Optimum Plot Size and Number of Replications with Short-day Onions for Yield, Seedstem Formation, Number of Doubles, and Incidence of Foliar Diseases

Abstract

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 Bartlettʼs test for homogeneity of variance, computed LSD values, maximum curvature of coeffi cient of variation plotted against plot size, Hathewayʼs method for a true mean difference, and Cochran and Coxʼs method for detecting a percent mean difference. Bartlettʼs 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 fi ve 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 fi ve basic units and three to fi ve 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 Belleʼ, a cultivar with a high incidence of doubling using computed LSD values. With 'Sweet Vidaliaʼ, a cultivar with low incidence of bulb doubling, a plot size of four basic units (6 m length) and fi ve replications is recommended by computed LSD values. Visualizing maximum curvature between coeffi cient 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, fi ve basic units (7.5 m length) for PB/S and BLB, fi ve basic units (7.5 m length) for 'Southern Belleʼ doubling, and 10 basic units (15 m length) for 'Sweet Vidaliaʼ doubling. A number of plot size-replication combinations were optimum for the parameters tested with Hathewayʼs and Cochran and Coxʼs methods. Cochran and Coxʼs method generally indicated a smaller plot size and number of replications compared to Hathewayʼs method regardless of the parameter under consideration.Overall, both Hathewayʼs 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 infl uence on the appropriate plot size.

Optimum Plot Size and Number of Replications for Determining Watermelon Yield, Fruit Size, Fruit Firmness, and Soluble Solids

“…Optimum plot size, shape, and number of replications have been studied in a number of crops such as sweetpotatoes [Ipomoea batatas (L.) Lam. ], onions (Allium cepa L.), peppers (Capsicum annuum L.), and potatoes (Solanum tuberosum L.) to name a few (Boyhan et al, 2003;Lana et al, 1953;Singh, 1989;Vallejo and Mendoza, 1992). Locascio et al (1966) found a sharp reduction in the watermelon yield CV from oneplant plots (40%) to nine-plant plots (11%).…”

Optimum Plot Size for Field Trials of Taro (Colocasia esculenta)

“…Often, optimum plot size has been estimated visually based on the maximum curvature in the plot of V x vs. x (Boyhan et al, 2003;Vallejo and Mendoza, 1992); however, the apparent curvature in a figure plotting V x vs. x is sensitive to the relative scaling in the y-and x-axes of the plot (Smith, 1938). Curvature is a well-defined mathematical concept and it is straightforward (see ''Materials and Methods'') to determine the point of maximum curvature.…”

“…Using uniformity data, the true difference between two treatments (expressed as a percent of the mean) is plotted against plot size and number of replications. The experimenter could decide on the desired difference between treatment means and then could estimate the plot size and number of replicates from the graph to detect this difference (Boyhan et al, 2003;Hatheway, 1961). This analysis was termed a power analysis, because it is related to the probability of finding a difference between treatments that does exist.…”

“…is a tropical root crop, and Vallejo and Mendoza (1992) plotted the relationship between the CV of yield and plot size using the maximum curvature method to visually estimate an optimum plot size of 30 to 60 plants covering 6 to 12 m 2 . Among several methods, Boyhan et al (2003) visually estimated maximum curvature and calculated optimum plot size for short-day onions (Allium cepa L.) to be 280 to 320 plants covering 19 to 22 m 2 . Based on the power analysis of Hatheway (1961), Boyhan et al (2003) estimated an optimum plot size of 240 plants or 11 m 2 and six replicates or an optimum plot size of 480 plants or 22 m 2 and three replicates.…”

“…Among several methods, Boyhan et al (2003) visually estimated maximum curvature and calculated optimum plot size for short-day onions (Allium cepa L.) to be 280 to 320 plants covering 19 to 22 m 2 . Based on the power analysis of Hatheway (1961), Boyhan et al (2003) estimated an optimum plot size of 240 plants or 11 m 2 and six replicates or an optimum plot size of 480 plants or 22 m 2 and three replicates. Using a segmented regression model to estimate the point of maximum curvature, Nokoe and Ortiz (1998) estimated optimum plot size for banana (Musa spp.)…”