Lime Amendments to Enhance Soil Phosphorus Adsorption Capacity and to Reduce Phosphate Desorption

Reduction in the dissolved phosphorus (P) desorption from agricultural soils could be an effective measure to prevent eutrophication. Lime is a high calcium-containing mineral that can have promising but varying responses on P desorption depending on soil type. The main objective of this research was to evaluate and compare the potential of hydrated lime and lime kiln dust, its cheaper alternative, as soil amendments to increase soil P adsorption capacity and to reduce dissolved P desorption from four soil types (sandy, sandy loam, loam, and clay loam). A batch adsorption study with varying P concentrations of 0, 0.2, 0.4, 0.6. 0.8, and 1.0 mM P and an adsorbent dose of 1% lime by air-dried soil mass at a fixed pH of 6.5 was carried out. The adsorption data fit best the Freundlich adsorption isotherm model. Both hydrated lime and lime kiln dust significantly increased the Freundlich adsorption coefficient by 3.2, 2.4, 2.0, and 1.6 times in loam, sandy, sandy loam, and clay loam soils, respectively. Although the hydrated lime showed a higher potential to increase the Langmuir maximum adsorption capacity in comparison to lime kiln dust, they both exhibited similar performance at lower P concentration ranges that are representative of the soil solution. The cumulative phosphorus desorption in the ten consecutive days agreed with the adsorption results. Therefore, lime kiln dust as a by-product could be a promising soil amendment to increase soil phosphorus adsorption capacity leading to less phosphorus desorption to water bodies. Further studies on its interaction with crop growth at field scale are required.