CROP PERFORMANCE TRIALS UNDER IRRIGATED AND DRYLAND CONDITIONS

Corn (Zea mays L.) and soybean [Glycine mar (L.) Merr.] performance trials are sometimes conducted under both irrigated and dryland conditions in the southeastern USA. It is not known whether irrigated trials are better trials statistically or if irrigation causes relative rank changes in hybrid or cultivar performance. To answer these questions, corn data were examined from four different environments 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 interactions in all soybean data sets and five of nine corn data sets. Irrigated corn trials produced year x hybrid interactions in seven of 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 r2 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 better trials than dryland trials in all situations. Water management x hybrid/ cultivar interactions suggest that data for irrigated and dryland trials' should be reported separately, and the year x hybrid/cultivar interactions indicated that multi-year data should be examined during hybrid/ cultivar selection. Error variances, F probability values, and r2 values should be examined to determine level of precision when comparing trials of equal composition.