Comparison of soil nitrate extracted by potassium chloride and adsorbed on an anion exchange membrane in situ

Abstract

The 2M potassium chloride (KCl) extraction method used to measure soil nitrate (NO₃ ^‐‐N) concentrations in soils may introduce some artifacts caused by soil sampling, processing, and handling. Furthermore, this method provides soil NO₃ ^‐‐N concentrations for soil sampled at a particular time, whereas the dynamics of this anion in situ need to be better understood. In order to develop a reliable in situ method as an alternative, an anion exchange membrane (AEM) was tested for its ability to adsorb NO₃ ^‐‐N from a soil cropped to corn (Zea mays L.) and amended with manure or inorganic nitrogen (N). In a field study, we compared the amount of NO₃ ^‐‐N adsorbed on an AEM and extracted with the 2M KCl method. The AEM was calibrated in the laboratory and placed at 15‐cm soil depth for 2‐wk periods during the corn growing season. Nitrate adsorption on the AEM and KCl‐extractable NO₃ ^‐‐N were larger in the inorganic N treatment than in the manure or the control treatments throughout the growing season. The NO₃ ^‐‐N concentrations measured by the AEM method were correlated with NO₃ ^‐‐N extracted with 2M KCl (r² = 0.78***), suggesting that the AEM method could be used to measure NO₃ ^‐‐N concentrations in agricultural soils.