Evaluation of DRAINMOD in predicting nitrogen and phosphorus losses from a drained field in northcentral Ohio

Authors: Askar, Manal; YOUSSEF, MOHAMMED - North Carolina State University; King, Kevin; SHEDEKAR, VINAYAK - The Ohio State University

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Agricultural crop production within the Great Lakes Basin continues to a be focal point for water quality concerns within the lakes, specifically those lands that are artificially (subsurface tile) drained. Implementing conservation practices has been offered as a solution to the tile drainage nutrient transport issues, particularly those associated with the Lake Erie watershed. However, the diversity of soils, climate, cropping practices, and fertility that exists in the watershed introduces uncertainty in quantifying the potential effects of conservation practice adoption. Simulation technologies such as modeling can be used to assess the impacts of single and multiple practices. DRAINMOD, a popular water quality model for tile drained landscapes, was parameterized, calibrated, and validated for a field site in the Western Lake Erie Basin watershed indicating its utility in the watershed for assessing nutrient movement through tile drainage. Model predictions were reasonable for discharge and soluble nutrients but improvements are needed for application to sediment bound nutrients. These findings highlight the applicability of the DRAINMOD technology, particularly the phosphorus component for practitioners needing or wanting to assess water quality in tile drained landscapes.

Technical Abstract: Field-scale modeling studies that report nitrogen (N) and phosphorus (P) dynamics in agricultural lands are scarce. DRAINMOD-P is a useful tool that is fully integrated with DRAINMOD-NII making it a useful tool to predict both N and P dynamics in drained croplands. However, DRAINMOD-P has been previously evaluated at only one field site. The objective of this study was to further test the P component of DRAINMOD-P while also calibrating and validating the N component for the same location. Four years (2017 – 2020) of measured data from a field in northwest Ohio were used parameterize calibrate and evaluate predictions for subsurface drainage discharge volume, nitrate (NO3--N), dissolved reactive P (DRP), and total P (TP) loading. Calculated Nash-Sutcliffe Efficiency (NSE) for mean monthly drainage discharge predictions was 0.77 and classified as “ very good” (i.e., NSE>0.75). Monthly subsurface NO3--N (NSE =0.63) and DRP (NSE = 0.63) load predictions were characterized as “satisfactory” (i.e., 0.50