Phosphorus availability in different aggregate sizes of tropical red soils amended with cassava starch waste

Abstract

The study was conducted to determine the role of aggregate size in three red tropical soils with varying clay content on the phosphorus (P) availability and the adsorption and desorption of P with the addition of cassava starch waste (CSW). Seven ranges of aggregate size up to 8 mm in diameter were carried out using dry-sieving method and each aggregate size was taken for the study of P sorption isotherm and determining P content. CSW had no impact on the P adsorption capacity of soils with a lower clay content but slightly increased the P adsorption capacity for most aggregate sizes of clay-textured soil, especially in the sizes 0.25 mm to <0.053 mm. Smaller aggregates adsorbed more P, resulting in P desorption being significantly being lower than that of larger aggregates; in turn, the latter released greater P, especially with CSW applied. The results indicated that most P was fixed in different aggregate sizes in different capacities, demonstrating the aggregation effect on plant P availability.