2. Alfalfa Autotoxicity
• Stand Reduction in 4
experiments
– Average 18% Range 7.9 to 32%
• Yield Reduction in 12
experiments
– Average 22% Range 6 to 52%
3. Effect of Waiting Period on Alfalfa Autotoxicity in No-Till
Plants per Square Foot
O Weeks 2 Weeks 4 Weeks Fall Killed After Corn
1994 14 34 40 34 29
1995 14 30 31 30 30
Cosgrove et al., 1996
Alfalfa Autotoxicity Conventional vs No-Till
Plants per Square Foot
O Weeks 2 Weeks 4 Weeks Fall Killed After Corn
Conventional 12 36 30 37 41
No-Till 14 32 35 32 30
Cosgrove et al., 1996
4. Effect of Waiting Period on Alfalfa Autotoxicity in No-Till
Yield (Percent of Check)
O Weeks 2 Weeks 4 Weeks Fall Killed After Corn
1994 11 30 42 58 100
1995 9 13 54 66 100
Cosgrove et al., 1996
Alfalfa Autotoxicity Conventional vs No-Till
Yield (Percent of Check)
O Weeks 2 Weeks 4 Weeks Fall Killed After Corn
Conventional 10 41 73 70 100
No-Till 10 21 48 62 100
Cosgrove et al., 1996
5. Alfalfa Zone of Influence -
distance from old plant
8”
16”
24”
Low survival
Survival but low
yield
No effect on yield
Source: John Jenkins, U of
MO
6. Autotoxicity Summary
• Reduces germination if severe
• Reduces yield for life of stand
• Effect most severe on light soils
• Effect most prolonged on heavy soils
• Area of influence around living plant is
16” radius
• Irrigation/rains can wash autotoxic
factor from soil
7. Recommendations
• Wait at least one year before
reseeding alfalfa if stand in for
two or more years
• Can reseed new seeding
failures anytime
8. Recommendations for
Emergencies
• Remove topgrowth before plowing to
reduce effect
• Tillage can reduce effect
• Irrigation/rains can wash toxic factor
from soil
• Select fields with lightest soils
• Accept some yield loss
