Considerations for Terminating Cover Cropspss.uvm.edu/pat/2015_Handouts/Cover_Crops_Hudson.pdf · Considerations for Terminating Cover Crops Daniel Hudson UVM Extension Agronomist
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Considerations for Terminating Cover Crops
Daniel HudsonUVM Extension Agronomist
Photo: University of Tennessee
A time to killTo everything there is a season,A time for every purpose under heaven:….A time to plant,And a time to pluck what is planted;
A time to kill,And a time to heal……
‐King Solomon (Ecclesiastes 3)
Photo: University of Tennessee
Major Cover Crop Species in the Northeast?
• Which species do you deal with?
• Which are most beneficial?
• What do they do?
• Trouble terminating the cover crop?
Why do farmers plant cover crops?
Slide credit: Kevin Bradley, U MO
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When should the cover crop be terminated?
Is it risky to plant cover crops if you can’t kill them when you ‘need’ to?
Considerations• Window of opportunity – weather and soil conditions
• Nitrogen immobilization
– What is the cost if it is too late? How much N can be tied up?
– 4000 X 0.16 X .0625 = 40 lb (taken up), more immobilized
Ideal C:N ~24:1 to avoid longer‐term immobilization
• Cereal Rye C:N– Stems: 99:1– Leaves: 29:1– Whole plant vegetative: between 13 and 26:1– Whole plant boot: 40:1
• Reduction in plant‐available N + uncertainty
From: USDA NRCS Publication Carbon to nitrogen ratios in cropping systems
Cover Crop C/N % N mineralized in 160 days
Crimson Clover leaves 10.1 61.4 stems 31.9 29
Cereal Rye leaves 28.9 32.6 stems 98.9 -32.3
Oat leaves 12.8 46.8 stems 78.8 -33.2
Quemada and Cabrera (1995)
Other Potential Secondary Problems
• Excessive rye biomass• Allelopathy
Byproducts with allelopathic activity
(and many others)
Killing Cereal Rye: Temperature considerations (OSU)
• Several days of ‘warm’ weather– Days in high 50s or low 60s– Nights above 40 F
• If nights below 40s, daytime temps need to be in the 60s (NDSU)
Slides attributed to Kevin Bradley are from: A Weed Scientist’s Perspective on Cover Crops in Missouri
This publication can be found at: http://extension.missouri.edu/sare/documents/cover04BRADLEYHerbicide14.pdf
Other experiences?
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Ryegrasses
• Annual and Italian
• Potential tool
• Like a sharp knife…
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From: http://www.ryegrass.com/publications/2014‐ARG‐Mgmt‐Guide.pdf
Annual or Italian Ryegrass: Termination Considerations
• 5‐7 days of good growing conditions– Minimum 55 degrees, above 60 better– If night temp drops below 38 F, wait three more days.
• Soil temperature above 45 degrees
• Be careful!
Annual or Italian Ryegrass: Termination Considerations
• Spray at least 4 hours prior to sunset (translocation)
• Herbicide antagonism very important• Be careful!!• More very relevant details:
– http://www.ryegrass.com/publications/2014‐ARG‐Mgmt‐Guide.pdf
Dr. Kevin Bradley, University of Missouri
Some of these herbicides have cereal rye replant restrictions of up to 18 months!
Terminate when…
• Weather: period of warmer weather• Active growth• Stage of development: vegetative• Window of opportunity: watch forecast• Err on the early side if you must err
Other considerations
• Timeframe of herbicide effectiveness• Could excessive biomass complicate planting process?
• Excessive water removal from soil (rare here)• Management complexity and risk varies with species
• Replant restrictions• Allelopathy??
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