Use of Boundary Lines in Establishing Diagnostic Norms

Abstract

Whether utilizing a critical value or a nutrient balance system such as the Diagnosis and Recommendation Integrated System (DRIS) for interpreting plant tissue composition, determination of accurate optima is of paramount importance. Two procedures for determining such optima, one using the mean of a high yielding population, the second establishing yield maxima at all nutrient values (henceforth termed the boundary line approach) were contrasted. Ear leaf nutrient composition and associated yield information were collected on over 8000 maize (Zea mays L.) samples from around the world. Values of N/DM, P/DM, K/DM (DM = dry matter), P/N, N/K, and K/P as well as the DRIS indices for N, P, and K were plotted against grain yields. Boundary lines confining the resultant scatters of points were then mathematically described. The boundary lines define yields that may occur under a given set of conditions and can be used to determine plant tissue optima, or as a yield specific alternative to the conventional critical value system. In addition, the maximum yield possible at any given compositional value may be predicted from boundary lines. A comparison of the optima determined via the boundary line approach and those estimated by the mean of the high yielding population revealed extremely small differences indicating that either method is acceptable for estimating these parameters.