NON‐SYMBIOTIC NITROGEN‐FIXING BACTERIA IN SOIL

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Abstract
Summary: The total nitrogen content of a field soil was increased when rye grass or medic was grown on it, and also when cane sugar was added. Both grass and medic yielded substantial amounts of nitrogen in top material in addition to the soil nitrogen gains. With the grass treatment the increased nitrogen of the soil and the plant nitrogen together amounted to at least 165 Ib. per acre over a 3‐year period, and appeared to be the result of biological nitrogen fixation. It is concluded that the free‐living nitrogen‐fixing micro‐organisms can make important contributions to the nitrogen economy of certain soils.The probable inhibition of non‐symbiotic nitrogen fixation by excessive soil aeration is discussed.