Soil classes and properties explain the occurrence and fruit production of Brazil nut

Abstract

Soil properties and classes can influence the occurrence of plants and the production of Brazil nut fruits and may have a different distribution between sites. This study aimed to evaluate the relationship of plants' occurrence, production of Brazil nut fruits, and spatial variability of the properties in different soil classes in two Brazil nut stand in the state of Acre, Brazil. The study was conducted in two plots in two native Brazil nut stand, Cachoeira (CP01 and CP02 -plots 1 and 2) and Filipinas (FP01 and FP02 -plots 1 and 2). The soil profiles were described morphologically. Sixty soil samples were collected in each plot. The chemical properties, granulometry, soil density, particle density, and estimated total porosity were determined. The average fruit production was calculated by counting the fruits in a sample of Brazil nut trees. Subsequently, the trees were divided into three classes of production: low (≤1.5 can; the can unit has 18-L, which is able to hold 59 and 77 fruits, respectively, for Cachoeira and Filipinas), medium (1.6 to 3.9 cans), and high (≥4.0 cans). The can unit is the traditional measure of volume in the region and varies according to the locality. Cluster analysis was performed to determine whether there was a difference between Brazil nut stands and soil profiles, and geostatistics was used to evaluate the spatial dependence of soil properties. The highest occurrence of Brazil nut trees with high fruit production (≥4.0 cans) was found in the Latossolo Vermelho Distrófico argissólico (Oxisol) and Argissolo Vermelho-Amarelo Distrófico típico (Ultisol). However, the Argisol also hosted the plants with the lowest productions (≤1.5 can). The pH, total organic carbon, sum of bases, P, N, granulometry, and porosity showed a greater spatial variability, and FP02 showed a greater number of properties with high spatial variability compared to the other areas. Although the occurrence of plants and the production of Brazil nut fruits (Bertholletia excelsa) were associated with the classes and the physical and chemical properties of the soil, pyxidium production differed between areas. In general, soil physical properties were limiting factors for Brazil nut production and/or higher tree occurrence. Filipinas environment showed a low fruit production and a greater spatial variability of soil properties compared to Cachoeira.