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Chemical Properties of Native Savanna and Forest Soils in Central Brazil

Agrotecnologica Amazonica S.A., Casilla 116, La Paz, Bolivia

* Corresponding author.

ABSTRACT

Recent research of the well-drained cerrados (savanna) soils of Brazil suggests that poor root growth associated with inferior crop production is often caused by subsoil Ca deficiency rather than Al toxicity. The present study was conducted to re-examine this hypothesis and to compare native soil vegetation patterns. Horizon samples from 48 representative soils of the Geo-Economic region of Brasilia, an area covering 22-million hectares of central Brazil, were analyzed for NH₄NO₃ exchangeable cations, and cation and anion exchange capacity. Thirty eight of these soils were found under cerrados and 10 under the minor inclusions of native forests scattered throughout the predominantly savanna landscape. Calcium deficient soil conditions were only found in cerrados, although cerrados also occurred on high Ca soils. The Ca/Mg ratios were significantly higher in the forest vs. cerrados soils. Low Ca/K ratios and high anion exchange capacity/cation exchange capacity AEC/CEC ratios were common in cerrados soils. The Mg/K ratios were satisfactory in most of the soils. It is concluded that the Ca/Mg ratios of the cerrados soils should be examined in an agricultural context.

Received for publication April 21, 1988.