I wrote about green manure about a year ago I think, but as I've done some bits and pieces on organic matter lately I thought it might be worth a revisit.
In the simplest terms, a green manure is an annual, leafy plant, that is cut down and dug into the soil at a certain stage in it's growth.
Green manure can be grown in between crops, instead of leaving the soil bare where it can be subject to damage from the elements, leaching of nutrients and erosion. It also helps to suppress weeds.
During growth, it will provide a habitat for beneficial insects. The roots will bring up nutrients that may be in deficit after growing a heavy feeding crop and, if you use legumes in your green manure, these will fix Nitrogen in the soil.
Some green manure crops can be given a mow and then allowed to continue growing, but most will be left alone until short of setting seed and then will be turned into the soil.
In the home garden, you can do this using a strimmer / whipper-snipper and then leaving the green manure on the surface for a week before digging into the soil. Allowing it to wilt in this way makes it easier to dig in.
Once dug in, green manures will continue to improve soil structure and feed the soil biota, giving an added boost to whichever crop is to follow.
There are many options for green manures and your choice will depend on what you want to achieve, the planting season and climatic conditions, your soil type (including pH, salinity etc), available water / irrigation and the length of time you have available.
In the home garden, there are many readily available commercial mixes of green manure seeds, which come pre-inoculated to ensure that the required Rhizobium bacteria will be present for Nitrogen fixation. In Australia, you can purchase a variety of green manures, including mixes, from The Diggers Club.
Autumn and Winter are the perfect time to plant green manures, so why not give them a try in your garden?
You will reap the benefits come Spring! :)
Basic information:
http://www.greenharvest.com.au/SeedOrganic/CoverCrops/GreenManureIntroduction.html
http://www.abc.net.au/gardening/stories/s1620940.htm
http://www.organicschools.com.au/Lessons/Lesson12Greenmanurecrops/tabid/193/Default.aspx
More in depth info:
http://www.covercrops.msu.edu/species/index.html
http://www.dpi.vic.gov.au/agriculture/farming-management/organic-farming/soil-management/green-manures-for-vegetable-cropping
http://www.dpi.vic.gov.au/agriculture/farming-management/organic-farming/soil-management/which-green-manure-should-i-grow
http://www.gardenorganic.org.uk/pdfs/international_programme/GreenMan.pdf
http://sustainablefarmer.net/pdflibrary/library-greenmanuring.pdf
http://www.organicadvice.org.uk/soil_papers/green_manures.pdf
Wherever you are in the world, check out your government's department of agriculture website, or those of local agricultural schools etc for more information :)
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