Drainage water management: A review of nutrient load reductions and cost effectiveness

Authors: FRANKENBERGER, JANE - Purdue University; MCMILLAN, SARA - Iowa State University; Williams, Mark; MAZER, KATY - Purdue University; ROSS, JARED - Michigan State University; SOHNGEN, BRENT - The Ohio State University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2023
Publication Date: 7/15/2023
Citation: Frankenberger, J., Mcmillan, S., Williams, M.R., Mazer, K., Ross, J., Sohngen, B. 2023. Drainage water management: A review of nutrient load reductions and cost effectiveness. Journal of the ASABE. https://doi.org/10.13031/ja.15549.
DOI: https://doi.org/10.13031/ja.15549

Interpretive Summary: Farm fields in the Midwestern U.S. are often too wet to farm and require subsurface drainage. Subsurface drainage lowers the water table, which allows for crop planting and harvesting. Drainage, however, is not needed all year. Keeping some water in the field during the winter or growing season can decrease nutrient loss and improve crop growth. Working with university partners, ARS scientists in West Lafayette, Indiana reviewed the cost-effectiveness of drainage water management. Drainage water management uses a control structure near the edge of the field to keep water in the field during certain times of the year. This water would otherwise be delivered downstream. Scientists used data from around the world collected between 1979 and 2022. Results showed that this practice can improve corn and soybean yield by up to 3%. Increased yield because of this practice can increase farm income by up to $125 per acre per year. Drainage water management also decreased nutrient loss by 40%. This practice can therefore increase farm income and improve water quality. There are 25 million acres of cropland in the Midwest where this practice could be used leading to $3 billion in revenue increase for American farmers.

Technical Abstract: Drainage water management (DWM) is the practice of seasonally adjusting the drainage outlet elevation with a control structure and is implemented to decrease nutrient loss in drained agricultural landscapes. In this study, we review the effect of DWM on annual nitrogen (N) and phosphorus (P) loads compared to free drainage and examine its cost-effectiveness using data from around the world published between 1979 and 2022. Studies included in the review were limited to row-crop agriculture without irrigation, with controlled drainage and free drainage compared during the same year. A total of 290 plot-years for N were compiled and analyzed using a mixed effects linear model to assess differences in flow, load, and concentrations and account for within and among site variability. Few studies examined dissolved reactive P (DRP) or total P (TP); thus, results from these studies were summarized and qualitatively compared. Analysis of N data showed that DWM reduced N loss on average by 13.3 kg/ha/yr (95% confidence interval: 9.4 - 17.3 kg/ha/yr), which corresponds to a 46% load removal efficiency (95% confidence interval: 37.4 - 54.5%). Drainage water management decreased annual DRP and TP load compared to free drainage by an average of 0.04 kg/ha/yr (34%) and 0.06 kg/ha/yr (36%), respectively. Economic analysis showed that cost of N reduction would range from $1 to $11 per kg N removed assuming no yield benefit, while a 3% yield increase would lead to a likely net economic benefit to the producer. Findings indicate that DWM can be an effective practice for decreasing nutrient loading from drained landscapes, however, losses through unmeasured flowpaths such as seepage and surface runoff may be contributing to this load reduction. Additionally, complex interactions among soil organic matter, soil nutrient levels and water table depths need to be accounted for to ensure both N and P removal is achieved. Recommendations for monitoring discharge and nutrient loads in future DWM studies are provided to better understand the processes influencing nutrient load reductions and/or increases and further quantify the effectiveness of DWM implementation in drained landscapes.