Analysis of nine mathematical functions as models for leaf diagnosis in wheat grown in fields

Abstract

Winter wheat was grown at five different experimental sites using various nutrient combinations of two nitrogen (N) and three calcium (Ca) doses. The three youngest leaves, including the flag leaf were sampled at anthesis together with the flag leaf post‐anthesis and the grain at final harvest. The leaves were weighed and their mineral nutrient contents analyzed and the grain was also weighed. Of the nine equations that were fitted the potential (log y versus log x) most consistently had the best correlation and, thus, best represents the relationships between leaf dry weights, while the inverse in both variables was best for estimating grain weight from leaf weight. The nutrient content of the leaves was related to leaf dry weight according to the following sequence of maximum R: ? (R = 0.703), potassium (K) (R = 0.580), Ca (R = 0.444), phosphorus (P) (R = 0.359), iron (Fe) (R = 0.291), and magnesium (Mg) (R = 0.290). The square‐root and the quadratic equations best reflected the maximum and minimum values for ? and K, respectively. Highly significant relationships between Ca and Mg, and leaf dry weight were less frequent. The leaf nutrients correlated with grain weight in the following order: Mg (R max = 0.521), ? (0.455), Ca (0.434), Fe (0.348), ? (0.346), ?n (0.339, and ? (0.323). Of these nutrients, only Ca affected grain weight according to a parabolic equation (quadratic or square‐root) while the rest were best fitted by logarithmic functions, both on X and Y or one variable separately and by a straight‐line in one instance.

The square‐root and the quadratic permit the calculation of the optimum concentration of nutrients, and thus, leaf nutritional diagnosis. The flag leaf at anthesis gives the most opportunities for this.

Notes

Departamento Biología Vegetal, Universidad Politécnica, Camino de Vera 14, 46022 Valencia, Spain.

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Notes on contributors

Rosa M. Belda

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