Field scale discharge and water quality response to drainage water management

Authors: King, Kevin; Hanrahan, Brittany; Stinner, Jedediah; SHEDEKAR, VINAYAK - The Ohio State University

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2021
Publication Date: 1/21/2022
Citation: King, K.W., Hanrahan, B.R., Stinner, J.H., Shedekar, V. 2022. Field scale discharge and water quality response to drainage water management. Agricultural Water Management. 264. Article 107421. https://doi.org/10.1016/j.agwat.2021.107421.
DOI: https://doi.org/10.1016/j.agwat.2021.107421

Interpretive Summary: Eutrophication continues to lead to harmful algal blooms, plaguing waterbodies worldwide. In poorly drained humid regions, nutrient transport from subsurface tile drainage has been identified as a significant source/pathway for nutrient delivery and is the focus for conservation practice implementation. Drainage water management (DWM), also known as controlled drainage, is a conservation practice that is being promoted to address both nitrogen and phosphorus transport from tile drainage. Using a before-after control-impact designed study on privately owned production lands in Ohio, DWM was shown to increase surface discharge as well as surface phosphorus losses while having little to no effect on subsurface discharge and phosphorus transport. However, DWM implementation significantly reduced tile drainage nitrogen losses. These findings are important for stakeholders and policy makers interested in identifying and promoting agricultural conservation practices to address water quality in tile drained landscapes. Furthermore, these findings highlight the need to understand the tradeoffs between surface and subsurface pathways as well as nitrogen and phosphorus when implementing conservation practices.

Technical Abstract: Subsurface (tile) drainage, while necessary for viable agricultural crop production in the humid, poorly drained regions of the world, has been linked to offsite nutrient transport, culminating in harmful algal blooms and hypoxia in downstream waterbodies. Drainage water management (DWM), also known as controlled drainage, has been promoted as a method to reduce nitrogen (N) and phosphorus (P) loss from tile drainage. Surface and subsurface discharge, N, and P loss from two sets of paired field sites in northwest Ohio, USA were evaluated to quantify the impact of DWM. Mean event surface runoff was significantly greater under DWM from one paired site and trending in that direction at the second. There was no significant difference in mean event tile discharge, though tile discharge from both sites was less under DWM. There was no significant difference in surface nitrate-N (NO3--N) loss; however, significant reductions in tile NO3--N loss under DWM were measured at both sites. Similarly, surface runoff dissolved reactive P (DRP) loss was significantly greater in one site under DWM and trending greater in the second, while no significant differences were noted in tile DRP losses with DWM. With respect to total P (TP), surface losses were significantly greater under DWM at the site with greater surface runoff; tile TP loss was less under DWM at one site with DWM. These findings suggest that DWM reduced tile NO3--N loss, while also highlighting that any benefit from DWM on tile DRP or TP loss could be negated in part by increased surface losses. Furthermore, these findings emphasize the need to understand the natural resource concern to which the practice is targeted and also call for additional research on DWM implementation that includes surface runoff across a range of soil textures, cropping management, and climates.