice for reducing nitrate losses to surface waters in areas of artificial drainage. But the practice is essentially untested in Midwest US conditions and its water quality and crop yield benefits unknown. This paper reports results from applying DWM to a 22 ha (54 ac) production field in central Iowa as part of a 5-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, nitrate concentration in the drainage, and crop yield were measured over 4 yr. The crop rotation was in a corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) 2-yr rotation with nitrogen fertilizer applied before the corn crop only. During 4-yr of monitoring tile flow, there was a significant 18% decrease in tile flow, no significant decrease in nitrate concentration, and a significant 21% reduction in nitrate leaching for the DWM treatment compared to conventional drainage. No yield benefits from DWM were measured for 2 yr of corn, but a significant yield increase of 7% was measured for 2 yr of soybean. From the 4-yr dataset of this study, it is unclear if this yield increase for soybean vs. no increase for corn was due to weather patterns in the 4 yr monitored or because corn and soybean responded differently to the raised water table caused by drainage management.