Control of interplot interference in grain maize: A multi-site comparison

Interplot interference is known to be potentially a major source of bias in cultivar trials of several plant species, but there are few published resu lts concerning grain maize (Zea mays L.) in France. Tao series of field exp eriments mere conducted in the North and in the South of France from 1994 t o 1996 to quantify interference in grain maize trials and compare methods o f control. Each experiment typically consisted of a reference Mal with two or three unharvested rows on each side of each plot, a four-row-plot trial with one unharvested row on each side or each plot, and a two-row-plot tria l. Trials had seven cultivars in 1994 and 1996, and four additional cultiva rs in 1995. Interference was found to occur in two-row-plot trials and to b e related to plant height, When a cultivar was 10 cm shorter than each of i fs neighbors, its yield was reduced by 0.16 Mg ha(-1) in the North series a nd by 0.30 Mg ha(-1) in the South series on average. Interference appeared much Ion;er in the four-row-plot trials. Methods for controlling interferen ce were assessed by comparing their cultivar estimates with those from the reference trials. Bias due to interference in the two-row-plot trials was r educed by using models for interference, but the four-row-plot trials appea red as a more reliable method fo avoid such bias.