Green Manure Toolkit

Module 2: Green Manure Profiles

1. Alfalfa

Alfalfa flower. Photo by Andy Hammermeister
Alfalfa flower. Photo by Andy Hammermeister
Quick Facts
Soil Preference Most, if deep and well-drained
pH preference in the range of 6.0-8.0
Zone Adaptation Performs well in the Dark Brown, Black and Gray soil zones. Not recommended in the Brown soil zone due to high water use. Not recommended in the Gray soil zone due to low tolerance of excessive soil moisture or flooding.
Seeding Rate 8-12 lb/ac
Seed Weight 226,800 seeds/lb
Termination Requires multiple tilage passes and may benefit from mowing before incorporation.
Grazability Excellent for livestock grazing or hay, but may cause bloat if fed as a high percentage of the diet.
Nitrogen Supply 50-200 lb/ac
Botany

Scientific name: Medicago sativa

Soil and climate preference

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Alfalfa beginning to flower. Photo by Andy Hammermeister.

Alfalfa performs well in most well-drained soils, and thrives in soils with a nearly neutral pH. Alfalfa can tolerate more alkaline soils, but does not perform well in more acidic soils, and has a pH preference in the 6.0-8.0 range.

Alfalfa should be used with extreme caution in drier areas, particularly the Brown soil zone, due to its high water use.

Alfalfa is also not well suited to growth in very wet conditions, and should be used with caution in areas with poor drainage, in soils with excessive soil moisture, or in areas that are prone to flooding. Good soil drainage is essential for healthy alfalfa stands. Alfalfa has some drought resistance, but growth will slow when moisture is lacking.

Integration into the crop rotation

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Alfalfa underseeded into oats. Photo by Laura Telford.

As a perennial crop, there are a number of potential ways to include alfalfa in a grain rotation, where it can be grown for multiple seasons, or for a shorter duration.

Alfalfa can be grown for a single season, but biomass and nitrogen contributions will be limited. If considering only a single season, explore non-dormant varieties. To reduce the time in the rotation dedicated solely to an alfalfa green manure while still benefiting from the inclusion of a perennial, options such as relay cropping and underseeding should be explored. With these strategies, a grain cash crop is harvested in the establishment year of the green manure. This cash crop also acts as a nurse crop while the alfalfa is establishing. The alfalfa can then persist into the following season, or longer.

Alfalfa can be relay seeded, or planted into an established crop, with cash crops in areas with sufficient soil moisture, allowing the establishment of an alfalfa green manure production without the loss of a cash crop.  Underseeding, or planting alfalfa with or shortly after grain planting, can also be successful. In both instance, the grain cash crop grows quickly to provide early ground cover and weed control. The alfalfa green manure establishes and grows more slowly, but provides continuous ground cover after cash crop harvest, over the winter and into the following spring. Alfalfa growth will be slow until the cereal is harvested. Expect reduced alfalfa biomass, perhaps only about 900 lb/ac, in this first season. When considering this strategy, also be aware of possible yield reductions of the cash crop or poor establishment of the alfalfa due to competition. If your goal is the establishment of a good green manure rather than to harvest a high yielding cash crop, the planting rate of the cereal should be reduced to half the recommended rate.

Alfalfa can also be harvested for hay or grazed, although there can be some risk of bloat in ruminants if alfalfa makes up a large portion of the forage. However, harvesting hay from the alfalfa green manure may reduce its nitrogen contributions to the soil. Haying may also reduce the competitive ability of the stand. If the alfalfa stand is given sufficient time to regrow after a hay harvest, nitrogen contributions to the soil when terminated and incorporated can still be substantial. Note that the removal of alfalfa biomass for hay will also remove other important nutrients (e.g. phosphorus) from the system. Grazing can be a better option, as most nutrients removed when animals consume the green are returned to the soil through livestock droppings. However, be aware that grazing does speed the cycling of nutrients, as manures contain readily available nutrient forms. Grazing timing should also be considered to ensure that grazing will not kill the stand, which can happen when stands are grazed too early after establishment, too late into the fall, or when stands are grazed too aggressively.

Nitrogen fixation and supply potential

Alfalfa produces substantial biomass, with biomass in the range of 2,000 to 5,600 pounds per acre typical in Prairie conditions. As with all green manures, biomass production in the field is dependent on many factors, including climate, variety and cropping method (i.e. whether used as an annual green manure, perennial stand, hayed, or relay cropped).

Alfalfa is a high nitrogen fixer, and can supply 50-200 pounds of nitrogen per acre under typical Prairie conditions.

Water use efficiency

Alfalfa is generally considered a high water user, and can deplete soil water. Alfalfa’s high water use can, however, be at least partially offset. The year-long ground cover provided by this perennial green manure can reduce evaporative water loss from the soil surface. Alfalfa also provides ground cover that can capture winter snows to replenish soil water.  Alfalfa should be used with much caution in grain rotations in dry soil zones, particularly the Brown soil zone.

Seeding rate, date and availability

Alfalfa should be seeded at 8-12 lb/ac, at a depth of ¼ – ½”. Alfalfa can be drilled or broadcast seeded, but does best when followed with a roller when broadcast. To improve establishment, plant seed in moist conditions in the early spring.

Be sure to inoculate alfalfa with the proper inoculant (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.

Alfalfa can be seeded on its own, but benefits greatly when seeded with a more competitive, early emerging cereal crop. Alfalfa is often underseeded or relay cropped into an established grain crop. This nurse crop suppresses early season weeds while alfalfa slowly germinates and establishes.

Termination options

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Alfalfa plowdown. Photo by Andy Hammermeister.

With its extensive rooting system and abundant biomass, alfalfa can be difficult to terminate. Mowing above-ground material before incorporation can help to ease incorporation and fully terminate the alfalfa green manure. Multiple passes with tillage equipment may be needed to completely terminate and incorporate the stand.

Alfalfa is not well suited to termination with a roller-crimper for a no-till phase of the organic rotation. Alfalfa can be grazed, but grazing does not typically terminate an alfalfa stand, unless grazed too early or too aggressively.

Weed management:

Alfalfa is often slow to establish, and so is vulnerable to weeds early in the growth phase. Nurse crops or relay planting can address this issue by providing early season, quick emerging ground cover.  When alfalfa is planted on its own, mowing annual weeds in early- to mid-summer can set back the weeds. Once established, alfalfa competes well against weeds.

A multi-year alfalfa stand can be an effective weed management tool, as it introduces a perennial phase into the rotation, disrupting weed cycles. Inclusion of an alfalfa stand can help to reduce Canada thistle populations, especially when the stand is repeatedly mowed.

Other management considerations:

Alfalfa leaves. Photo by Laura Telford

Alfalfa leaves. Photo by Laura Telford

Alfalfa is very attractive to pollinators and other beneficial insects. Its deep taproots can also help to break up compacted soils, improve soil structure, and bring nutrients up from deeper in the soil profile.

Alfalfa can be vulnerable to insect pests, including lygus bugs, alfalfa weevil, and aphids. Alfalfa is also vulnerable to diseases, including wilts, crown and root rots, and foliar diseases. Crop rotation is the best way to reduce the incidence of these pests and diseases.

Benefits:
      • Attractive to pollinators and other beneficial insects
      • Deep taproot can improve soil structure and bring up nutrients
      • Can tolerate drought once established
      • Can be grazed or harvested for hay, with a caution that alfalfa can cause bloat
Cautions:
      • Can drain soil water
      • Can be slow or difficult to establish
      • Isolation distance (3 km) or other measures to limit risk of GE contamination when GE varieties are present in the area
      • Some pest and disease pressures

 

2. Red clover

Red clover flowers, a favourite of pollinators. Photo by Andy Hammermeister

Red clover flowers, a favourite of pollinators. Photo by Andy Hammermeister.
Quick Facts
Soil Preference Grows well on most soils, from loam to clay with good to poor drainage.
pH preference in the range of 6.2-7.0
Zone Adaptation Performs well in the Dark Brown, Black, Dark Gray and Gray soil zones. Not recommended for the Brown soil zone due to high water use. Recommended as the best option for moist the Gray soil zone.
Seeding Rate 8-12 lb/ac
Seed Weight 272,200 seeds/lb
Termination Multiple tilage operations often required
Grazability Excellent for livestock grazing or hay
Nitrogen Supply 25-170 lb/ac

 

Botany

Scientific name: Trifolium pratense
Lifecycle: Short-lived perennial
Winter hardiness: Zone 3, perhaps lower

Growth habit

Upright stem that grows to be up to 3’ tall, with branching.
Deep taproot.

Varieties common on the Prairies

Medium or double cut varieties, such as Arlington and Juliet varieties in use on the Prairies, flower the year they are seeded and regrow quickly after cutting. Mammoth varieties, such as Altaswede, require vernalization (cold) to flower and so do not flower in the year they are planted. Mammoth varieties also grow more slowly, but may be more drought tolerant than double cut varieties.  Seed may be more costly for double cut varieties. Non-marked varieties, or “common” seed, is also commonly used.

Soil and climate preference

Red clover grows well on most soils, even with a range of drainage. Red clover performs best on soils with a neutral pH, but is more tolerant to acidic soils than alfalfa.

Red clover should be used with extreme caution in drier soil zones, particularly the Brown soil zone, due to its water use and requirement for moisture.  Red clover performs best in moist and cool conditions, and so can be very well suited to the moister Dark Gray and Gray soil zones. In dry or droughty years in these typically wetter regions, red clover may not be the best choice, and growers may wish to consider sweetclover or an annual legume.

In some areas of the Prairies, or in some production years, red clover may not establish well. This is often largely due to insufficient moisture at planting. Red clover has variable overwintering ability under Prairie conditions and climate, and Prairie red clover stands often fade after two or three years of growth. Alternatively, a mixture of moisture-loving red clover and drought-tolerant sweetclover can be planted. One component of this mix should do well no matter the soil conditions.

Integration into the crop rotation

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Red clover field in blossom. Photo by Brenda Frick.

As a perennial crop, there are a number of potential ways to include red clover in a grain rotation, where it can be grown for multiple seasons, or for a shorter duration.

Red clover can be grown for a single season, but biomass and nitrogen contributions will be limited. Red clover is a short-lived perennial, and is likely to persist for two or three growing seasons if allowed. To reduce the time in the rotation dedicated solely to a red clover green manure, options such as relay cropping (planting into an established cash crop) and underseeding (planted with or soon after a cash crop) can be explored. With these strategies, a grain cash crop is harvested in the establishment year of the green manure. The grain also acts as a nurse crop to help the red clover establish. The red clover can then be terminated after the cash crop is harvested, or can be allowed to continue to grow into the following season, or longer.

Red clover is shade tolerant, and so is a good candidate for undersowing or relay cropping in areas with sufficient soil moisture. These methods allow the establishment of the green manure without the loss of a cash crop in the first year. With underseeding or relay seeding, the grain cash crop grows quickly to provide early ground cover and weed control. The red clover green manure establishes and grows more slowly, but provides continuous ground cover after cash crop harvest, over the winter and into the following spring. Red clover growth can be expected to be slow until the cereal is harvested, but will grow more rapidly in the remainder of the growing season. Prairie studies in southern Manitoba suggest that red clover is an ideal candidate for relay planting with winter wheat.

Caution should be taken if underseeding or relay cropping. Red clover is a legume that has a high water requirement and usage. So, these options should be restricted to the moister soil zones. Undersown legumes can reduce cash crop yields, or alternatively, the grain nurse crop can outcompete the newly establishing legume green manure.  If your goal is the establishment of a good green manure rather than to harvest a high yielding cash crop, the planting rate of the cereal should be reduced to half the recommended rate.

