The geochemistry of minor elements in Pernambuco soils. II. Cobalt in the "Zona Litoral-Mata"

Abstract

Eleven soil profiles of the region known as "The Zona Litoral-Mata" of the State of Pernambuco were studied. These profiles represent the major soil types of the region involved (coastal region). In these soils, the total and soluble (acetic acid 2.5 per cent) cobalt was spectrophotometrically analysed in order to obtain data on the geochemistry of cobalt in these soils and its availability for the growth of forage on which healthy animals depend. The total cobalt content for most of the soils studied is surprisingly high (7-35 ppm) when compared with reports from other countries. Cobalt is even apparently concentrated in the soil with relation to the parent rock material. The high content of cobalt in these soils is probably derived from the titanium minerals, and/or biotites contained in the parent material. The cobalt shows a general trend to concentrate in the B horizon, as would be expected from the fact that it has been found that the content of this element is correlated in general in the soils studied, with the content of clay. SiO₂ Al₂O₃ and Fe₂O₃. ( Fig. 1, 2 and 3) In order to predict cobalt deficiency tentatively for local animals, the results of total and acetic acid (2,5 per cent) soluble cobalt determination, were Compared with the minimum content given by most workers in this field. Only one soil typical of the Goiana region (N.° 6964-6968), has a total cobalt content below the level reported for a soil to be considered deficient (Fig. 4). When the amount of Co extracted from the soil by 2,5 per cent acetic acid is considered, however - an index which apparently is considered by most modern authors as more reliable - the situation is substantially altered, as far as cobalt deficiency in the soils of the Pernambuco "Zona Litoral-Mata" is concerned. Only four localities have a soluble cobalt content above the level commonly reported in soils carrying healthy stock. These soils comprise most of the soils from Cabo, Água Preta, Timbaúba and Aliança countries (Fig. 5). For the other soils studied, with a soluble cobalt content in the range of < 0.1 and 0.2 ppm., cobalt deficiencies may be predicted. The areas in which Co deficiency might be expected are shown in Fig. 5.