Spatial dependence and experimental precision in snap bean ( Phaseolus vulgaris L.) trials related to the number of plants and harvests

Abstract

Spatial dependence and experimental precision in snap bean (Phaseolus vulgaris L.) trials related to the number of plants and harvestsDependência espacial e precisão experimental em ensaios com feijão- ABSTRACTThe productive variability in horticultural crops affects the planning and quality of the experiments, leading to wrong conclusions. The objectives of this study were to verify the spatial dependence of the fresh biomass of snap beans and to dimension the number of plants and harvests that are necessary to improve experimental accuracy in trials. The data of the fresh biomass of snap beans from uniformity trials carried out in a greenhouse and in the field with semivariograms were created with data transformed into indicators. Thus, they were combined on scenarios of plot size and harvest grouping, and they were adjusted to the spherical, exponential and Gaussian models. A response surface was also applied, with the variation coefficient as a dependent variable and the numbers of plants per plot and harvests as independent variables. The estimates of the semivariogram models parameters indicated a weak spatial dependence. The average of the fresh biomass of snap beans is distributed randomly in the trials, and it is not influenced by the number of plants per plot or by the number of grouped harvests. The best combinations between the number of plants per plot and harvest, for the smaller variation coefficients, are plots of 24 plants for plastic greenhouse and field, and 28 plants for plastic tunnel, in the autumn-winter, combined with the grouping of all harvests. In the spring-summer the number of plants per plot was 30 for plastic tunnel and field, also combined with the grouping of all harvests.Index terms: Geostatistic; spatial variability; multiple regression models; experiment planning; variation coefficient. RESUMOA variabilidade produtiva em cultivos olericolas afeta o planejamento e a qualidade de experimentos, levando a conclusões errôneas. Os objetivos foram verificar a dependência espacial da fitomassa fresca de vagens de feijão-de-vagem e dimensionar os números de plantas e de colheitas para melhor precisão experimental. Com os dados da fitomassa fresca de vagens de ensaios realizados em cultivo protegido e a campo com feijão-de-vagem foram ajustados semivariogramas com os dados transformados em indicadores. Foram combinados diferentes tamanhos de parcela e de agrupamentos de colheitas, sendo ajustados os modelos teóricos esférico, exponencial e gaussiano. Também foi ajustado um modelo de superfície de resposta tendo como variável dependente o coeficiente de variação e, como independentes, os números de plantas por parcela e de colheitas. As estimativas dos parâmetros dos modelos teóricos de semivariograma indicaram fraca dependência espacial. A média de fitomassa fresca de vagens possui distribuição aleatória nos ensaios, não sofrendo influência do número de plantas por parcela ou do número de colheitas agrupadas. As melhores combinações entre os números de plantas por parcela e de colheita...