Red clover can be harvested for hay or grazed. However, note that harvesting red clover hay may reduce its nitrogen contributions to the soil, and may reduce the competitive ability of the stand. Note as well that the removal of biomass for hay will also remove important nutrients (e.g. phosphorus) from the system. If the red clover stand is given sufficient time to regrow after a hay harvest, nitrogen contributions to the soil when terminated and incorporated can still be substantial. Grazing can be a better option, as most nutrients removed through grazing are returned to the soil through livestock droppings. Be aware that grazing does speed the cycling of nutrients, as manures contain readily available nutrient forms. Grazing timing should also be considered to ensure that grazing will not kill the stand, which can happen when stands are grazed too early after establishment, too late into the fall, or when stands are grazed too aggressively.

Nitrogen fixation and supply potential

Red clover can produce abundant biomass when well suited to the growing conditions, with biomass accumulations of 2,000-7,000 lb/ac under Prairie growing conditions. Biomass production in the field is dependent on many factors, including climate, variety and cropping method.

Red clover is a moderate nitrogen fixer, and can be expected to supply 25-170 lb of nitrogen per acre under Prairie conditions.

Water use efficiency

Red clover has a medium to high use of soil water, and should be approached with caution or avoided in drier areas. In contrast, red clover does well under moist conditions, and has some flooding tolerance.

Seeding rate, date and availability

Seed clover at 8-12 lb/ac at a depth of ¼ – ½”. Red clover can be planted with a drill or can be broadcast seeded.

Frost seeding is also a good option for red clover. In this case, red clover seed is broadcast over a field before the ground thaws in the spring. Red clover seed is quite frost resistant, so this can be done early in the season. As the ground thaws and freezes, it opens and closes, drawing the seed into the soil. The seed will then germinate when soil moisture and temperature allow.

Red clover is slow to establish, and so is a poor competitor against weeds early in its lifecycle. Planting a cereal nurse crop with the red clover, or underseeding or relay cropping red clover with an established grain crop are options that support the establishment of the red clover green manure while also allowing a harvestable cash crop.

To reduce the number of planting operations required to establish a red clover-grain intercrop, red clover can be seeded in the same operation as the cereal by placing the clover seed in an auxiliary planter box.

Be sure to inoculate red clover with the proper inoculant (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.

Termination options

Red clover terminated with discs. Photo by Brenda Frick

Red clover terminated with discs. Photo by Brenda Frick

With its extensive rooting system and abundant biomass, red clover can be difficult to terminate. Mowing above-ground material can ease incorporation and ensure termination. Multiple passes with tillage equipment may be needed to completely terminate and incorporate the stand.

Double cut red clover often flowers around 65 days after planting, and will continue to flower every month or so if being harvested as hay or grazed. To maximize the nitrogen contribution of a red clover green manure, it should be terminated at mid-bloom in its second season of growth.

Weed management

Red clover is often slow to establish, and so is vulnerable to weeds early in the growth phase. Nurse crops or relay planting can address this issue by providing early season, quick emerging ground cover.  Once established, red clover competes well against weeds.

A multi-year red clover can be an effective weed management tool, as it introduces a perennial phase into the rotation, disrupting weed cycles.

Other management considerations

Red clover can be susceptible to a number of insects and diseases, including root-knot nematodes.

Benefits
      • Low seed cost
      • Attractive to pollinators and other beneficial insects
      • Can be grazed or harvested for hay
      • Deep taproot can improve soil structure and bring up nutrients
      • More tolerant of high moisture than other perennial green manure options
Cautions
      • Can be difficult to establish in some regions
      • Can drain soil water

 

3. Sweetclover

A field of flowering yellow sweetclover. Photo by Joanne Thiessen Martens.

A field of flowering yellow sweetclover. Photo by Joanne Thiessen Martens.
Quick Facts
Soil Preference Grows well in most soils, if well drained.
pH preference in the range of 6.5-7.5
Zone Adaptation Use with caution in Brown and Dark Brown soil zones. Good option in the Black, Dark Gray and Gray soil zones.
Seeding Rate 8-12 lb/ac
Seed Weight 260,000 seeds/lb
Termination Requires multiple operations
Grazability Good for grazing, use caution when haying
Nitrogen Supply 50-140 lb/ac

 

Botany

Scientific name:
Yellow sweetclover = Melilotus officinalis
White sweetclover = Melilotus alba
Lifecycle: Biennial (grows for two seasons)
Winter hardiness: Sweetclover is often indicated as hardy through to Zone 4, but may be able to survive winters in more northern zones as well.

Growth habit

Upright growth of up to 7-8’ tall, with branching in the second year of growth. Can reach up to 2-3’ in the first year.
Deep taproot and extensive rooting system.
Flowers in the second season.

Varieties common on the Prairies

While both yellow and white sweetclovers are grown as green manures on the Prairies, yellow varieties are more commonly used. Yellow sweetclover tends to be more drought tolerant, earlier blooming and produces more abundant biomass than white sweetclover. White sweetclover tends to be taller and have coarser stems.

Norgold and Yukon are commonly used yellow sweetclover varieties. Polara and Arctic are white sweetclover varieties in use on the Prairies. Unless otherwise specified, the text here refers to yellow sweetclover.

Soil and climate preference

Yellow sweetclover is one of the most commonly used green manures on the Canadian Prairies, and is often a reliable producer of biomass and nitrogen.

Sweetclover is tolerant of many soil conditions, but does best on loam soils with a neutral pH. Sweetclover does not tolerate poorly drained or acidic soils.

Sweetclover is often noted as the most drought tolerant prairie green manure crop, and can germinate even in dry conditions. Nonetheless, caution should be taken when using sweetclover in dry areas, particularly the Brown soil zone, where its water use may deplete water availability for the following cash crop. In drier regions, early termination of sweetclover in the bud or early bloom stage can reduce soil moisture depletion and allow an opportunity for water replenishment after the green manure is terminated. Snow capture and the constant ground cover provided over the fall, winter and early spring can also help to offset moisture uptake by a sweetclover green manure. Consider these same management strategies when using sweetclover in dry or droughty years even in the soil zones that typically have higher moisture availability.

Integration into the crop rotation

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Sweetclover underseeded into a cereal. Photo by Brenda Frick.

As a biennial crop, there are a number of potential ways to include sweetclover in a grain rotation, where it can occupy two years or a shorter duration in the rotation.

Sweetclover can be grown for a single season, but biomass and nitrogen contributions will be limited. Instead, explore options like underseeding or relay cropping that can allow two years of sweetclover growth while still providing a cash crop harvest in the first year.

Sweetclover is often underseeded, and can be planted at the same time as a grain cash crop, such as wheat or oats. Sweetclover can also be relay seeded with cash crops, meaning they are seeded into an established cash crop stand.  With underseeding or relay seeding, the grain cash crop grows quickly to provide early ground cover and weed control. The sweetclover green manure establishes and grows more slowly, but provides continuous ground cover after cash crop harvest, over the winter and into the following spring. In this way, two years of green manure can be included in the rotation, but a cash crop harvest can still occur in the first year.

Caution should be taken if using underseeding or relay cropping. Some studies on the Prairies have found reductions in cash crop yield when undersown with sweetclover, while other studies have found cash crop yields unchanged. Should sweetclover grow tall enough to interfere with harvest of the cash crop, the harvested grain may have sweetclover taint, an off smell that can spoil a crop. Observations suggest that yield reductions or harvest difficulties tend to occur when there is excessive moisture that allows the sweetclover to thrive and outgrow the grain cash crop. Alternatively, the cash crop may outcompete sweetclover, resulting in poor green manure establishment. Reducing the grain seeding rate can mitigate this effect, as can harvesting the grain early as a greenfeed or silage crop.

Sweetclover can also provide income during the green manure years through harvests of hay or grazing, and has been shown to be successful for both in Prairie studies. Grazing or hay harvests can be done in the second year of sweetclover growth. Caution should be taken when harvesting hay, as spoiled hay can develop a harmful compound, coumarin, which can be lethal. It should also be noted that harvesting hay from the sweetclover green manure will reduce its nitrogen contributions to the soil, and may reduce the competitive ability of the stand while also removing other soil nutrients. Grazing timing should also be considered to ensure that grazing will not kill the stand, which can happen when stands are grazed too early after establishment, too late into the fall, or when stands are grazed too low.

Nitrogen fixation and supply potential

Sweetclover is often noted as a green manure that produces substantial biomass, and in many Prairie studies it is among the top biomass producers in comparisons between green manure crops. Typical biomass production for yellow sweetclover ranges from 2,000-5,500 lb/ac.

Sweetclover is often described as a moderate to high nitrogen fixer, with studies on the Canadian Prairies reporting nitrogen levels of 50-150 lb of nitrogen per acre as typical. Sweetclover has also been noted for its ability to scavenge and pull up insoluble plant nutrients (such as phosphorus and potassium) from deep in the soil and convert them to available forms. When the sweetclover is terminated and incorporated, these nutrients are then made available to following crops.

While many annual green manures are terminated and incorporated while young, sweetclover flowers in the second year of growth. Sweetclover thus has taken up as much nitrogen as it can in its second year of growth, and this is typically when the green manure is terminated. These older tissues are tougher and woodier than annual green manures when terminated. This slows decomposition and nitrogen release.

Water use efficiency

Yellow sweetclover uses moderate to high amounts of soil water to support the growth of high amounts of biomass. The longer stand duration for this biennial crop also means that this green manure takes up more water over a longer time frame than annual legume green manure options. Some of this water uptake is countered by the ground cover provided by the green manure, which can reduce water loss from the soil surface by evaporation and can capture snow. Sweetclovers can be terminated earlier in the season than spring-seeded annual green manures, which can allow a longer window for soil water recharge before the next crop is planted. In drier soil zones, it is often recommended that sweetclover green manures be terminated in the bud stage.

Seeding rate, date and availability

Seed at 8-15 lb/ac by broadcast or drill.

Plant at a depth of less than 1 inch. Sweetclover does not germinate well when planted deeper in the soil. Use a well prepared, firm and well packed seedbed.

Sweetclover is small seeded, and so can be planted at a low seeding rate. Seed is generally affordable and available.

Be sure to inoculate sweetclover with the proper inoculant (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.
Broadcast seeding is recommended only when there is readily available soil moisture, and should be done using an increased seeding rate.

Sweetclover is best planted in the spring, at the time of grain seeding or once the grain crop has sprouted. Broadcast seeding followed by harrowing can be effective for both controlling weeds and establishing a sweetclover understory. Sweetclover is also amenable to frost seeding.

When underseeding sweetclover with a grain crop, reduce the seeding rate of the grain by up to one half to reduce competition. If using a seeder rather than broadcast seeding into the established grain crop, consider planting the sweetclover in alternate rows, or planting perpendicular to the grain crop.

Sweetclover seeds are very hard and often require scarification to break the seed coat and allow germination. Most commercially available seeds have been scarified.

Termination Options

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Sweetclover being terminated. Photo by Andy Hammermeister.

Mowing, sometimes multiple times, or rolling before incorporation may ease difficulties that can be associated with these types of stands. Mowed residues can be left on the surface for some time before incorporation, although this may result in some nitrogen loss from the decomposing green manure.
Terminate sweetclover green manures at flowering in their second year of growth for maximum nitrogen. In drier areas, terminate at the bud stage to conserve soil moisture.
sweetclover-discing-LT

 

 

 

 

 

 

 

 

 

 

 

 

 

Sweetclover being disced. Note the abundant biomass. Photo by Laura Telford.
Weed management

Sweetclover can be an effective weed management tool, and has been observed to be a good competitor against weeds. However, sweetclover can be slow to establish, providing early season opportunities for weeds. This can be countered by underseeding sweetclover with a grain cash crop.

