THE EFFECT OF ORGANIC MATTER TYPES ON THE BEHAVIOR OF ZINC IN SEDIMENTARY SOILS OF DIFFERENT TEXTURES

Abstract

This research paper has discussed the zinc (Zn) adsorption-desorption processes in calcareous alluvial soils with different textures that were amended with various organic materials. Two soils (sandy loam, T1; clay loam, T2) gathered in Al-Musayyib District, Babil Governorate, Iraq, were described in the terms of chosen physical and chemical characteristics. In a laboratory equilibrium experiment, 2 g of soil were mixed with 20 mL of ZnSO 4 solution (5, 10, 25, 50, 100 and 150 mg L -1 ) with the amendment of cattle, sheep or poultry manure. The Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models were used to determine adsorption and subsequent desorption by the use of 0.01 N CaCl 2. Langmuir gave the most consistent fit to the adsorption data, which had an R 2 value of 0.88 to 0.98, versus 0.86 to 0.96 with both Freundlich and D-R. Langmuir maximum adsorption capacity (Xmax) was between 29.22 to 256.41 mg kg -1, meanwhile the value of D-R adsorption energy was between 8.74 to 11.81 kJ mol -1 and this shows that ion exchange was predominant. Overall, heavy-textured soil exhibited higher retention and low desorption of Zn compared to the light-textured soil. Sheep manure enhanced adsorption capacity in several cases, whereas poultry manure tended to reduce Zn retention, particularly in the light-textured soil. The results demonstrate that soil texture and organic amendment type jointly control Zn behavior and that the Langmuir model is the most suitable for describing Zn adsorption under the conditions of this study