Home - Tour BHUOT - Cover Crops and Green Manures
Cover Crops and Green Manures
What and why
Cover Crops are an essential part of annual cropping systems.
A cover crop can be any crop grown for the purpose to cover the soil for a certain period of
time.
A cover crop becomes a green manure crop once it has been incorporated into the soil for
the benefits of adding additional organic matter and nitrogen to the soil. This is usually done
just before or at early flowering stage.
Cover crops and green manures can be annual, biennial or perennial plants. They can be
grown in a pure or mixed stand.
A cover crop planted after a main crop in order to reduce nitrogen leaching is called a catch
crop.
Traditionally cover crops are gown over the winter period to protect the soil surface and reduce
leaching effects. It is then turned under in spring time in order to break down and release
nutrients for the following crop.
If legumes are chosen as part of a cover crop they will be able to help fix nitrogen from the
atmosphere and make this available to the following main crop.
The amount fixed by a legume crops becomes not all available immediately. For a nutrient
budget usually 50% is calculated as available for the following main, annual crop.
Some green manure crops are sending their roots deep
into the subsoil and thus act as nutrient pumps making
nutrients available for following crops in the topsoil.
Some green manure crops, such as mustard can act as a ‘soil cleanser’ and reduce the pressure of soil borne diseases
in a soil. Calendula used as a green manure crop can reduce nematode occurrence substantially.
Once a green manure crop is been turned
under it needs to be given sufficient time
to break down sufficiently before the next
crop is sown. Otherwise the incompletely
decomposed organic matter can have toxic
affects on the following crop.
Depending on soil temperature, moisture
and biological activity this break down takes
about 4 weeks.
Typical winter cover and green
manure crops for Canterbury are:
- Tick Beans
- Vetch
- Rye
- Peas
- Oats
- Mustard
Growing summer green manure crops will mean missing out on a cash crop but they can
serve a special purpose such as building up fertility of a poor soil in preparation for other
annual or perennial crops.
If a soil has a high weed load, e.g. of twitch grass (Agropyron repens) a crop of buckwheat
sown and incorporated several times during the summer can reduce the weed load substantially.
Cover crops and green manures can be placed very strategically in a crop rotation sequence,
e.g. a nitrogen fixing green manure before a heavy feeding main crop such as corn or a
nematode controlling green manure before establishing strawberries.
Cover crops have an important role to play in organic no till systems.
ard
See ‘No Till Area’.
More information on: www.attra.ncat.org