A field of flowering yellow sweetclover. Photo by Joanne Thiessen Martens

A field of flowering yellow sweetclover. Photo by Joanne Thiessen Martens

Sweetclover becomes vigourous and competitive once established and can reduce weed pressures through competition for light and resources, and by altering the growing environment.

Sweetclover has also been noted as allelopathic, providing additional weed control after termination by interfering with weed seed germination and weed growth. Varieties higher in coumarin (Yukon) are more allelopathic than lower coumarin varieties (Norgold, Polara), which are better for grazing.

Other management considerations

Sweetclover stands can be vulnerable to the sweetclover weevil that can defoliate the crop. The effects of this pest can range from mild to complete stand destruction. Crop rotation is important for reducing the incidence of this pest on organic grain operations.

Benefits
      • Deep taproot and extensive root system can improve soil structure and mine nutrients from soil depths.
      • Produces abundant biomass and nitrogen.
      • Good competitor against weeds once established, and is also allelopathic.
      • Perform well in many growing and soil conditions.
      • Provides winter and spring ground cover, which reduces erosion and controls weeds.
      • Noted for ability to attract beneficial organisms, particularly pollinators.
      • Affordable seed.
      • Can be grazed or harvested for hay.
Cautions
      • While drought tolerant, caution should be taken in drier soil zones.
      • Vulnerability to sweetclover weevil.
      • Abundant biomass may require multiple operations for complete termination.
      • Spoiled hay releases coumarin, an anticoagulant that can be fatal for livestock.
      • Sweetclover taint: When underseeded with a cash crop grain, use caution at harvest to avoid sweetclover in the combine that can taint the grain with its aroma.

 

4. Faba bean

Close-up of faba bean plants. Photo by Brenda Frick.

Close-up of faba bean plants. Photo by Brenda Frick
Quick Facts
Soil Preference Well drained loam to silt clay
pH preference in the range of 5.5-7.3
Zone Adaptation Performs well in most soil zones, but not recommeded for the dry Brown soil zone due to high moisture requirements.
Seeding Rate 150-300 lb/ac
Seed Weight 655-1360 seeds/lb (varies by variety)
Termination Easy to terminate with tilage, mowing or roller-crimper
Grazability Can be used as silage
Nitrogen Supply 75-150 lb/ac

 

Botany

Scientific name: Vicia faba
Lifecycle: Annual
Also known as fava bean, broad bean, horse bean, tick bean

Growth habit

Faba bean has an upright growth habit, and can reach 2-5’ in height.
Deep taproot.
Flowers in 45-65 days

Varieties common on the Prairies

Due to its large seed size, faba bean can be an expensive green manure to plant. To reduce costs, choose smaller seeded varieties. Snowbird, Snowdrop and CDC SSNS-1 are faba bean varieties commonly used as green manures on the Prairies.

Soil and climate preference

Faba beans perform best on well-drained soils of loam to silt clay, and prefer neutral to slightly acidic soil pH.

Faba beans perform well under most Prairie conditions. However, faba beans require a steady supply of abundant soil moisture for peak growth and nitrogen fixation. As such, faba beans are not well suited to drier soil zones, particularly the Brown soil zone. Even in the Black, Dark Gray or Gray soil zones, faba bean may not perform well in dry years.  But, faba beans do have a higher tolerance for excess moisture than many other annual green manure species, and so are a good options for moister regions or years. Faba beans also have low drought tolerance and prefer cooler temperatures.

Integration into the crop rotation

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Faba bean growing in field plots in Winnipeg. Photo by Brenda Frick.

As an annual green manure, faba beans can be integrated into the crop rotation in a number of ways.  They can be grown for a full season, or included as a partial season green manure following a cash crop harvest.

A full season can be dedicated to a faba bean green manure crop. This practice provides some flexibility in timing of planting that can allow additional weed management operations before the green manure is planted or after it is terminated.

Faba beans may be candidates for double cropping, although this has not yet been explored through regional research trials to date.  If considering double cropping, note that this strategy is best suited to areas with sufficient soil moisture and with a sufficient amount of growing season remaining after grain harvest. See Choosing a Green Manure for more information.

To limit pest and disease issues, pulse crops should not be grown immediately before or after a faba bean green manure in the crop rotation.

Faba beans can serve as a good forage material, and can be grazed on farms that include livestock. Grazing a faba bean green manure will terminate the stand, so time grazing to coincide with flowering for optimal nitrogen contributions.
In years where weather is uncertain, faba bean can be intercropped with another annual legume. For instance, research trials have employed an intercrop of heat-tolerant soybean with cool-favouring faba bean to ensure that a successful annual green manure stand is established each year. Faba beans also have potential for intercropping with a cereal or grass cover.

Nitrogen fixation and supply potential

Under Prairie conditions, a faba bean green manure can be expected to generate moderate to high amounts of biomass, often in the range of 3,000 to 6,000 pounds of dry biomass per acre.

Faba bean is an excellent nitrogen fixer, and will continue fixing nitrogen throughout its lifecycle. This makes faba bean the highest nitrogen-fixing legume green manure option. Anecdotal reports also suggest that faba bean may associate with Rhizobia for nitrogen fixation even in situations where soil nitrogen is available. As an excellent nitrogen fixer with moderate biomass, faba bean can be expected to contribute in the range of 75-150 lb of nitrogen per acre as a green manure under Prairie growing conditions.

Water use efficiency

Faba bean has been reported to require sufficient soil moisture (8-10”) to fix nitrogen at a high rate. With this requirement, faba bean is not well suited for the dry Brown soil zone and drier regions of the Dark Brown soil zone. Aside from the need for sufficient moisture, the water use of faba bean is similar to other annual legume green manures.

Seeding rate, date and availability

Faba bean should be planted at a seeding rate of 170-300 lb/ac, with seeding rate largely dependent on the seed size of the chosen variety. Smaller seeded varieties can be planted at a lower seeding rate, and can reduce overall seed costs. In general, aim for a plant population of 50 plants per m2. Seeding rates are reduced when using smaller seeds as the same number of seeds weigh less when seed size is small than when it is large.

Faba bean should be planted at a depth of 1 ½ to 3 inches with a seed drill into a well prepared seed bed.

Be sure to inoculate faba beans with the proper inoculant (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.

Faba bean can be seeded early in the season, as its low growing points that lay below the soil surface lend it tolerance to early season frosts.

Faba beans can do well when intercropped with a cereal. While it is typically recommended that legumes in green manure mixes be seeded at their full rate, when intercropping the seeding rate of the expensive faba bean can be reduced while still producing a green manure stand with enough biomass for nitrogen fixation and weed suppression. The cereal component of the mix contributes biomass, provides rapid ground cover for weed suppression and can take up available soil nitrogen to encourage nitrogen fixation by the faba beans. Faba beans should make up at least 50% of the green manure stand to optimize nitrogen contributions. The cereal seeding rate should be reduced to at least half of the recommended rate to allow the faba bean enough presence in the stand.

Termination options

Faba beans terminated with a roller-crimper in research plots. Photo by Brenda Frick

Faba beans terminated with a roller-crimper in research plots. Photo by Brenda Frick

Faba bean can generally be terminated with ease with tillage or mowing. Faba bean can also be terminated with the roller-crimper, although its lower biomass makes faba bean a poorer option than hairy vetch when attempting to include a no-till phase in the rotation. Grazing livestock can also be used to terminate faba bean green manures.
Faba bean flowers 45-65 days after planting, and this is generally the recommended termination timing for maximum nitrogen contributions.

Weed management

Like most legumes, faba bean can be slow to establish, and is vulnerable to weeds early in its lifecycle. However, faba bean has been noted to establish more quickly than other green manure legumes. Once established, faba bean green manures can often compete well with weeds.

For weed control, faba beans should be planted at a high seeding rate to encourage a dense stand, or should be intercropped with a cereal.

Other management considerations

Larger-seeded faba beans require specialized seeding equipment that can handle the larger seeds without injury or equipment blockage. Smaller-seeded varieties are recommended for green manures, as they do not require specialized seeding equipment and can be seeded at a lower seeding rate that can reduce cost.

Faba beans have some susceptibility to root rot, although may have higher tolerance than pea. When other cash crop pulses are part of the rotation, be sure that they are not directly preceded or followed by a faba bean green manure to limit disease spread.

Benefits
      • High nitrogen fixation
      • Tolerates wet conditions
Cautions
      • High seed costs
      • Requires soil moisture to perform well

 

5. Field Pea

Pea leaves and tendrils. Photo by Brenda Frick.

Pea leaves and tendrils. Photo by Brenda Frick.
Quick Facts
Soil Preference Well-drained to somewhat poorly-drained loam to clay soils
pH preference int he range of 6.0-7.0
Zone Adaptation Performs well in all Prairie soils zones. Alter management in dry soils. Best suited for the Dark Brown and Black soil zones.
Seeding Rate 120-175 lb/ac
Seed Weight  Average 1800 seeds/lb, but dependent on variety.
Termination Terminate with tilage, mowing or roller-crimper. Vining nature may complicate termination and require multiple operations.
Grazability Excellent forage crop when grown alone or with a small grain.
Nitrogen Supply 75-150 lb/ac

 

Botany

Scientific name: Pisum sativum
Lifecycle: Annual

Growth habit

Vining and climbing, with vines 3-6’ in length.
Shallow, fibrous roots.
Flowering begins ~50 days after planting and can last 2-4 weeks.

Varieties common on the Prairies

Commonly used pea varieties for green manuring on the Prairies include Sirius, 4010 and Trapper. Choose smaller seeded pea varieties to reduce seeding costs. Austrian winter pea is also used.

Soil and climate preference

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Field pea blossom. Photo by Brenda Frick

Field peas perform well as a green manure in a range of conditions, and so do well in most Prairie soil zones. Peas will grow on most well-drained to somewhat poorly-drained soils, but cannot withstand waterlogged soils. Peas perform best when grown in cool and moist conditions, and are not tolerant of droughts. Biomass and nitrogen fixation in peas can be reduced when moisture is lacking or temperatures are high. In years where climate extremes are experienced, such as droughts or floods, peas may not be the best option.

Prairie studies suggest that peas, like many other annual green manures, may produce twice as much biomass in the moister Dark Brown and Black soil zones when compared to the drier Brown soil zone. When growing a pea green manure in the Brown soil zone or in other dry conditions, consider planting and terminating early to reduce water use and allow a period of water recharge before the following crop.

Integration into the crop rotation

A field of green manure peas. Photo by Brenda Frick.

Peas are an annual green manure that can be grown as a green manure with some flexibility in the crop rotation. Peas lend themselves well to being grown for a full season, or included as a partial season green manure following a cash crop harvest.

A full season can be dedicated to a pea green manure crop. This practice provides some flexibility in timing of planting that can allow additional weed management operations before the green manure is planted, or after termination.

A young mixed green manure of peas and oats. Photo by Natural Systems Agriculture Laboratory.

Peas are also a good candidate for double cropping. In double cropping, the pea green manure is seeded following the harvest of a winter cereal crop. If considering double cropping, note that this strategy is best suited to areas with sufficient soil moisture and with a sufficient amount of growing season remaining after grain harvest. See Choosing a Green Manure for more information.

