Winter cover crops have the potential to supply a host of economic and environmental services for grain farmers in the North Central Region (NCR). Alternative nutrients obtained from winter legumes combat rising fertilizer prices while vegetative cover sustains soil health. Red clover and hairy vetch are the only legume cover crops that survive NCR winter conditions, but are also difficult to manage and often become weeds in succeeding cash crops. Phenological and morphological knowledge of hairy vetch and red clover varieties and mixtures must be distributed to farmers in order for them to successfully manage their cover crops. On many NCR farms, extreme winter climactic conditions limit hairy vetch and red clover vigor, especially in dry-land systems. Farmers can buffer winter plant stresses through enhanced genetic diversity within a cover crop species. Certain complementary mixtures within winter-hardy legume species have the potential to maximize resource use throughout the season.
An experiment was conducted at the Kellogg Biological Station (KBS) for three years to assess varieties of hairy vetch and red clover for beneficial characteristics and to make specific genotypic combinations that buffer changing winter conditions. Understanding of the botany of red clover and hairy vetch under controlled research conditions and in real farm situations will allow us to effectively manage these winter cover crops, which are essential for NCR grain farmers using low input methods.
Field evaluations of hairy vetch as a winter cover crop in row crop ecosystems concluded that varieties varied in morphology, phenology and produced different amounts of biomass, but the difference between varieties did not influence final corn crop biomass in year two. Planting time for hairy vetch was markedly important influence on biomass produced. Mixtures of hairy vetch varieties were either beneficial or detrimental depending on the specific varieties in the mixture, and monocultures were surprisingly high performers. Data were consistent with common hairy vetch (Oregon origin) as being the best adapted variety for October seeding in SW Michigan, although locally adapted varieties were also promising.
Objectives of this student project were as follows:
1. Hairy vetch varieties characterized identified and characterized for MI and NE grain producers.
2. Evaluation of genetic diversity within a cover crop species.
3. Knowledge disseminated to farmers about the benefits and drawbacks of diversified cover crop mixtures, and effect of planting time on performance.
1. Optimal hairy vetch and red clover varieties identified and characterized for MI and NE grain producers
In controlled environment conditions, three hairy vetch varieties (Common – Oregon origin, Nebraska origin and ‘AU Early Cover’) survived freezing temperatures of -6 oC. Common hairy vetch has few leaf hairs, grows quickly, and is sold throughout the U.S. under the ‘VNS’ label, and is primarily produced on seed farms in the U.S. Pacific Northwest. Nebraska hairy vetch is large seeded, slow growing, very pubescent and appears to be related to what was once known as the ‘Madison’ hairy vetch cultivar. ‘AU Early Cover’ is an early flowering variety, and grows for a shorter period of time than other varieties.
2. Climactically and environmentally buffered cover crops in non-irrigated fields
Mixtures of hairy vetch varieties produced mixed results in terms of biomass, but the variability in biomass production across research plots was lower than the variability across monoculture plots. This result indicates that variety mixtures may help to provide more stable cover crop production in variable climates, soil conditions and when knowledge about cover crop performance is unknown. We have also identified three hairy vetch varieties that survive winter conditions in Southwest Michigan (Common, Nebraska and ‘AU Early Cover’). When seeded in October, 2006, these three varieties did not deplete soil moisture more than the no-cover crop control plots.
When seeded in October, 2006, Common hairy vetch produced more biomass (114 g / m2) than Nebraska (78 g / m2) and ‘AU Early Cover’ (86 g / m2) by May 19, 2007. Nebraska hairy vetch produces larger seeds than the other two varieties, which resulted in the need to seed this variety at a higher rate than the other two varieties to maintain similar plant density, resulting in higher seed costs. On average, varieties supplied 36% of the nitrogen needed for subsequent corn crop growth in 2007, which was a drought year. In non-drought years, we estimate that October seeded hairy vetch would supply about one-third of the needed nitrogen for corn growth due to higher demands by the corn crop.
On-farm trials in Nebraska determined that October seeding of cereal rye / Nebraska hairy vetch mixtures reduced subsequent corn crop growth, likely due to limited growth at late planting and soil status with immobilization of N from residues.
