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.
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.