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

Table 1. Reduction of soil acidi.ty after liming at experimental sites.
Acidity (cmol kgl) lime added
Site A1 3 • + H" A1 3 • kg hal Initial After liming
1. Chibwe 0.20 0.10 360 5.1 5.3
2. GART 1.00 0.66 1500 4.1 5.2
3. Magoye COT 0.30 0.24 510 4.1 4.5
4. Mwanachingwala 0.34 0.28 450 4.4 5.1
5. lusitu 0.12 0.10 450 4.3 5.4
als were extended to three other sites - one site in
Eastern Province (Region II) and two in Northern
Province (Region III).
Phosphorus was applied as mono-ammonium phosphate
(MAP) as the reference fertilizer and as partially
acidulated phosphate rock (PAPR) produced
at the Pilot Plant of the School of Mines at the University
of Zambia from Chilembwe phosphaterbck.
The trials were designed as On-Farm, or On-Station
in which the plots were 100 m2 and 22.5 m2 respectively.
The P application rates were 0, 60 and 120 kg
P20S ha· J in On-Farm trials and 0, 40, 80, 120, 160
and 200 kg P20 S ha- 1 in On-Station trials. All treatments
were replicated fouT times in a randomized
complete block design. The fertilizer was banded in
the planting furrow below the seed at planting. All
treatments received adequate amounts of K, S as
recommended for the particular sites (70 kg and
26.4 kg ha- 1 respectively). Nitrogen was applied as a
basal application at 24 kg N ha- 1 at On-Farm sites
and 44 kg N ha- 1 at On-Stati0n sites. The test crops
were maize; sorghum, sunflower and legumes
(soybean, groundnut and cowpea). A peat-based
inoculum was applied to soybean at planting using
the recommended rate.
The test crops were grown for . two seasons, and in
all cases improved varieties of test grain legumes
were planted according to the suitability and importance
of the legume in the locality of the trial. In Onstation
trials in Region II, soybean variety Kaleya
and groundnut variety MGV4 were planted. These
varieties are well adapted to Region II and are very
responsive to inoculation with Rhizobium. The
MGV 4 groundnut variety is tolerant to soil acidity
and has low pod failure (Pops) in these soils. Soybean
was grQwn at Kafuku Farm Institute and
UNZA Farm, groundnut at Magoye CDT. Cowpea
variety Bubebe was grown at Lusitu in Region 1.
The variety was grown because of its earliness and
high yields, the former attribute being particularly
important in this drought prone Region.
Soybean was drilled at an inter row spacing of 75
cm. Groundnut was grown at an inter- and intrarow
spacing of 75 cm and 10 cm respectively. The
spacing for cowpea was 75 cm between rows and 10
em between plants.
pH
During the second cropping season (2001/2002), ~he
planting furrows from the first season were maintained.
However, the crops were rotated around the
plots at each sit~ . No further applications of P were
made to the higher rates of P application (120, 160
and 200 kg P20S ha- I ), and the residual effects were
evaluated from these treatments. Other nutrients, N,
P, K and S including the application of inoculum
were repeated as in the first season according to the
current fertilization practice. An absolute control
treatment in which no fertilizer was applied was
included for sites where space permitteQ. adjacent to
the current trial.
The treatments were split, and a lime treatment was
included to evaluate its effect on crop growth, especially
on the acid soils at Chibwe, GART, Magoye
(both on-station and on-farm) and Lusitu sites. Each
original treatment plot was split into two equal subplots,
and one half was limed while the other was
not limed. The amount of lime applied was calculated
based on the exchangeable aluminium values
(Table 1).
The lime was broadcast on the surface and then
worked into the soil by light cultivation using hand
hoes before planting. Crop growth was monitored
during the season, and some plant growth parameters
were recorded. Crop management both in the
first and second cropping seasons was carried out
according to the conventional agronomic practices
for these crops.
Results and Discussion
Although various test crops were evaluated, only
the results for the grctin legumes are presented and
discussed in this paper. These results are discussed
according to crop across trial sites.
Soybean
At Kafuku Farm Institute (sited on Mushemi soil
series), a response to soybean biomass and grain
yield was obtained in the second cropping season
only with the application of PAPR at 40 kg P20S
ha- 1 . There was a tendency for the residual effect of
both MAP and PAPR to decrease with increasing P
level, reaching a minimum when P was applied at
160 kg P20S ha- 1 and subsequently increasing at the
highest rate of P application. This is illustrated in
Figure 2, showing the effect of source and level of P
on soybean grain yield.
The soils at Chibwe On-Farm sit-e · were similar to
those at Kafuku Farm Institute except that the soils
were higher in initial soil P. Consequently in the
first cropping season (2001/02), there was no yield
Grain Legumes and Green Manures for Soil Fertility in Southern Africa
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