NITROGEN FIXING PLANTS

Though nitrogen makes up 80 percent of the volume of the atmosphere, it is relatively useless to plants, until it is changed into a compound. Lightning combines or fixes small amounts of this nitrogen and oxygen in the air,  forming oxides of nitrogen, which are washed out of the atmosphere by rain or snow to reach the soil.

Nitrogen fixing bacteria living in nodules on he roots of legumes, however, can change atmospheric nitrogen into nitrogen compounds useful to themselves and other plants.  These bacteria also change the atmospheric nitrogen into proteins in the roots of alfalfa, beans, clover,  kudzu, lespedeza, peas, peanuts, soybeans, winter (hairy) vetch and other leguminous plants.  Farmers for centuries have rotated their crops to take advantage of this increased soil fertility produced by legumes.

Clover is particularly beneficial when used as green manure and plowed under prior to planting a crop of wheat or corn.  A green manure crop of alfalfa will benefit a crop of cotton.  Red clover may be used on soils too acid and too poorly aerated for alfalfa.  The optimum pH for red clover is between 5.8 and 6.8 but it can stand a pH below 6.0 and still do reasonably well.