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

Abstract

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 ([Formula: see text]), ammonium ([Formula: see text]), and nitrite ([Formula: see text]) 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 [Formula: see text], [Formula: see text], and [Formula: see text] 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 [Formula: see text] ranged from 62 to 437 kg ha(-1), while losses of [Formula: see text] and [Formula: see text] 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 [Formula: see text] 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 [Formula: see text] in solution, while the secondary leaching might be attributable to the diffusion-controlled transfer of [Formula: see text] between mobile and immobile liquid phases. Analysis of variance indicated that the effects of soil type on total [Formula: see text] leaching were highly significant (p < 0.001). The results showed that soil [Formula: see text] concentration was positively correlated with the peak concentration of [Formula: see text] (r = 0.86; p < 0.01) and the total [Formula: see text] leached (r = 0.93; p < 0.01). In addition, the total [Formula: see text] 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 [Formula: see text] and [Formula: see text] leaching from calcareous soils. Nitrate leaching from soils could threaten groundwater supplies, so possible strategies for minimizing [Formula: see text] leaching losses may need to be considered.