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 sufficiencies 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.

Corn (Zea mays L.) and soybean [Glycine nuJX (L.) Men·.] perfonnance trials are sometimes conducted under both irrigated und dryland conditions in the southeastern USA. It is not known whether irrigated trials are better trials statistically or if irrigation causes l"l~lative rank changes in hybrid or cultivar perfonnance. To answer these questions, corn data were examined from four different environmemts and three maturity groups, and soybean data were examined from five different environments and three maturity groups between 1987 and 1990. Water management x hybrid/cultivar interactions were evident in 8 of 12 corn data sets and 7 of 16 soybean data sets. Combining data across years eliminated the water management x hybrid/cultivar interac· tions in all soybean data sets and five of nine corn data sets. Irrigated corn trials produced year x hybrid interactions in seven ·~f nine data sets while dryland trials produced year x hybrid interactions in four of nine data sets. Irrigated trials were only slightly better than dryland trials in accounting for variation; i.e., larger r values but produced smaller error variances in four of 12 data sets of corn. Irrigated trials separated entries better in nearly half of the soybean data sets. The data suggested that irrigated trials were not statistically llletter trials than dryland trials in all situations. Water management x hybrid/ cultivar interactions suggest that data for irrigated and d1yland trials should be reported separately, and the year x hybrid/cultivar interactions indicated that multi-year data should be examine~! during hybrid/cultivar selection. Error variances, F probability values, and r values should be examined to detennine level of precision when comparing trials of equal composition.