Pradoo wood biochar has been tested in order to explore sustainable solutions to the development of agriculture on poor sandy soils in marginal areas in Northeast Thailand. Some basic physicochemical properties of biochar, for example pore size distribution, cation exchange capacity (CEC), specific surface area (SSA), and water and nutrient adsorption, were determined and compared to soil properties in order to determine appropriate biochar application to soil. Pradoo wood biochar showed important adsorption properties with high SSA, CEC and nutrient adsorption. The water retention properties were also improved on the dry end of the water retention curve. Phosphorous and ammonium adsorption–desorption isotherms were established and their respective affinity for the biochar surface was quantified, by the means of a retention index and thermodynamical parameters. We found that despite excellent retention properties, biochar needs to be added in large amounts (between 10 and 70 kg m−2) to soil to be able to modify noticeably the resulting soil properties.