Asian Journal of Soil Science and Plant Nutrition

The study included the selection of two sites for two different textured soils within Nineveh Governorate - Iraq, with the aim of knowing the role of biochar in the chemical behavior of positive ions (Ca⁺², Mg⁺², Na⁺, K⁺) as well as dispersion parameters (SAR, MCAR, CROSS). Soil samples were collected from the surface layer and brought to the laboratory, after drying and sifting them with a sieve with a 4 mm diameter, biochar was added to them at three levels (0%, 2% and 4%) of the soil weight. These soils were filled with plastic columns (column length 25 cm and diameter 7 cm). The experiment was carried out by adding water to each column in a volume equal to the pore volume PV, and alternating wetting was carried out for ten consecutive cycles with a period of 10 days between each cycle. After the end of the first cycle PV₁, the fifth cycle PV₅ and the tenth cycle PV₁₀, each soil column was cut into two depths (0-10 cm) and (10-20 cm). The soil was analyzed to determine the role of the number of wetting cycles on the positive ions and dispersion parameters under the influence of biochar. The results of this study indicated that there is a clear variation in the values ​​of the dissolved positive ions released from the two study soils when using different wetting periods and for different levels of biochar addition. As for the wetting periods, there was a gradual increase in the values ​​of both Ca⁺² and Mg⁺² with the increase in the number of hydration periods, starting from the first cycle PV₁ after 10 days and up to the tenth cycle PV₁₀ after 100 days. Regarding Na⁺ and K⁺, we noticed that there was no consistent behavior of increasing or decreasing values ​​with the number of wetting periods, in some treatments, there was a release up to the fifth pore volume, after which there was a decrease in the release process, and in others, there was adsorption up to the fifth pore volume, after which there was a decrease in the amount of adsorbed ions, which clearly indicates the saturation of the exchange surfaces with these ions and their return to the solution. As for the levels of biochar added to the two study soils, they had a clear role in increasing the values ​​of the four dissolved positive ions with the increase in the level of addition and in all wetting periods. When comparing the two study soils, the values ​​of the released positive ions in the clay loam soil were generally higher compared to the clay soil. As for the dispersion measures, the lowest values ​​for each of SAR, MCAR and CROSS were in the clay soil and the highest in the clay loam soil.