SAMPLE SIZE AND LINEAR RELATIONS IN SLENDER LEAF RATTLEBOX

Abstract

Objectives of this work were to determine the sample size (number of plants) to estimate the mean of slender leaf rattlebox (Crotalaria ochroleuca) traits and investigate the relations among traits. In an experimental area of 8 m × 20 m (160 m2), at 147 days after sowing, 110 plants were randomly selected. The following traits were evaluated for each plant: plant height, stem diameter, number of nodes, number of leaves, leaf fresh matter, stem fresh matter, shoot fresh matter, leaf dry matter, stem dry matter and shoot dry matter. Measures of central tendency, variability, skewness and kurtosis were calculated. Normality was verified using the Kolmogorov-Smirnov test and the sample size was calculated to estimate the mean of the traits, assuming estimation errors (semi-amplitudes of the 95% confidence interval) equal to 1%, 2%, …, 30% of the mean. The relations among traits were investigated by scatter plots, correlation and path analysis. To estimate the mean of these ten traits, with a maximum error of 10% of the mean and 95% confidence level, 67 plants are needed. In an experiment, to estimate the mean of each treatment with 10% precision, 67 plants per treatment must be evaluated. The number of leaves has a positive linear relation with leaf fresh and dry matter. Number of leaves and stem diameter have a positive linear relation with stem and shoot fresh and dry matter.