Traditionally, cover crops are non-harvested crops that provide important agronomic benefits including reductions in erosion, landscape diversification, nutrient addition and soil quality improvement. Distinct from other Forever Green focus crops, after being planted in the fall, traditional cover crops are typically not harvested for economic benefit, but instead are killed in the spring and all plant biomass returned to the soil to reap soil quality benefits. New winter cover crops of this type are needed to enhance the sustainability of annual agroecosystems. Currently, species options for Minnesota are very limited. Hairy vetch (Vicia villosa) is one winter annual crop that can reduce soil erosion, increase soil quality, sequester soil nutrients, and since it is a legume, can contribute biologically fixed nitrogen (N) to soils that other non-legumes can then use for growth. Many U.S. farms already take advantage of these hairy vetch cover crop benefits, however Minnesota is challenged as no existing varieties fit into our current corn-soybean production system. These systems typically require October planting of cover crops and early May incorporation prior to row crop planting. October is often to late for legumes such as hairy vetch to establish and survive the winter, and May too early to result in ample cover crop spring growth. We propose to develop new hairy vetch varieties adapted for use as a winter cover in Minnesota to overcome these limitations of the currently available cultivars, as well as investigate soil health benefit resulting from hairy vetch use.
Our plant breeding approach will be to use methods that include traditional field-based breeding and selection using current ecotypes and breeding populations with the objectives being: 1) to select for reliable winter hardiness, 2) to select for earlier maturity in the spring, and 3) to maintain spring biomass yield, seed production potential, and nitrogen fixation capability. Hairy vetch is primarily cross-pollinated with a high frequency of outcrossing coupled with strong self-incompatibility. Our choice of plant population improvement methods therefore are limited to using recurrent selection procedures. Recurrent selection involves evaluation of plants from a population for traits of interest, selection of a proportion of these plants exhibiting the desired traits, intermating of selected individuals usually in isolation, harvesting seed from selected plants and initiating a second cycle of selection and/or evaluation of progeny from these matings. Based on an evaluation of 30 hairy vetch populations including local ecotypes, released varieties, and commercially-available entries, a plant breeding program was initiated in 2015 using the most promising populations to start our breeding program. The first cycle of selection for improved winter hardiness and other important agronomic traits will be done in 2016.
The purpose of our team is to provide legume cover crop options to growers in the upper Midwest that can be used in our variable climates to help increase soil quality and nutrient availability to cash crops, and reduce nutrient losses that have been implicated in the pollution of Minnesota waterways. We have three specific agronomic outputs of our project:
1) Identify winter annual legumes, with a focus on hairy vetch ecotypes, that are winter hardy
2) Identify winter annual legumes that have early spring productive capacity and can produce abundant biomass
3) Evaluate nutrient and health status of soils following production of winter annual legumes, such as hairy vetch
Our team will address the lack of winter hardy legume cover crop species options that can contribute to soil quality, fertility and active microbial functioning in northern climates. Soil health and nutrient benefits resulting from hairy vetch use will be evaluated by examining key soil microbial processes that regulate nitrogen (N) cycling in select winter-hardy legumes. Legume cover crops are extraordinary sources of fertility and if well managed can completely replace external N fertilizer additions in organic systems. Additionally, since the N is released slowly via decomposition and the activity of soil microorganisms, N release from legumes has been shown to be more tightly-coupled with summer crop plant need, resulting in greatly reduced N losses to waterways. Recent work by our team in warmer regions of the U.S. shows certain varieties of hairy vetch to have high biomass nitrogen production and nitrogen-fixation capacity, with some producing over 200 kg N ha-1, and more than 170 kg N ha-1 of this derived from nitrogen fixation (Parr et al., 2011). However, challenges unique to regions with short growing seasons and cool soils exist and have limited its adoption in northern regions, where N contributions from currently available germplasm have been identified in the range of 50-190 kg N ha-1 (Teasdale, 2004).
Through rigorous and cutting edge analysis of soil samples from fields where hairy vetch and other legumes are grown, we will assess N contributions and cycling as related to hairy vetch use. In particular, we are quantifying total nitrogen contribution of promising legume cover crops resulting from our breeding efforts, and measuring the amount of nitrogen derived from soil and from atmospheric pools (biological nitrogen fixation). A collection of vetch-nodulating rhizobia (Rhizobium leguminosarum) from around Minnesota has already been established by our team, with over 500 nitrogen-fixing strains isolated and preserved in our lab. These strains are currently being independently evaluated for nitrogen fixation potential. As well, we are assessing the impact of hairy vetch ecotypes, as well as other legumes or legume mixes, on biological soil quality parameters, including labile organic matter pools (POM and POX), dissolved C and N pools, microbial biomass C and N. We are evaluating the currently-available hairy vetch germplasm as new vetch germplasm more suitable to our region is developed.
Nancy Ehlke, Professor and Department Head, Department of Agronomy and Plant Genetics
Julie Grossman, Assistant Professor, Department of Horticultural Science
Jessica Gutknecht, Assistant Professor, Department of Soil, Water and Climate
Craig Sheaffer, Professor, Department of Agronomy and Plant Genetics
Thanwalee Sooksanguan, Post-Doctoral Associate, Department of Horticultural Science
M. Scott Wells, Assistant Professor, Department of Agronomy and Plant Genetics
Nicholas Wiering, Research Assistant, Department of Agronomy and Plant Genetics
Donald Wyse, Professor, Department of Agronomy and Plant Genetics
USDA Sustainable Agriculture Research and Education (SARE)
Minnesota Department of Agriculture
Minnesota Agricultural Experiment Station
Forever Green Initiative
USDA-ARS Sustainable Agriculture Laboratory
North Carolina State University