Cover Crops: Sweet Clover

Table of Contents

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

Description

Figure 1: Sweet Clover in flower.

Figure 2: Sweet Clover by roadside.

Family

• Leguminosae;species Melilotus spp

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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

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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

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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 (U.S. $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 and Fertilizer Use: Cover Crops
• Soil Management
• Soil Water Management
• Publication 75, Guide to Weed Control

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