Development of winter cover crop varieties and complementary mixtures for North Central Region grain systems

Development of winter cover crop varieties and complementary mixtures for North Central Region grain systems

Summary

Multiple experiments comparing hairy vetch and red clover varieties as cover crops in Midwestern grain cropping ecosystems determined that variety, planting date and growing degree days are three important factors influencing cover crop utility. Hairy vetch varieties differed in many respects, including relative growth rates and winter survival, which ultimately led to differences in value for grain farmers. Across experiments, data suggested that common hairy vetch (variety not stated – VNS) was the best adapted hairy vetch variety for Upper Midwest systems. Mixtures of hairy vetch varieties did not increase nor stabilize the amount of above ground biomass compared to single varieties.

Objectives/Performance Targets

Short Term Outcomes
1. Hairy vetch varieties 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.

Intermediate Term Outcomes
4. Cover crop-mediated nitrogen cycles for reduced leaching and external inputs,
5. Climactically and environmentally buffered cover crops in non-irrigated fields,
6. Sustainable options for farmers as they face rising external fertilizer prices.

Accomplishments/Milestones

1. Optimal hairy vetch and red clover varieties identified and characterized for MI and NE grain producers.

Between 2006 and 2008, we conducted one controlled greenhouse experiment, three field experiments and five on-farm studies to evaluate hairy vetch and red clover varieties as cover crops in grain cropping ecosystems. These studies have collectively provided a variety of insights regarding the differences between varieties of these cover crop species, and how these trait differences affect cover crop performance in different environmental and agronomic conditions.
We’ve focused on three specific varieties of hairy vetch which originated from distinct breeding lines. Two of these varieties are landraces from Nebraska and Oregon, commonly sold with the label “Variety Not Stated (VNS)” while the third variety (AU Early Cover) was developed relatively recently at Auburn University. Based on data from our experiments, we’ve made the following conclusions regarding these three varieties:
1) ‘Nebraska VNS’ is available through Kaup Forage and Turf, and is very pubescent, grows close to the ground, and exhibited the best winter survival, making it the best adapted variety for cold winter conditions. Data from one experiment also suggest that ‘Nebraska’ is the best variety for early spring termination (late April) as its relative growth rate during April was higher than the other varieties.
2) ‘Oregon VNS’ is commonly sold throughout the Upper Midwest, and is less pubescent, grows faster during warm periods, and grows taller than ‘Nebraska,’ but still exhibited relatively high winter survival. Thus, ‘Oregon’ produced the most biomass by late May in two of our three field trials.
3) ‘AU Early Cover’ is the earliest flowering of the three varieties, making it well-suited for early termination. ‘AU Early Cover’ produced a substantial amount of flowers by May 15, 2007, but was not flowering by that same date in 2008 (the 2007/2008 winter and spring were cold, which limited growth early in the spring). However, winter survival was less than the other two varieties, and potential growth was limited by more of a determinate growth pattern.

We also evaluated three additional hairy vetch varieties that were evaluated in the greenhouse and planted in the field following wheat harvest (late July) and incorporated the following spring. The variety descriptions are as follows:
1) ‘Minnesota VNS’ is an organically produced variety available through Albert Lea Seed House, that is very similar to ‘Nebraska’ in morphology, and performed similarly in field trials.
‘Maine VNS’ is an organically produced variety sold by Johnny’s Selected Seeds. It’s growth pattern is similar to ‘Oregon,’ but has been selected for higher winter survival.
2) ‘Lana’ is a distinct cultivar developed in California for Mediterranean climates. When planted in Michigan in late July, ‘Lana’ was the fastest growing variety of all six varieties trialed. However, ‘Lana’ completely winterkilled during the following winter. Thus, it would be well suited variety for farmers who are looking for fall biomass production, but are not looking for spring growth.
3) Finally, we evaluated a total of seven red clover varieties in one field experiment and three on-farm studies. The seven varieties studied were ‘Red Planet,’ ‘Cardinal,’ ‘Starfire,’ ‘Canada Mammoth VNS,’ ‘Medium VNS,’ and two local Michigan landraces.

In the field experiment, there were small morphological differences visible between the varieties, but all seven varieties produced similar amounts of above ground biomass, none being statistically higher than another. The above ground biomass produced by the red clover was lower than the best hairy vetch varieties, but was higher than some of the poor growing hairy vetch varieties. On farm studies produced similar results, where we were not able to detect statistical differences between red clover varieties. In one of the Nebraska on farm studies, red clover establishment was very poor, but the same varieties were well established the following year, indicating that environmental and agronomic conditions are more important than variety planted.

2. Evaluation of genetic diversity within a cover crop species

We hypothesized that cover crop mixtures containing multiple varieties of the same species would enhance productivity and stability due to niche partitioning (e.g. varieties grow best at different times of the year). However, our results indicate that variety mixtures did not increase biomass production above the average of the individual varieties in monoculture, nor did they reduce variability between plots. In fact, sometimes the mixtures reduced biomass production.

