Leaching of nitrogen from calcareous soils in western Iran: a soil leaching column study

Nitrogen (N) leaching has become a matter of worldwide concern. The objectives of this study were: (1) to use soil columns to investigate the leaching of nitrate (), ammonium (), and nitrite () from calcareous soils that had received an average of 200 kg(-1) N ha(-1) year(-1) for the previous 30 years and (2) to determine the relationship between soil properties and , , and leaching. The soils used in this study ranged in texture from clay to sandy loam. Leaching experiments were conducted under saturation conditions and consisted of the collection of 1,047-2,524 mL of leachate (12 pore volumes (PVs)), which was equivalent to 534-1,286 mm from rainfall or irrigation. Losses of ranged from 62 to 437 kg ha(-1), while losses of and ranged from 2.5 to 19.3 kg ha(-1) and 0.1 to 10.6 kg ha(-1), respectively. Leaching rates differed between soil samples. The initial and secondary rate of leaching was determined using an exponential model, and it ranged from 2.8 to 14.7 mg kg(-1) PV-1 and 0.11 to 0.32 mg kg(-1) PV-1. Greater leaching rates in the initial period could be due to leaching of in solution, while the secondary leaching might be attributable to the diffusion-controlled transfer of between mobile and immobile liquid phases. Analysis of variance indicated that the effects of soil type on total leaching were highly significant (p < 0.001). The results showed that soil concentration was positively correlated with the peak concentration of (r = 0.86; p < 0.01) and the total leached (r = 0.93; p < 0.01). In addition, the total leached was positively correlated with silt (r = 0.67; p < 0.05), clay (r = 0.61; p < 0.05), and pH (r = 0.77; p < 0.01), which suggests that soil parameters might be useful indicators of and leaching from calcareous soils. Nitrate leaching from soils could threaten groundwater supplies, so possible strategies for minimizing leaching losses may need to be considered.