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

3500
.f"'3000
ca
,c2500
CI
"" - 2000
.PO
~
'ti
>. 1500 • MAP
.PAPR
c 1000
~
(!) 500
0
o 40 80 120 160 200
P level (kg P 2 0 S ha- 1 )
Figure 2_ Effect of source and level of P on soybean grain yield at
Kafuku Farm Institute. Means followed by the same letter are not
significantly different.
response to applied P on soybean regardless of P
source. The soil available P was adequate to meet
the nutrient demand of the crop.
In the second cropping season, there was no response
of biomass and grain yield on the control
treatment to lime application. This is because the
initial soil pH for this site of 5.1 was high and consequently
the exchangeable aluminium of 0.1 cmol
kg-I was low to be detrimental to plant growth. Liming,
therefore, did not reduce exchangeable aluminium
any lower than was already in the soil to negatively
influence plant growth (Table I, Figures 3 and
4).
High biomass yields of 1.7 and 1.3 times over the
control were obtained for the recurrent and residual
appiication of MAP respectively. Similarly, high
grain yields of 1.6 times over the control treatments
were obtained for both the fresh and residual application
of MAP. Liming increased biomass and grain
yields largely in the fresh than in the residual application
of MAP.
;::-- 5000 ,...,~=-.........~~----_~~
~ . 4500 .1--------.......",~----4;,..-~
~ 4000
;- 3500
Qj 3000
': 2500
~ 2000
E 1500
.S!
..0 1000
500
-tV
0 0
~
o 13.5 27 60 120
P level (kg P 2
0 S ha- 1 )
.PO L
.1'0 UL
.MAP L
.MAP UL
• PAPR L
ill PAPR UL
Figure 3. Effect of source of P, level of Pand lime on soybean
biomass yield at Chibwe On·farm site. Means followed by the same
letter are not significantly different.
With PAPR·there was a response to P for soybean
biomass and grain yields only to residual application
of the fertilizer. Highest biomass and grain
yields were obtained at the lower rate of 13.5 and 27
kg P20S ha- 1 for biomass and 27 kg PiOs ha- 1 for soybean
grain yield. Both the biomass and grain yields
decreased with increased rate of P so that there was
no response to P at the ·highest rate (120 kg P20S
ha- 1 ) with and without liming for grain yield and
without liming for biomass. The effect of lime for
MAP was similar, except at the lowest rate of P for
grain and biomass yield. The reduction of soybean
grain yield with increasing rate of residual P application
suggested adequacy of soil P for crop production.
The residual effect of P for PAPR was thus
more effective than that of the fresh and residual
application of MAP because adequacy in soil P for
plant growth -:vas reached at a lower rate of P application.
On Makeni soil series at GART, higher grain yields
of soybean were obtained in the first cropping season
with the recommended level of P application of
60 kg P20S ha- 1 for MAP than at the improved technology
level of 120 kg P20S ha- 1 . This is shown in
Figure 5. The yields were 2.4 times more than the
control treatment. In the case of P APR, the soybean
yields were similar for both the recommended and
improved technology with a two-fold increase in
soybean yield compared to the unfertilized control.
There was a significant reduction (p