DIAGNOSING NUTRIENT DEFICIENCIES IN SOYBEAN, USING M-DRIS AND CRITICAL NUTRIENT LEVEL PROCEDURES

Plant nutrient deficiencies may be diagnosed with DRIS (diagnosis and recommendation integrated system) or critical nutrient level (CNL) pro cedures. While extensive efforts have been made to improve diagnoses b y DRIS and M-DRIS, little has been done to refine CNL diagnoses for so ybean [Glycine max (L.) Merr.]. In this study, rye compare diagnoses m ade by M-DRIS with those from CNL and modify these procedures to impro ve their diagnostic accuracy. Two databases of R2 (full bloom) soybean leaf nutrient concentrations from 828 field observations of known K, Mn, Zn, or P deficiencies or sufficiencies were used for comparing the procedures. We optimized critical nutrient levels (modified CNL) usin g the same cases from a database that was used earlier to improve M-DR IS. Using this optimization database, the M-DRIS and modified-CNL proc edures had less than or equal to 13 misdiagnoses each of K nutrient st atus compared to 81 by unmodified CNL. M-DRIS was more accurate than t he two CNL procedures in diagnosing P deficiencies from cases in the o ptimized and independent data sets. Unmodified CNL produced 18 misdiag noses for Zn status from cases in the independent data set, versus >27 for M-DRIS or modified CNL. Generally, M-DRIS was the same or more ac curate than CNL methods in diagnosing nutrient status. We recommend CN L concentrations for R2 stage soybean of 3.1 g P kg(-1), 15.1 g K kg(- 1), 17 mg Mn kg(-1), and 21 mg Zn kg(-1). For M-DRIS, we recommend cri tical index values of zero for K and Mn, 18 for P, and -19 for Zn.