Biomass production, weed suppression, and soil water use of cover crops in dryland wheat production systems

Authors: BARROSO, JUDIT - Oregon State University; Reardon, Catherine; SINGH, SURENDRA - Oregon State University; MACHADO, STEPHEN - Oregon State University; GOURLIE, JENNIFER - Oregon State University; NAMDAR, GRAYSON - Oregon State University; OREJA, FERNANDO - Oregon State University; PRITCHETT, LARRY - Oregon State University; KRIETE, LINNEA - Oregon State University; CALDERON, FRANCISCO - Oregon State University; BERRY, PETE - Oregon State University; McGee, Rebecca; Durfee, Nicole; Adams, Curtis; HAGERTY, CHRISTINA - Oregon State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2025
Publication Date: 4/21/2025
Citation: Barroso, J., Reardon, C.L., Singh, S., Machado, S., Gourlie, J., Namdar, G., Oreja, F., Pritchett, L., Kriete, L., Calderon, F., Berry, P., McGee, R.J., Durfee, N.M., Adams, C.B., Hagerty, C.H. 2025. Biomass production, weed suppression, and soil water use of cover crops in dryland wheat production systems. Agronomy Journal. 117(2). Article e70053. https://doi.org/10.1002/agj2.70053.
DOI: https://doi.org/10.1002/agj2.70053

Interpretive Summary: Cover cropping in the fallow phase of the winter wheat-fallow rotation in the semi-arid Pacific Northwest (PNW) has been identified as an opportunity to build resilience and enhance farm profitability. Nine different fall- and spring-sown cover crops (CCs) that were grown during the traditional fallow period were evaluated in the low and intermediate precipitation regions of the inland PNW in a three-year study (2020, 2021, and 2022). The fall-sown CC treatments included winter pea, winter lentil, and fall species mix; and the spring-sown CC treatments included common vetch, yellow mustard, lacy phacelia, tillage radish, spring barley, and a spring species mix. Cover crops were evaluated for biomass production and impacts on soil water and weeds. Cover crop performance was dependent on location, year, planting timing, and CC species. Fall-sown CCs generally produced more biomass than spring-sown CCs across site-years, with winter peas and the fall species mix generally being most productive. Following a year of greater than average precipitation, marginal differences in fall soil moisture were observed at the intermediate precipitation site, while fall-sown CCs resulted in lower soil moisture compared to other treatments at the low precipitation site. Cover crops did not reduce the incidence of weeds. However, terminating fall-sown CCs in the spring before weeds set viable seeds could save an herbicide application in the fallow phase and reduce herbicide pressure without exacerbating future weed issues. Overall, select fall-sown CCs showed promise to provide ecosystem services during the traditional fallow period in dryland wheat systems of the PNW.

Technical Abstract: Cover cropping in the fallow phase of winter wheat (Triticum aestivum L.)-fallow systems of the semiarid Pacific Northwest has been identified as an opportunity to build resilience and enhance farm profitability. Nine fall- and spring-sown cover crops (CCs) grown during the traditional fallow period were evaluated at sites in the low and intermediate precipitation zones of the region in a 2-year study (2021 and 2022). The fall-sown CCs included winter pea (Pisum sativum L.), winter lentil (Lens culinaris Medik.), and fall species mix; and the spring-sown CCs included common vetch, yellow mustard, lacy phacelia, tillage radish (Raphanus sativus L.), spring barley (Hordeum vulgare L.), and a spring species mix. CCs were evaluated for biomass production and impacts on soil water and weeds. CC growth was dependent on location, year, planting timing, and CC species. Fall-sown CCs generally produced more biomass than spring-sown CCs across site-years, with winter peas and the fall species mix being most productive. Following a year of greater than average precipitation, no negative effects of CCs on fall soil moisture were observed at the intermediate precipitation site, while fall-sown CCs reduced soil moisture at the low precipitation site. The suppressive effect of CCs on weeds ranged from null to moderate, depending on site, year, and CC seeding time. Fall-sown CCs more consistently suppressed weeds than spring-sown CCs. Additionally, fall-sown CCs were terminated in the spring before weeds set viable seeds, saving a herbicide application and reducing herbicide pressure without exacerbating future weed issues. Overall, select fall-sown CCs showed promise to enhance ecosystem services during the traditional fallow period.