Desorption of adsorbed ammonium in some Gypsiferous soils, Tikrit Governorate, Iraq

This study aimed to investigate the ability of Gypsiferous soil to desorb the adsorbed ammonium in Gypsifereous soils. Desorption of ammonium by Gypsiferous soils is a significant process to identify the rout of ammonium nitrogen in soil systems. Two samples of Gypsiferous soils were collected from Tikrit University and Al-Alam city fields. The samples were contained different gypsum concentrations: low 65 g kg -1 and high 235 g kg -1 . Soil columns were utilized by using the method of (Head Constant) and various concentrations of ammonium (5, 10, 20, 40, 80, 100, 120 and 150) mg (NH4) L -1 was added. Then, samples were collected at different times (1, 2, 4, 8, 24, and 48) hr; then, 0.01 M of KCl were added to each of the soil columns in order to desorb the adsorbed ammonium in the first stage. Best fitting of different kinetic models have been used to evaluate the desorption process (Zero order, First order, Diffusion, Power function, and Elovich models). The ammonium desorption in Gypsiferous soils was found to conform to the Power function equation more than the other used equations. The results showed that the process of ammonium desorption was affected by the content of calcium carbonate in soil.