Persian Abstract Potassium Fixation and Charge Characteristics of Clay in some Soils of Central and Northern Iran

Potassium fixation and release by phillosilicate clay minerals in soils are very important processes influencing the availability of K to plants. This investigation was conducted to determine the potassium fixation capacity and charge characteristics of soil clays of 15 surface soils (0-30 cm) from central and northern Iran. After clay particle separation, both total and tetrahedral cation exchange capacity of soil clays were determined. Tetrahedral CEC was measured after saturation with Li and heating at 300 C to reduce octahedral charge to near zero. Potassium fixation was obtained in both wet (1:10 soil:solution, 16 h on a shaker) and dry conditions (after drying for 24 h at 70°C) using three different levels of added K The total CEC in soil clays of Isfahan, Char-Mahal and Gilan provinces ranged from 22.1-36.0, 33.0-55.8 and 31.3-47.9 cmol kg-1, respectively. Tetrahedral CEC in soil clays of Isfahan, Char-Mahal and Gilan provinces ranged from 17.9-4504, 26.2-32.5 and 8.3-23.8 cmol kg-1, respectively, which consisted of 81.0-98.4, 58.5-95.8 and 24.7-72.5% of their total charge, respectively. The amount of K fixation increased with drying and the level of k added. Mean potassium fixation in soil clays of Isfahan, Char-Mahal and Gilan ranged from 5.42-9.13, 6.63-14.67 and 8.87-10.36, respectively. Mean potassium fixation by soil clays (except for soil clays of Gilan) best correlated with total CEC. In the soil clays of Isfahan, mean potassium fixation correlated with tetrahedral CEC, whereas no correlation was observed in soil clays from other places. The average amount of potassium fixation in clay fractions was in the order: Gilan clays > Char-Mahal clays > Isfahan clays.