RESUMO
The most significant and important interactions in 2, and 3-year sorghum zonal trials were location x year, cultivar x location and cultivar x location x year. Cultivar x year interaction was significant in one out of four ecologic zones used in the trials. The variance components were relatively small with the second order interaction variance component larger than the first order types involving cultivars. Environmental variance was the largest in all four zones.Computations on theoretical standard error of cultivar means suggest that six replications, eight locations and four years is an ideal testing procedure in the Northern Guinea Savanna, while in the Sudan Savanna, the combination is better with four replications, eight locations and three years. The true value or performance of a variety is most effectively obtained by increasing the number of years, while increasing number of replications is the least effective.
