THE QUANTITATIVE MINERAL NUTRIENT REQUIREMENTS OF PLANTS

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Abstract
From a study of the relationship between the % content of a nutrient in a plant and the sufficiency of the nutrient as measured by yield response, it is found that there is a critical percentage of each nutrient in each kind of plant (or part thereof), above which there is luxury consumption, and below which there is poverty adjustment, which is almost proportional to the deficiency until a minimum percentage is reached. The conclusions of previous investigators that other growth factors in general may also affect the % content of a nutrient in a plant have been met with proof from their own data, and from other data, that the sufficiency of the nutrient is likewise affected, so that these relationships still hold. From pot expts. it was found that extreme effects of other growth factors on the yield and N content of barley straw had no significant effects on these relationships. The data for the barley grain indicate the same relationships but are uncertain partly because of excessive N applications. It is proposed that the critical nutrient composition of a plant is an "ideal" but inherent characteristic of the plant, the critical and minimum percentages varying only under special conditions. The Mitscherlich law of the minimum holds only during poverty adjustment; the Liebig law of the minimum holds over the rest of the yield curve. The critical % is a criterion of fertilizer needs.

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