Western Sustainable Agriculture Research & Education
(SARE) Farm Internship Curriculum and Handbook
Tom and Maud Powell and Michael Moss, Sustainable Farmers, Jackson County, OR.
Technical advisor: Tim Franklin, Jacksonville, OR.
Curriculum advisor: Peter O’Connell, Jacksonville, OR.
Web advisor: National Center for Appropriate Technology, Butte, MT.
The learner will:
- Be introduced to various types of cover crops and their specific applications.
- Be able to identify various benefits of cover crop application.
Why Use Cover Crops?
The role of cover crops in organic farming systems:
Cover crops are one of the primary fertility and soil management tools available to the organic farmer, and are an important strategy for preventing nutrient and soil loss from a field. They are crops grown primarily for soil or ecosystem improvement rather than cash and can provide a variety of services, from increased nitrogen (N) input, to soil protection, to weed and disease suppression. However, they can also have negative consequences if they are managed incorrectly or the wrong species are chosen.
Cover crop, green manure, and catch crop refer to different primary functions of the crops planted.
- Cover crop: Mainly used to prevent soil erosion by covering soil with living plants
- Green manure: Crop grown mainly to be turned under for soil improvement
- Catch crop: Used to “catch” nutrients left after harvest of a cash crop and prevent leaching
These are not mutually exclusive functions. For example, a fall-planted cereal + legume crop that is incorporated the following spring can serve as a cover crop, green manure, and catch crop. However, different species and mixes may perform one function better than another.
Perennial Cover Crops
- Perennial cover crops are most often planted in pastures and orchards.
- Often perennial cover crops require irrigation.
- Perennial cover crops have multiple purposes and benefits.
- Providing forage
- Holding soil/preventing runoff and erosion
- Retaining moisture in soil/drought tolerance
- Fixing nutrients through root system
- Preventing leaching of nutrients from runoff
- Smothering weeds
- Cycling nutrients up from subsoil
- Penetrating hard subsoil
- Improving soil structure.
Self-Seeding Annual Cover Crops
- Self-seeding annual cover crops are most often planted in fallow fields and in orchards.
- Often annual cover crops do not need to be irrigated.
- Annual cover crops have similar purposes and benefits as the list above. But the seed cycle makes it an ideal option for western climates with a dry summer.
- Green manure is a term for an annual crop sown for the purpose of incorporating the back into the soil. The green manure crop can be fall, spring, or summer sown, and irrigated or not.
- Green manure has benefits similar to those of other cover crops, but when the crop is incorporated into the soil the following additional benefits are realized:
- Trapping nutrients (nitrogen, phosphorus) in the soil that were fixed from atmosphere via root systems
- Adding tons of carbon (organic matter) to the soil. This builds humus, a biological soil network that is the key to unlocking nutrients in the soil. (Addition of organic matter is also beneficial to soil structure, water holding capacity, air circulation, and friability.)
How to Choose a Cover Crop
- Identify what you want the cover crop to do:
- Provide nitrogen
- Increase soil organic matter (SOM) and improve nutrient availability by increasing soil biological activity
- Scavenge nutrients left in the soil after the cash crop and prevent loss by leaching
- Prevent soil erosion
- Improve soil structure
- Improve drainage
- Protect water quality
- Provide mulch to conserve soil moisture
- Provide habitat for beneficial insects and spiders
- Suppress weeds
- Suppress soil borne pests and diseases
- Identify the cover crop planting niche:
- Define timing of critical field operations for cash crop production
- Winter cover crops
- Summer cover crops
- Select cover crop species or mix to meet the goals and requirements from steps 1 and 2
Examples – Field Activity
Tour various cover crops, identify components (nutrient fixing plants, scaffold plants, carbon source plants) and dig holes to expose soil profile.
- Perennial – alfalfa, some clovers, rye, fescue, orchard grass, birdsfoot trefoil
- Self-seeding annual – rose clovers, sub-clovers, medic, rye
- Green manure
- Cold weather – peas, oats, fava beans, vetch (vulnerable at seedling below 20 F), rye, triticale
- Warm weather – buckwheat, black-eyed peas, cow peas, sudan grass
- What are the three basic types of cover crops?
- What are the specific benefits of each type of cover crop application?
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