FACTORS INFLUENCING EXCRETION OF NITROGEN BY LEGUMES

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Abstract
Expts. concerned with the excretion of N by inoculated leguminous plants made at the Wisconsin Expt. Station during 1937-1940 are discussed from the point of view of the factors which influence the occurrence of the phenomenon. Several hundred cultures were included in these trials, most of which were negative. It was concluded that type of sand, strain of bacteria, species of plants, type of container, etc., may influence the quantitative aspects of excretion if and when it occurs, but that none of these is a crucial factor in the sense that it controls the occurrence or absence of excretion. It is believed rather that all are important only as they, with other factors in the environment, alter the plants'' physiology. At the Wisconsin station, for example, a long day and low temp. apparently favored excretion in pea and vetch plants, but control of these factors did not insure its occurrence. Although excretion may be an important factor in the benefits of mixed cropping in certain areas, the universal application of the latter on this account appears unwarranted since deleterious as well as beneficial interactions between species may result.

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