The National Turfgrass Evaluation Program (NTEP) took its cultivar testing in a new and exciting direction by instituting a new statistical procedure, ‘AMMI’, for the first time this spring. ‘AMMI’ (which stands for Additive Main Effect and Multiplicative Interaction) was developed and tested by statisticians at the University of Massachusetts and Cornell University over the last fifteen years. In contrast, the statistical procedure NTEP has been using since its inception, ANOVA (Analysis of Variance), has been used for statistical analysis of agricultural experiments since the 1930’s.
Because NTEP trials are evaluated at many locations across the U.S., cultivars and experimental selections (called genotypes) vary in their performance, based primarily on the location (environment) in which they are tested. These differences in performance result from what is termed a ‘genotype by environment interaction’ (G x E for short). In other words, different climatic conditions, weather patterns, soil types, diseases, etc. among the locations affect the performance of the grasses NTEP tests. The traditional ANOVA procedure is not designed to adequately analyze the way the genotypes interact with the different environments. AMMI was developed to more accurately analyze the ‘G x E’ interactions in crop yield trials. This is the first instance of AMMI being used for turfgrass cultivar trials.
NTEP instituted this new procedure after careful consideration, analysis and testing on NTEP data and trials over the last ten years. AMMI is currently used on only new trials (those started in 2007 or later). More information on AMMI and how it is used can be found in the NTEP News Room at http://www.ntep.org/newsroom.htm.
NTEP, established in 1981, coordinates evaluation trials and publishes objective data on turfgrass performance. For additional information on NTEP or the trials, visit http://www.ntep.org or contact Kevin Morris, NTEP Executive Director, at (301) 504-5125.