2 Helen Philbrick and Richard B. Gregg, Companion Plants and How to
Use Them (Old Greenwich, CT: Devin-Adair Company, 1966), pp. 75–
76.
3 Legumes fix atmospheric nitrogen in nodules on their roots during
the first part of their growth. As the legume begins to flower and set
seed, all of this nitrogen is transferred through the plant and goes
into the seed to form protein. In this way, the growing of mature
legumes provides a period of “soil nitrogen resting,” since nitrogen
in the soil is not needed for their growth, provided the appropriate
bacteria are present in the soil.
4 This way of looking at crops was developed many years ago. It is
based on how much nitrogen crops generally consume or produce.
Actually, it is not always accurate. For example, potatoes, a root crop
and therefore a light feeder, consume some of the largest amounts of
nitrogen. As a result, they are functionally a heavy feeder.
Nonetheless, this system can be a way to organize crop rotation. See:
Francis Chaboussou, Healthy Crops (Charlbury, England: Jon
Carpenter Publishing, Alder House, Ox7-3PH, 2004).
5 Also see Emanuel Epstein, “Roots,” Scientific American, May 1973,
pp. 48–58.
6 Illegal in California, where it is considered a noxious weed that
aggressively takes over cattle lands and prevents fodder from
growing. It is probably also toxic to cattle.
7 Audrey Wynne Hatfield, How to Enjoy Your Weeds (New York:
Sterling Publishing, 1971).
8 Ibid, p. 17.
9 From Organic Gardening and Farming, February 1972, p. 54.