Cover crops are used to protect and improve soil productivity. They are generally non-cash crops and rarely harvested.
A cover crop may be used:
as green manure ?tilled over? and incorporated into thesoil to increase soil organic matter, stimulate soil biologi-
cal activity or improve soil physical characteristics;
to protect the soil from wind and water erosion;
to recycle valuable nutrients that are present but not read-ily available to crops;
to catch or conserve nutrients that may be lost through leaching;
to interrupt pest and disease cycles and/or suppressweeds; and
as supplemental feed for livestock or to provide an addi-
tional food source for pollinators (honey bees and leafcut- ter bees) and other beneficial insects.
Adding organic matter to soil
Green manures break down into various types of organic mat- ter. Mature and fibrous crop materials are characterized by a relatively high carbon to nitrogen (C:N) ratio, and generally consist of complex lignin compounds that do not readily de- compose.

Note: Lignin is found in all vascular plants, mostly between the cells, but also within the cells, and in the cell walls. Lignin is what makes vegetables firm and crunchy and gives us fibre.
This slow decomposition generates long-lived or stable organ- ic matter frequently referred to as “humus”. Often, only a very small portion of crop residues are transformed into this stable organic matter. Gardeners looking to increase soil organic matter content should consider cover crops that produce large amounts of mature, fibrous materials. It is best to avoid nitro- gen fixing legumes and crops that produce young “succulent” materials.
See Table 1.


Soil Amendment and CN Ratio
Sawdust highest
150-400:1
Straw
40-80:1
Autumn Leaves
40-80:1
Corn stalks
60:1
Solid manure (no bedding)
16:1
Fresh Ryegrass
25:1
Alfalfa hay
15-20:1
Produce Waste
11-25:1
Grass clippings
9-25:1
Poultry manure lowest
5-10:l

Table 1— The outcome of amendments shows the highest on the list forms as ?long-lived‘ or ?stable‘ organic matter (humus like) and the lowest on the list as ?gives an outcome of biological stimulation‘.

STIMULATE SOIL BIOLOGICAL ACTIVITY
Young, fresh crop materials (including legumes) contain readily available compounds which serve as food for soil micro-organisms. When worked into the soil, they may pro-
duce very little, if any, stable organic matter. They may, how- ever, significantly stimulate soil biological activity which in turn leads to enhanced mineralization (release of nutrients from decomposing organic matter for plant uptake). Soil biological activity will also make certain nutrients more readily available for crop uptake.

IMPROVE SOIL STRUCTURE
Soils with a high organic matter content and intense biological activity generally have excellent soil structure. In fact, soil or- ganic matter and biological activity promote good soil aggre- gation, improved soil stability and improved soil porosity. The- se, in turn, lead to improved water retention and erosion pro- tection. In addition, field equipment will not compact soils that are well structured quite as easily as they would soils that are not.
Soil macro-organisms (such as earthworms) and micro- organisms play an important role in improving the soil‘s physi- cal characteristics by digging tunnels, decomposing or digest- ing organic matter and secreting ?glue-like? compounds that improve soil aggregation. Many crops, including root vegeta- bles, benefit greatly in terms of higher yields and quality from improved soil structure.
In addition, most forage crops (clovers and grasses) and small grains are excellent soil conditioners because their vig- orous, shallow and fibrous root systems are able to loosen the soil and improve soil tilth. Perennial pasture and hay/haylage mixtures, annual ryegrasses and winter rye are good exam- ples of such crops.
Some crops, such as oilseed radish, sweet clover, and alfalfa can be used as "biological sub-soilers". Used strategically, their deep tap roots can break-up hard and compacted soil horizons. In combination with mechanical sub-soiling, deep tilling and improved soil drainage, such cover crops can pro- vide superior soil loosening effects.
Buckwheat
fastest growing cover crop
fibrous root system; moderately aggressive
very cold sensitive; easily killed by frost
effective at extracting phosphorus from the soil; used byorganic farmers for this purpose not a big biomass producer especially if planted late summer
Fall Rye
will germinate in cold temperatures 1 to 2 C but vegetative growth requires 4 C
will flower when daylight hours exceed 14 hrs. and temperatures average 5 to 10 C when flowering starts vegetative growth stops, then mow
roots are fibrous, extensive and will go to 2m depth of soil
does not winter kill ? can tie up nitrogen in spring when needed by crops
helps to increase the concentration of potassium at the surface due to its extensive root system
competitive growth habits, good for suppressing weeds
allelopathic effect - prevents weed germination and growth
cut out strips for planting, leave the rest for weed control