Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

Table 3. Residual effects of liming sources on soil pH,
exchangeable calcium and magnesium for Mufulira soil
series during the 1996/97 season
Treatment Soil pH (CaCh) Ca Mg
(cmolc kg 1 )
Control 4.3b 0.45b O.lOb
Nampundwe tailings 4.8a 0.82b 0.30a
Agricultural lime 5.0a 1.3a 0.18b
Means in columns followed by the same letter are not
significantly different at P - 0.05.
Both NMT and AgLi produced a linear increase in
soil pH with increasing rates of liming (Figure 1).
However for AgLi, no further increase in soil pH
occurred beyond 2.0 t ha ot • The soil pH at the new
site was raised more quickly than that at the old site
established in 1995/96. It appears that management
practices of the research field in which the trial site
was located could be the reason for differences in
the overall soil chemistry of the two locations belonging
to the same study soil. The pH result for
1996/97 strongly indicates that 2.0 t ha ot is the optimal
liming rate for this soil. This confirms the finding
by Munyinda (1984) that 2.0 t ha oJ was the optimal
liming rate for the Mufulira soil series.
The liming materials did not significantly increase
soybean grain yield in the 1995/96 season (Figure
2). However, the residual effect of both NMT and
AgLi applied in the 1995/96 season did not significantly
(P < 0.05) increase soybean grain yield. It appears
that despite the increase in soil pH of Mufulira
soil series from 4.3 to 5.0, and the increase in exchangeable
calcium by . AgLi and exchangeable
magnesium by NMT, the soil conditions for healthy
growth of soybean were not attained. Mufulira soil
series is dominated by the kaolinite type of clay
mineral with a substantial amount of amorphous
iron and aluminium oxides. Since tmder most conditions
complete neutralization is not achieved
when acid soils are limed, hydroxyl compounds of
aluminium and iron could remain (Coleman and
Thomas, 1967). There is a time lag between a change
in soil pH and subsequent changes in the concentration
of aluminium (Mtmyinda, 1984) before signifi-
cant yields are realized. It follows that though .the
soil pH of Mufulira soil series was increased from
4.3 to 4.8, the alumirlium polycomplexes were not
instantaneously. reduced to their chemical inert
forms, which reduce slowly over several years.
Thus, at a soil pH 4.8 that was attained by NMT it
appears that monomeric exchangeable aluminium
that remained tm-neutralized could have affected
the soybean yield. Coleman and Thomas (1967) indicated
that the products of complete neutralization
that are attained at a pH higher than 8.3 aTe exchangeable
calcium and magnesium and inert hydroxides
of aluminium and iron. Therefore, to attain
near or complete neutralization of soil acidity for
soils of the Mufulira series requires a longer period
of residual effect than the two-year period of this
study.
NMT increased soybean grain yield linearly with
increasing liming rates, with the maximum yield of
1.1 t ha ot obtained at3 t ha o 1Jime (Figure 3). The soybean
grain yield obtained . is similar to yields obtained
by Coma et al. (1990) at the liming rate of 2.0
t ha ot on a related soil series. NMT significantly increased
soybean grain yield over AgLi and the control
treatment. The trend in soybean yield after the
AgLi treatment was not consistent. At 2 t ha oJ AgLi
produced a lower grain yield than NMT. The depressed
soybean yield could have been due to the
loss of AgLi through water erosion in two AgLi
treated plots that had a slope.
.E'"
'"~ ..,
Qi
'>'
c
'n;
(j,
c
Q)
'"
.g,
0
en
3000
1500
0
01995116 D19H111 I
Control Agric. lime Mine Tailings
Treatment (tlha)
Figure 2. Effects of liming sources on soybean grain yield for
1995/96 and 1996/97 seasons
6
5.5
5
4.5
4
a 3.5
'5 3
en 2.5
2
1.5
1
0 .5
o
IB Agrie. LIme 111 Mine Tailings I
control 2 3
lime rates (tlha)
Figure 1. Effects of liming rates on soil pH, planted in 1996/97
season
_ 1200
i .. 1000
..,
800 a;
'>'
c 600
i!
0>
iii
400
~ 200
0
r/l
0
control 2 3
Lime rale (tlha)
Figure 3. Effect of liming rates on soybean grain yield (Cv. Santa
Rosa) for the new site planted in 1996/97 season
Grain Legumes and Green Manures for Soil Fertility in Southern Africa
207