Cover Crops: Sweet Clover

Table of Contents

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

Description

 

Figure 1: Sweet Clover in flower.

Figure 2: Sweet Clover by roadside.

Family

• Leguminosae;species Melilotus spp

Growth Habits

Germination

• White sweetclover have hard shells and need to be scarified prior to germination
• Require the same strain of rhizobial bacteria as alfalfa for inoculation

Top Growth

• Yellow sweet clover: 30-280 cm
• White sweet clover: 100-200 cm., annual or perennial, grows as a 1 m stem
• Flowers May-September; seeds in mid-to late fall

Root System

• Strong taproot system – can penetrate up to 2 m
• Can penetrate compacted silty and clayey soils

Overwintering

• Seldom winterkills

Site Suitability

• pH tolerance 6.5 to 7.5;
• Average annual temperature range between 5° and 22° C
• White sweetclover does well does on a wide range of soil textures
• Tolerates calcareous conditions;
• Sweetclovers perform well in moderately well drained conditions

Sensitivity to Herbicides

• There are no herbicides available that are safe for use on sweet clover and control these broadleaf weeds.
• Sweet clover is also sensitive to the soil residues of atrazine and some Group 2 herbicides.

Weed Control

• Sweet clover 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.

Benefits and Cautions

Nutrient Management

• Fixes nitrogen and should be credited for N-additions;
  believed to move P and K to the root zone via its tap root system

Pest Management

• Attracts beneficial flowering insects

Organic Matter

• Biennial whites yield 2,200-3,500 lbs/ac (Yr. 1) and 2,200-8,100 lbs/ac (Yr. 2)
• Yellow sweetclover 4,200-4,500 lbs/ac (Yr. 1) and 5,500-8,500 lbs/ac (Yr. 2)

Erosion Control

• Strong taproot said to reduce hard pan problems

Soil Moisture

• Shows intermediate values for water use efficiency

Getting Started

Establishment

• Plant in early spring – March-April
• May need to be scarified
• Needs to be covered lightly
• Planting rate: 10-30 lbs/ac, depending upon variety. Most require 8-10 lbs/ac
• Seeding depth ~ 1.25 cm
• Can be underseeded into corn

Cost & Availability

• Inexpensive to moderate cost (US $0.80 to $ 2.50/lb.)
• Most varieties suitable to Ontario conditions are widely available

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Related Links

• Cover Crop Seed Suppliers
• Cover Crop Seeds Available
• Soil Management: Cover Crops
• Soil Management
• Soil Water Management
• Publication 75, Guide to Weed Control