An essential part of organic farming is the use of
cover crops. These are special crops specifically to benefit the
soil. As the name implies, cover crops are grown to cover and protect
the soil from erosion.
Another important use of cover crops, or green manure crops, as
they are often called. is to provide organic matter for the soil. Organic
matter is the lifeblood of the soil. There are two ways to get
organic matter into the soil: haul it in, as with manure or compost,
or grow it in place, as with a cover crop.
Cover crops provide plant nutrients. Legumes such as clover,
alfalfa, and beans fix nitrogen from the air into nitrates which can
be used by the plants. Deep rooted cover crops such as alfalfa.
if allowed to grow long enough, bring up nutrients from deep in the soil.
One can divide cover crops into o 4 groups according to when they
are planted and how long they grow.
1) Fall seeded over winter crops. Winter rye, wheat and hairy
vetch are planted in the fall after the row crops are harvested. They
provide writer cover and continue growth in the spring. Then they
can either be tilled in before planting or, in the case of rye and
wheat, harvested for grain and straw later. For best winter cover,
plant early in September or early in October. If the previous crop
will not be harvested soon enough, the cover crop can be seeded into some
standing row crops. This can be done in August before the last cultivation,
which will then cover the seed.
2) Short term cover crops. Soybean and buckwheat are examples
of cover crops planted in early summer and tilled in about 2 months or
less. Soybean is a good nitrogen fixer. Buckwheat makes fast,
lush growing and is good at suppressing weeds.
3) Longer term perennials. Alfalfa and the various clovers
are biennials or perennials which should be grown at least a whole season,
or longer if possible, to get the maximum nitrogen fixing and soil building
effects. One common practices is to over seed them into rye or
wheat in the spring. After the grain is harvested or just cut for
straw, the legume cover crop comes on.
4)Living Mulch. Low growing white clover can be seeded into
standing crops such as corn or tall vegetables in the middle of the sea=son
after early cultivation.
Cover crops should be tilled into the soil at least 2
weeks before the next crop is planted. The soil organisms breaking down
the cover crop can tie up available soil nitrogen. After breakdown
is about completed the organisms start dying back and release nitrogen
for soil use.