Studies of vertisols in Tanzania as a basis for future land use planning

The properties of sixteen vertisols in Tanzania were investigated the discover which easily detectable features indicate an ability to produce arable crops. 2 three vertisols, which produce arable crops, were compared with thirteen which do not, using standard field descriptions, laboratory data, the “Soil Taxonomy System” of soil classification and a land suitability classification. Observation of the cracking seasons were supplemented by prediction based on monthly soil moisture balances, and potential cracking ability was estimated with COLE measurements. 3 A fine clayey particles size class and calcium rich substrate with moderate to moderately slow permeability were features which indicate an ability for arable cropping. The best Vertisol was over 50 cm deep in granular material with no signs of internal pressure and allowing the surface to be easily drained. 4 Limited depth and permeability and magnesium or sodium rich substrata with slickensides or very coarse prisms were features apparently indicating unsuitability for arable cropping. Some diagnostic features of the Soil Taxonomy System were not easily recognized in the field and separated too many Vertisols with the same land suitability. The five subgroups with 13 series were regrouped into five categories of significance to soil genesis and land suitability. The data indicate that rainfall in relation to evapotranspiration. The contents of exchangeable sodium and magnesium, and probably the content of smectitesin the clay fraction, influence the kind of structural aggregate, the permeability of the soil, the case with which it can be worked, and its potential for arable cropping