The main objective of the present experiment has been the study of the behavior of organic matter, i. e., non decomposed mass of leguminous and gramineous plants when incorporated into the soil right before the planting time of dry beans and its effects. Data obtained showed that the incorporation of non decomposed plant mass had the following results: (a) moisture was retained in a greater degree and temperature variations were somewhat reduced, although it was in fact less efficient than mulch; (b) there was a tendency of forming a larger number of nodules in the roots, especially when gramineous plants were incorporated, even if this is not directly related to higher productivity; (c) increase in the content of potassium in the leaves, in the development of the plant and root system and in the seed production of dry beans. These effects were particularly significant when soybeans were applied, either incorporated into the soil or as top dressing.