Preliminary N, P, and K Foliar Diagnostic Norms for Soybeans
1977
Sumner, M. E.
The previous successful application of Beaufils' Diagnosis and Recommendation Integrated System (DRIS) to crops such as corn and sugarcane as a foliar diagnostic tool capable of revealing mineral imbalances led to the need for the development of DRIS norms for soybeans [Glycine max (L.) Merr.]. Preliminary DRIS norms for soybean leaves are developed from 1,245 sets of data on elemental (NPK) leaf composition and corresponding yields. This is done by dividing the population of observations into two subpopulations on the basis of yield. The norms are calculated from those forms of expressing the leaf parameters which significantly discriminate between the two subpopulations. The degree of nutrient imbalance in the plant is expressed in terms of a DRIS index which measures the extent to which a particular nutrient deviates from the established norm. The norms are developed in such a way that the influence of age of tissue sampled on the diagnostic index is minimized. The DRIS norms enable one to diagnose whether N, P, or K is the nutrient most limiting to soybean production in a particular case to be diagnosed. The results show that the diagnosis can be made irrespective of variety and age at which the leaf is sampled. The advantage of the DRIS system in predicting nutrient imbalances even when the nutrient concentration in the plant is in or above the critical or sufficiency level range, is illustrated.
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