INTRODUCTION

The procedures described in this manual are those used by the Soil, Plant , and Water Analysis Laboratory to analyze soil, feed, water, plant tissue, environmental samples and other substances for chemical and physical constituents. Many of the methods used are those found in standard reference methods publications such as Official Methods of Analysis of AOAC International, Standard Methods for the Examination of Water and Wastewater, EPA Methods for Chemical Analysis of Water and Wastes, as well as other books, journal articles, and publications. Reference to the source of the analytical method is given whenever possible. Some modifications may have been made to accommodate instrument or sample requirements. Expression of results will vary depending on the use of the data and changing developments in the field.

This manual gives sufficient details for one to follow without referring to other sources. However, procedural details are written at a level that a technician, skilled in fundamental analytical procedures, will be able to follow. An unskilled technician may have difficulty following steps given in some of the methods.

Those who would use this manual as a guide for conducting analysis should be aware that those methods that use automated equipment and instruments may not be suitable for manual methods without modification.

SOIL SAMPLES

Soil samples are tested for extractable phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), and manganese (Mn) using the Double Acid (0.05 N HCl + 0.025 N H2SO4) extraction method frequently referred to as the Mehlich I extract. This procedure is applicable for the analysis of extractable elements in acidic, low cation exchange capacity soils which are commonly found in Georgia. Soils which contain sizable quantities of clay or organic matter or are alkaline cannot be satisfactorily analyzed using the Mehlich I extract. Other extraction procedures should be used on these types of soil.

Soil pH is determined in a 1:1 soil to water slurry. A pH meter, calibrated with pH 4.00 and pH 7.00 buffers, is used for this measurement. Values are recorded to the nearest tenth of a pH unit. Lime requirement for soils is determined by the Adams-Evans buffered pH procedure.

Extractable elements (P, K, Ca, Mg, Zn, Mn) are analyzed using an ICP emission spectrograph.

Boron is extracted with hot water at 80 °C and analyzed using an ICP emission spectrograph.

Organic matter is determined by the Walkley-Black wet oxidation procedure. Soluble salts are determined on a 1:2 soil to water extract using a conductivity meter. Extractable chloride is determined using a ion specific electrode.

Greenhouse soils and potting mixes are analyzed differently. The soil or mix is saturated with water and pH is determined on the slurry. The slurry is then vacuum filtered. The filtrate is analyzed for conductivity (soluble salts), ammonium-nitrogen (NH4-N), nitrate-nitrogen (NO3-N), by steam distillation and for P, K, Ca, and Mg by ICP. