Plant Composition as an Index of Soil Fertility

'""T'HE recent trend in the study of fertility problems A is a gradual turning toward the plant for more definite information as to its nutrient needs for optimum growth. Yield data as determined by field or pot tests have been the most widely accepted criteria for evaluating fertilizer responses, while plant analyses have also received considerable emphasis since the work of Wolff (io) who clearly demonstrated that plant composition was affected by the nutrient content of the growing medium. A more thorough knowledge of optimum nutrient requirements for plants may be obtained by a combined study of these criteria. Thus plant analysis at the maximum yield should show the nutrient requirements of such critical elements as calcium, phosphorus, and potassium from which more efficient fertilizer recommendations could be obtained. An index of fertilizer needs based on this assumption should be applicable to soils of lateritic origin as such soils are especially low in available plant nutrients, in base exchange capacity, are moderately to strongly acid in reaction, but in general respond favorably to proper fertilization. The soil conservation program in the southeast has caused a shift from the usual wide spaced cultivated crops to more close growing types. Consequently, certain legumes have been recommended without sufficient attention being given to their ecological array and as a result numerous questions have arisen in regard to their optimum fertility requirements and to what extent soil treatment can offset these changed ecological factors. In order to throw more light upon this question studies were conducted with lespedeza and Austrian winter peas to determine their fertilizer needs and pH range for maximum growth.