Peas, especially when intercropped with a cereal, can serve as a good forage material, and can be grazed on farms that include livestock. Grazing a pea green manure will terminate the stand, so time grazing to coincide with flowering for optimal nitrogen contributions.

To limit pest and disease issues, pulse crops should not be grown immediately before or after a pea green manure in the crop rotation.

Nitrogen fixation and supply potential

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Field pea green manures can produce abundant biomass, with dry matter biomass accumulations in the range of 3,000 to 6,000 lb per acre expected under Prairie conditions.

Field pea is considered a moderate nitrogen fixer, and can be expected to supply on the order of 75 to 150 lb of nitrogen per acre. Nitrogen fixation may be limited by heat or lack of moisture, especially at flowering.

Water use efficiency

The water use of peas is similar to many other annual green manures. When green manuring peas in dry conditions, such as those predominant in the Brown soil zone, consider planting early in the spring and terminating at the bud stage. While this will reduce the amount of nitrogen fixed by the peas, it will reduce water use and allow a period where rainfalls can replenish soil moisture before the next cash crop is planted.

Seeding rate, date and availability

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Seed peas at 120-175 lb/ac, at 1 to 3” deep with a seed drill. The seeding rate will be dependent on seed size, which is dependent on variety chosen, but aim for a plant population of approximately 50 pea plants per m2. Plant at a depth where soil moisture is available. Peas can be planted quite early in the spring, as they thrive in cooler weather and seedlings tolerate frost damage.

Be sure to inoculate field peas with the proper inoculant (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.

When planting into a field with known weed pressure, consider increasing the seeding rate by up to double to encourage the establishment of a dense and competitive pea stand.

Peas do well when intercropped with a cereal.  One of the most common mixed crop green manures in use on the Prairies is a mixture of peas and oats or barley. In these mixed green manures, the cereal provides early ground cover, soaks up excess soil nitrogen to encourage nitrogen fixation by the peas, contributes additional biomass, and acts as a trellis to support upright growth of the pea plants, which in turn improves light penetration and air flow. This mixed green manure is terminated when the peas flower. The more carbon-rich cereal residue can slow decomposition and nitrogen mineralization. When intercropping peas with oats or another cereal, it is generally recommended that peas be seeded at their recommended seeding rate, while the cereal is seeded at ¼ to ½ of its recommended rate. For optimal nitrogen contributions, peas should make up at least 50% of the established green manure stand.

In areas where the growing season and soil moisture permit, peas can be an excellent double crop. In this case, peas are seeded following the harvest of a winter cereal. The peas provide ground cover through the fall and provide the opportunity to benefit from a green manure without dedicating an entire growing season. Carefully consider the harvest timing of a winter cereal crop, your growing season length, moisture availability and frost dates before planting a double crop pea green manure to ensure the pea green manure can establish and produce enough biomass to benefit your rotation.

Termination options

Field pea green manure terminated with the roller-crimper in research plots. Photo by Brenda Frick

Field pea green manure terminated with the roller-crimper in research plots. Photo by Brenda Frick

The vining nature of field peas, which can form a dense mat of plant material that tangles around equipment, may complicate termination. Pea green manures may require multiple tillage passes or mowing before tillage for good incorporation. Mowing may serve only to flatten, rather than cut, the peas, but may still ease incorporation. Termination with a roller-crimper and grazing are also excellent options where the proper equipment and infrastructure are in place.

Peas typically begin to bloom within six to nine weeks of planting. Termination of a pea green manure at full flower maximizes nitrogen contributions to the soil.

Studies have shown that pea green manures can be successfully terminated by rolling, and so can be integrated into reduced-till organic systems, although its lower biomass makes it less well suited to a no-till phase of an organic rotation than hairy vetch.

Weed management

Field peas are slow to establish, and so are not good weed competitors early in their lifecycle. Once established, their abundant biomass and sprawling ground cover make peas good competitors.

To increase the competitive ability of peas, seed at a higher rate in fields known to be weedy. Intercropping peas with a quick-emerging cereal can also provide critical early-season weed control.

Pre-emergent harrowing can also give peas an advantage over weeds.In weedy fields, post-emergence harrowing can also be an effective option at the seedling stage, before branching begins.

Other management considerations

Be aware of the potential for building disease pressures, such as Sclerotinia, Fusarium, and root rot if peas or other susceptible crops (other pulses, flax) are also cash crops in the crop rotation.

Benefits
      • Abundant biomass
      • Weed suppression
      • Well suited to most Prairie regions
Cautions
      • High seed costs
      • Disease build up, especially when other pulses are part of the rotation

 

6. Lentil

Lentil field. Photo by Laura Telford.
Lentil field. Photo by Laura Telford.
Quick Facts
Soil Preference Most, if well drained
Prefers a pH around 7.0
Zone Adaptation Well suited to the Brown soil zone if terminated early. Recommended for the Dark Brown and Black soil zones. Not recommeded for the Gray and Dark Gray soil zones dur to high moisture conditions.
Seeding Rate 35-40 lb/ac
Seed Weight  15,000 seeds/lb
Termination Incorporation, roller crimper, grazing
Grazability Good for grazing
Nitrogen Supply 40-75 lb/ac

 

Botany

Scientific name: Lens culinaris
Lifecycle: Annual

Growth habit

Short upright growth, with stems reaching 8-30” in height.
Shallow taproot and root system.
Flowers 60-70 days after planting.

Varieties common on the Prairies

Indianhead black lentil is the most commonly used lentil species for green manuring on the Prairies. In fact, Indianhead lentil was bred for smaller seed size and for use as a green manure crop for the Prairies by Dr. Alan Slinkard at the University of Saskatchewan.

Soil and climate preference

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Lentil flower. Photo by Laura Telford.

Indianhead lentil performs well in cool, dry conditions and has good drought tolerance. This crop is generally not recommended for higher rainfall areas or areas with excessive soil moisture, as even a short period of waterlogging may kill the green manure. Lentil is best suited for well drained soils, but can grow well under a wide range of soil conditions. Lentils are more tolerant of drought and high temperatures than field peas.

While many research trials deem lentil green manures to perform moderately, Indianhead is often recommended as an ideal option for the Dark Brown soil zone. While also better suited than other green manures to the dry conditions of the Brown soil zone, expect to see only about half of the biomass generated here in comparison to the moister Dark Brown and Black soil zones. In drier soil zones, the lower biomass of Indianhead lentil in comparison to other green manure options can be better accepted, due to their lower water use. Lentil may also be a good option when the soil zones that typically have abundant moisture, such as the Black, Dark Gray and Gray zones, experience drought or untypically dry conditions.

When considering a lentil green manure in the drier Brown soil zone, caution should be taken to make sure that enough soil moisture remains for a following cash crop. Planting lentil green manures early (at least by the time of grain planting) and harvesting early (by the first week of July, even if not yet to the full bloom stage) are recommended to reduce soil water use by the green manure and to allow a period of water replenishment before the next cash crop.

Integration into the crop rotation

Lentil field. Photo by Laura Telford.

Lentil field. Photo by Laura Telford.

Lentils are an annual green manure that can be grown for a full season, or included as a partial season green manure following a cash crop harvest. To limit pest and disease issues, pulse crops should not be grown immediately before or after a lentil green manure in the crop rotation.

A full season can be dedicated to a lentil green manure crop. This practice provides some flexibility in timing of planting that can allow additional weed management operations before the green manure is planted in the moister soil zones. Dedicating a full season to an Indianhead lentil green manure works well in the dry Brown soil zone. In this case, Indianhead lentil can be planted and terminated early to reduce water use, while the interval between the termination of the green manure and the planting of the next crop can allow a period of water replenishment.

Lentil is also a good candidate for double cropping. In double cropping, the lentil green manure is seeded following the harvest of a winter cereal crop. If considering double cropping, note that this strategy is best suited to areas with sufficient soil moisture and with a sufficient amount of growing season remaining after grain harvest. See Choosing a Green Manure for more information.

Lentil can serve as a good forage material, and can be grazed on farms that include livestock. Ruminants not accustomed to grazing lentils may need an acclimatization period before grazing, and may not find lentils as palatable as some other annual green manures. Grazing a lentil green manure will terminate the stand, so time grazing to coincide with flowering for optimal nitrogen contributions.

Nitrogen fixation and supply potential

Lentils tend to have a high rate of nitrogen fixation. However, given their short stature, lentils do not produce as much biomass as some other green manures. This can limit the total nitrogen contributions that they can provide.

In general, Indianhead lentil can be expected to produce 1,500-3,000 lb of biomass per acre under Prairie organic production. As a result, lentil green manures can provide 40-75 lb of nitrogen per acre.

Water use efficiency

In general, lentils have a fairly low water usage among green manure crops, and so are particularly well suited to growth in dry regions.

In drier areas, such as the Brown soil zone, lentil green manures should be seeded and terminated early to reduce soil water use and allow a period of moisture recharge.

Seeding rate, date and availability

Plant Indianhead lentil 1-2” deep at a seeding rate of 35-40 lb/ha. Plant with narrow row spacing to improve growth and ability to compete with weeds.

Indianhead lentil has a smaller seed size than many other annual legume green manures, and so can be seeded at a lower seeding rate that improves affordability. Seed is generally readily available. Be sure to inoculate the lentil green manure with the proper inoculant (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.

When possible, and especially in dry areas, seed lentil as early as is practical in the spring. Lentils can often tolerate frosts after planting, and so can be planted early. Plant the seeds at a depth that places them into moisture.

If double cropping, plant lentil as soon as possible following the harvest of a winter cereal to allow opportunity for biomass production before cold terminates the green manure crop.

Lentils can be intercropped with cereals for a mixed green manure. The rapid growing cereal provides early season weed control, uses available soil nitrogen to encourage nitrogen fixation by lentil, and also lends more biomass to the mixture. When intercropping a lentil green manure, reduce the seeding rate of the cereal crop to ensure that the lentil makes up at least 50% of the stand so that nitrogen contributions are not reduced.

Termination options

For optimal nitrogen contributions, annual green manures should be terminated in the bloom stage and before seed is set. Lentils tend to flower within 60-70 days of planting. In dry soil zones, earlier termination at the bud stage should be considered – this may reduce nitrogen contributions, but can lessen the green manure’s impact on soil moisture.

There are a range of termination options for a lentil green manure. As a green manure with lower biomass and an upright growth habit, lentil is perhaps one of the easiest green manures to terminate. Simple incorporation is often sufficient for termination. The stand can be mowed before incorporation for ease of tillage, but this may not be required.

A lentil green manure can also be terminated by grazing. Research has suggested that lentil green manures are highly consumed by sheep, after training the animals to develop a taste for it.

Lentil has also been demonstrated to be successfully terminated by rolling with a roller-crimper for use in reduced-till organic systems. However, its lower biomass makes lentil less well suited to a no-till phase of an organic rotation than hairy vetch.

Weed management

Photo by Laura Telford

Photo by Laura Telford

Lentils germinate quickly and have vigourous growth. However, lentil’s upright growth and low plant canopy makes it a poor competitor against weeds.

Research suggests that increasing seeding rates, especially when planting into a field that is known to be weedy, can help to improve the competitiveness of a lentil green manure against weeds. Planting with narrow row spacing can also reduce opportunities for weeds.

Additional harrowing operations following planting may help to give lentil a competitive edge over weeds. If post-emergence harrowing is to be used, seed at a higher rate to compensate for potential plant damage or loss.

