Inter‐plot competition in yield trials of potatoes (Solanum tuberosum L.) with single‐drill plots

Abstract

SummaryAn experiment was carried out to assess the significance of inter‐plot competition in a yield trial of potato cultivars. Seventeen cultivars were deliberately chosen and assessed for yield in single‐drill and four‐drill plots. Inter‐plot competition for fresh‐weight yield was a significant factor in the single‐drill plots. It was modelled using a common competition coefficient with a covariate based on neighbour fresh‐weight yields. In contrast, there was no statistically significant inter‐plot competition for specific gravity. After adjustment for inter‐plot competition, varietal ranking in estimated monoculture yield differed little from that based on unadjusted means. However, there was a reduction in the range of yield estimates, and a closer agreement with the observed pure‐stand yields from the inner two drills of the four‐drill plots. The adjustment for monoculture performance was most pronounced for the higher and lower yielding varieties, as expected from the assumption that the performance of high yielding varieties was enhanced in a competitive environment at the expense of low yielding ones.A general and flexible method of estimating competition coefficients in variety trials, together with a suitable algorithm, was developed and is explained in an appendix. It was used to check for inter‐plot competition in a number of potato trials with single‐drill plots and a large number of entries. Competition was found in some trials but not in others. Thus, where potato tubers are grown in single‐drill plots for assessment of fresh‐weight yield, adjustment should be made for inter‐plot competition when evidence of inter‐drill competition is found.