Evaluation of agronomic practices for optimising biological nitrogen fixation and yields of Bambara groundnut [Vigna Subterranea (L.) Verde.]
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Date
2009
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Sokoine University of Agriculture
Abstract
Studies were conducted to evaluate agronomic practices for optimizing biological nitrogen
fixation of bambara groundnut [Vigna subterranea (L.) Verde.]. An experiment was
conducted during 2005/6 at Sokoine University of Agriculture (SUA) to screen ten
bambara groundnuts landraces for their ability to withstand effect of nutrients and moisture
stress in N2 fixation. During the 2005/6 cropping season, field experiments were also
conducted at Msisi and Hombolo villages in Dodoma to study the effects of three selected
landraces and three crop densities of bambara groundnut on yields and nitrogen fixation.
Treatments were arranged in a split plot in a Randomised Complete Block Design (RCBD)
with six replications using the mother and baby system approach. Bambara groundnut
landraces were the main treatments while intra row spacing was the sub plot treatment.
During the 2006/07 cropping season the experiment was repeated on the same plots to
assess the residue N benefit to subsequent cereals against weed fallow and continuous
cereal cropping. Results showed significant differences (P<0.05) between landraces in
most of the variables tested. Under moisture stress conditions, Red landrace fixed
significantly (P<0.05) highest levels of N2 (0.27gplanf’) while Nkonya, the least efficient,
fixed only O.Mgplant'1. Under moisture stress growth variables with strong influence on
the amount of N2 fixed were leaf area (r= 0.400, P<0.01), number of nodule (r - 0.470,
P<0.01) and plant weight (r = 0.286, P<0.05 ). A plant density of 16 plants m"2 (20 cm by
30 cm) with mean seed yield of 4.07gplant (625.6kg/ha), residue dry matter yield of
12.16g/plant (2tha**) and mean fixed N2 of 25.77kg/ha was optimal for yield and N2
fixation. Drought tolerance and ability of bambara groundnut to form effective nodule with
native rhizobia are major physiological basis of sustaining N2 fixation under moisture
stress. The fertilizer N equivalent value contributed by bambara groundnut suggests that sorghum is a more suitable crop to Follow bambara groundnut in rotation as compared to
maize. However, analysis of marginal rate of returns showed that continuous bambara
groundnut is economically profitable. Hence, under marginal conditions, growing landrace
Cream at spacing of 20 cm by 30 cm continuously was recommended under moisture
stress. The fertilizer N equivalent value contributed by bambara groundnut suggests that
sorghum is a more suitable crop to follow bambara groundnut in rotation as compared to
maize. However, analysis of marginal rate of returns showed that continuous bambara
groundnut is economically profitable. Hence, under marginal conditions, growing landrace
Cream at spacing of 20 cm by 30 cm continuously was recommended.
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Keywords
Agronomic practices, Biological nitrogen fixation, Bambara groundnut, Vigna Subtcrranea