COMPARISON OF SOIL NITRATE EXTRACTED BY POTASSIUM-CHLORIDE AND ADSORBED ON AN ANION-EXCHANGE MEMBRANE IN-SITU

The 2M potassium chloride (KCl) extraction method used to measure soil nitrate (NO3(-)-N) concentrations in soils may introduce some artifac ts caused by soil sampling, processing, and handling. Furthermore, thi s method provides soil NO3(-)-N concentrations for soil sampled at a p articular 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 abil ity to adsorb NO3(-)-N from a soil cropped to corn (Zea mays L.) and a mended with manure or inorganic nitrogen (N). In a field study, we com pared 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. Nit rate adsorption on the AEM and KCl-extractable NO3(-)-N were larger in the inorganic N treatment than in the manure or the control treatment s throughout the growing season. The NO3(-)-N concentrations measured by the AEM method were correlated with NO3(-)-N extracted with 2M KCl (r(2) = 0.78**), suggesting that the AEM method could be used to meas ure NO3(-)-N concentrations in agricultural soils.