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Switchgrass + Légumineuse, un fourrage de qualité! (en)

Switchgrass + legumes, a quality forage combination!

The Switchgrass (Panicum virgatum) is a versatile perennial grass, used for the production of forage, alternative litter, biofuels, or as a hunting cover plant. However, its productivity and nutritional quality (especially in proteins) can be limited in monoculture. Assessment The impact of the association with legumes (vetch and peas or alfalfa) on the productivity and quality of forage, with or without nitrogen fertilization.

Key Results

1. Productivity (dry yield)

  • in monoculture, the Switchgrass produces approximately1.2 to 2.6 t/ha(depending on the year).
  • In combination with legumes, the yield achieved4 to 7.7 t/ha(either2 to 3 times morethan in monoculture).
  • Effect of legumes: The vetch and the peas significantly increase the yield, especially in favorable climatic conditions (2020).
  • Fertilization: The intake of fertilizer (40-40-40 kg/ha NPK) slightly improves yield, but the effect is more marked with the vetch.

2. Nutritional quality

  • proteins: the forage associated with legumes contains12-13% protein(against5% in monoculture).
  • Fiber (NDF, ADF): the values remain stable, with an advantage for digestibility (ADF < 30%).
  • Ashes: Slight increase in 2019 with legumes (5 to 7%).

3. Economic benefits

  • Implementation cost: ~330 €/ha (seeds + labor).
  • Extra income: up to720 €/ha/year(depending on climatic conditions), thanks to the sale of fodder (€210/t).
  • Input reduction: less need for nitrogen fertilization (legumes fix nitrogen).

summary table

 
ParameterSwitchgrass (monoculture)Switchgrass + VetchSwitchgrass + Peas
Yield (t/ha)1.2 – 2.63.8 – 7.04.1 – 7.7
Protein (%)~512 – 1312 – 14
NDF (%)48 – 5047 – 4945 – 48
ADF (%)~28~26~25
Net profit (€/ha/year)–90 – 72090 – 720

System Advantages

  • triples productivityand protein content.
  • cost reduction(Less fertilization, better climate resilience).
  • Environmental benefits: Fewer inputs, better ground cover.

recommendations

  • Focus on association withpeafor optimal performance.
  • Adapt fertilization according to climatic conditions (little effect in dry years).
  • Ideal for Mediterranean or marginal areas.

Method for implanting a sod-seeding system (over-seedling) of legumes (vetch or pea) with Switchgrass to increase feed productivity

 

1. Context and objectives

  • Problematic: The shortage of green forage limits the agricultural economy, especially in the summer when cold season grasses are not very productive.
  • Solution: the Switchgrass (Panicum virgatum), high yield perennial grass, is used for the production of forage and biomass. Its association with legumes (vetch or peas) in intercropping increases the productivity and nutritional quality of forage, while reducing nitrogen inputs.
  • Key Results:
    • triple productivity(up to 7.5 t/ha) and protein content (up to 12.5%).
    • Economic profit: Annual gain from 90 to 720 €/ha depending on weather conditions.
    • Environmental benefits: reduction of inputs and improvement of biodiversity.

2. System implementation method

2.1. Choice of species and varieties
  • Switchgrass: Perennial cultivar already established (9th and 10th year in the study).
  • legumes:
    • Vetch(Vicia SativaL.), Variety “Alexandros”.
    • Pea(pisum sativumL.), Variety “Olympus”.
  • Sowing dose: 140 kg/ha for each legume.
2.2. Preparation and sowing
  • sowing date:
    • Vetch and dots sown inautumn(November 21, 2018 and December 10, 2019 in the study), using a cereal seeder innon-ploughing(no-tillage).
    • The Switchgrass is already in place with a spacing between rows of12.5cm.
  • Technical:
    • Direct sowing of the legumes in the Switchgrass canopy, without disturbance of the soil.
    • No use of pesticides (manual weeding if necessary).
2.3. Fertilization
  • Three levels of fertilizationTested (applied after the first harvest):
    1. Witness: 0 kg N-P-K/ha.
    2. Average level: 40-40-40 kg N-P-K/ha (or 50 kg N/ha for the second harvest).
    3. high: 80-80-80 kg N-P-K/ha (or 100 kg N/ha for the second harvest).
  • Source of fertilizer: NPK (15-15-15) and Urea (40-0-0).
  • Objective: support the growth of legumes and Switchgrass, especially in fertile soil conditions (pH 7.6-7.9, 2.91% organic matter on the surface).
2.4. Water management
  • Irrigation: additional contribution in summer by sprinkling (4 times 50 mm), especially in case of drought.
2.5. Harvest
  • first harvest(end of May):
    • Joint harvest of legumes (at the flowering stage) and Switchgrass (5th-6th leaf).
    • Yield: up to 10 t/ha in the intercalary system (compared to 3 t/ha in monoculture).
  • Second harvest(October-November):
    • Only Switchgrass, with an increased yield if the legumes were present in interculture the previous winter.
    • Yield: up to 7 t/ha (compared to 4.5 t/ha in monoculture).
2.6. quality measures
  • Forage analysis:
    • Content of proteins, ash, fiber (NDF, ADF), and digestibility.
    • Method: sampling with 1 m² frames, drying at ≤60°C, near-infrared spectroscopy (NIR) analysis.

