Amending a tropical Arenosol:increasing shares of biochar and clay improve the nutrient sorption capacity

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(NH_(4)^(+)-N),nitrate-N(NO_(3)^(−)-N),potassium(K^(+)),and phosphate-P(PO_(4)^(3−)-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 NH_(4)^(+)-N maximum sorption capacity(q_(max))of the Arenosol,by 34%and 130%,respectively.The q_(max)of PO_(4)^(3−)-P slightly increased with ascending biochar shares(1-10%)by 14%,30%,26%,and 42%,whereas the undiluted biochar released PO_(4)^(3−)-P.Biochar addition slightly reduced NO_(3)^(−)-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 NH_(4)^(+)-N by 30%and 162%;ascending clay rates(1-100%)increased q_(max)for PO_(4)^(3−)-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 NO_(3)^(−)-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.