Aims: Growers in northern U.S. regions rely on winter annual legume cover crop symbiotic nitrogen fixation (SNF) to reduce the need for spring fertilization and build soil organic matter. However, cold transitional fall temperatures potentially limit SNF. This study examined the effects of cold temperatures on nodulation and SNF in legume cover crops. Methods: In a growth chamber experiment, hairy vetch (Vicia villosa Roth), Austrian winter pea (Pisum sativum L.) and crimson clover (Trifolium incarnatum L.) were sown in growth pouches, inoculated with rhizobia, and placed in growth chambers ranging from 5℃ to 20℃ for six weeks. In a field experiment, the same legumes were sown in fall, with destructive sampling at four time points from November to May. In both experiments, plant biomass, nodulation, and SNF was assessed. Results: In the controlled environment, incrementally lower temperatures negatively affected legume cover crop biomass and nodulation parameters across all species, especially at 5 °C (41°F). Controlled environment results also suggest that optimum temperatures for SNF in cover crop legumes falls in the range of 15 °C to 20 °C. In the field, winter conditions negatively affected legume cover crop productivity, with plant biomass, nodule number, and nodule mass greatest in fall and spring, and lowest in winter. Hairy vetch had the best growth response to spring warming, suggesting it is well-suited to over-winter protected environment production. SNF also decreased during winter and failed to recover by spring cover crop termination. Conclusions: Winter annual legume cover crops may not experience reduced growth, nodulation, or SNF until temperatures fall below 10℃; this estimate is lower than previously reported for cover crop legumes. These temperatures are typical of cover crop establishment periods, suggesting winter cover crop species selection is critical; the over-wintering performance of hairy vetch makes it a promising option for temperate regions.
Bibliographical noteFunding Information:
We thank the Organic Agriculture Research and Extension Initiative project 2015-2018 (Award #2015-51300-24192) for funding to complete this project.
© 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
- Cover crops
- Nitrogen fixation