How many trials are needed in crop variety testing?

A method is proposed for determining the required number of trials in crop variety testing. The main focus is on estimating the correct ranking of the varieties. Correlation between observed and correct ranks, as a function of the number of trials, can be studied by simulation. Similarly, the effect of the number of trials on the expected genetic advance under selection can be explored. The result from such simulations can be used as a basis for selecting the number of trials. Swedish one-year and multi-year series in spring barley and winter wheat are used as examples.