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Susan C. Miyasaka, Charles E. McCulloch, Graham E. Fogg, and James R. Hollyer

calculating optimum plot size (defined as number of measured plants in a plot): 1) determine maximum curvature of the relationship between variance of yield and plot size ( Lessman and Atkins, 1963 ; Meier and Lessman, 1971 ; Smith, 1938 ); 2) minimize cost

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George E. Boyhan

. As new varieties are introduced to the market, growers, seed companies, and extension personnel are interested in how well they will perform. Consequently, there is an ongoing need for varietal evaluations. Optimum plot size, shape, and number of

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George E. Boyhan, David B. Langston, Albert C. Purvis, and C. Randell Hill

Five different statistical methods were used to estimate optimum plot size and three different methods were used to estimate optimum number of replications with short-day onions (Allium cepa L.) for yield, seedstem formation (bolting), purple blotch and/or Stemphylium (PB/S), botrytis leaf blight (BLB), and bulb doubling with a basic plot size unit of 1.5 × 1.8 m (length × width). Methods included Bartlett's test for homogeneity of variance, computed lsd values, maximum curvature of coefficient of variation plotted against plot size, Hatheway's method for a true mean difference, and Cochran and Cox's method for detecting a percent mean difference. Bartlett's chi-square was better at determining optimum plot size with transformed count and percent data compared with yield data in these experiments. Optimum plot size for yield of five basic units (7.5 m length) and four replications is indicated using computed lsd values where the lsd is <5% of the average for that plot size, which was the case in both years of this study. Based on all the methods used for yield, a plot size of four to five basic units and three to five replications is appropriate. For seedstems using computed lsd values, an optimum plot size of four basic units (6 m length) and two replications is indicated. For PB/S two basic units (3 m length) plot size with four replications is indicated by computed lsd values. For BLB a plot size of four basic units (6 m length) and three replications is optimum based on computed lsd values. Optimum plot size and number of replications for estimating bulb doubling was four basic units (6 m length) and two replications with `Southern Belle', a cultivar with a high incidence of doubling using computed lsd values. With `Sweet Vidalia', a cultivar with low incidence of bulb doubling, a plot size of four basic units (6 m length) and five replications is recommended by computed lsd values. Visualizing maximum curvature between coefficient of variation and plot size suggests plot sizes of seven to eight basic units (10.5 to 12 m length) for yield, 10 basic units (15 m length) for seedstems, five basic units (7.5 m length) for PB/S and BLB, five basic units (7.5 m length) for `Southern Belle' doubling, and 10 basic units (15 m length) for `Sweet Vidalia' doubling. A number of plot size-replication combinations were optimum for the parameters tested with Hatheway's and Cochran and Cox's methods. Cochran and Cox's method generally indicated a smaller plot size and number of replications compared to Hatheway's method regardless of the parameter under consideration. Overall, both Hatheway's method and computed lsd values appear to give reasonable results regardless of data (i.e., yield, seedstems, diseases etc.) Finally, it should be noted that the size of the initial basic unit will have a strong influence on the appropriate plot size.

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Gavin R. Sills and James Nienhuis

The interactive effects of genotypes, plant population densities, and harvest methods on snap bean (Phaseolus vulgaris L.) yield evaluation were investigated using a split-split plot factorial arrangement of treatments at two locations Six snap bean processing cultivars were grown at 5.5, 11, and 22 plants/m2 and harvested either by machine or by hand. Each' of three commercial seed companies provided two cultivars, one of which was described as “good” and the other as “poor” for machine harvesting. Genotype × harvest method interactions were not significant for pod count, but were significant when yield was evaluated as pod weight. This latter interaction was explained by a single-degree-of-freedom contrast of genotypes × (“good” vs. “poor” harvestability). Genotype × density and genotype × density × location interactions were significant for both pod count and weight. The density × harvest method interaction was nonsignificant for both yield variables. These results suggest that breeders can evaluate yield of genotypes using either hand or machine harvest but should use plant population densities appropriate to commercial production. Optimum plot size for snap bean yield evaluations at these locations under the various conditions imposed were estimated.

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Roger L. Vallejo and Humberto A. Mendoza

The objective of this research was to determine optimum plot size and number of replications to evaluate yield of sweetpotato (Ipomoea batatas Lam.) clones. The optimum plot size was estimated using the methods of maximum curvature and comparison of variances. The adequate number of replications was determined using the Hatheway method. Using the maximum curvature method, the estimated optimum plot size was 10 basic units (b.u. = six plants or 1.2 m2) for La Molina and San Ramon, and 5 b.u. for Tacna, Peru. Using the comparison of variances method, the optimum plot size was 15 b.u. for all locations tested. The adequate number of replications with a plot size of 15 b.u. was four.

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Addenda

105th Annual Conference of the American Society for Horticultural Science, Orlando, FL, 21–24 July 2008: The following changes were made to the conference schedule after the Program and Abstracts issue [HortScience 43(4)] went to press.

: Culture & Management—Vegetable Crops 1 Note correction in the second sentence of the abstract (in bold): Optimum Plot Size and Number of Replications for Watermelon Yield Trials —George Boyhan, Randy Hill, and Denny Thigpen Three different methods