Cover Crops: Alfalfa

Table of Contents

  1. Description: Family
  2. Cover Crop Use
  3. Growth Habits
  4. Control Options
  5. Weed Control
  6. Sensitivity to Herbicides
  7. Benefits and Cautions
  8. Getting Started
  9. Related Links

Description

Figure 1. Lush green alfalfa

Figure 1. Lush green alfalfa

Figure 2. Root systems for alfalfa plants

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 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 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
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

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

  • Tillage
  • Herbicides

Weed Control

Alfalfa is frequently underseeded into a cereal crop and any weed control herbicide program must be:

  1. safe to the cereal crop
  2. effective on the weeds
  3. 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

  • Requires high P and K levels
  • efficient nitrogen fixer 45 kg/ha+ for plowdown

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

Related Links


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca