Field-scale nutrient loss assessment following cover crop and manure rate change

Authors: Askar, Manal; Hanrahan, Brittany; King, Kevin; Stinner, Jedediah

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2023
Publication Date: 3/27/2023
Citation: Askar, M.H., Hanrahan, B.R., King, K.W., Stinner, J.H. 2023. Field-scale nutrient loss assessment following cover crop and manure rate change. Journal of Environmental Management. 337. Article #117709. https://doi.org/10.1016/j.jenvman.2023.117709.
DOI: https://doi.org/10.1016/j.jenvman.2023.117709

Interpretive Summary: Nitrogen (N) and phosphorus (P) loss from artificially drained agricultural lands continue to be linked to downstream water quality problems. Conservation practices, including cover crops and reduced fertilizer rate have been suggested as ways to reduce nutrient loss. Six years of measured data were used to investigate the water quality impacts of implementing cover crops, reduced manure rate, and the combination of the two Reducing fertilizer rate did not have an impact on N or P loss whereas, implementing cover crops decreased N concentration in drainage discharge even when fertilizer rates were doubled. These findings should be beneficial to conservation professionals and practitioners and help inform conservation related policy.

Technical Abstract: Eutrophication due to elevated nitrogen (N) and phosphorus (P) loss from croplands remains one of the most pressing water quality issues throughout the world. Understanding the effect of implementing conservation management practices is critical for meeting nutrient reduction goals as well as informing conservation programs and policies. A before-after-control-impact (BACI) analysis was used to evaluate the individual and combined effect of cover crops and manure application rate on discharge and nutrient loss using six water years (WY2014-WY2019) of measured data across four distinct drainage zones (1X-NCC; 1X-CC; 2X-NCC; 2X-CC) within an Ohio USA crop production field. Neither the use of white mustard, doubling manure rate, or the combination of the two had a significant impact on mean monthly drainage discharge, nitrate (NO3--N), dissolved-reactive P (DRP), or total P (TP) load. However, white mustard significantly reduced mean monthly NO3--N concentration regardless of manure application rate (i.e., 65 m3 ha-1 and 130 m3 ha-1). Seasonal analysis confirmed that NO3--N concentration in the cover crop zones was signficantly less in fall, winter, and spring. However, significant increases in spring discharge, NO3--N, DRP, and TP loads as well as TP concentration were noted with cover crop and greater manure rate treatments. These findings confirm that cover crops have a reducing effect on NO3--N concentration but may not have any effect on addressing P concerns. Further research is warranted; however, this study highlights that the resource concern (e.g., N or P) should be considered prior to implementing cover crops as a conservation management practice.