Nitrate-N, ammonium-N, and organic matter in relation to profile characteristics of Dark Brown Chernozemic soils

Thirty-six deep soil profiles (3.3 m) from a 32-ha irrigated field in southern Alberta were evaluated to determine the relationship between pedogenic development and nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), and organic matter (OM) content and distribution. The soils were classified into three fine-loamy Dark Brown subgroups. Three classes of solum thickness and slope position were identified. The NO3-N, NH4-N, and OM content in the 3.3-m profile, and below the solum, the control section, and the 1.2-m rooting depth were compared and correlation analyses were conducted between these properties and properties of the saturation extract.The OM content decreased exponentially with increase in profile depth, but the NO3-N and, to some extent, the NH4-N contents varied according to solum thickness regardless of subgroup classification. On average, soils with a thin (< 35 cm) or thick (> 75 cm) solum had a zone of high NO3-N concentration between the 100- and 150-cm depths. This was ascribed to less favorable soil moisture conditions for crop growth on the thin-solum soils and probably more frequent leaching events in the thick-solum soils. Distinctly different correlation coefficients between NO3-N, NH4-N, and OM and the saturation extract properties of the control section supported the series designations of the solum-thickness separations. Solum thickness and topographic position should be considered when applying nitrogen fertilizers or irrigations.