Does a legume green manure crop provide a “free” source of soil N?
Nitrogen fixed in a green manure crop is not a “free” source of additional N, but it can be an effective option for some cropping systems, such as organic crop production. There is a cost to buy the seed, inoculate, and plant it, and a cost to terminate the green manure crop at the right stage. There is also the added cost of not growing a marketable crop in that year, and greater depletion of soil moisture reserves in drier areas, compared to tillage or chemical fallow options.
