SPATIAL HETEROGENEITY AFFECTS VARIETY TRIAL INTERPRETATION

Observations in neighboring plots of variety trials are often spatiall y dependent. This may reduce the utility of applying the classical ana lysis of variance (ANOVA) due to trends and correlated errors. Identif ying the presence, magnitude, and pattern of spatial heterogeneity is useful for assessing the utility of ANOVA. Our objectives were to esti mate the effects of spatial heterogeneity on the independence of error s, and appraise a nearest-neighbor analysis (NNA) to improve the analy sis of a variety trial experiment. A semivariogram for organic C at on e field site showed a substantial soil spatial dependence and was cons istent with the semivariogram for residuals in grain yield. Semivariog rams of classical residuals for grain yield had large nugget variances and exhibited spatial structure. Similarly, semivariograms of the non classical residuals showed large spatial dependence, accounting for 40 to 80% of the sample variance. Genotype effects were not always stati stically significant when the raw data were analyzed using ANOVA. The NNA was used to adjust data for the effects of large- and small-scale spatial dependencies in the variety trial experiment. The ANOVA on NNA -adjusted data showed highly significant P less-than-or-equal-to 0.01) genotypic effects. The improved analysis also showed reduced error va riance (from 57-78%), and dramatically increased R2 values compared wi th the ANOVA on unadjusted data. The estimates of variance between gen otypes from ANOVA on unadjusted data were from 99% smaller to 63% larg er than the error variance. On the other hand, the variance component estimates between genotypes from ANOVA on adjusted data ranged from 0 to 300% larger than the error variance. The spatial heterogeneity can have serious effects on the interpretation of variety trials experimen ts. In general, nonclassical deviations appear more sensitive to the e ffects of spatial heterogeneity than classical residuals, and are more useful as a test for violations in the classical assumption of spatia l independence.