Rapid direct determination of ammonium and nitrate in soil and plant tissue extracts

Abstract

The diffusion‐conductivity method (DCM) for NH₄ ⁺ and NO₃ ^‐determinations in soil and plant tissue extracts is tolerant of sample color and turbidity. The instrument can be calibrated for direct analysis of extracts from either low or high level samples. Extracts can be processed at one per minute. Ammonium and NO₃ ^‐ can be determined simultaneously at this rate with a two channel prototype instrument. The use of serum filters simplifies sample extract preparation and avoids the NH₄ ⁺ and NO₃ ^‐ contamination problem that has been documented for filter papers. The instrument sample intake tube can aspirate extracts directly from the serum filter tube. A variety of soil or plant extracting solutions can be used for both NH₄ ⁺ and NO₃ ^‐ determinations. Interference in NO₃ ^‐determinations has been encountered in a few samples where it appears to be due to a high phenolic content. For these samples, interference is minimized by using two NO₃ ^‐ reduction cartridges in series. Comparisons of the DCM procedure with steam distillationtitration for soil extracts and NO₃ ^‐ electrode for plant tissues showed excellent agreement. Recovery of standard additions of NH₄ ⁺ and NO₃ ^‐ range from 97.4% to 103%.