The elaboration of maps to characterize the spatial variability of soil attributes assists in the strategic planning and decision making of agricultural managers. Precision and accuracy of maps are related to the ideal sampling density to characterize the variability pattern. This study was conducted with the aim of identifying the sampling density to represent the variability of soil physical quality using attributes with different magnitudes of variation in an area cultivated with coffee. Three approaches were used to find the most adequate sampling density (geostatistical analysis, percentage of error associated with the sampling density, and coefficient of variation). A total of 145 soil samples were collected at a depth of 0-0.20 m at the crossing points of a regular grid with a spacing of 50 m. The percentage of clay, silt, and sand, macroporosity, microporosity, total pore volume, and soil density were determined. The data were submitted to descriptive statistical analysis. For elaborating the variability maps with up to 15% error and soil attributes with a coefficient of variation close to 50%, a sampling density of 3 points ha −1 is suggested.

The açai palm (Euterpe oleracea Mart.), a native of the Amazon region, is a food of great importance. Recently, due to the discovery of its nutraceutical properties, the rational production in upland areas has been encouraged. However, to support the rational implementation of its cultivation for fruit production, which is a sort of domestication process, it is necessary to identify its germplasm. The aim of this study was to evaluate and quantify the genetic diversity based on phenotypic characters among açai palm mother plants derived from 11 areas of the Amazonian estuary. Twenty-nine phenotypic descriptors were used: (i) 9 from the plant, (ii) 7 related to the fruit, and (iii) 13 of agronomic nature. Principal component analysis was used to assess the phenotypic variability from standardized data obtained from selected açai palm mother plants. In the selection of the descriptors, the methods of direct selection and selection with re-analysis were used. The disposal efficiency was estimated by comparing dissimilarity groups formed by 11 origins of the açai palms based on 29 original characters and 23 selected characters. The groups were formed using the average standardized Euclidean distance and Tocher's optimization method. All the analyses were performed using the GENES program. The selection of 79.31% of the descriptors used was significant and was considered sufficient for the evaluation of the açai palm germplasm for fruit production. The selected descriptors were shown to be capable of quantifying the phenotypic diversity of mother plants of this species, consistently grouping them using the optimization method. The cluster method showed small differences in the number and composition of the groups due to variability among the selected mother plants. Key words: Descriptors. Diversity. Euterpe oleracea. Germplasm. Plant breeding. ResumoO açaizeiro (Euterpe oleracea Mart.) é uma palmeira nativa da região amazônica, de grande importância alimentar e, recentemente, devido à descoberta de suas propriedades nutracêuticas, está estimulando a produção racional em áreas de terra-firme. Para viabilizar essa expansão é necessário o conhecimento do seu germoplasma a fim dar suporte à implantação racional do cultivo para a produção frutos, pois trata-se de uma espécie em processo de domesticação. O objetivo deste trabalho foi avaliar e quantificar a diversidade genética entre matrizes de açaizeiro oriundas de 11 procedências do estuário amazônico, territórios do Arquipélago do Marajó e do Baixo Tocantins, baseada em caracteres fenotípicos. Foram empregados 29 descritores fenotípicos subdivididos em (i) nove relativos à planta, (ii) sete relativos ao fruto e (iii) 13 agronômicos. Foi utilizada a análise de componentes principais para avaliação da