The role of biosolid derived compost on cation exchange

In most productive agricultural soils, organic matter (OM) makes up a small percentage (3-6%) but plays a vital role in biogeochemical processes, particularly nutrient availability and soil structure stability as influenced by cation exchange processes. The loss of soil OM is one of the most severe threats to much of the World's arable areas. Thus, OM application (e.g. biosolids, livestock manure, and compost) is widely recommended due to its cost-effectiveness, and high macro- and micro-nutrient contents. In this regard, the intrinsic properties of soil OM in conjunction with cation exchange processes have not been thoroughly addressed. Therefore, it is essential to quantify cation exchange in biosolids and biosolid-amended soils, specifically, the competitive cation exchange process. The main objective of this study was to evaluate cation exchange equilibria on biosolid-derived compost in binary cation solutions. The target cations were NH₄⁺, K⁺, Na⁺, Ca²⁺, and Mg²⁺, which are relevant to plant nutrient availability and the efficiency of remediation strategies for saline and sodic soils. Here, binary exchange isotherm experiments were conducted in which the biosolid was pre-saturated with Ca²⁺. The selectivity coefficient was calculated from the measured exchange isotherms. The results showed that the shape of the exchange isotherm curves and the amount of cations exchanged varied in different binary systems. The biosolid characteristics, as well as the preference of particular cations to the biosolid, will be presented and discussed.

Keywords: soil organic matter, biosolid, cation exchange, selectivity coefficient.