ANALYSIS OF 9 MATHEMATICAL FUNCTIONS AS MODELS FOR THE RELATIONSHIP BETWEEN THE CHEMICAL-COMPOSITION AND DRY-WEIGHT OF LEAVES, SHOOTS, AND EARS OF WHEAT

Winter wheat was grown in Mitscherlich pots on soils obtained from 12 sites from the provinces of Salamanca, Valladolid, and Zamora (Spain). The plants were fertilized with combinations of nitrogen, phosphorus, and potassium, and the crop was watered as necessary. Plants were har vested at flowering and were divided into leaves, ears, and the remain ing above-ground parts. Dry weight was recorded and the mineral conten t determined. The relationships between nutrient content and dry matte r production were fitted by nine functions: quadratic, square-root, in verse in x, inverse in y, inverse in both variables, and the straight line. Analysis showed that a square-root function fitted the relations hip between mineral content and dry matter production in the different parts of the plant better than the other equations. The quadratic fun ction was also frequently significant and had large coefficients of co rrelation. However, the parameters of the square-root functions had sm aller standard than the quadratic, especially for the intercept. Leaf nitrogen, calcium, and magnesium, shoot nitrogen, calcium, and potassi um and ear nitrogen, potassium, and magnesium contents were well fitte d by the square-root or quadratic functions, but the relationship betw een phosphorus content and dry matter showed a dilution effect which w as fitted best with the logarithmic function on y, although the levels of significance were not large.