Rapid Analysis of Soil Nitrate with Chromotropic Acid

Abstract

Abstract Colorimetric analysis of nitrate in soil extracts using chromotropic acid (CTA) was studied and compared to the results obtained by the phenoldisulfonic acid (PDA) method. Extracting solutions of 0.5 M MgSO 4 , saturated CaSO 4 , and a 0.2% Ca(OH) 2 suspension were investigated. The three extractants were equally effective in recovering NO 3 ‐ ; however, the clearest extracts were obtained with Ca(OH) 2 . Soil‐to‐extractant ratios of 1:2.5, 1:5, and 1:10 were studied. The 1:5 ratio effectively extracted NO 3 ‐ and resulted in appropriate NO 3 ‐ concentrations for color development. A shaking time of 15 min was adequate to extract a maximum of NO 3 ‐ . In a NO 3 ‐ ‐N recovery study, equivalent amounts of NO 3 ‐ were recovered by the CTA and PDA methods. Results of nitrate analyses by the two methods were significantly correlated ( p = .01). Nitrate determined by the chromotropic acid procedure was positively correlated ( p = .05) with the yield of winter wheat ( Triticum aestivum L.) and was negatively correlated ( p = .01) with response of winter wheat to N fertilizer additions. The new procedure has the advantages of rapidity, simplicity, sensitivity, and relative freedom from interference.