Estimates of Optimum Plot Size and Shape from Uniformity Data in Burley Tobacco (Nicotiana tabacum L.)1

Abstract

AbstractTo obtain estimates of optimum plot size and shape for burley tobacco (Nicotiana tabacum L.), we conducted uniformity trials during 1969 and 1970 at Greeneville, Tennessee, and during 1970 at Spring Hill, Tennessee. Each trial consisted of 3,000 plants which were subdivided into 600 basic units of 5 plants each. Data from each basic unit were recorded for yield of cured leaf, number of days to flower, number of harvestable leaves, plant height, and the length and width of the fifth leaf from the top of the plant.Hatheway's “convenient plot size” and Smith's soil heterogeneity index methods were used to estimate optimum plot size. The results from Hatheway's method suggest that the greatest precision would be gained by minimizing the number of plants per plot and maximizing the number of replications in the experiment. Because 25 to 30 plants are required for visual evaluation of burley tobacco, it appears that a convenient plot size for yield and quality trials is 30 plants with the number of replications adjusted to the desired difference to be detected or the maximum number permitted by space and cost of production. We found that most other agronomic characters may be measured with acceptable precision on 10 to 20 plants per plot. For percent total alkaloids, precision is expected to increase rapidly with either an increased number of plants per plot or replications in the experiment. The optimum size of plot for yield computed by Smith's minimum cost procedure ranged from 9 to 179 plants. These results do not appear as useful as those from Hatheway's method.Our data suggest that one‐row plots may be slightly better than two‐row plots. Taking into consideration the optimum number of plants per plot and shape, we concluded that single‐row plots containing 30 plants each are most desirable for yield and quality trials. Smaller one‐row plots with increased replication may be more efficient for obtaining genetic information relative to specific characters.