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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:tut/oai:encore.tut.ac.za:d1001475 |
| Date | January 2009 |
| Creators | Pule-Meulenberg, F, Dakota, FD |
| Publisher | Symbiosis |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | |
| Rights | ©2009 Balaban, Philadelphia/Rehovot |
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