Figure 1 - Lush green alfalfa
Figure 2 - Alfalfa has a strong tap root.
Several years of alfalfa growth can help to reduce soil compaction.
Figure 3 - Alfalfa has shown good establishment
in seed corn, many years as an interseeded cover crop.
Figure 4 - This alfalfa cover crop was interseeded
in seed corn and established well. It protected this sandy loam
well over winter from erosion and improved soil structure.
Figure 5 - Good growing conditions can result
in alfalfa underseeding that is as tall as the wheat.
Figure 6 - Alfalfa is not often used as an underseeding
in wheat due to seed costs. However it is relatively shade tolerant
and works well as an underseeded forage cover crop.
Family:
- Leguminosae
- Species Medicago sativa L.
- Herbaceous perennial legume not commonly used as an annual
cover crop
- Some annual varieties available
Cover Crop Use
- interseeded into standing corn, particularly seed corn
- frost seeded/underseeded in a cereal crop
Growth Habits
Germination
- Inoculation needed if alfalfa not regularly grown
- Slow to establish
Top Growth
- 5 to 25 stems per crown
- Growth of 40-60 cm in height
Root System
- Tap root
- Nitrogen fixing nodules on main tap and lateral roots
Overwintering
- Perennial varieties go dormant over winter and generally survive
well unless heaving, waterlogging or icing occurs
- Cutting or mowing during the "critical fall harvest period"
increases the risk of winter injury or winterkill with perennial
varieties
- Annual varieties continue to grow all fall and will usually
winterkill
Site suitability
- Performs best on a deep permeable soil – adequate soil
moisture but no prolonged periods of standing water
- Not tolerant of severely compacted soils
- Intolerant of acidic soils (pH < 6.2)
Control Options
Weed Control
Alfalfa is frequently underseeded into a cereal crop and any weed
control herbicide program must be:
- safe to the cereal crop
- effective on the weeds
- safe to the cover crop
Usually the major weed control problems will be with winter annuals
in fall seeded crops and with annual broadleaf weeds in spring cereals.
Sensitivity to Herbicides
There are several herbicides available if weed control is necessary
(See Publication 75, Guide to Weed Control). Alfalfa is also
sensitive to the soil residues of atrazine and some Group 2
herbicides.
Benefits and Cautions
Nutrient Management
Pest Management
- Provides a break in crop rotation
- Host to slugs – a problem for subsequent reduced till
crops
Organic Matter
- Large biomass producer
- Breaks-up some compacted layers
Erosion Control
- Excellent cover once established
- Improves soil infiltration and permeability
Getting Started
Establishment
-
13 kg/ha seeding rate
-
Firm seedbed, no till seeding works with care
-
Shallow seeding depth
-
Requires adequate seedbed moisture –
spring preferred; August seeding is more inconsistent
Cost & Availability
- Expensive seed, particularly as a single season cover crop
- Perennial seed – widely available
- Seed for annual varieties – less available
