13 research outputs found
Physicochemical Properties of Soil from Five Villages in Botswana with Respect to Soil Degradation
A field study was conducted at five villages of Botswana namely, Tsabong, Tshane, Mathathane,
Motlhabaneng and Tsetsejwe during the periods of June to August 1999 and June to August 2000. The
objective of the study was to assess and compare the soil physicochemical properties of soils at the five
villages and to study the effect of cultivation on some soil physical properties. Parameters measured in the
field included soil pH, organic carbon (OC), phosphorus (P), cation exchange capacity (CEC),
exchangeable cations (Ca, Mg, K and Na), bulk density (BD), soil penetration resistance and infiltration
rate. Soil pH, OC, CEC, Mg, Ca and BD were found to be significantly different in the five villages. The
non-cultivated soil was found to have significantly lower bulk density, higher infiltration rate and higher
penetration resistance compared to the cultivated soil. Soil from the Kgalagadi area was found to be
significantly lower in nutrients in comparison with the soil from the Bobirwa area. The cultivated soil was
found to have higher, bulk density, lower infiltration rate and lower penetration resistance
Assessing the symbiotic dependency of grain and tree legumes on N2 fixation for their N nutrition in five agro-ecological zones of Botswana
Abstract
To assess the symbiotic dependency of grain and shrub/tree legumes within five agro-ecological zones of Botswana, fully
expanded leaves of the test species were sampled from about 26 study sites within Ngwaketse, Gaborone, Central, Ghanzi
and Kalahari agro-ecological zones. Isotopic analysis revealed significant differences in 1)15N values of the grain legumes
[cowpea (Vigna unguiculata L. Walp), Bambara groundnut (Vigna subterranea L. Verde.), and groundnut (Arachis
hypogaea L.)] from the 26 farming areas in both 2005 and 2006. Estimates of %Ndfa of leaves also showed significant
differences between farming areas, with cowpea deriving more than 50% of its N nutrition from symbiotic fixation. In
terms of distribution, many more symbiotic shrub/tree species were found in the wetter Ngwaketse agro-zone compared to
the fewer numbers in the drier Kalahari region. Acacias were the more dominant species at all sites. Leaf 1)15N values of
shrub/tree species also varied strongly across Botswana, with 11 out of 18 of these legumes deriving about 50%, or more, of
their N from symbiotic Nz fixation. Acacia caffra, in particular, obtained as much as 93.6% of its N nutrition from
symbiotic fixation in the wetter Ngwaketse agro-zone. This study has shown that grain legumes sampled from farmer's
fields in Botswana obtained considerable amounts of their N from symbiotic fixation. We have also shown that shrub and
tree legumes probably play an important role in the N economy of the savanna ecosystems in Botswana. However, the
decline in the number of functional Ny-fixing shrub/tree legumes along an aridity gradient suggests that soil moisture is a
major constraint to Nz fixation in the tree legumes of Botswana