A Study of Root Distribution in Prairie Claypan and Associated Friable Soils

Soil surveyors, in attempting to increase the value of their work, have been turning their attention more to the practical side of soil science. An expression of this fact was the establishment of a Committee on Edaphic Relationships. In furtherance of this spirit we are presenting the results of some field studies made on the distribution and penetration of roots with relation to soil horizons. Several investigators have made rather detailed studies of the root development of various plants, but apparently none have made more than extremely general descriptions of the soils in which the roots were found. In only one case have we found a definite soil horizon recognized and described in relation to root penetration and distribution. Weaver (l6) found in Colorado that wheat and other small-grain roots did not penetrate a horizon of hardpan, but that perennial grasses, such as buffalo grass and bluestem, did penetrate below the hardpan. His description indicates that the material was a hardpan cemented by lime accumulation rather than a true claypan. Weaver (15) also found that roots do not penetrate dry soil and that they penetrate more deeply in soils having friable loamy or silty subsoils. Depth of penetration of native grass roots has been reported to range from 9 Inches in New Jersey to 7 feet in Nebraska (15). Exceptional depths of root penetration have also been noted in sandy soils (15). All these investigators have-used very slow and extremely laborious methods of root study. Weaver (15), who has probably done more work on root investigation than any one else, digs a deep trench and, using a light pick and ice pick removes the soil from around roots and draws diagrams showing location of the roots in the soil. Eyck Ten (l4), one of the pioneers in this field, digs out prisms of soil and washes the soil away from the roots with a water Jet, then takes pictures of the roots. Other investigators have altered this method by weighing the roots occurring at different depths. A simplified method for studying root distribution and penetration is presented in this paper. This method appears very satisfactory for cereals, grasses, and other fibrous-rooted plants. A 5-foot section of I pipe was sharpened to a cutting edge at one end and was driven downward into the soil to the desired depth. The pipe was then pulled out, and the root ends exposed on the lower end of the core thus obtained were counted and recorded. After obtaining the first core, the soil surrounding the sampling hole was removed with a 5-inch auger to the depth of the core, in order to facilitate sampling at the next depth. This procedure was repeated after each sampling as the work progressed downward. In this study, a root count was made at a depth of 1 inch, another at 3 inches, and others at 3-inch intervals to a point below the depth of root penetration. Counts made at every inch would be more satisfactory but require more time. Texture and color of the soil in each core were recorded, together with the depth and root count. All previous methods of root study have been very slow and laborious and have therefore discouraged root studies except in the very friable soils. The method of counting roots on the exposed ends of cores is simple and requires very little time or equipment. Doubtless, the exact number of roots per square inch of soil at a given depth can not be determined by counting but at least a relative figure for the various soil horizons may be obtained. Investigators with more time and having laboratories at their disposal could alter the methods suggested above by weighing dried cores of soil and the roots contained therein, expressing the results in percentage. The process of weighing roots contained in soil cores or prisms is beset with several obstacles. This is particularly true when dealing with heavy horizons which are present in many soils of the United States. It is doubtful if any known method of separating roots from soil would be successful in cases of this kind. Removing soil from roots by use of a water Jet would not be advisable because many hours or even days would be required to remove the soil material of a comparatively small prism of soil. Increasing the pressure of the water Jet to accelerate the process would destroy a great many of the finer roots. It