Other management considerations

Indianhead lentil can host plant diseases that may impact other legume crops in the rotation. If other pulses are a part of your rotation, make sure that they do not immediately precede or follow the lentil green manure. However, in the Prairie region, pest and disease pressures in lentil tend to be low. Indianhead lentil may be vulnerable to damage by grasshoppers.

Benefits
      • Lower seed cost than many other annual green manure species.
      • Lower water use than many other alternatives, although should still be used with caution in dry regions.
      • Demonstrated positive effects on soil health, with positive impacts on soil biology, chemistry and physical characteristics.
Cautions
      • Water use in dry soil zones should be considered.
      • Susceptible to weed pressures.
      • Can host diseases that may infect other legume or pulse crops in the rotation.
      • Does not perform well under high moisture conditions or extreme heat.

7. Chickling Vetch

Chickling vetch plant. Photo by Iris Vaisman.

Chickling vetch plant. Photo by Iris Vaisman.
Quick Facts
Soil Preference Most
pH preference in the 6.0-7.0 range
Zone Adaptation Best suited to Brown and Dark Brown soil zones. Okay for others.
Seeding Rate 60-80 lb/ac
Seed Weight  7,500 seeds/lb
Termination Multiple passes may be required when terminating with tillage.
Grazability Can be grazed for termination. Some chickling vetches may cause lathyrism, although AC Greenfix has only low levels of the compound responsible for this affliction and is considered safe to graze.
Nitrogen Supply 40-100 lb/ac

 

Botany

Scientific name: Lathyrus sativus L.
Lifecycle: Annual
Also known as grass pea

Growth habit

Climbing or creeping vine that can reach 1 to 2’ in height.
Shallow root system with extensive nodulation.
Reaches full bloom in 60 days.

Varieties common on the Prairies

AC Greenfix is the most common chickling vetch variety in use as a green manure on the Prairies. AC Greenfix was bred on the Canadian Prairies at Agriculture and Agri-Food Canada’s Swift Current research station by Dr. Biederbeck for use as a green manure.

Soil and climate preference

AC Greenfix has been bred for Prairie conditions, and performs well in most Prairie soils and climates. With its drought tolerance, short time to flower, high nitrogen fixation, and high water use efficiency, chickling vetch is an especially good option for the dry Brown soil zone. Chickling vetch is also a good option for droughty years in more typically moist soil zones.

Integration into the crop rotation

Photo by Iris Vaisman.
Photo by Iris Vaisman.

Chickling vetch can occupy a full season in the rotation, allowing flexibility in planting timing to permit weed control operations before planting or after termination.

In areas where moisture and climate allow, chickling vetch has been successfully used as a double crop following the harvest of a winter grain crop. When considering this strategy, be sure that your local climate and growing season can allow the generation of enough biomass and nitrogen by the chickling vetch before freeze-up to justify the investment in chickling vetch seed.

Chickling vetch can also serve as a good forage for livestock, but will be terminated by grazing. When considering using hairy vetch as a livestock feed, be aware that some varieties of chickling vetch may cause lathyrism sickness in livestock. AC Greenfix has only low levels of the compound responsible for this affliction and is generally considered safe to graze.

Nitrogen fixation and supply potential

Photo by Iris Vaisman.

Photo by Iris Vaisman.

Chickling vetch can be expected to generate moderate amounts of biomass under Prairie conditions, in the range of 1,500-4,000 lb per acre in a season.

Chickling vetch is highly nodulated, and so can fix large amounts of nitrogen even with its moderate biomass. Expect contributions in the range of 40-100 lb of nitrogen per acre from a chickling vetch green manure. Prairie studies suggest that a chickling vetch green manure can supply enough nitrogen to fully support a cereal crop. Nitrogen fixation is optimized when chickling vetch is properly inoculated.

Water use efficiency

One of the main benefits of chickling vetch is its high water use efficiency. While chickling vetch may use a similar amount as other annual green manures, it is able to produce more biomass with this water investment.

Seeding rate, date and availability

Plant chickling vetch at a depth of ½ to 1 ½ inches, at a seeding rate of 60-80 lb/ac with a seed drill. Chickling vetch is large seeded, and seed costs can be high, so chickling vetch may be an expensive option. Be sure to inoculate chickling vetch with the proper inoculant (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.

Chickling vetch is best planted early in the spring, and can also be planted in the late summer following a cereal crop harvest where conditions allow.

Termination options

A chickling vetch plot. Photo by Iris Vaisman.

A chickling vetch plot. Photo by Iris Vaisman.

For maximum nitrogen content, terminate chickling vetch at the full bloom stage. Chickling vetch is faster maturing than many other annual green manure legumes, with plants generally reaching full bloom approximately 60 days after planting. This can be up to a week earlier than lentil, another annual legume well suited to dry conditions. This earlier maturity allows for earlier termination that can reduce water withdraw and allow a period of water recharge after termination.

With its viney growth, chickling vetch may require multiple passes when being terminated with tillage alone. Studies have shown that chickling vetch can be successfully terminated by rolling, and so can be integrated into reduced-till organic systems, although its lower biomass makes chickling vetch less well suited to a no-till phase of an organic rotation than hairy vetch.

Chickling vetch can also serve as a good forage for livestock, and will be terminated by grazing. Time grazing to coincide with chickling vetch flowering for maximum nitrogen contributions. Some chickling vetches may cause lathyrism, although AC Greenfix has only low levels of the compound responsible for this affliction and is considered safe to graze.

Weed management

Chickling vetch grows rapidly and produces moderate biomass, but is not generally qualified as a good weed competitor. Increase seeding rates by up to double when seeding into a field known to have high weed pressure.

Other management considerations

Chickling vetch is reported to have resistance to many insects and diseases, but may be vulnerable to grasshoppers.

Benefits
  • High water use efficiency
  • Drought resistant
  • Not susceptible to many diseases or insect pests
  • Rapid maturity
Cautions
  • Seed cost may be high
  • Not a strong weed competitor

8. Hairy vetch

Close up of a hairy vetch flower. Photo by Laura Telford.
Close up of a hairy vetch flower. Photo by Laura Telford.
Quick Facts
Soil Preference Will grow in most soils
Prefers soil pH in the 5.5-7.5 range
Zone Adaptation Performs well in most soil zones. Use with caution in the dry Brown soil zone.
Seeding Rate 20-40 lb/ac
Seed Weight  12,000-16,000 seeds/lb
Termination Can be difficult, requires multiple tilage passes and/or mowing. A good option for no-till organic phase, using a roller-crimper.
Grazability Can be grazed, but may cause bloat or other toxic effects.
Nitrogen Supply 80-250 lb/ac
Botany

Scientific name: Vicia villosa

Lifecycle: Winter annual.

Winter hardiness: Zone 4, potentially into Zone 3 with snow cover.

Growth habit

Vining or climbing growth habit. Hairy vetch can reach 2’ in height when grown on its own, but vine length is much longer (up to 12’).  If given structural support (such as intercropping with a cereal), can gain more vertical height.

Hairy vetch has a shallow rooting system with a small taproot.

Flowers in 70-90 days when spring planted. When fall planted, flowers the following spring.

Varieties common on the Prairies

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 A hairy vetch green manure from above. Photo by Iris Vaisman.

Generally, the unnamed common variety is used. The named varieties, such as Purple Prosperity and Purple Bounty, generally produce less biomass and are not as winter-hardy.

Soil and climate preference

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Hairy vetch flowers and leaves. Photo by Laura Telford.

Hairy vetch has some drought tolerance, and can grow in most soils. As with most green manure crops, caution should be taken in dry areas, particularly the Brown soil zone. This is especially true where hairy vetch overwinters, as its spring water use can be high.

Hairy vetch is winter hardy when planted later in the growing season in many regions of the Prairie, but winter hardiness in the more northern areas can be dependent on snow cover. Consideration should be given as to whether or not a hairy vetch stand will survive the winter in your area, and whether or not this is desirable. If hairy vetch flowers before freeze-up, it can be expected to winter-kill.

Integration into the crop rotation

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Young mixed green manure of hairy vetch and barley. Photo by Joanne Thiessen Martens.

Hairy vetch green manures are often seeded in an intercrop with barley or another cereal. The cereal’s rapid early growth provides ground cover while the hairy vetch is slowly establishing. In addition, the cereal provides structural support that the hairy vetch can climb, while also providing additional biomass.  Hairy vetch-cereal mixtures also work well in reduced-till systems, where the roller-crimper terminates the cereal, but the spring-planted hairy vetch survives and continues to grow, smothering weeds and fixing additional nitrogen. The hairy vetch then winter-kills, providing an abundant weed-suppressing mulch for no-till planting the following spring.

Hairy vetch can also be integrated into the rotation as a double crop. In this case, hairy vetch is seeded following a winter cereal harvest in August and in some areas will persist into the following year. This option should be explored only in areas where the growing season is long enough to allow the green manure to establish well enough to overwinter, and where sufficient moisture is available. The biomass generated at the end of the growing season with a fall-planted hairy vetch will be much less than that produced by a full-season hairy vetch green manure. If double cropping, hairy vetch should be planted 30-45 days before a killing frost if overwintering is planned.
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Mixed green manure of hairy vetch and barley. Photo by Natural Systems Agriculture Lab.

Hairy vetch is also well suited to grazing on mixed operations that include livestock. Hairy vetch can regrow after light grazing, but heavy grazing can terminate a hairy vetch green manure stand. Be cautious of potential bloat. Occasional cases of hairy vetch toxicity have also been reported in the literature. Growing hairy vetch in a mixture with other crops helps to avoid both bloat and toxic effects.

Nitrogen fixation and supply potential

Hairy vetch can leave a dense mulch of plant material on the soil surface. Photo by Laura Telford.

Hairy vetch is one of the best annual green manures for biomass production and nitrogen fixation. Under Prairie conditions, expect 2,300 to 8,000 lb per acre of biomass in a season, with nitrogen fixation of 80-250 lb of nitrogen per acre.

Hairy vetch mulches can remain thick after the winter, and can be good for no-till organic production. Photo by Laura Telford.

Hairy vetch is slower to reach peak biomass than many other annual green manure options, and flowers over a prolonged period. This means that peak nitrogen is more difficult to predict than many other annual green manures, where the peak is reached at flowering. Nonetheless, the abundant biomass produced by hairy vetch allows it to contribute a substantial amount of nitrogen to the crop rotation. A long growth period, in the order of 120 days, is required for hairy vetch to achieve abundant levels of biomass.

Water use efficiency

Hairy vetch is considered to have a moderate water use efficiency. Caution should be taken in the drier soil zones, particularly the Brown soil zone.

Seeding rate AND DATE

Seed at 20-40 lb/ac, at ½ to 1 ½” deep. Hairy vetch is large seeded, and seed costs are often quite high.
Be sure to inoculate hairy vetch with the proper inoculant (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.

Hairy vetch can be planted in the spring, in which case it will often remain actively growing until freeze-up, and will then winter-kill. Hairy vetch can also be planted in the late summer to establish an overwintering stand that will produce well the following year. In areas where hairy vetch overwinters, this can provide ground cover for the fall, winter and spring that can reduce erosion and limit weeds.

When interseeding hairy vetch with a cereal, aim for a mixture that is about 30% hairy vetch. Typical seeding rates for hairy vetch-cereal mixes are around 25 lb/ac for the hairy vetch, and 60-70 lb/ac for the cereal.

Termination options

The abundant and viney biomass produced by hairy vetch can make termination challenging. If tilling, multiple passes may be required, and vines may wrap around tillage equipment. Flail mowing before tillage can ease incorporation. Hairy vetch vines can wrap around and bind rotary mowers.

