IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Titles Nodulation studies of cowpea and its response to phosphorus application in
Botswana under glasshouse conditions
Authors Kenneth K. Keakile and Tebogo Balone, Flora Pule-Meulenberg
Poster Board Number 15
Department of Crop Science and Production, Botswana College of Agriculture, Private Bag
0027, Gaborone, Botswana
Cowpea (Vigna unguiculata L. Walp) is an indigenous leguminous plant grown mostly in tropical Africa as a food
crop. Its fresh young leaves and fresh pods are consumed as vegetables by many Africans whereas the seed is
used in many food preparations. It is known to form symbiotic partnerships with some members of Rhizobiales as
well as some β-proteobacteria ( “rhizobia”), where the legume provides the microsymbiont with carbon for its
energy needs and in turn receives fixed-N for its nutrition from the rhizobia. In Botswana, nodulation status of
many economically important legumes such as cowpea is not known. This study assessed if soils of Sebele
harboured bacteria that nodulates cowpea. The study also assessed the response of cowpea to phosphorus
application under glasshouse conditions. Two cowpea genotypes, Black eye and Tswana, were planted in a
completely randomised design using pots in a glasshouse at the Botswana College of Agriculture in Sebele. In
the first experiment which tested for nodulation, all plants received a basal application of P equivalent to 130 kg
P/ha. In the second experiment, treatments consisted of four levels of P equivalent to 0, 65, 130 and 195 kg P/ha
using single superphosphate. Both genotypes formed effective nodules when grown in the soil from Sebele.
Black eye produced significantly more nodules and higher nodule dry matter compared to Tswana, which was
reflected in significantly higher shoot N concentration in this genotype. The highest P fertilisation resulted in
significantly higher nodule number, shoot and root dry matter as well as shoot N. It was also observed that Black
eye plants that received 195 kg P/ha flowered significantly earlier than the rest. In conclusion, the Sebele soil
harboured rhizobia that nodulated cowpea genotypes Black eye and Tswana. Further studies will include
evaluating a wider selection of legumes including potential forage plants grown on different soil types. Levels of
N-fixed will be measured, root-nodule bacteria isolated and cross-infectivity studies conducted.
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