A Geostatistical Analysis of Rubber Tree Growth Characteristics and Soil Physical Attributes

Abstract

The cultivation of rubber trees [Hevea brasiliensis (Willd. ex Adr. To Juss.) Muell. Arg.] plays an important role in Brazilian forestry production. However, the relationship between tree production and soil physical attributes is poorly understood. Geostatistical tools such as spatial variability modeling assist the study of the relationships between plant and soil attributes. The objective of this paper is to determine the spatial variability of rubber tree growth characteristics and its relationship to soil–water physical properties (soil mechanical resistance to penetration and field saturated hydraulic conductivity of soil). The experiment was located at Campinas, State of Sao Paulo, Brazil, at a experimental station of the Instituto Agronomico, in a 10 ha area with rubber trees planted in 1992. Samples were taken at 232 points in a 20 ×20 m grid. Average diameter at 1.30 m height and tree height were calculated from average measurements of four trees. The soil physical attributes studied were soil resistance to penetration at 0.40 m depth and field saturated soil conductivity at two depths (0–0.10 m and 0.10–0.20 m). All tree and soil parameters showed moderate to weak spatial dependence among samples. The linear correlation between the attributes of rubber trees and soil was weak. The cross-semivariograms used to evaluate cross-spatial correlations revealed that most of the studied properties did not follow a similar cross-spatial pattern. Spatial variability maps show that areas with higher field saturated hydraulic conductivity of soil have lower soil mechanical resistance to penetration. The field saturated hydraulic conductivity of soil in the 0–10 cm layer showed strong linear and spatial correlation with the diameter of rubber trees, as confirmed by the spatial variability maps of both attributes.