ASSESSMENT OF ADVANCED COMMON BEAN (Phaseolus vulgaris L.) LINES FOR NUTRIENT UPTAKE, PHOSPHORUS EFFICIENCY AND YIELD IN LOW PHOSPHORUS SOIL TYPES OF KAKAMEGA COUNTY

Abstract

Common bean (Phaseolus vulgaris L.) is an important source of food protein and cash in Kakamega County. Production is constrained by soil phosphorus which is mainly due to low phosphorus content of soils, export of phosphorus in crop produce, soil erosion and fixation by oxides in acidic soils. A study was conducted to evaluate bean genotypes in two sites in KARI Kakamega (34032’ and 34057’E, 00 07’ and 0015’N); this site has rhodic-nitisol in which P availability is limited by active iron and the second site was Kabras (34052’E and 0052’N) with nito-rhodic ferralsols in which P availability is limited by Iron (Fe) and aluminium (Al) oxides. Assessment of germination/emergence, plant count at harvest was taken to determine the plant tolerance as affected by low soil P. Shoot P and N uptake, phosphorus use efficiency (PUE), yield and economic analysis components were done using two levels of phosphorus, P0 (control) and P30 (30 kg ha-1 P) and 13 common bean lines with two local checks (GLP2, GLP585) in a randomized block design. Data for germination stand count, harvest, and yield were subjected to analysis of variance using the SAS software programme. Nutrient uptake and nutrient efficiency were subjected to student t- test. The means were separated using least significant difference (LSD) (protected) test. The pH of the soils was found to be 4.90 and 5.38 for Kabras and KARI site respectively implying, that the soils are acidic. The available P was low (2.45 ± 0.96 ppm and 7.69± 0.96 ppm for Kabras and KARI, respectively). The total nitrogen (%) was also low with 0.13 ± 0.02 and 0.2 ± 0.02) for Kabras and KARI Kakamega sites. Kabras site had soils which have good physical characteristics but are chemically poor while KARI Kakamega site had soils which are considered fertile but have low level of ‘available’ phosphorus. The germination and emergence of the different common bean lines varied between the sites with a weak inter-genotypic relationship between applied P on the stand count at both germination and harvest. There was varying response of genotypes in performance in terms of shoot biomass P uptake, PUE, N uptake, yield and marginal rate of return (MRR) in treatments with addition of P. No significant difference (p<0.05) was observed between lines CC13, CC547, MLB-48-89A, FEB195, A774, 286/6 and DOR755 for phosphorus uptake but it was higher compared to local checks. Lines 217-2, 222/1, AB136, and RWR221 had low uptake as the local checks (p<0.05). The inter-genotypic difference for nitrogen uptake was strong in the biomass and in the grain. Lines such as FEB195, DOR755, CC13, 3MS8-3, A774, UBR(95), and CC547 had a high uptake compared to the mean and local check but lines 217-2, 222/1, 286/6, AB136, RWR221, and MLB-48-89A had a lower uptake together with local check GLP585. Yield (tons/ha) increased with applied P with Kabras site having average of 0.479tons/ha and KARI had 0.548 tons/ha. There was however a weak inter genotypic significance (p<0.05) within the lines for yield both at KARI and Kabras sites. The highest net present value of benefits (PNB) for all the varieties was obtained from variety FEB 195 (Kshs 64,650 ha-1) at KARI site with application of phosphorus , while the lowest(D) was from the local Check G585) at Kabras site. The varieties had a normal trend at both sites but KARI had a high return to land compared to Kabras. Genotypes DOR755, CC13, FEB195, UBR(95), A774 and CC 547 were outstanding in all parameters tested. Therefore, these genotypes can be recommended for use in low- phosphorus environments as well as breeding materials.