Effect of low molecular weight organic acids on phosphorus (P) adsorption in acidic soils limed at differing levels

Low phosphorus availability in acidic soils due to the formation of aluminum and iron phosphates was a significant concern for agricultural productivity. Liming is often applied to improve soil fertility. However, altering pH could also affect the dynamics of existing organic matter in the soil, leading to changes in the effective concentrations of competing low molecular weight acids involved in phosphorus adsorption. The study aims to investigate the effects of citric, oxalic and malic acids in acid soils from tea and hazelnut cultivation regions of the Eastern Black Sea, which had been limed at different levels and incubated for 15 months, on phosphorus adsorption in 11 acid soils. The obtained data were used to estimate the Langmuir and Freundlich adsorption parameters of soils using the spreadsheet program developed by Bolster and Hornberger (2007). Furthermore, the effects of liming levels and organic acids on the phosphorus adsorption parameters of Freundlich and Langmuir isotherms were analyzed using ANOVA, and differences between means were compared by the Duncan test (p<0.05). The results demonstrated that citric acid was the most effective organic acid in reducing phosphorus adsorption, followed by oxalic acid, malic acid, and CaCl2. With its three carboxyl groups (-COOH), citric acid could form more complexes with adsorbed phosphorus on the soil surface. Additionally, 100% liming was found to substantially decrease phosphorus adsorption. The results indicated the significant influence of low molecular weight organic acids and liming application on soil adsorption.