Yield response of soybean and cowpea to rock phosphate fertilizer blend and rhizobial inoculation on two benchmark soils of northern Ghana
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Date
2017-01-30
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Abstract
Two field experiments were conducted on a Gleyic Lixisol and a Ferric Luvisol at
Bontanga and Nyankpala, respectively during the 2012 and 2013 cropping seasons.
The aim of the study was to assess the effects of Rock Phosphate Fertilizer Blend
(RPFB) and rhizobial inoculation on yield of soybean and cowpea. The effect of
combined application of low rates of nitrogen fertilizer and RPFB on N and P uptake
in soybean and cowpea were also determined. The experiments were laid out in a
randomized complete block design with split-plot arrangement of the treatments
which were replicated three times. At each experimental site, inoculated (+Rh) and
uninoculated (-Rh) treatments constituted the main plots. The following treatments
were assigned as sub-plots on the Gleyic Lixisol at Bontanga: To = 0 kg P2O5
ha
-1
; T1
= RPFB 34.35 kg P
2O5
ha
-1
; T2
= RPFB 68.70 kg P
2O5
ha
-1
; T3 = TSP 34.35 kg P
2O5
ha
-1
and T
4
= TSP 68.70 kg P
2O5
ha
-1
while To = 0 kg P2O5
ha
-1
; T1 = RPFB 68.70 kg
P2O5
ha
-1
; T2
= TSP 68.70 kg P
2O5
ha
-1
+ 25 kg N ha
-1
; T3
= TSP 68.70 kg P
2O5
ha
-1
and T4
= RPFB 68.70 kg P
2O5
ha
-1
+ 25 kg N ha
-1
constituted the sub-plots on the
Ferric Luvisol at Nyankpala.
Phosphorus fertilizer application and rhizobial inoculation increased soybean
nodulation on the Gleyic Lixisol. Application of TSP 34.35, 68.70 and RPFB 68.70
kg P
2O5
significantly increased nodule dry weight of soybean while cowpea nodule
dry weight increased with the application of TSP 68.70 and RPFB 34.35 kg P2O5
.
The application of TSP 68.70 kg P
2O5
fertilizer significantly increased soybean shoot
dry matter yield by 84% while RPFB 68.70 kg P
2O5 gave an increase of 25% relative
to the control. Similarly, cowpea shoot dry matter yield increased by 81 and 67% due
to application of TSP and RPFB, respectively compared to the control. The TSP
xviii
68.70 kg P
2O5 + 25 kg N and RPFB 68.70 kg P
2O5
+ 25 kg N treatments also
increased soybean grain yield on the Ferric Luvisol by 74 and 9%, respectively over
the control while that of cowpea was increased by 53 and 51%, respectively .
Soybean grain N and P uptake on the Ferric Luvisol were significantly increased by
78 and 120%, respectively over the control as a result of the application of TSP 68.70
kg P
2O5 + 25 kg N. Application of RPFB 68.70 kg P
2O5
+ 25 kg N did not
significantly increase soybean grain N and P uptake. Cowpea grain N and P uptake
were also increased by 40 and 81%, respectively over the control due to application
of TSP 68.70 kg P
2O5
+ 25 kg N. The RPFB
68.70 kg P
2O5
+ 25 kg N treatment gave
an increase in grain N and P uptake of 44 and 74%, respectively over the control.
Value-cost ratio analysis indicated that TSP 68.70 kg P
2O5 + 25 kg N is a promising
treatment combination for profitable soybean and cowpea production on the Ferric
Luvisol than RPFB 68.70 kg P
2O5 + 25 kg N.
Results of this study have shown that, application of triple superphosphate and 25 kg
N better enhances soybean N and P uptake than rock phosphate fertilzer blend. For
cowpea, application of both triple superphosphate and rock phosphate fertilizer blend
equally enhanced grain N and P uptake. The study further revealed that in the short
term, application of TSP 68.70 kg P
2O5
+ 25 kg N on the Ferric Luvisol is more
profitable for soybean and cowpea production than RPFB 68.70 kg P
2O5
+ 25 kg N
Description
A thesis presented to the Department of Crop and Soil Sciences, Faculty of Agriculture, College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfilment of the requirements for the award of degree of Doctor of Philosophy in Soil Science, 2016