Cationic Activities, Exchangeable Bases and Uptake by Plants

B soil science and plant physiology there exists, as all are aware, a broad range of mutual interest. This has long been recognized and many conscious efforts have been directed towards interchange of ideas and cultivation of the common ground. The quantitative comparison of results, however, has so far proved almost entirely impracticable, for the simple reason that we have not been able to define the chemical environment of the plant root in the soil as we can that of the same root in a culture solution. Under some circumstances the assumption that plants obtain their nutrients entirely from soluble substances present in the soil water may be justified. Nevertheless, a considerable body of evidence has accumulated in the past few years which points towards interchange and adsorption reactions between plant root and soil particle as controlling factors in the uptake of plant nutrients from soils of medium and low fertility. Now that new experimental methods are becoming available it is worthwhile to reexamine the relationship between the chemical environment of the root and the composition of the plant.