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Land degradation as a result of land-use practices is a major environmental
concern to sustainable agricultural production in Tanzania. The effect of clearing and
long-term cultivation on physical, chemical, and biological characteristics is described
in two representative soil formations from eastern Tanzania: Mkindo (Eutric Fluvisol)
in the Mvomero district and Mafiga (Ferric Lixisol) in the Morogoro district. The
results have shown that in the Mkindo site, 10 years of continuous rice cultivation
has led to severe changes in most characteristics of the soil. Significant effects of cul-
tivation coincide with those considered to favor clay dispersion and crusting
phenomena, including changes in soil reaction, clay content, and mineralogy as well
as generalized desaturation of the exchange complex, increasing sodicity, and severe
losses of soil organic matter (SOM). In contrast, at the Mafiga site, 30 years of a
less disturbing cultivation system, including periodic fallows, have also modified
some soil characteristics but to a lower extent than at Mkindo. Decreased soil
colloidal properties at the Mkindo site and lower stability against biological degra-
dation, reflected by carbon (C) – release curves, than the Mafiga site could be
causally connected to clay illuviation processes leading to accumulation of calcium
(Ca) and magnesium (Mg) but mainly caused by changes in SOM characteristics
such as losses of humic (HA) and fulvic acid (FA) and accumulation of humin. |
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