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This paper deals with investigations on nitrate determination with a nitrate-specific ion electrode. Analytical results for the nitrate content in soil extracts are compared with analyses carried out by two colorimetric methods. The extracting agents used are 0.02 N copper sulphate, 2 N potassium chloride and distilled water. Results for nitrate determinations in soil suspensions and corresponding filtrates are also compared.The stability of soil extracts, the influence of variation in the ratio of grams of soil to millilitres of extracting agent and in the shaking time, interferences caused by ionic strength and anions, accuracy and reproducibility axe also discussed.The investigation shows that nitrate determination with the electrode is reliable both for soil extracts and for soil suspensions. The determination is rapid, and the interferences are not serious.NUMEROUS distillation and colorimetric methods for nitrate determinations in soil extracts have been described.l to l4 They are often time consuming or the interferences are serious.Over the past few years several commercially available ion-selective electrodes have appeared. They are differentiated by the type of membrane which they incorporate.15 In the nitrate-selective electrode, the membrane is replaced by a liquid ion exchanger, which is insoluble in water. If this electrode is placed in a solution containing nitrate, the potential can be measured against a standard calomel electrode. This potential is a measure of the nitrate activity. By comparison with potentials measured in standard nitrate solutions, it is possible to determine the nitrate content in unknown solutions. The electrode responds to nitrate ion from 0.1 to 1 0 -s ~. Potterton and Shultsls have published an evaluation of the performance of this electrode. Paul and Carlsonl' have studied nitrate determination in plant extracts by the nitrate electrode. After writing this article, we also noticed that Myers and Paul18 had published some investigations on nitrate determination in soils.The Orion nitrate-ion activity electrode appears to be convenient for nitrate determinations in soil extracts. It would be of interest to ascertain this by comparing determinations made with this electrode with determinations made with the colorimetric xylenol methodlS and a Technicon AutoAnalyzer method.20 (These two were chosen because they are used for routine analysis in our laboratory.)The results from different analytical methods are compared.In this investigation, different types of soil and extracting solutions were used.

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