Project overview
Leguminous cover crops are an important source of nitrogen (N) in organic production systems. Hairy vetch, one such legume, is commonly used as a cover crop in regions with colder climates. However, the performance of hairy vetch as a cover crop (both with regards to growth and N-fixation) varies widely, making it difficult for farmers to accurately predict vetch N contributions. As such, there is a need to better understand which variables impact vetch performance.
This study assessed how interactions between soil fertility, vetch genotype, and symbionts (i.e. rhizobia bacteria and arbuscular mycorrhizal fungi) impacted the N acquisition capabilities of hairy vetch in organic systems.
Farmer takeaways
- Shoot biomass and N accumulation in hairy vetch vary most strongly with temperature and ecotype (genotype), suggesting that the most productive path forward to improve N accumulation in vetch may be to focus on plant breeding, rather than harnessing specific associations with rhizobia.
Project objectives and approach
Elucidate how interactions among soil fertility, plant genotype, and symbionts (i.e. rhizobia bacteria and arbuscular mycorrhizal fungi) drive the N acquisition strategies of hairy vetch
- 24 hairy vetch lines were selected and planted at two research farms (MN, NY).
- Soil samples were collected from each field and analyzed for key differences in soil properties and N.
- Data was collected on % emergence; relative vigor at three key points (fall, spring green-up, and 10% flowering); % winter survival; and biomass, and shoots from each line were analyzed for N, C, and d15N. Roots were collected and preserved at the time of biomass sampling for later quantification of arbuscular mycorrhizal fungi colonization.
- In a separate greenhouse experiment, the N-fixation performance of 8 hairy vetch lines were assessed under 5 distinct (controlled) N atmospheres (approximating 0, 2, 10, 20, and 40 ppm).
- Data was collected on shoot biomass, # of nodules, and total N, from which symbiotic nitrogen fixation (SNF) rates were calculated.
Characterize rhizobia populations that reflect different selection pressures and identify strains with improved plant growth benefits for hairy vetch
- In specialized growth chamber environments, six strains of rhizobia inoculants were assessed under four different temperatures, simulating temperature conditions encountered during early spring in the Upper Midwest/Northeast. The rhizobia strains included three genetically-distinct cold-adapted strains from Minnesota and three non-cold-adapted strains from North Carolina.
Quantify differences in arbuscular mycorrhizal fungi colonization across hairy vetch breeding lines/populations
Key findings
Vetch genotype and temperature drive symbiotic nitrogen fixation (SNF) in hairy vetch
- Vetch plants fixed significantly less N and accumulated less shoot biomass under cold conditions than warm conditions.
- The hairy vetch genotype AU Merit accumulated more shoot N than most other genotypes under both cold and warm conditions, despite being considered a ‘cold-susceptible’ ecotype (low freezing tolerance). The researchers postulated that certain plant genotypes may be better at selecting beneficial rhizobia than other genotypes within the same species, and that vetch plants with greater shoot N tend to associate with superior rhizobia strains.
Soil origin and rhizobia population differentiation do not strongly influence shoot biomass or N accumulation in hairy vetch
- Rhizobia population differentiation only varied with soil origin, and soil origin had no effect on shoot biomass or N accumulation in hairy vetch.
Location
Minnesota, New YorkCollaborators
Region
North Central, Northeast
Topic
Soil Health, Crop Nutrient Management, Cropping Systems
Year Published
2024
