Choosing soybean varieties from yield trials: Multiple maturity groups and yield variability

Soybean [Glycine max (L.) Merr] variety trials are used to compare relative yields among soybean varieties. The value of these trials derives from their ability to predict which varieties producers should grow in the next year. The objective of this study was to evaluate the predictability of 20 different variety selection methods, not only for maximum yield but also for the variability in yield. Eighteen selection methods involved constantly changing varieties while two methods (stable methods) reduced the number of replacement varieties. Data from the Kentucky Soybean Performance Tests 1988-1994 were analyzed. The yield increases (mean of 28 environments) produced by the first 18 methods ranged from 4.0 bu/acre (8%) to 1.1 bu/acre (2%); 13 of the 18 methods produced increases significantly greater than zero. Averaged across all other factors, the selection of one variety provided significantly higher yield increases (+2.9 bu/acre) than the selection of three varieties (+1.9 bu/acre), but the yield variation was significantly greater when one variety was selected than when three varieties were selected, particularly when the three varieties were selected from three different maturity groups. The stable methods involved growing a selected variety until its yield fell below the statewide 1-yr mean yield of all varieties in the test. The stable methods had a variety turnover rate of approximately 25%, compared with approximately 80% for the other methods. These stable methods provided yield increases (+2.3 bu/acre for selecting one variety and +1.8 bu/acre when three varieties were selected) and yield variability equal to the other methods. The stable method of selecting three varieties, one from each maturity group, appears to provide a compromise between yield benefits and yield variability while reducing variety changes.