Hairy vetch is well suited to reduced-till organic production. In studies in Manitoba, spring-planted hairy vetch was not terminated with the roller-crimper. The roller-crimper did, however, terminate any weeds in the stand. The hairy vetch rebounded and continued to grow into the fall until it was winterkilled, leaving behind a good layer of mulch for no-till planting a cash crop in the spring. Researchers recommend hairy vetch for no-till prairie organic grain systems.

Weed management

A field of hairy vetch in flower. Photo by Keith Bamford

A field of hairy vetch in flower. Photo by Keith Bamford

 

A healthy, established stand of hairy vetch can outcompete most weeds. However, vetch is slow to establish, and so can be prone to weediness early in growth. Intercropping hairy vetch with a cereal can provide early season weed competition while the hairy vetch establishes. However, the cereal will mature before the hairy vetch has reached its full growth potential. Terminating the cereal with a roller-crimper is recommended, as this will allow the hairy vetch to persist and continue to grow.

Other management considerations

Hairy vetch seed can be difficult to clean from grains, and can volunteer from previously non-germinated hard seed. Use caution when including hairy vetch before a milling grain in the rotation.

When hairy vetch is included in a rotation also containing pulses, be aware of diseases that can impact both the vetch and cash crop pulse, particularly nematodes.

Benefits
  • Produces abundant biomass and nitrogen, especially high among the annual green manure legumes.
  • Fits well in a reduced-till organic rotation.
Cautions
  • Seed costs may be high.
  • Termination can be challenging and may require multiple passes or additional equipment.
  • Requires a prolonged period for growth to produce a lot of biomass. Slower to reach peak nitrogen than other annual green manure legumes.
  • Overwintering ability can be variable in some parts of the Prairies, often dependent on whether or not there is snow cover.
  • Hairy vetch seed can be difficult to clean from grains, and has volunteer potential.

9. Legume-Cereal Mixes

Legume-cereal mix. Photo by Laura Telford.
Legume-cereal mix. Photo by Laura Telford.
Quick Facts
Soil Preference Combinations can be made that perform well in most soil conditions.
Zone Adaptation Combinations can be made that perform well in most soil zones.
Seeding Rate Varies with the mixture. Aim for a seeding rate that allows the green manure to make up at least 50% of the stand.
Seed Weight Varies with the mixture.
Termination Varies with the mixture. Mixing vining legumes with cereals can ease termination. For maximum nitrogen contributions, find a mix that can do well when terminated when the legume flowers.
Grazability Legume-cereal mixes are often excellent candidates for grazing that are highly nutritious and can reduce bloat.
Nitrogen Supply In general, if the green manure makes up at least 50% of the mix, nitrogen supply can be considered equivalent to that produced with a pure legume stand.
Botany

Scientific name: Green manure mixes can be composed of a wide variety of species. The most common include a legume along with a cereal.

Lifecycle: Legume-cereal mixes can be composed of annuals, or the legume component of the mix can be a perennial or biennial. The cereal component of the mix generally has an annual or winter annual lifecycle.

Growth habit

Perhaps the best legume-cereal green manure mixes include species with varying growth habits. The upright growth of cereals can complement the climbing or vining nature of many of the annual legumes. In this case, the cereal can provide a structural support, like scaffolding, to allow the legume green manure to grow upright, rather than sprawl on the ground.

The heights of the components of the mix should also be considered. This is especially true when using mixes of annual cereals with perennial or biennial legumes, where the cereal is often harvested for grain. Legumes that grow to be too tall can interfere with grain harvest. For annual mixes that will be strictly green manured, it is still important to consider the heights and shade tolerances of the components of the mix. Mixing a tall cereal with a short legume that does not grow well when shaded can lead to a stand dominated by the cereal with little representation, and hence nitrogen fixation, from the legume. See the Green Manure Decision Tools for information on the shade tolerance of the main legume green manure options on the Prairies.

Varieties common on the Prairies

The potential options for green manure mixes can be endless. Most common are two-species mixes that include a cereal and legume, with the most common of these being mixes of peas and oats, as well as a mix of hairy vetch with a cereal such as barley or oats. Faba beans and lentils can also be grown in a mix with a cereal crop.

Perennial and biennial green manures, including red clover, alfalfa and sweetclover perform well when intercropped with a cereal in their first year of growth. These small-seeded legumes can be planted at the same time as the cereal, or can be later broadcast-seeded into an early established cereal stand. This is known as underseeding or relay cropping. In these mixes of annual cereals with longer-lived legumes, the cereal is often harvested for grain, while the established green manure crop is allowed to grow into the following growing season or longer.

More and more, producers are beginning to explore green manure mixes with more than two species. These multiple-species mixes can be very productive, and can include plants with varying growth habits that bring with them a number of different advantages, and are often very competitive against weeds.

Intercropping green manures can be a wonderful opportunity to experiment with different mixes that meet your needs. While intercropping cash crops requires careful consideration of maturity and the ability to separate harvested crops, these considerations do not come into play for green manure mixes. For more information on intercropping, and starting points for experimenting with green manure intercrops, see the Intercropping Factsheet.

Soil and climate preference

With the nearly endless combinations of legumes and cereals or other plants, mixed green manures can have a wide range of soil and climate preferences.

Some green manure mixtures can even act as a form of crop insurance by mixing legume crops with varying soil and climate preferences. A mixture of sweetclover and red clover is one such example. The red clover does well in higher moisture situations, and so can perform well in wet years, or in wet areas of fields. The sweetclover prefers drier conditions and has some drought tolerance once established, and so can perform well in drier years or in drier areas of a field.

Integration into the crop rotation

Legume-cereal mixes can be planted together and occupy a full year of the crop rotation. This is often the case for mixes of annual legumes with cereals. Mixes of longer-lived legumes with cereals are often underseeded or planted as a relay crop; while the cereal will persist for only a year, the perennial or biennial legume can carry forward into the next growing season.

Nitrogen fixation and supply potential

Mixing legumes and cereals combines both a nitrogen-fixer and a nitrogen-user. This can be advantageous, as the cereal can take up excess available soil nitrogen. This can then encourage the partnership between the legume and its associated Rhizobia for nitrogen fixation.

It is generally thought that so long as the legume makes up at least 50% of mixture, nitrogen contributions will not differ largely from those seen in pure legume stands. A general guideline is to expect the green manure to be made up of roughly 2.5% nitrogen. So, a mixed green manure stand with a dry biomass of 1000 lb/ac, at least 500 lb/ac of which being from the legume, can be expected to contribute 25 lb of nitrogen per acre. Some suggest that even stands composed of as little as 25% legume can still contribute the same amount of nitrogen as a pure legume stand, but aim for higher than this to ensure adequate nitrogen contributions.

Including a cereal in the mix can also have implications for the rate of green manure breakdown and nitrogen release. Depending on how mature the cereal is when terminated, it can provide additional carbon. This can slow the breakdown of the plant tissues and nitrogen release. The more mature the cereal is at termination, the more carbon it will provide.

Water use efficiency

The water use efficiency of mixed crops is variable, and will depend on the crops used in the green manure mixture. Consider the water use and needs of all crops in the mixture when choosing your mixture.

Seeding rate, date and availability

Seeding rates for mixed crops can be variable, and determining the ideal rate for each component of the mixture can be difficult. To ensure that the legume makes up at least 50% of the final plant stand, it is recommended that the legume be seeded at its full rate. However, to reduce seed costs, especially for expensive annual legumes like hairy vetch, it can be attractive to reduce seeding rates. Experiment with seeding rates that balance reduced seed costs through lowered seeding rates with optimal stand composition to ensure maximum nitrogen fixation. The cereal component of the mix is often seeded at ¼ to ½ of its recommended seeding rate.

When planting a very competitive cereal with a less competitive legume crop, it may be wise to further reduce the seeding rate for the cereal to 20 to 30 lb/ac, to ensure that the legume is able to establish amongst the competitive cereal and is able to make up enough of the mixture to contribute as much nitrogen as is possible.

Be sure to inoculate the mixed crop with the proper inoculant for each legume included in the mixture (refer to the Managing Green Manures module) for optimal growth and nitrogen fixation.

Mixed green manures can be seeded in a number of ways. Seed can be mixed and seeded in one operation. If using this option, be sure that seeds are of a similar size and density and are well mixed at planting, so that they do not become separated during transport and seeding. When planting small seeded legumes with cereals, an auxiliary box on the seed drill, or even a fertilizer box, can be used for the small seeded crop.

If seeding in separate operations, consider planting the components of the mix at a 90 or 45 degree angle for better ground cover. Broadcast seeding can also be used to plant a small-seeded legume into an established cereal.

Termination options

Deciding when to terminate a mixed green manure can be challenging. The legume may reach flowering, and peak nitrogen, before the cereal matures. If your end goal is nitrogen contribution, the mixed green manure stand should be terminated when the legume flowers. Earlier termination can reduce water use in drier soil zones, or drier years.

If terminating a mixed legume-cereal green manure later, as the cereal approaches maturity, be aware that the mature cereal will be much tougher and contain more carbon.  This will slow decomposition and nitrogen mineralization and availability.

Mixed green manure stands can be terminated with mowing, tillage, or in some cases roller-crimper. Adding a cereal to the legume green manure can greatly increase biomass, and may complicate termination. Higher biomass stands often benefit from mowing before incorporation to ease tillage and ensure complete termination. When terminating a mixed cereal-legume stand with the roller-crimper, be aware that the roller-crimper only successfully terminates plants that have flowered. In the case of spring-planted hairy vetch-cereal green manures, rolling after the cereal has flowered will terminate the cereal component of the mixture, but not the hairy vetch.

Weed management

One of the advantages of mixed green manures is their ability to outcompete and suppress weeds. In legume-cereal pairings, the cereal is vigourous and establishes early to provide early season weed suppression while the slower-growing legume germinates and establishes. Once established, the legume provides additional ground cover that provides few opportunities for weeds.

Other management considerations

If including a legume-cereal green manure, consider whether there are cereal diseases or pests that will carry over from the cereal component of the green manure into future cash cereal crops, especially should the same cereal be grown both as part of the green manure and as a cash crop.

Benefits
  • Produces abundant biomass and nitrogen
  • Can reduce seed costs when using costly legumes, such as hairy vetch, while still generating abundant biomass and nitrogen
  • Synergies between the components of the mix
  • Weed suppression
Cautions
  • More complicated management
  • Need to source multiple seeds

10. Hairy Vetch-Barely Mix

Hair Vetch Barely. Photo by Laura Telford

Quick Facts
Soil Preference Grows well on most soils, especially when well-drained.
pH preference in the 6-7.5 range
Zone Adaptation Barley has a low flood tolerance, both crops have some drought tolerance. Use with caution in the dry Brown soil zone.
Seeding Rate Seed hairy vetch at its recommended seeding rate (25-30 lb/ac) and reduce the seeding rate of barley to 30-70 lb/ac
Termination Very well suited to termination with the roller-crimper. Abundant biomass otherwise typically requires multiple operations for termination. The vining nature of the hairy vetch component of the mix can wrap around and disable implements.
Grazability Can be grazed. Beware of bloat and toxicity, although these will be less than if a pure hairy vetch stand is grazed.
Nitrogen Supply Dependent on the composition of the stand. If the stand biomass is made up of at least 50% vetch, expect nitrogen contributions in the 80-250 lb/ac range. Leaving terminated green manure on the soil surface for no-till planting may reduce nitrogen availability.
Botany

Scientific name:

Hairy vetch: Vicia villosa
Barley: Hordeum vulgare

Lifecycle: Hairy vetch is a winter annual legume, while barley is an annual cereal.

