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Diagnosing Nutrient Deficiencies in Soybean, Using M-DRIS and Critical Nutrient Level Procedures

Agronomy Dep., LSU Agric. Ctr.,, Baton Rouge, LA 70803-2110
Iberia Res. Stn., P.O. Box 466, LSU Agric. Ctr.,, Jeanerette, LA 70544

W. E. Sabbe and D. G. Dombeck

Agronomy Dep., Univ. of Arkansas, Fayetteville, AR 72703.

^* Corresponding author(Email: pbell{at}lsuvm.sncc.lsu.edu).

Plant nutrient deficiencies may be diagnosed with DRIS (diagnosis and recommendation integrated system) or critical nutrient level (CNL) procedures. While extensive efforts have been made to improve diagnoses by DRIS and M-DRIS, little has been done to refine CNL diagnoses for soybean [Glycine max (L.) Merr.]. In this study, we compare diagnoses made by M-DRIS with those from CNL and modify these procedures to improve 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 sufiiciencies were used for comparing the procedures. We optimized critical nutrient levels (modified CNL) using the same cases from a database that was used earlier to improveM-DRIS. Using this optimization database, the M-DRIS and modified-CNL procedures had 13 misdiagnoses each of K nutrient status compared to 81 by unmodified CNL. M-DRIS was more accurate than the two CNL procedures in diagnosing P deficiencies from cases in the optimized and independent data sets. Unmodified CNL produced 18 misdiagnoses 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 accurate than CNL methods in diagnosing nutrient status. We recommend CNL 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 critical index values of zero for K and Mn, 18 for P, and –19 for Zn.

Received for publication July 15, 1994.

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