The aim of this study was to estimate the sample size for lettuce cultivated in different environments, and for this four lettuce crops were cultivated. Two of them were conducted in 2007, with the cultivar Vera and two in 2008 with the cultivar 'Amanda'. The environments in 2007 were greenhouse and field and in 2008, greenhouse and tunnel. In both years of cultivation the fresh biomass and dry weight were evaluated. For each variable in each row of plants was estimated the mean, variance and coefficient of variation (CV%). To test the homogeneity of variances among the lines was applied Bartlett's test at 5% significance level. In cases where the variances were homogeneous lines, was also calculated an average CV% for each environment, and this CV% was used to calculate the sample size. In cases where variances were heterogeneous, the highest CV% of the environment for the calculation of sample size was used. The results showed that in 40% of trials when the variable was fresh biomass and 60% when it was dry, the different production environments provided variability significantly different between the rows of cultivation. It was found that, with the half-width confidence interval of 10% 30, 40 and 33 plants should be sampled in the row of plants in the greenhouse, tunnel and field respectively, for the fresh biomass of plants. Already for plants dry biomass, should be sampled 27, 29 and 32 plants, respectively, for greenhouse, tunnel and field.
experimental precision; Lactuca sativa L.; Protected environment; sampling
