Abstract
ABSTRACT The variability within rows of cultivation may reduce the accuracy of experiments conducted in a complete randomized block design if the rows are considered as blocks, however, little is known about this variability in protected environments. Thus, our aim was to study the variability of the fresh mass in lettuce shoot, growing in protected environment, and to verify the border effect and size of the experimental unit in minimizing the productive variability. Data from two uniformity trials carried out in a greenhouse in autumn and spring growing seasons were used. In the statistical analyses, it was considered the existence of parallel cultivation rows the lateral openings of the greenhouse and of columns perpendicular to these openings. Different scenarios were simulated by excluding rows and columns to generate several borders arrangements and also to use different sizes of the experimental unit. For each scenario, homogeneity test of variances between remaining rows and columns was performed, and it was calculated the variance and coefficient of variation. There is variability among rows in trials with lettuce in plastic greenhouses and the border use does not bring benefits in terms of reduction of the coefficient of variation or minimizing the cases of heterogeneous variances among rows. In experiments with lettuce in a plastic greenhouse, the use of an experimental unit size greater than or equal to two plants provides homogeneity of variances among rows and columns and, therefore, allows the use of a completely randomized design.
Highlights
In 2013, the area planted with horticultural crops in Brazil achieved 800,1 thousand hectares, reaching a total production of ~18.8million tons (IBGE 2014)
The experiments were conducted in greenhouses, one in the autumn and other in the spring, with the cultivar Vera
These results show that the growing season influences the productive variability of horticultural crops and agrees with results found by Carpes et al (2008; 2010), Lúcio et al (2008; 2011), and Santos et al (2010)
Summary
In 2013, the area planted with horticultural crops in Brazil achieved 800,1 thousand hectares, reaching a total production of ~18.8million tons (IBGE 2014). Characteristics inherent to horticultural crops such as the presence or absence of fruits suitable for harvesting, the multiple harvests that are carried out in some crops, and the more intensive cultural management in relation to other crops, are additional sources of variability (Lorentz et al 2005; Lúcio et al 2008) In this type of experiment, often strategies to reduce experimental error such as the use of concomitant observations, adequate experimental design, selection of the experimental unit size and shape, choice of sample size and number of replications cannot be used due to space limitations, or even when used, satisfactory results are not obtained. The experiments do not present the necessary precision in order to adequately identify the differences between treatments
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