Summary prepared by: Jane Frankenberger, Agricultural and Biological Engineering, Purdue University
Frankenberger, J., McMillan, S.K., Williams, M.R., Mazer, K., Ross, J. and Sohngen, B., 2024. Drainage water management: A review of nutrient load reductions and cost effectiveness. Journal of the ASABE. 67(4): 1077-1092. https://doi.org/10.13031/ja.15549
Major findings:
We synthesized results of drainage water management (controlled drainage) studies from all available studies that met criteria from 1979 to 2022, and determined the following average effects:
- Nitrogen: The average nitrate reduction from DWM for 290 plot-years at 31 sites was 12 lb/ac/yr or 46%.
- Phosphorus: Very limited studies showed that dissolved reactive phosphorus was reduced by 0.04 lb/ac/yr (34%) on average, and total phosphorus was reduced by 0.06 lb/ac/yr (36%).
- Economics: Yield effects of DWM are highly variable, so economic analyses were done assuming no yield benefit and a 3% yield increase. With no yield benefit the cost of N reduction through DWM is $1 to $11 per kg N removed, while a 3% yield increase would lead to a likely net economic benefit to the producer.
Sites used to synthesize the N or P reductions from drainage water management in the United States, Canada, and Europe. Symbol size indicates the number of years of comparison between controlled and free drainage, and shape/color indicates whether both N and P were included or only N.
Contributions to the conservation drainage community
These findings confirm and quantify what was already generally accepted, indicating that DWM can be an effective practice for decreasing nitrogen loading from drained landscapes. However losses through unmeasured flow paths such as seepage and surface runoff may lead to overestimating the effectiveness of DWM, and 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. This study did not evaluate effects on greenhouse gas emissions. The dataset used in this analysis is provided at https://doi.org/10.13031/23596572.v1 and also at https://conservationdrainage.net/resources/controlled-drainage/reviewdata so other researchers can continue to build on this analysis to better understand the impacts of DWM. Our goals in providing it is to provide easy access for drainage researchers in understanding our interpretation of published research, and to serve as the basis for future synthesis studies. We hope that others will add additional studies as they are completed and published, so that this version can be kept up to date with current research. Please contact Jane Frankenberger, frankenb@purdue.edu, with additions or modifications to this spreadsheet.
Distribution of NO3-N load reductions in percent of NO3-N load in free drainage. Sites are arranged from highest to lowest median. Boxes show 25th and 75th percentile, the whiskers are +/-1.5 x the interquartile range, and all points outside those values are shown. The blue lines show the grand mean and confidence interval from the mixed effect model.