Effect of Irrigation Water Quality and Wetting and Drying Cycles on the Release of Calcium and Magnesium in Two Soils of Different Textures

Abstract The study included two sites for two soils of different textures (Al-Mazara and Bashiqa) within Nineveh Governorate - Iraq. Soil samples were taken from the surface depth (30 cm) naturally by means of columns. The experiment was carried out by adding two types of water (river water and well water) to each column with a volume equivalent to The pore size, and alternating wetting and drying were done for ten cycles, and the period between one cycle and another was 10 days. Soil samples were analyzed after the first cycle, the fifth cycle, and the tenth cycle to find out the effect of the number of humidification cycles on the exchanged ions, the relative effectiveness, and the Gapon constant. The results indicated that the released amount of exchanged calcium ions in the soil of Bashiqa was higher than the amount released in the soil of the Al-Mazara, while the amount of magnesium ions released in the soil of Al-Mazara was higher than the amount released in the soil of Bashiqa and when using both types of water, while the relative effectiveness values for calcium, the values ​​were higher when wetting with well water, except for the first cycle in the soil of Al-Mazara and the tenth cycle in the soil of Al-Mazara and Bashiqa, while the relative effectiveness of magnesium in the two study soils, the values ​​were higher when wetting with well water and for all cycles except the fifth cycle in Bashiqa soil, while the Gapon constant for calcium in the two study soils had higher values ​​when wetting with river water in the fifth cycles, while in the first and tenth cycles the values ​​were higher when wetting with well water, except for the first cycle in Bashiqa soil, while the Gapon constant for magnesium in the two study soils, the values ​​were higher when wetting with well water and for all cycles except for the first and fifth cycle in Al-Mazara soil. Then the following kinetic equations were applied: zero order equation, first order equation, diffusion equation, Eluvich equation and power function equation, the power function equation was the best equation that describes the process of release calcium and magnesium ions in the study soil.