Selecting & Using Cover Crops
Part 1 – 270 | Unit 1.6
Lecture 1: Definition, Benefits, & Challenges of Cover Crops
- Increased insect pest and disease pressure. While some cover crops may help decrease pest
and disease pressure, others may exacerbate such problems. For example, many legumes
are excellent hosts for nematodes, allowing nematode populations to increase rapidly
in the soil unless the cover crop is incorporated before the nematodes complete their
life cycle. However, if the timing is correct the legume may actually reduce nematode
populations by stimulating the nematodes’ emergence and then killing them when the
crop is incorporated, with the cover crop acting as a kind of trap crop in this way.
Some cover crops (including phacelia, Austrian pea, and vetch) are hosts to the pathogen
Sclerotinia minor and can have adverse effects on lettuce crops. Fava beans can be affected
by Impatiens necrotic spot virus, which can then negatively affect lettuce and radicchio.
See Cover Cropping for Vegetable Production: A Grower’s Handbook (listed in Resources) for
a more detailed discussion of current known cover crops and their positive and negative
relationships with pathogens.
- High percent of cereal biomass. Even where legumes make up 90% of a legume/cereal
blend, you often end up with more cereal biomass than legume biomass. This can be a
result of dry weather conditions, which favor the cereals, and soil fertility, where higher
fertility and residual nitrogen can favor cereal growth. Thus, getting a significant benefit
from the higher-priced legume component can be a challenge. - Financial outlay. Cover crop production costs vary significantly depending on many factors,
including seed selection and seeding rate, duration of the cover crop, and methods of
planting and incorporation. Production costs include:
a) Seed purchase
b) Pre-plant land preparation (discing/ripping)
c) Planting
d) Irrigation (if necessary)
e) Termination (mowing and incorporation). Depending on the amount of biomass
produced, soil incorporation and seedbed preparation following cover cropping can be
a significant cost in terms of the labor and equipment involved.
f) Revenue lost while land is out of production
N contribution from legume cover crops can offset some of the costs of cover crop
production. Other benefits, such as improvements in overall soil fertility, tilth, aeration,
and water infiltration, are more difficult to quantify, making it difficult to calculate a
cost/benefit analysis.