Cover crops differentially influenced nitrogen and phosphorus loss in tile drainage and surface runoff from agricultural fields in Ohio, USA

Authors: Hanrahan, Brittany; King, Kevin; DUNCAN, EMILY - Los Angeles Regional Water Control Board; SHEDEKAR, VINAYAK - The Ohio State University

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2021
Publication Date: 6/4/2021
Citation: Hanrahan, B.R., King, K.W., Duncan, E.W., Shedekar, V.S. 2021. Cover crops differentially influenced nitrogen and phosphorus loss in tile drainage and surface runoff from agricultural fields in Ohio, USA. Journal of Environmental Management. 293. Article 112910. https://doi.org/10.1016/j.jenvman.2021.112910.
DOI: https://doi.org/10.1016/j.jenvman.2021.112910

Interpretive Summary: Nitrogen (N) and phosphorus (P) loss from crop production agriculture is transported to adjacent and downstream water bodies, which can cause negative environmental impacts including harmful and nuisance algal blooms. Cover crops are a conservation management practice that replaces bare soil with vegetation outside of the cash crop growing season, purportedly reducing N and P loss by increasing water and nutrient demand in agricultural fields. We compared nitrate (NO3-N), total N (TN), dissolved reactive P (DRP), and total P (TP) loads in subsurface (tile) drainage and surface runoff from fields with cover crop management (CC) and fields without cover crop management (NoCC) using continuous monitoring data from 40 agricultural fields located throughout northcentral Ohio, United States (US). We found that average monthly tile NO3--N and TN loads from CC fields were significantly less than NoCC fields, while average monthly tile discharge, DRP, and TP loads were similar between CC and NoCC fields; cover crops did not significantly influence average monthly surface metrics though trends suggested reduced discharge and nutrient loads from CC fields. Cover crops reduced tile NO3-N and TN loads most significantly from January to June (winter and spring), coinciding with critical periods of nutrient loss from agricultural fields in the midwestern US, but increased tile DRP and TP loads in most months. We found similar patterns at the annual time scale whereby CC fields had reduced cumulative annual totals of tile NO3-N and TN but greater cumulative annual totals of tile DRP and TP. These results show that the influence of cover crops on N loads, but not P, were consistent, demonstrating that cover crops effectively increased N demand and mitigated N losses from agricultural fields. The influence of cover crops on P was variable, which underscores the need for a greater understanding of the factors and mechanisms that control P loss in agricultural fields with cover crops. Furthermore, these findings stress the importance of identifying and selecting conservation management practices tailored to the natural resource concern.

Technical Abstract: Nitrogen (N) and phosphorus (P) loss from crop production agriculture is transported to adjacent and downstream water bodies, resulting in negative environmental impacts including harmful and nuisance algal blooms. Cover crops are a conservation management practice that replaces bare soil with vegetation outside of the cash crop growing season, purportedly reducing N and P loss by increasing water and nutrient demand in agroecosystems. In this study, we compared nitrate (NO3--N), total N (TN), dissolved reactive P (DRP), and total P (TP) loads in subsurface (tile) drainage and surface runoff from fields with cover crop management (CC) and fields without cover crop management (NoCC) using continuous monitoring data from 40 agricultural fields located throughout northcentral Ohio, United States (US). We found that average monthly tile NO3--N and TN loads from CC fields were significantly less than NoCC fields, while average monthly tile discharge, DRP, and TP loads were similar between CC and NoCC fields; cover crops did not significantly influence average monthly surface metrics though trends suggested reduced discharge and nutrient loads from CC fields. Cover crops reduced tile NO3--N and TN loads most significantly from January to June (winter and spring), coinciding with critical periods of nutrient loss from agroecosystems in the midwestern US, but increased tile DRP and TP loads in most months. We found similar patterns at the annual time scale whereby CC fields had lesser cumulative annual totals of tile NO3--N and TN but greater cumulative annual totals of tile DRP and TP. These results show that the influence of cover crops on N loads, but not P, were consistent across temporal scales of examination, demonstrating that cover crops effectively increased N demand and mitigated N losses from agricultural fields. The variable influence of cover crops on P loads underscores the need for greater understanding of the factors and mechanisms that control P loss in systems that include cover crop management. Furthermore, these findings stress the importance of identifying and selecting conservation management practices tailored to the natural resource concern.