USE OF STABILITY ANALYSIS FOR LONG-TERM SOIL FERTILITY EXPERIMENTS

Long-term fertility experiments with replications are often statistically analyzed as split plots in time. Years are often shown to be significantly different and the inconsistency of treatment effects over years enters into significant year-by-treatment interactions which are difficult to interpret. The objectives of this study were to evaluate long-term fertility experiments by stability analysis and relative stability and to observe possible benefits of these analyses to complement conventional analysis of variance procedures. Stability analysis which is the linear regression of treatment yield on the location/year environment mean yield was performed on long-term wheat (Triticum aestivum) and corn (Zea mays L.) fertility trials. Stability analysis on wheat data from the Magruder Plots, indicated that beef manure applications (269 kg N ha-1) responded poorly compared to the NPK treatment when environment means were low (<2.0 Mg ha-1) and visa versa when environment means were high (>2.0 Mg ha-1). Similarly, anhydrous ammonis applied as sidedressing in an irrigated corn experiment at Mead, NE, was found to be superior to urea-ammonium nitrate applied either pre-plant or sidedressed when environment means were less than 8.0 Mg ha-1. Stability analysis provided a simple method of interpreting significant year-by-treatment interactions detected in analysis of variance models from these long-term experiments. Stability analysis may also be useful for multilocation experiments and continuous site experiments where treatments are applied to the same plot year to year. However, stability analysis may be misleading when employed on continuous site experiments where autocorrelations are present year to year.