Superficie de muestreo y número de submuestras para evaluar la fertilidad en suelos cultivados con Brachiaria brizantha en las mesas orientales de Anzoátegui, Venezuela

Abstract

Sampling methodology is governed mainly by soil spatial variability. The objective of this work was to evaluate spatial variability of macro and microelements of a soil cultivated with Brachiaria brizantha, located in the Agrarian System Alto Río Tigre, in order to determine optimal sampling surface and minimum number of subsamples needed to obtain a bulk sample representative of chemical conditions of the selected area. Consequently, the analysis of this sample would render more precise results for recommendations of fertilizers and amendments. To obtain this objective, intensive and systematic samplings were made at 10 farms representative of the region. At each farm 49 sampling points, separated by a distance of 100 m were marked and referenced with coordinates (X, Y). Each point had a depth of 20 cm. Determinations of macro and microelement concentrations, pH, texture and organic matter were done for each sample. Geoestadistical analysis was performed to obtain semi- variogram parameters (range, sill and nugget effect). These parameters were used to calculate the sampling area and the number of subsamples required by each bulk sample. Average scope of variables fluctuated between 201 and 244 m with low coefficients of variation (<30%). A sampling surface of 4-6 ha was established. Moreover, variables presented medium spatial variation at short distances, thus a number of 25 subsamples by bulk sample was established.