RAPID DIRECT DETERMINATION OF AMMONIUM AND NITRATE IN SOIL AND PLANT-TISSUE EXTRACTS

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 distillation-titration for soil extracts and NOO3-electrode for plant tissues showed excellent agreement. Recovery of standard additions of NH4+and NO3-range from 97.4% to 103%. © 1990, Taylor & Francis Group, LLC. All rights reserved.