However, mixtures were beneficial when one of the two varieties had very poor establishment or high winterkill rates. In a scenario such as this, there was still one successful variety in the plot. Thus, variety mixtures could be considered as a safeguard against complete failure, especially when trying a cover crop species for the first time.

3. Knowledge disseminated to farmers about the benefits and drawbacks of diversified cover crop mixtures.

Michigan farmers and extension agents visited field trials at the W. K. Kellogg Biological Station (KBS) in September, 2007, and October 2008. Data from on farm studies was distributed to participating farmers, and the farmers were urged to share results with other farmers in the area. Project participants made personal contact with other farmers in both Michigan and Nebraska, discussing the idea of using hairy vetch and/or red clover as cover crops, as well as discussing specific varieties for use in grain cropping ecosystems. Farmers seemed eager to identify alternate ways to bring nitrogen onto their farms. Finally, a journal article titled “Winter cover crops for local ecosystems: linking plant traits and ecosystem function” was published in 2008 in the Journal of the Science of Food and Agriculture.

An effort will be made in 2009 to discuss cover cropping strategies with crop consultants in Nebraska. A final report will be written for dissemination through the New Agriculture Network, and a one page handout will be distributed to interested farmers in Nebraska and Michigan.

4. Cover crop-mediated nitrogen cycles for reduced leaching and external inputs

Two long term experiments in agroecology at KBS have collected data on nitrogen inputs and exports for 19 years and 15 years respectively. Data from these two experiments shows that red clover cover crops can be used to reduce nitrogen fertilizer rates by 67% while maintaining equal or higher grain yields. Yet, these low-input fields have similar levels of nitrate leaching compared to fully fertilized fields. Fields managed with only red clover cover crops and no inorganic fertilizer have lower nitrate leaching losses than those managed with inorganic fertilizer, but comes at a tradeoff of lower grain yields.

We are conducting a complete analysis of nitrogen use efficiency in fields using inorganic fertilizer versus those that relied specifically on legume cover crops as a nitrogen source. Preliminary data suggest that cover cropped fields have higher nitrogen use efficiency than those managed with chemical fertilizers.

5. Climactically and environmentally buffered cover crops in non-irrigated fields

Preliminary data suggested that mixtures of hairy vetch varieties reduced the variability in biomass production across research plots compared to monoculture plots. However, further testing found that this trend did not hold up across years, and the variability in biomass production was the same in variety mixtures and monoculture plots. We have also identified five hairy vetch varieties that survive winter conditions in Southwest Michigan (Oregon VNS, Nebraska VNS, Minnesota Organic VNS, Maine VNS, and ‘AU Early Cover’), and one variety that does not (Lana). Across all experiments, hairy vetch cover crops did not deplete soil moisture more than adjacent control plots, while cover cropped plots planted to corn appeared to retain more moisture during extremely dry conditions than control plots planted to corn.

6. Sustainable options for farmers as they face rising external fertilizer prices

October hairy vetch planting, which is a realistic time for corn-soybean farmers, provided at most, 36% of the nitrogen needed by subsequent corn crops in a drought year. Hairy vetch seed can range from $25 – $50 per acre, which makes it currently uneconomical to use hairy vetch as an October seeded cover crop.

A much more promising time for incorporating hairy vetch and red clover into grain cropping ecosystems is following small grain harvest. Hairy vetch seeded following wheat harvest produced up to 435 grams of above ground biomass per square meter, which equates to approximately 136 lbs of nitrogen per acre in the above ground biomass alone. Red clover cover crops produced up to 290 grams of above ground biomass per square meter, which equates to approximately 90 lbs of nitrogen per acre. It is important to consider that these calculations are for above ground biomass in the spring only, and don’t incorporate root biomass and senescent biomass. Plus, organic nitrogen sources are released slower than chemical fertilizers, which also influences the effect of these cover crops on subsequent cash crops.

Impacts and Contributions/Outcomes

• 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. Five hairy vetch varieties were identified as winter hardy in the North Central Region, including ‘Oregon VNS,’ Nebraska VNS,’ Minnesota Organic VNS,’ ‘Maine Organic VNS,’ and ‘AU Early Cover,’ which flowers earlier in the spring than other varieties and may be easily killed using organic no-till management. One hairy vetch variety (‘Lana’) grew very rapidly in the fall, but winterkilled completely which could actually ease the process of termination in the spring. Seven red clover varieties were found to differ very little in terms of overall biomass production. Thus weather and agronomic conditions are much more important than variety of red clover chosen as a cover crop. October hairy vetch plantings were ineffective at producing enough biomass to significantly impact subsequent corn crop yields, and are thus not recommended. However, late July and early August hairy vetch plantings produced significant amounts of biomass that may be economically beneficial for farmers depending on growing conditions for subsequent corn crops. Mixing hairy vetch varieties could be beneficial when farmers are growing hairy vetch for the first time, to ensure that at least one variety establishes and grows. However, variety mixtures did not improve overall biomass production. 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. Planting dates and total growing degree days can substantially influence total biomass production by hairy vetch cover crops.

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