Agriculture Reference
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is a structural element required by Rhizobia for synthesis of nucleic acids and phospholipids
(O'Hara and Glenn, 1994). Acute deficiency of P can prevent nodulation and nitrogen
fixation of legumes (Giller, 2001). Mullen et al. (1988) observed delayed infection of the
primary root and reduced yield benefit from biological N fixation when soybean was grown
under low P conditions. However, high soil nitrate has been reported to inhibit biological N
fixation (Abaidoo and van Kessell, 1989).
The objectives of this study were (i) to assess the tolerance of soybean cultivars widely
grown in southern Africa to soil acidity and the response of these cultivars to liming, and (ii)
to determine the effect of N and P fertilisation on the growth of a selected soybean cultivar
grown in acidic or limed soil. It was hypothesized that smallholder farmers, who do not have
access to lime, can successfully grow soybean if a cultivar tolerant to soil acidity is available.
2.
M
ATERIALS AND METHODS
2.1. Site Description, Soil Sampling and Land Preparation
The field experiment was conducted over two cropping seasons (2002/3 and 2003/4) at
Domboshawa Training Centre (DTC), Zimbabwe (17
o
35′S; 31
o
14′E, altitude 1574 m). DTC is
located in agroecological natural region II characterised by unimodal rainfall (750-1000 mm
annum
-1
, October-April) and mean annual temperature of 18.8
o
C. Soils at the site are
relatively highly weathered, leached and well-drained sandy clay loams derived from
granodiorite gneiss and classified as Haplic Lixisols (FAO) (Nyamapfene, 1991). The site had
been under a grass fallow for at least five years.
The experimental site was disc-ploughed at the beginning of each cropping season. Soil
sampling was done before ploughing and at the end of the first cropping season. Ten sub-
samples were randomly collected from each plot using a soil auger (0-15 cm) and sub-
samples mixed to make one composite sample. The soils were taken to the laboratory, air-
dried and passed through a 2-mm sieve before basic characterisation.
2.2. Experimental Layout and Planting
Two experiments were set up, one to assess the tolerance of selected soybean cultivars to
soil acidity, and another to determine the effect of liming, N and P fertilisation on the growth
of a selected soybean cultivar. For the first experiment four soybean cultivars (Magoye,
Safari, Solitaire and Storm) and two lime rates (0 and 1500 kg ha
-1
applied in the first year)
were used. A split-split-plot design was used, with lime as the main plot and cultivar as the
sub-plot, with four replications. A basal application of compound L fertiliser (5%N, 8% P,
8%K, 8%K and 0.25% B) was banded in rows at 225 kg ha
-1
in both cropping seasons.
In the second experiment only one cultivar, Solitaire, was used. The treatments were 2
lime rates (0 and 1500 kg ha
-1
applied in the first year), two N rates (0 and 30 kg ha
-1
) and
four P rates (0, 7.5, 15 and 22.5 kg ha
-1
) arranged in a split-split plot design with lime as the
main plot, N as subplot and P and sub-sub plot, with four replications. All the N and P were
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