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.

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. 9 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 –7 to 38 kg grain kg P–1 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 10 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

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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