QUANTITY OF LIVING PLANT MATERIALS IN PRAIRIE SOILS IN RELATION TO RUN-OFF AND SOIL EROSION

The menace of soil erosion did not appear in the west until much of the prairie was broken for cropping or weakened by continuous overgrazing. The grassland sod is a great conserver of rainfall; the amount of run-off water is relatively small, and the soil is firmly held against the forces of erosion. This study is concerned with the role that the living underground plant parts play in promoting the absorption of water by the soil, and especially their importance in reducing run-off. Their holding of the soil against the forces of water erosion has been experimentally determined. A study of the quantity of living plant materials in native prairies and pastures near Lincoln, Nebraska, has just been completed. These materials-largely the underground parts of grasses-are composed of roots, rhizomes, and the bases of stems. In the case of non-grassy species or forbs, they sometimes include corms, bulbs, and certain other underground plant structures. The relation of the vegetation to the effectiveness of the precipitation in supplying water to the soil is one of great importance. When the fate of the water falling as drops of rain is studied, it is found that a part is intercepted by the vegetation and never reaches the soil. Much water is lost as run-off when absorption is not sufficiently rapid. This frequently results in erosion. Large amounts are absorbed by the soil and again used by the plant, especially when the vegetation has produced good soil structure and abundant humus. Some water may percolate beyond the depths of the roots of even the most deeply rooted species. The cover of vegetation and the amount of living and dead organic materials in the soil both play an extremely important role in all of these processes. Although this study is not concerned primarily with the effects of the cover of vegetation on soil water relations, yet plant cover is closely related to quantity of underground plant parts and to run-off. Hence, brief consideration will be given to the interception of rainfall, decrease in run-off, and promotion of absorption by the cover of vegetation