Abstract

 This study was conducted to determine the phosphorus sorption characteristics and phosphorus requirement of mungbean in selected soils ofsoutheastern Nigeria. The soils for the study were collected from Ikom (Basalt), Akamkpa (Basement complex), Bcndc (Shale), Amaeke (Sandstone) and Umudike (Coastal Plain sands). From the P Sorption curves constructed the standard P requirement for the soils were calibrated. The values were very low ranging from 11.1 ppm in Bende to 60.2ppm in Ikom. The P adsorption maximum was determined using the Freundlich arrd Langmuir models. The values varied with the locations. It ranged from 65.7 mgkg'1 in Akamkpa to 516 mgkg'1 in Bende in the Freundlich model and from 231 mgkg’1 in Akamkpa to 369 mgkg'1 in Bende using the Langmuir model. Similarly the P maximum buffering capacity was determined using the two models. I hc values varied from 993 mgkg'1 in Amaeke to 1180 mgkg'1 in Akamkpa with a mean of 1087 mgkg'1. The bonding energy of P in the soils was highest in Akamkpa with a mean value of 6.05 ml/g and lowest in Bcndc with a mean value of 0.76ml/g. From the study, the P sorption data of the soils conformed better with the Freundlich model than the Langmuir model. This model is therefore recommended for this soils. Different phosphorus levels were calibrated from the sorption isotherm curves and used in fertilizing mungbean in potted experiment. The results obtained showed that, there was a significant response of the mungbean to the applied phosphorus in terms of nodulation and grain yield at 5/o probability level, from the study, solution concentration of 0 4 ppm in Ikom gave the best nodulation, while solution P concentration level of 0.2 ppm equivalent to 44.8 kgha'1 P in Akamkpa arrd 8.38 kgha'1 I? in Bende arrd solution P concentration of 0.3 ppm equivalent to 49.61 kgha'1 P in Ikom, 26.5 kgha'1 P in Amaeke and 53.9 kgha’1 P for Umudike gave the optimum grain yield. The mungbean performmed best in Ikom with yield of 9.16g per plant and the least in Akamkpa with a yield of 0.53g per plant.