Growth habit

One of the strengths of this mixture is the combination of plants with different growth habits. Barley has a slender stem and upright growth, with some tillering. This gives barley a fairly open canopy that allows hairy vetch to also establish. Hairy vetch is a vining legume that can use the upright barley as a structural support for vertical growth. Barley can reach about 3-4’ in height, as can hairy vetch vines.

Barley has a thick root system that, alongside vetch’s small taproot, can help to improve soil structure and water infiltration.

Varieties common on the Prairies

Unnamed, common hairy vetch is generally recommended, as it produces more biomass and is more winter hardy than the named varieties currently available.

Barley varieties well-suited to organic grain production on the Prairies can also be used in green manure mixes. Including left-over or stored barley seed in a green manure can be a cost-effective way to bulk up the biomass of a green manure while using seed that might otherwise go to waste. However, high quality seed with a good germination rate is important in establishing a healthy and productive green manure stand.

Soil and climate preference

Barley and hairy vetch both perform well in most Prairie soil zones. Combining barley’s low tolerance for acidity (pH 6-8 recommended) with hairy vetch’s preferred pH range (5.5-7.5) suggests that a pH of 6-7.5 is best for this mix.

Barley tends to grow best in cool, dry conditions and has low flood tolerance, while hairy vetch grows well on most soils and in most Prairie climates. Both crops have some drought tolerance. As with most green manure crops, caution should be taken in dry areas, particularly the Brown soil zone.

Integration into the crop rotation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hairy vetch-barley mixtures are most commonly added to organic rotations with the goal of including a tillage-free period in the crop rotation. Hairy vetch-barley green manures can also be grown for a full season and mowed or tilled into the soil.

Barley is a fast-growing cereal that can establish and grow quickly in the spring to outcompete weeds. Hairy vetch is a slow-growing legume that establishes slowly, but can generate abundant biomass and fix a lot of nitrogen when given a long growing period. The combination of these two different growth strategies is another aspect that makes the combination of these two crops in a green manure mixture successful.

Intercropping hairy vetch with a cereal is a common green manure practice employed in organic reduced-tillage rotations in North America and Europe. Typically hairy vetch is interseeded with a winter cereal crop, such as fall rye, in the late summer or early fall. This allows the green manure to establish, overwinter and resume rapid growth in the spring. The green manure is then terminated with a roller-crimper when the winter cereal flowers.  In warmer climates, this coincides well with the planting timing for the next crop.  In the colder Canadian Prairies, this green manure system has been adapted, as the growth window following the termination of an overwintered hairy vetch-cereal green manure is too narrow for successful growth of most cash crops.

On the Prairies, the hairy vetch is instead planted with a spring cereal early in the growing season. The mixed green manure then grows and accumulates substantial biomass throughout the growing season. The green manure is roller-crimped when the cereal begins to flower. When roller-crimped at the flowering stage, the barley the mixture is successfully terminated – its stem is crimped and cannot recover to allow the flow of water and nutrients to the plant’s tissues. However, the hairy vetch is slower to reach full flower, which makes it more resilient to the action of the roller-crimper. This allows the hairy vetch to continue growing, building biomass and nitrogen, until it is winterkilled. Using the roller-crimper on hairy vetch-barley stands results in a thick mulch of plant material that protects soils from erosion and water loss, smothers weeds, and supplies nitrogen. The following cash crop is then no-till seeded into the mulch the following spring.

Hairy vetch-barley mixes can also be harvested for hay, or can be grazed. Note that removing hay from the stand also removes nitrogen and other important nutrients. If haying, cut the green manure in late July to allow a period of regrowth for the hairy vetch before termination. When using hairy vetch-barley mixtures for livestock feed, be cautious of potential bloat and hairy vetch toxicity. However, growing hairy vetch in a mixture with barley will helps to reduce or avoid these issues.

Nitrogen fixation and supply potential

One of the benefits of intercropping a hairy vetch with barley as a green manure is in the nitrogen dynamics of the intercrop. The quick-growing barley will use up available soil nitrogen. This will make the hairy vetch more likely to form an association with its Rhizobia to fix the nitrogen that it needs for growth. In general, including a cereal alongside a legume in a green manure can improve the efficiency of nitrogen fixation by the legume.

While there have been few studies to date on which estimates of expected biomass and nitrogen contributions can be based, expect a hairy vetch-barley mixture to produce abundant biomass. Studies in southern Manitoba showed biomass production on the order of 6700 lb/ac or more. Similarly, scientific results to date are few for expected nitrogen contributions. However, it is generally acknowledged that mixed green manure stands that are composed of at least 50% legume can be expected to provide a similar amount of nitrogen as a pure green manure stand. With this, expect 80-250 lb of nitrogen per acre from a hairy vetch-barley green manure.

Hairy vetch is slower to reach peak biomass than many other annual green manure options, and flowers over a prolonged period. This means that peak nitrogen is more difficult to predict than many other annual green manures, where the peak is reached at flowering. Nonetheless, the abundant biomass produced by hairy vetch allows it to contribute a substantial amount of nitrogen to the crop rotation. A long growth period, in the order of 120 days, is required for hairy vetch to achieve abundant levels of biomass.

If green manures terminated with a mower or roller-crimper are left on the soil surface for no-till planting the following crop, nitrogen supply can be expected to be reduced. Studies with the roller-crimper suggest that approximately 44% less nitrogen may be available when rolled residues are left on the soil surface. This nitrogen reduction can be overcome when terminated residues initially left on the surface are later tilled into the soil. Adequate nitrogen can still be supplied to the following cash crop, even in spite of this reduction in availability, when hairy vetch-barley green manures with abundant biomass and nitrogen content are used.

Including a cereal and legume in a mixture together may alter the breakdown and nitrogen release of the green manure. Cereals tend to be tougher and higher in carbon than legumes, which can slow decomposition and nitrogen mineralization. Cereals become tougher as they mature, so the later the stand is terminated, the more slowly the residues will break down. With the prolonged growing period of hairy vetch, termination timings can be variable. If the barley is more mature when terminated, decomposition and nitrogen mineralization from the mixed green manure will be slowed down.

Water use efficiency

Hairy vetch is considered to have a moderate water use efficiency, and so the same can likely be expected from this mix. Barley is less water-demanding than many other cover crops, and so can be a good option on the Prairies.  Nonetheless, caution should be taken in the drier soil zones, particularly the Brown soil zone.

Seeding rate, date and availability

Seed the hairy vetch at its recommended rate, and reduce the seeding rate of barley to ¼ to ½ of its recommended seeding rate. In reality, this means seeding rates like 30 lb/ac of vetch seeded with 40 lb/ac of barley. Research trials have in some cases used even higher barley seeding rates of up to 70 lb/ac. Barley seeding rates are reduced to ensure that the hairy vetch can also establish amongst this competitive cereal.

Hairy vetch is a costly seed, and planting vetch in a mixture with barley may be an opportunity to reduce vetch seeding rate to reduce the overall cost of the green manure. When doing so, beware that reducing seeding rates can reduce the overall density of hairy vetch in the stand. If the hairy vetch makes up less than 50% of the final stand biomass, nitrogen contributions will be reduced. You may wish to experiment with alternate seeding rates in a small, representative area of your farm before planting a larger acreage to ensure the stand performs as you hope.

Seed the mixture in the early spring. Be sure to inoculate the mixture with the appropriate inoculant for hairy vetch. There is overlap in the recommended seeding depths for the two components of the mix, suggesting that seeding can be planted in a single operation, with seed mixed in the seeder, and seed placed at a depth of ¾-1 ½”.  If seeding in separate operations, consider planting at 45 or 90 degree angles to improve soil coverage.

Termination options

Hairy vetch-barley mixtures lend themselves well to termination with the roller-crimper (see Integration into the crop rotation section, above). When using the roller-crimper, terminate when the barley is flowering. This will kill the barley, but the hairy vetch will continue to grow until it is winterkilled.

A hairy vetch-barley mixture can also be terminated using traditional tillage. Discs may not work well on this dense and vining mixture, which can wrap around and clog the implement.  Multiple passes are generally needed to ensure complete termination. Moldboard plows can typically successfully terminate this high biomass green manure, although be aware of soil exposure to moisture loss and evaporation.

Mowing can also be used to terminate a hairy vetch-barley green manure. Mowed residues can be immediately incorporated, or can be left on the soil surface. Mowing before incorporation can ease equipment passage, ensure complete termination, and break up residues. When mowing, use a flail mower, as the viney hairy vetch is prone to wrapping around rotary mowers, disabling them.

Time termination with a mower or tillage to limit seed set by both the barley and hairy vetch, which can create volunteer problems in the following crop.

Heavy grazing can also be used to terminate a hairy vetch-barley green manure. This is a good option when the required infrastructure and livestock are available. Be aware of possible bloat and toxicity issues when grazing vetch, although these are often offset with the inclusion of barley in the mix. When grazing, note that nitrogen will be made quickly available from livestock droppings.

Weed management

The combination of hairy vetch and barley tends to result in a highly competitive green manure that can smother or outcompete most weeds. The fast-growing barley provides early season weed suppression while the slower-growing vetch becomes established.  The hairy vetch then adds additional biomass that shades and smothers weeds. Barley is also allelopathic, which can further hinder weed growth.

Post-emergence harrowing is not recommended, as hairy vetch is sensitive to injury early in its growth.

Other management considerations

Hairy vetch seed can be difficult to clean from grains, and can volunteer from previously non-germinated hard seed. Use caution when including hairy vetch before a milling grain in the rotation.

When hairy vetch is included in a rotation also containing pulses, be aware of diseases that can impact both the vetch and cash crop pulse, particularly nematodes.

Also note that including barley in this mix does not provide a cereal-free break in the rotation that is otherwise provided by a legume-only green manure. This can allow the proliferation of cereal diseases in the rotation.

Benefits
  • Synergies between the components of the mixture allow for high biomass production, nitrogen fixation, and weed suppression.
  • Very well suited to a no-till production phase in the rotation.
Cautions
  • Does not provide a break from cereals in the rotation, which can continue disease cycles.
  • High biomass can make termination challenging.
  • Hairy vetch seed is costly.
  • Hairy vetch seed can be difficult to clean from grains, and has volunteer potential.

11. Pea-Oat Mix

Pea Oat Alfalfa. Photo by Laura Telford.
Pea-oat Alfalfa. Photo by Laura Telford.
Quick Facts
Soil Preference Performs well on most soils
pH preference in the 6-7 range
Zone Adaptation Performs well in all soil Prairie soil zones. Alter management in dry soils. Best suited for the Dark Brown and Black soil zones.
Seeding Rate 100-120 lb/ac of pea
30-50 lb/ac of oats
Termination Terminate with tillage, mowing or roller-crimper. Vining nature and high biomass may complicate termination and require multiple operations.
Grazability Excellent forage crop
Nitrogen Supply 75-150 lb/ac
Botany

Scientific name:

Pea: Pisum sativum
Oat: Avena sativa

Lifecycle: Annual

Growth habit

One of the strengths of this mixture is the combination of plants with different growth habits. Oat has a slender stem and upright growth, with some tillering that allows a fairly open plant canopy. Field pea is a vining legume that can use the upright oats as structural support for vertical growth. Oats reach about 3-6’ in height, and will be climbed by the peas.

Varieties common on the Prairies

Use pea varieties recommended for green manuring. These are typically smaller-seeded varieties that are used to reduce seed costs. Commonly used pea varieties for green manuring on the Prairies include Sirius, 4010 and Trapper.

