Analysis of nine mathematical functions as models for the relationship between the chemical composition and dry weight of leaves, shoots, and ears of wheat

Abstract

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 harvested at flowering and were divided into leaves, ears, and the remaining above‐ground parts. Dry weight was recorded and the mineral content determined. The relationships between nutrient content and dry matter production were fitted by nine functions: quadratic, square‐root, inverse in x, inverse in y, inverse in both variables, and the straight line. Analysis showed that a square‐root function fitted the relationship between mineral content and dry matter production in the different parts of the plant better than the other equations. The quadratic function was also frequently significant and had large coefficients of correlation. However, the parameters of the square‐root functions had smaller standard than the quadratic, especially for the intercept. Leaf nitrogen, calcium, and magnesium, shoot nitrogen, calcium, and potassium and ear nitrogen, potassium, and magnesium contents were well fitted by the square‐root or quadratic functions, but the relationship between phosphorus content and dry matter showed a dilution effect which was fitted best with the logarithmic function on y, although the levels of significance were not large.