3. Agronomic and economic results

  • Productivity:
    • first harvest: The interlayer system produces 2 to 5 t/ha more than monoculture.
    • Second harvest: The Switchgrass benefits from the nitrogen fixed by the legumes, even without additional nitrogen fertilization.
  • Quality:
    • Protein contenttriple(12% vs 5% in monoculture).
    • Better digestibility (ADF < 30%, NDF < 50%).
  • Costs and benefits:
    • Installation cost: ~330 €/ha (seedling + seeds).
    • Selling price of hay: €210/t (example for similar quality hay).
    • gross margin: 420 to 1,050 €/ha (depending on the yield), i.e. a net gain of90 to 720 €/ha/year.

4. Practical recommendations

  • Climate: Suitable for Mediterranean climates (mild winters, dry summers).
  • Soil: prefer fertile, clay-limestone soils, with good water retention.
  • Rotation: The system is permanent, with an annual renewal of legumes.
  • Benefits:
    • Reduction of inputs (fertilizers, herbicides).
    • Improved resilience in the face of climatic hazards.
    • Valorization of marginal lands.

5. Points of vigilance

  • climatic conditions: summer drought can reduce yields (e.g. summer 2020 in the study).
  • Choice of legumes: The pea showed better synergy with Switchgrass for the second harvest.
  • Fertilization: to be adjusted according to the soil analysis and precipitation.

Source: study published inseedlings(2022), University of Thessaly, Greece.

Forage production with association of legumes across the Atlantic

The most recommended Switchgrass varieties by American and Canadian references are as follows, classified by ecotype and regional adaptation:

1. Ecotypes “Upland” (Upland) – Suitable for temperate/cold climates (North, Midwest, Canada)

These varieties are ideal for forage because of their hardiness, good nutritional value and their tolerance to harsh winters.

  • RC Chippewa

    • Region: Midwest, Northeast, Canada.
    • Benefits:
      • Best variety for forage production among the Uplands, with excellent yield and excellent persistence.
      • Suitable for a wide range of soils, resistant to drought and harsh winters.
      • Suitable for mixing with forage legumes for grazing.

  • cellar-in-rock

    • Region: Midwest, Northeast, Canada.
    • Benefits:
      • Good variety for forage production among the uplands, with good yield and excellent persistence.
      • Suitable for a wide range of soils, resistant to drought and cold winters.
      • Used in forage mixes and for hunting.

  • Shawnee

    • Region: Midwest, Northeast, Canada.
    • Benefits:
      • Developed specifically for feeding livestock, with improved digestibility.
      • Good production of biomass and summer green forage.

  • sunburst

    • Region: Central North of the United States, Canada.
    • Benefits:
      • Very tolerant to cold winters, high yield in biomass.
      • Suitable for loamy or sandy soils.

  • blackwell

    • Region: Oklahoma, Midwest.
    • Benefits:
      • Resistant to rust and disease, good forage production.
      • suitable for poor or dry soils.

  • pathfinder

    • Region: Midwest, northeast.
    • Benefits:
      • Good establishment and stable yield, often used in combination with other grasses.

2. “Lowland” ecotypes – suitable for hot and humid climates (south, southeast)

These varieties are more productive in biomass, but less hardy in winter. They are suitable for areas where winters are mild.

  • Kanlow

    • Region: South, Southeast, Midwest.
    • Benefits:
      • Very high yield (up to 9 t/ha), ideal for biomass and forage in hot climates.
      • Imposing size, suitable for deep and moist soils.

  • alamo

    • Region: South, Southeast (Texas, Georgia, etc.).
    • Benefits:
      • The most productive Lowland variety, often used for biomass and fodder in hot and humid climates.
      • average annual yield of 5 tonnes/ha in the South-East.

  • liberty

    • Region: Midwest (Indiana, Illinois).
    • Benefits:
      • Combination of upland and lowland genes, offering a good compromise between yield and hardiness.
      • Superior performance at Shawnee in some studies, with good winter wear.

3. Hybrid Varieties

  • Carthage(Pland)

    • Region: Northeast, Midwest.
    • Benefits: leafy, good spring recovery, suitable for fertile soils.

  • timber(Pland)

    • Region: Northeast.
    • Benefits: Used for forage and wildlife cover, resistant and productive.

Recommendations for association with legumes

  • for the north: favorRC Chippewa,cellar-in-rock,Shawneeorsunburstfor their hardiness and fodder value.
  • for the south:RC Sundance orKanlowandalamoFor their high yield, but beware of persistence in cold winters.
  • Management: Upland varieties (such as Cave-in-Rock or Shawnee) are the most suitable for intercropping with legumes (vetch, peas), because they better support frequent cuts and associations.

Key source: USDA-NRCS and American Universities Studies (Purdue, Wisconsin, Penn State)