Evaluation of changing process of Ammonium and Nitrate in soil profile in three crop rotations.

Abstract
About 30 to 50 percent of applied nitrogen fertilizers leached from soil to ground waters which can causes environment contamination and various human health problems. The rotation type can affect nitrogen mobility rate, so it is necessary to study effect of rotation type in on nitrogen movement. In order to evaluate effects of three main rotations in Khuzestan province on inorganic forms of nitrogen (Ammonium, Nitrate), a split factorial experiment was conducted in the form of complete randomized design with three replications. Type of crop rotation as a main plot and soil depth and sampling time as a sub plots were considered. Soil samples were collected from three depth including 0-30,30-60 and 60-90 cm after each irrigation or rainfall event. In the soil samples, the concentrations of total nitrogen, ammonium and nitrate were measured. The results showed that three rotations had a significant effect on soil nitrate profile. Soil nitrate concentrations in wheat-corn rotation (26.59 mg/kg) was significantly more than the other rotations; while wheat- rice rotation profile had the lowest nitrate concentrations (6.38 mg/kg). Type of rotation did not have any effect on ammonium concentration in soil. Comparison of Nitrate and Ammonium concentration in different times and depths showed that Ammonium concentration was more lower than Nitrate.