Using chemical analysis and modeling to enhance the understanding of soil solution of some calcareous soils

The chemistry of soil solutions can be altered by human activities, due to the intense agricultural and husbandry, leading to leaching of nutrients and subsequently elevating ground water levels. Multivariate statistical and inverse geochemical modeling techniques were used to determine the main factors controlling soil solution chemistry of calcareous soils. In this research, a total of 21 calcareous soils was characterized and assessed for soil solution using soil column. The major cations in the studied soil solutions were in the decreasing order as Ca2+ > Mg2+ > Na+ > K+. The anions were also arranged in decreasing order as HCO−3 > Cl− > SO2−4 > NO−3. Concentrations of NO−3, P, and K+ in soil solutions were in the range of 6.8–307.5 mg l−1 (mean 63.2 mg l−1), 5.0–10.4 mg l−1 (mean 5.9 mg l−1), and 2.8–54.6 mg l−1 (mean 11.3 mg l−1), respectively. Results suggest that the concentration of P in the soil solutions could be primarily controlled by the solubility of dicalcium phosphate dihydrate and dicalcium phosphate. Interactions between soil properties and observed solubility of nutrients were described, and put into empirical multivariate formulations. Obtained equations contained electrical conductivity (EC) as a key factor in determining nutrients solubility. Inverse geochemical modeling of soil solution using PHREEQC indicates the dissolution of calcite, anhydrite, halite, CO2 (g), N2 (g), and hydroxyapatite, and precipitation of sulfur. Cation exchange between Ca2+, Mg2+, K+ and Na+ occurred with Mg2+ and K+ into the solution, and Ca2+ and Na+ out of the solution. Determination of soil solution will improve soil management in the area, and preventing groundwater deterioration.