Exploring the effectiveness of drainage water management on water budgets and nitrate loss using three evaluation approaches

Authors: SHEDEKAR, VINAYAK - The Ohio State University; King, Kevin; Fausey, Norman; ISLAM, RAFIQ - The Ohio State University; SOBOYEJO, ALFRED - The Ohio State University; KALCIC, MARGARET - The Ohio State University; BROWN, LARRY - The Ohio State University

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2020
Publication Date: 9/18/2020
Citation: Shedekar, V.S., King, K.W., Fausey, N.R., Islam, R.R., Soboyejo, A.B., Kalcic, M., Brown, L.C. 2020. Exploring the effectiveness of drainage water management on water budgets and nitrate loss using three evaluation approaches. Agricultural Water Management. 243. Article 106501. https://doi.org/10.1016/j.agwat.2020.106501.
DOI: https://doi.org/10.1016/j.agwat.2020.106501

Interpretive Summary: Subsurface (tile) drainage is critical to agricultural viability in poorly-drained, humid regions of the world. However, subsurface drainage has been identified as a significant pathway for nutrient loss and transport. The practice of drainage water management or artificially raising the tile outlet elevation was shown, through measured and simulated data, to significantly reduce the amount of water and nitrate nitrogen leaving the farm field. However, due to field slopes and hydraulic connectivity some uncertainty is introduced in the findings. Water quality specialists, researchers, and policy makers should more confidently be able to simulate the benefits of implementing drainage water management as a water quality practice and quantify the uncertainty associated with the potential adoption of the practice.

Technical Abstract: Subsurface (tile) drainage is a necessary practice for economic crop production in humid, poorly-drained regions of the world. However, subsurface drainage has been linked to water quality issues, which have led to the development of a practice known as controlled drainage or drainage water management (DWM). DWM is the practice of seasonally adjusting the outlet elevation of subsurface drains to reduce discharge and nutrient loads. The impact and assessment of DWM within simulation modeling frameworks has been limited by available data. In this study, we used DRAINMOD-NII model to simulate free drainage and DWM scenarios. The model was calibrated using drainage discharge and nitrate-nitrogen (NO3-N) loads measured at the outlet of a systematically drained agricultural field in the Upper Big Walnut Creek Watershed in central Ohio. The field was under a conventional or free drainage mode from 2005 through 2008, and under DWM mode from 2009 through 2014. Overall, the water budget was simulated with greater accuracy (R2=0.87) than predictions of NO3-N loads (R2=0.75). Even though NO3-N concentrations were observed to be slightly greater in DWM mode than in free drainage mode, the differences were generally only statistically significant (p>0.05) in certain non-growing season (NGS) months. The observed data and model simulations indicated drainage water management resulted in annual average reductions of 8.3 to 9.3% (~19 mm) in drainage outflow and 9.3 to 25.3% (~2.8 to 10.3 kg ha-1) in NO3-N loads compared to free drainage. Overall, DWM reduced the measured and simulated loss of water and nitrate, however the magnitude of the reduction is uncertain. The effective zone of DWM influence and lateral seepage to hydraulically connected fields and/or adjacent drainage ditches are important factors likely to cause under- or over-estimate of the effectiveness of DWM.