Oat varieties well-suited to organic grain production on the Prairies, such as Leggett, can also be used in green manure mixes. Including left-over or stored oat seeds in a green manure can be a cost-effective way to bulk up the biomass of a green manure while using seed that might otherwise go to waste. However, high quality seed with a good germination rate is important in establishing a healthy and productive green manure stand.

Soil and climate preference
 pea-oat-laura-telford

 

 

 

 

 

 

 

 

 

 

 

 

Pea-oat Alfalfa. Photo by Laura Telford.

Field peas perform well as a green manure in a range of conditions, and so do well in most Prairie soil zones. Similarly, oats are well-suited to most Prairie conditions. Peas and oats both perform at their best when grown in cool and moist conditions, and are not tolerant of droughts. Both also have quite low tolerance to flooding. This makes this mixture particularly well-suited to the Dark Brown and Black soil zones.

While oats have a fairly broad range of pH tolerance (4.5-7.5), peas have a somewhat narrower range in which they can perform at their peak. This mixture should do best when planted in fairly neutral soils, with a pH in the 6-7 range.

Integration into the crop rotation

Pea-oat green manure mixtures fit into the crop rotation in the same way as green manure consisting solely of peas. They are typically used when a full season can be dedicated to the green manure. This allows some flexibility in planting timing to allow additional weed control operations before planting or after termination.

Pea-oat mixes can serve as a good forage material, and can be grazed on farms that include livestock. Grazing a pea-oat green manure will terminate the stand, so time grazing to coincide with pea flowering for optimal nitrogen contributions.

Nitrogen fixation and supply potential
 Pea-oat mix. Photo by Joanne Thiessen-Martens.
Pea-oat mix. Photo by Joanne Thiessen-Martens.

One of the benefits of intercropping peas with oats as a green manure is in the nitrogen dynamics of the intercrop. The quick-growing oat will use up any available soil nitrogen. This will make the peas in the mix more likely to form an association with their Rhizobia to fix the nitrogen that the pea needs for growth. A green manure mix of peas and oats can improve the efficiency of nitrogen fixation by the legume.

While there have been few studies to date on which estimates of expected biomass and nitrogen contributions can be based, expect a pea-oat mixture to produce fairly abundant biomass. Prairie studies (southern Manitoba) have achieved biomass production on the order of 3000-6000 lb/ac in mixed pea-oat stands. Similarly, scientific results to date are few for expected nitrogen contributions. However, it is generally acknowledged that mixed green manure stands that are composed of at least 50% legume can be expected to provide a similar amount of nitrogen as a pure green manure stand. From this, 75 to 150 lb of nitrogen per acre can be expected from a well-balanced oat-pea green manure grown on the Prairies.

Including a cereal and legume in a mixture together may alter the breakdown and nitrogen release of the green manure. Cereals tend to be tougher and higher in carbon than legumes, which can slow decomposition and nitrogen mineralization. Cereals become tougher as they mature, so the later the stand is terminated, the more slowly the residues will break down. If the mixture is terminated at pea flowering, the oats will still also be quite young and tender, and may not slow decomposition and nitrogen mineralization substantially.

Water use efficiency

The water use of peas is similar to many other annual green manures, while that of oat is similar to many other cereals.

When green manuring peas, whether alone or in mixture with oats, in dry conditions, such as those predominant in the Brown soil zone, consider planting early in the spring and terminating at the bud stage. While this will reduce the amount of nitrogen fixed by the peas, it will reduce water use and allow a period where rainfalls can replenish soil moisture before the next cash crop is planted.

Seeding rate, date and availability

Pea-oat mix. Photo by Joanne Thiessen-Martens.

Pea-oat mix. Photo by Joanne Thiessen-Martens.

To allow a single seeding operation, the mixed pea-oat green manure can be seeded at a depth that accommodates both the peas and oats. Seeding depth recommendations for these two crops overlap at 1 – 1 ½” planting depth. If seeding in a single operation, be sure that the seeds are well-mixed in the seeder, and that settling and separation does not occur as the tractor travels.

If seeding the two components separately, consider planting at 45 or 90 degree angles to improve ground coverage. This can also allow more flexibility in planting depths – oats should be planted at ½-1 ½” in depth, while pea can be planted at 1-3” depth.

Seed the pea at its recommended rate, and reduce the seeding rate of oats to ¼ to ½ of its recommended seeding rate. In reality, this means seeding rates like 100-120 lb/ac of pea seeded with 30-50 lb/ac of oats. Some recommendations suggest that ratio of seeds in the mix should be 70% peas and 30% oats, by weight.

In some instances, the seeding rate for the pea can be reduced to cut seeding costs. When doing so, beware that reducing seeding rates can reduce the overall density of peas in the stand. If the peas make up less than 50% of the final stand biomass, nitrogen contributions will be reduced. You may wish to experiment with alternate seeding rates in a small, representative area of your farm before planting a larger acreage to ensure the stand performs as you hope.

The mixture can be seeded early in the spring, as both components of the mix have some cold tolerance.  Be sure to inoculate the mixture with the appropriate pea inoculant.

Termination Options

Pea mix. Photo by Laura Telford.

Pea mix. Photo by Laura Telford.

Pea-oat green manures should be terminated when the peas are flowering for maximum nitrogen contributions. The high biomass that results from mixed green manures of peas and oats can be a challenge for termination. Multiple passes may be required if terminating by tillage with discs.

Mowing can be used to terminate the green manure stand as well, and the addition of oats to the mix can make mowing easier than it would be in a stand of pure peas (which are often flattened rather than cut by mowing). Mowed residues can then be left on the soil surface, or can be immediately or later incorporated.

Pea-oat green manures are an excellent livestock feed, and grazing can be used to terminate the green manure. This is an excellent option when the livestock and infrastructure are available. When grazing, note that nitrogen will be made quickly available from livestock droppings.

Pea-oat green manures can also be successfully terminated with the roller-crimper. However, high biomass (6-8 tonnes of biomass per hectare) is recommended for weed suppression if you are considering no-till planting into rolled residues.

Weed management

The combination of peas and oats tends to result in a highly competitive green manure that can smother or outcompete most weeds. The fast-growing and vigorous oats provide early season weed suppression while the slower-growing field peas become established. As the season progresses, the peas adds additional biomass that shades and smothers weeds.

Some farmers also harrow their pea-oat green manure for weed control. The recommendation for harrowing peas (on their own) is less than 4″ and cereals (on their own) is typically in the 2-4 leaf stage. Therefore, it would depend on how the two crops emerge together. It is recommended to do a couple strips to determine the aggressiveness of the harrows.

Other management considerations

Be aware of the potential for building disease pressures, such as Sclerotinia, Fusarium, and root rot if peas or other susceptible crops (other pulses, flax) are also cash crops in the crop rotation.  Also note that including oats in this mix does not provide a cereal-free break in the rotation that is otherwise provided by a legume-only green manure. This can allow the proliferation of cereal diseases in the rotation.

Interplanting peas with oats may reduce disease in the peas, as the oats provide a structural support that the peas can climb. This improves airflow and light penetration, conditions that are unfavourable for disease development.

Benefits
  • Synergies between the components of the mixture allow for high biomass production, nitrogen fixation, and weed suppression.
Cautions
  • Continuation of pest and disease cycles.

12. WANT TO DIG DEEPER? SUPPORTING REFERENCES

Alberta Agriculture and Forestry. 2004. Improving Soil Fertility with Green Manure Legume Crops – Frequently Asked Questions. Available at http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/faq7979 [Link verified 17 May 2016]

Alberta Agriculture and Forestry. 1993. Legume Green Manuring. Available at http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex133 [Link verified 17 May 2016]

Bowren, K.E., V.O. Biederbeck, H.A. Bjorge, S.A. Brandt, B.P. Goplen, J.L. Henry, H. Ukrainetz, T. Wright and L.A. McLean. Date Unknown. Soil Improvement with Legumes: Including Legumes in Crop Rotations. Saskatchewan Agriculture Soils and Crops Branch. Available at https://www.saskatchewan.ca/business/agriculture-natural-resources-and-industry/agribusiness-farmers-and-ranchers/crops-and-irrigation/soils-fertility-and-nutrients/soil-improvements-with-legumes [Link verified 16 March 2016].

Clark, A. [Editor]. 2012. Managing Cover Crops Profitably – Third Edition. Sustainable Agriculture Research and Education. Available at http://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition [Link verified 14 April 2016].

eOrganic. 2013. Hairy Vetch for Cover Cropping in Organic Farming. eXtension. Available at http://articles.extension.org/pages/18570/hairy-vetch-for-cover-cropping-in-organic-farming [Link verified 26 May 2016].

Frick, B. (Ed). 2013. Organic Farming on the Prairies, Second edition. Saskatchewan Organic Directorate.

Midwest Cover Crops Council and Purdue Crop Diagnostic Training and Research Center. 2014. Midwest Cover Crops Field Guide – Second Edition.

Green Cover Seed. https://greencoverseed.com/species

Hardy BBT Limited. 1989. Manual of Plant Species Suitability for Reclamation in Alberta, Second Edition. Alberta Land Conservation and Reclamation Council Report No. RRTAC 89-4.

Innovations in Cover Crops. Date Unknown. Cover Crops Decision Tool. Available at http://decision-tool.incovercrops.ca/  [Link verified 14 April 2016].

MacKenzie, J.L. and A.M. Hammermeister. 2015. Green Manures on the Canadian Prairies: A Literature Review.

Midwest Cover Crops Council. Date Unknown. Cover Crop Decision Tool. Available at http://mcccdev.anr.msu.edu/VertIndex.php [Link verified 14 April 2016].

Natural Systems Agriculture. 2011. Organic Crops Field Laboratory: Carman, Manitoba. Natural Systems Agriculture website. Available at http://www.umanitoba.ca/outreach/naturalagriculture/articles/fieldlab.html. [Link verified 26 May 2016].

Northern Great Plains Research Laboratory. Date Unknown. Cover Crop Chart, Version 2.1. Available at http://www.ars.usda.gov/Services/docs.htm?docid=20323 [Link verified 18 April 2016].

Ontario Ministry of Agriculture, Food and Rural Affairs. 2001. Cover Crops. Available at http://www.omafra.gov.on.ca/english/crops/facts/cover_crops01/covercrops.htm [Link verified 18 April 2016].

Saskatchewan Ministry of Agriculture. Date unknown. Green Manuring with Legumes – FAQ. Saskatchewan Ministry of Agriculture. Available at https://www.saskatchewan.ca/business/agriculture-natural-resources-and-industry/agribusiness-farmers-and-ranchers/crops-and-irrigation/soils-fertility-and-nutrients/green-manuring-with-legumes [Link verified 17 May 2016].

University of California Cooperative Extension. Date Unknown. Cover Crop Database. Available at http://ucanr.org/sites/asi/db/covercrops.cfm [Link verified 14 April 2016].

Wallace, J. (ed). 2001. Organic Field Crop Handbook, Second edition. Canadian Organic Growers.

White, C., M. Barbercheck, T. DuPont, D. Finney, A. Hamilton, D. Hartman, M. Hautau, J. Hinds, M. Hunter, J. Kaye and J. La Chance. 2015. Making the Most of Mixtures: Considerations for Winter Cover Crops in Temperate Climates. eOrganic. Available at http://articles.extension.org/pages/72973/making-the-most-of-mixtures:-considerations-for-winter-cover-crops-in-temperate-climates [Link verified 5 May 2016].