Agriculture Reference
In-Depth Information
Table 1. Soil properties of the experimental sites
Textural
class
Clay
(%)
pH
(CaCl
2
/H
2
O)
OC
(%)
N (%)
Olsen P
(mg
kg
-1
)
Cation exchange (cmol
c
kg
-1
soil)
Site
1
mSaCL
22
3.9/4.6
0.47
26
0.035
4.86
4.0
2.00
0.50
0.26
0.14
1.10
Site
2
mSaL
12
4.6/5.3
0.40
24
0.030
1.00
2.7
1.10
0.20
0.13
0.13
1.14
mSaCL - medium grained sandy clay loam; mSaL - medium grained sandy loam, OC - organic
carbon.
3.
R
ESULTS
3.1. Site Description and Weather Conditions
The 2002/03 season recorded 911 mm of rainfall and was similar to the long-term
average for DTC, whereas the 2003/04 season was drier (643 mm). The rainfall was well
distributed in both seasons although brief periods of moisture stress occurred during the
2003/04 season. The soils were moderately leached (58-73% base saturation), strongly acidic
(pH<5.0), and organic matter (<1% organic C) and mineral N were low (Table 1;
Nyamangara et al., 2000). Available P was more deficient at site 2 compared to site 1, and at
both sites exchangeable Mg was relatively low compared to Ca (Table 1).
3.2. Effect of Soil Acidity on Nodulation of Selected Cultivars
There were significant (P<0.001) differences in the number of nodules produced by the
different soybean cultivars and over the two seasons (Table 2). In the first season, Safari
produced the largest number of nodules (87 per 10 plants) in acid soil (unlimed) compared to
other cultivars (≤52 per ten plants) whereas in the second season Solitaire had the highest
(122 per ten plants) compared to others (≤101 per ten plants). Increase in the number of
nodules due to liming was only significant (P=0.004; 72-454%) in the second season (Table
2). Magoye, a promiscuous variety widely grown in southern Africa, had the largest response
in both seasons (91 and 454 %, respectively). Lime x cultivar interaction was only significant
in the second season (P<0.001).
There were no significant nodule dry matter yield (NDMY) differences between cultivars
in unlimed soil for both seasons. Responses were higher in the second season (>56 %)
compared to the first season (5-48 %) and liming significantly increased NDMY in the second
season for Magoye (368 %) and Safari (194 %) (Table 3).
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