Tropical Arenosols may be challenging for agricultural use, particularly in semi-arid regions. The aim of this study was to evaluate the impact of the addition of increasing shares of biochar and clay on the nutrient sorption capacity of a tropical Arenosol. In batch equilibrium experiments, the sorption of ammonium-N (NH4+-N), nitrate-N (NO3--N), potassium (K+), and phosphate-P (PO43--P) was quantified for mixtures of an Arenosol with increasing shares of biochar and clay (1%, 2.5%, 5%, 10%, 100%) and the unmixed Arenosol, biochar, and clay. The mid-temperature biochar was produced from Prosopis juliflora feedstock; the clayey material was taken from the sedimentary parent material of a temporarily dry lake. Only the Arenosol-biochar mixture with 10% biochar addition and the biochar increased the NH4+-N maximum sorption capacity (q(max)) of the Arenosol, by 34% and 130%, respectively. The q(max), of PO43--P slightly increased with ascending biochar shares (1-10%) by 14%, 30%, 26%, and 42%, whereas the undiluted biochar released PO43--P. Biochar addition slightly reduced NO3--N release from the Arenosol but strongly induced K+ release. On the other hand, clay addition of 10% and clay itself augmented q(max) of NH4+-N by 30% and 162%; ascending clay rates (1-100%) increased q m for PO43--P by 78%, 130%, 180%, 268%, and 712%. Clay rates above 5% improved K+ sorption; however, no q(max) values could be derived. Sorption of NO3--N remained unaffected by clay amendment. Overall, clay addition proved to enhance the nutrient sorption capacity of the Arenosol more effectively than biochar; nonetheless, both materials may be promising amendments to meliorate sandy soils for agricultural use in the semi-arid tropics.