As fall has just arrived, many gardeners are beginning to finish up with their gardens for the year. The question that remains for many is “what do I do with it now?”
When gardening organically, one of the most useful things that we as gardeners can do is to build up the amount of organic matter in our soil and avoid having bare soil as much as possible to help prevent weed establishment and also keep useful nutrients actively cycling in the soil ecosystem.
A useful and sustainable way to accomplish this is through the use of cover crops. Cover crops can be very useful for a number of purposes including but not limited to:
Protection Soil from Erosion – A cover crop’s roots hold the soil in place, and the crop canopy protects the soil from being splashed away by heavy rains.
Building Organic Matter – Cover crops’ grow and build biomass. Quite often, once they are done growing and it is time to plant cash crops, the cover crop is cut down and turned into the soil. As the cover crop residue decomposes, it adds organic matter to the soil, which can help improve the texture, moisture holding capacity, and nutrient holding capacity of most soils.
Building and Maintaining Soil Nutrition – Leguminous cover crops can actually take unavailable elemental nitrogen out of the air and convert it into biologically available nitrogenous compounds that plants need to grow. They do this through a symbiotic relationship that they form with Rhizobia, a type of beneficial soil bacteria. Nitrogen is one of the most actively-managed essential plant nutrients, largely because plants use a lot of it, and it can be quickly and easily lost from the soil through a number of mechanisms such as volatilization, denitrification, and leaching. One way to prevent nitrogen and other nutrients from being depleted in the soil is to have them tied up as living plant matter. This is how cover crops keep nutrients sequestered in biologically-available forms (and can potentially also bring up trace nutrients from deeper down in the soil), and save them to become gradually available at the right times for the cash crops that are growing as the cover crops decompose in the soil.
Suppressing Weeds – Large, dense, fast-growing cover crops can be used to help choke out problematic weeds by out-competing them for nutrients, water, space, and sunlight.
Loosening Soil – Certain cover crops with very strong and aggressively growing taproots can be used to loosen compacted soil. Certain varieties of large radish cover crops can even grow strong and deep enough to crack through the hard-pan layer of compacted soil sometimes created by frequent and repeated plowing.
Habitat – The pollen and nectar from some cover crops can provide food for many beneficial insects, as well as habitat for a variety of beneficial wildlife. One should be cautious of this though, and ensure that the cover crops don’t potentially also function as a reservoir for pests or diseases that feed on similar cash crops.
Fora wealth of additional information about specific cover crops and how to manage them effectively and profitably for a variety of purposes, check out “Managing Cover Crops Profitably, 3rd Edition” by the SARE (Sustainable Agriculture Research and Education).