THE QUANTITATIVE MINERAL NUTRIENT REQUIREMENTS OF PLANTS

Abstract

Liebig (14) considered the percentage nutrient content of plants as constant and the nutrient composition, therefore, as representing their nutrient needs. He proposed returning to the soil in the fertilizer all of the constituents of the crops removed. Lawes and Gilbert (13) found, however, that plants may need in the fertilizer more phosphorus than other nutrients although they contain less phosphorus than many other nutrients, so they concluded that the nutrient composition of the removed no direct guide whatever ' ' to fertilizer needs. (26), using increments of nutrients in water cultures, reported the minimum requirements of the mature oat plant for the single nutrients in terms of their percentage content in the plant. His minimum percentage is really the threshold optimum, and it corresponds to the critical percentage as used herein. Although Fraps, and Pfeffer have each reported this work by Wolff, the method has not become accepted. Wolff did not report the constancy of the nutrient requirements under various conditions, but his values of 1.0 per cent. N and 0.35 per cent. P2O5 for the oat plant agree well with the values obtained herein. Hall (10) considered the idea of a critical proportion of each nutrient being needed in the ash of plants, but he concluded that, while the supply of a nutrient did affect its percentage content in the plant, the effect of other factors was as great or greater. This was the conclusion of almost all later investigators. Hall's own paper contains the key to these erroneous conclusions. The phrase will reflect the amount of plant food available in the soil, as measured by the response of the crop embodies the concept of the sufficiency of a nutrient relative to all of the growth factors influencing yield rather than the absolute nutrient supply, about which Hall drew his conclusion. Table I presents the data selected by Hall to prove his point, together with