Approach, Activities, Methods, and Inputs
An experiment was conducted at the Kellogg Biological Station to assess functional characteristics such as biomass, winter hardiness, nitrogen production and recalcitrance to decomposition of several promising and commercially available hairy vetch and red clover genotypes. Field experiments with these promising varieties and combinations of spatial and temporal complementary genotypes grown with non-legume species (cereal rye) provided a comparison for importance of genetic diversity in the cover crop community. Experimental timing involved parallel practices currently used by temperate grain crop producers, which normally occur following fall harvest until spring planting.
Years 2 and 3.
Corn was grown subsequent to experiment 1 comparison of cover crop mixtures and varieties. Two on-farm experiments were conducted using the most promising cultivars and combinations of cover crops observed during the first year of research. In Nebraska, research will be conducted on Brook Wilke’s family farm near Columbus that has been under dry-land corn and soybean production for at least 30 years without winter cover crop use. Three vigorous varieties and mixtures of legume and non-legume cover crops were grown and assessed for cover crop productivity and winter hardiness. In Michigan, one farmer with winter cover crop experience participated in growing the best cover crop mixtures identified during year one that also fit into the farmers system. Farmers in both trials participated in decisions about which mixtures might be suitable for their farm and they contributed to much of the management in conducting the experiment.
Cover crop species and timing of planting experiment influenced the amount of biomass produced by cover crops. When planted in October (after a soybean crop), common hairy vetch produced significantly less total biomass than cereal rye in both years, while the July planted (after wheat) hairy vetch produced markedly more total biomass than October-planted rye or hairy vetch (Figure 1). Above and below ground biomass analyzed separately exhibited similar patterns to total biomass.
In the second year, total above ground corn biomass and grain biomass were lower in the rye treatment relative to common hairy vetch and the two bare plots. No differences existed between common hairy vetch and bare plots, in this very dry year.
Nebraska hairy vetch exhibited higher winter survival than the other two hairy vetch varieties across both October experiments. All three hairy vetch varieties had lower survival in the 2007 planted experiment relative to 2006, but cereal rye maintained similar survival percentages across years.
Overall, the net biodiversity effect on above ground biomass averaged -13 g m-2 for the Common / AU Early Cover mixture, and -8 g m-2 for the Nebraska / AU Early Cover mixture, indicating that mixtures performed more poorly than monocultures, yet neither of the values were statistically different from 0. However, a significant interaction was found between treatment and experiment indicating that the net effect of the mixtures was not consistent across experiments. The Common / AU Early Cover mixture significantly underyielded the monospecific hairy vetch treatments in the July 2007-planted experiment (t12 = 3.30, P = 0.006), but no other mixtures significantly overyielded or underyielded across the experiments.
Given the variability in growth among varieties, variety mixtures still may be a wise choice for farmers given the unpredictable outcome of individual varieties in different environments. Thus, planting variety mixtures reduces the risk when initially trying cover crop plantings, in case one variety underperforms.
Educational & Outreach Activities
Wilke, B.J. and S.S. Snapp. 2008. Winter cover crops for local ecosystems: Linking plant traits and ecosystem function. J. Sci. Food Agric. 88:551-557.
Impact and Contributions/Outcomes
Impacts of this project:
-Through experimenting with hairy vetch / rye cover crops, a Nebraska farmer discovered that August seeded cereal rye provided substantial amounts of feed for cattle via grazing in the winter.
-Three hairy vetch varieties were identified as winter hardy in the North Central Region, including ‘AU Early Cover,’ which flowers earlier in the spring than other varieties and may be easily killed using organic no-till management.
-October hairy vetch plantings reduced nitrogen fertilizer needs by an average of 36% during a drought year.
-Mixing hairy vetch varieties reduced variability in cover crop growth, and one mixture outyielded the respective hairy vetch monocultures.
-Now that we have characterized several hairy vetch varieties in the greenhouse and field, farmers have information to help match hairy vetch varieties to specific functions in crop fields, such as early flowering and low soil water depletion.
– Brook Wilke completed his PhD and is now in the process of publishing research papers based on these findings, including one paper published in J. Sci. Food Agric. 88:551-557.
Areas needing additional study
Variety mixtures of cover crops assumed to provide complementary qualities did not necessarily increase cover crop productivity or stability, a somewhat surprising result and research carried out more years (with variable precipitation and temperature regimes) will provide further insights on how mixtures interact with climate.
Combinations across species, rye and hairy vetch for example, at different plant population density combinations may be warranted to elucidate water by N by climate interactions with competition and facilitation as possible mechanisms to explore in plant-plant interactions to design more stable, sustainable cover cropping systems.