VARIABILITY WITHIN COWPEA GENOTYPES TO APPLIED PHOSPHORUS AND RESIDUAL EFFECT ON SORGHUM PRODUCTION ON P DEFICIENT SOILS OF SUDAN AND SAHEL SAVANNAS.
VARIABILITY WITHIN COWPEA GENOTYPES TO APPLIED PHOSPHORUS AND RESIDUAL EFFECT ON SORGHUM PRODUCTION ON P DEFICIENT SOILS OF SUDAN AND SAHEL SAVANNAS.
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Date
2005-10
Authors
ADDAM, KIARI SAIDOU
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Abstract
Variability within cowpea genotypes to applied phosphorus and residual effects on
local sorghum production were studied in the field and screen house on P-deficient soils
of Sudan and Sahel Savannas in West Africa. The soils are infertile, acidic and present
deficiencies of phosphorus and nitrogen. Identification of some new cowpea breeding
genotypes with tolerance to low P or response to added P fertilizer is an alternative to P
deficient soils. In the field 147 cowpea genotypes were screened for tolerance to low P
soils or response to applied P fertilizer as Single Super Phosphate (SSP) and Rock
Phosphate (RP) at Minjibir (Sudan savanna, Nigeria) and Toumnia (Sahel savanna, Niger
Republic). The rate of 90kg P ha-1 for RP and 30kg P ha-1 as SSP were used after being
determined in a P calibration curve study in the screen house. The design was a strip plot
design with the phosphorus as vertical (A) factor and the cowpea genotypes as horizontal
(B) factor and replicated four times. Results obtained after cropping the 147 genotypes
indicated the relationships between the cowpea genotypes for P use efficiency at low P
(0P) and high P (RP and SSP) was significant and led to the separation of the cowpea
genotypes into four groups: the tolerant non responders (TN); the tolerant responders
(TR); the sensitive responders (SR) and the sensitive non responders (SN). The P use
efficiency ratio was highly significant among the cowpeas and varied from 9 to 45 kg
grain kg-1 P applied at Toumnia and 10 to 43 at Minjibir under SSP application and from
5 to 13 kg grain kg-1 P at Minjibir and from 4 to 10 kg grain kg-1 P at Toumnia under rock
P conditions. Fifteen cowpea genotypes were selected for further P use efficiency
screening in the field and screen house experiments. These 15 selected were screened at
both locations in new fields for tolerance to low P soils or response to applied P.
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The design was the same as the previous screening. The results indicated that there was
highly significant variability among the cowpea genotypes in terms of grain and fodder
yields. There was correlation (r = 0.59**) between grain yield and AMF infection rate
even though P suppressed AMF infection rate in more than 50% of the cowpea
genotypes; there was correlation between the fodder (r = 0.59**) and the percentage
nitrogen fixed. The cowpea genotype IT98K-476-8 was observed to be efficient
responder at both sites and IT97K-813-21 was recorded as non-responder. The root
length was correlated with grain yield (r = 0.56**); as well as to AMF infection rate (r =
0.54**). The root length density was well correlated (r = 0.63**) to grain yield and to
fodder (r = 0.55**). Significant difference was observed in relative P use efficiency ratio
that varied from ā7 to 38 kg grain kg Pā1 applied. Significant effect of P to shoot: root
ratio was recorded among the cowpea genotypes. The percentage N fixed increased with
P applied at Toumnia and not at Minjibir.
The 15-cowpea genotypes screened in the screen house were carried out in river
sand in pot experiment using similar treatments as in the field in a randomised strip plot
design with 3 replications. Results showed highly significant (P < 0.001) difference for root
length variation among cowpea genotypes; P had significant effect (P < 0.05) on shoot: root
ratio. P had highly significant (P < 0.001) effect on the biomass.
Test of the performance of sorghum on pots previously grown to fifteen cowpea
genotypes in pot was carried out. The results have shown significant (P < 0.001) growth
of the sorghum in rotation. Sorghum performance and yield following cowpea and
different residual sources of P in rotation in the field was conducted. No significant
difference was observed at Toumnia in grain yield whereas at Minjibir, significant
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difference (P= 0.05) was observed in terms of grain and stover production. The trend of
response was in the order RP > SSP > Control. Residual P had significant effect on the
AMF infection rate at Minjibir but not at Toumnia. Strong correlation (r = 0.99***) was
recorded between the AMF infection rate and grain yield.
Contributions have been towards the farmers of the Sahel and Sudan savannas by
giving some information on the cowpea genotypes tolerance and responsive to P that are
relevant to their areas. For example the genotypes TN256-87, TN28-87, ALOKA,
IT99K-826-119, 97K-819-154 and 97K-819-170 are relevant to the Sahel savanna
farmers because of their tolerance to low P soils and response to applied P fertilizer and
adaptability to that area. On the other hand the cowpea genotypes such as IT90K-277-2,
Danila, IT98K-1399 and 99K-213-21 are adapted to Sudan savanna area
Description
A Thesis submitted to the Postgraduate School, Ahmadu Bello University in partial
fulfilment of the requirements for the award of the Degree of Doctor of Philosophy in
Soil Science
October, 2005
Keywords
VARIABILITY,, COWPEA,, GENOTYPES,, APPLIED,, PHOSPHORUS,, RESIDUAL,, EFFECT,, SORGHUM,, PRODUCTION,, DEFICIENT,, SOILS,, SUDAN,, SAHEL,, SAVANNAS