Comparison of potentially mineralizable nitrogen using electro-ultrafiltration and some other procedures

There is an urgent need for a rapid and reliable laboratory procedure capable of predicting soil N availability during the treatment of organic wastes or other sources of nitrogen. Soil systems which have been treated with organic wastes will likely to exhibit a relatively high potential to mineralize organic N into soluble forms under oxidation conditions. Large mineralizable and unused N-pools in soil systems may leach into the ground water or may be washed off with surface water, which in turn may lead to the degradation of body of water. Although several soil N availability indexes have been set forth, none of those tests have gained cohesive acceptance in the scientific community. Electro-ultrafiltration (EUF) is one such procedure that has been proposed to effectively quantify soil PMN. This technique provides for extraction of NO-3- and NH-4+ and of readily soluble N compounds from soils using the principles of ultrafiltration and electrodialysis. The objective of this study was to assess the nature of the relationship between N extracted by the EUF technique and several other indexes of soil N availability for a group of benchmark soils from Nebraska. The data showed a correlation coefficient of 0.71 between the results obtained with the waterlogged method and those achieved using the EUF technique. However, the autoclave, KCl, pH 11.2 phosphate-borate buffer, and NaHCO-3-UV methods were found more highly correlated (r gtoreq 0.87) with the EUF technique than was the waterlogged method. The results obtained with the alkaline KMnO-4 method yielded the lowest correlation coefficient (r = 0.25) with the EUF technique. The slopes of the regression equations between EUF and the chemical indexes tested indicated that the EUF procedure was a relatively stronger extractant than the KCl method. Assessing soil N supplying capacity as a criterion represents a practical and efficient approach that can minimize the potential hazard of group and surface water contamination for applying organic wastes or other N sources to the land.