Effect of Si-rich substances on phosphorous adsorption by sandy soils

The poor adsorption capacity of sandy soils is one of the primary reasons of a high level of phosphorus (P) leaching. Silicon (Si)-rich soil amendments have the potential to improve the low absorption capacity of sandy soils for P. The objective of this study was to evaluate the ability of different Si-rich materials to regulate P adsorption and retention by sandy soils. Amorphous fine silica (FSS), calcium silicate (CaSiO₃), chemically pure CaCO₃, and two types of Ca-silicate slags from metal industry (Pro-Sil) and chemical industry (TS) were used in laboratory experiments being conducted with pure quartz sand and cultivated and virgin Entisols and Spodosols collected in the South Florida. The binding energy-related constants were evaluated for soils treated by Si-rich materials and then incubated during 2 months. The following row of tested materials on the increasing level of "affinity parameter" was determined: for virgin Spodosol, Pro-Sil < CaCO₃ < FSS< CaSiO₃ < TS; for cultivated Spodosol, FSS < Pro-Sil < CaCO₃< CaSiO₃ < TS; for virgin Entisol, Pro-Sil < CaSiO₃ < CaCO₃ < FSS < TS; and for cultivated Entisol, FSS < Pro-Sil < CaSiO₃ < CaCO₃ < TS. Chemical, physical, and physical-chemical mechanisms of increasing soil adsorption capacity are hypothesized and discussed to explain the results obtained. The conducted experiments have demonstrated high prospective of Si-rich materials for reduction of P leaching from cultivated sandy soils.