Phosphorus Adsorption and Buffering Capacity as a Guide for P Fertilization in Some Selected Sudanese Soil Series

Phosphorus (P) sorption in soils is a key process governing its availability to crops. There has been scanty information available on the P sorption in relation to soil properties and plant P uptake for soils of Sudan. In this study P sorption, phosphorus buffering capacity at equilibrium concentration 0.25 mg 1E-1 (PBCo.25), phosphorus requirement at standard equilibrium concentration 0.25 mg lE-1 and plant P uptake were determined in six soil samples belonging to different major soil orders located in (Akked and Kerma from Dongola in north Sudan, Remitab and Permanent Fallow of Remitab soil from central Sudan (Gezira), Entisols (Atra) from the Blue Nile River bank and Khashm elgirba form east. The amount of P sorbed by the soils differed significantly (P 0.001) among various soil series ranged between 9.8 to 23.03 mg P kgE-l soil. The statistical analysis showed that there were no significant differences in P sorption for central clay plain soils (Remitab, Permanent Fallow and Khashm elgirba). The Entisols soil sorbed high Quantity of P compared with other soils followed by Akked series. The phosphate adsorption described well by the Freundlich equation (square r2 =_0.95). The Freundlich coefficient (af) expressed to the P sorption capacity of soil ranged between 2.43- 22.78 mg P kg E-l soil, PBCO.25 ranged between 2.53 to 20.74. Soil organic carbon and iron content were significantly (P 0.0l) correlated to the soil P sorption and there was no significant relationship between clay and CaCO3 contents and P sorption capacity. The P sorbed at standard equilibrium solution concentration (0.25 mg 1E-l) ranged between 1.06 for Kerma series to 13.22 mg P kg soilE-1 for the Entisols. The study revealed that the P requirement at standard concentration 0.25 mg El-1 ranged between 0.77 for Kerma to 21.89 for Entisols. Significant (P 0.00l) differential response of maize to phosphorus application levels compared with the control grown in different soils was detected. Maize dry weight and P uptake were significantly (P 0.05) higher in Entisols and Remitab soils while Kerma series had a lowest dry weight and P uptake compared with the rest of the soils. Phosphorus uptake by maize was significantly related to the soil P sorption indices (P sorbed at 0.25mg lE-1, (r 0.879, P 0.05), PBC (P buffering capacity, (r 0.957, P 0.00l), P requirement at 0.25mg 1E-1 (r 0.940, P 0.0l) and Available P, r 0.807, P 0.0l). High correlation between P sorption capacity mg P kgE-1 soil and iron content, (r 0.96, P 0.01), organic carbon (r 0.805, P 0.01). Clay content and CaC03 were found to be less important factors affecting P adsorption