Sample size to estimate the mean of morphological traits of rye cultivars in sowing dates and evaluation times

Abstract

The objectives of this study were to determine the sample size (number of plants) required to estimate the mean of morphological traits of rye (Secale cereale L.) and verify the sample size variability between the traits, cultivars, sowing dates, and evaluation times for distincts mean estimation errors. Ten uniformity trials were performed with two rye cultivars (BRS Progresso and Temprano) in five sowing dates (05/03/2016, 05/25/2016, 06/07/2016, 06/22/2016 and 07/04/2016). Evaluations of traits plant height, number of leaves, and number of stems were performed during the development of the crop. In order to verify the difference of the traits between cultivars and between sowing dates and evaluation times, the F-test was applied to test the hypothesis of homogeneity of variances and the Student’s t-test was used to test the hypothesis of equality of means. The sample size of each trait was calculated for distincts mean estimation errors. There is sample size variability between the traits, cultivars, sowing dates, and evaluation times. In order to estimate the mean of plant height with the same precision, smaller sample sizes are required at the intermediate and final evaluation times compared to initial evaluation times. For the traits number of leaves and stems, smaller sample sizes are required in the initial evaluation times than in the final evaluation times. For mean estimation of traits with maximum estimation error of 15% between sowing dates and evaluation times, 83 and 103 plants are required respectively for cultivars BRS Progresso and Temprano.