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Environmental Influences on Soil Chemistry in Central Semiarid Tanzania

Dept. of Geography, Univ. of California, Santa Barbara, CA 93106

*Corresponding author.

ABSTRACT

This study assessed the effectiveness of landscape features for predicting the variation in a set of chemical properties from 81 soil profiles sampled in a 236-km² site in central Tanzania. Soil samples were treated as points and coded by horizon and by groups, including landform, parent material, vegetation type, vegetation percent cover, and presence or absence of hypogeal termites. The variation captured by these groups in eight soil chemical properties (organic C, total N, acid-extractable P, exchangeable cations, and extractable Al) was assessed using analysis of variance, Duncan's multiple range test, and discriminant analysis. Soil development fits the catena model along hillslope transects, but lateral subsurface transport of dissolved Fe and cations has produced plinthite and highly base-saturated horizons just above the lithic or paralithic contact downslope of transitions between ferruginous sediments and granitic sediments. Nevertheless, biotic factors (vegetation type and density of termites) captured more variation than other groups at the regional level. Vegetation species composition and the density and type of termites in central Tanzania reflect soil depth, texture, clay mineralogy, and drainage characteristics influenced by landform and parent material. Root symbioses of native miombo and Acacia spp. woodlands may also modify local soil chemistry via selective uptake of C and exchangeable cations. Termites contribute to the depletion of organic C, total N, and associated nutrients throughout the soils they occupy in this region.

Contribution from the Dep. of Geography and the Environmental Studies Program, Univ. of California at Santa Barbara.

Received for publication February 5, 1988.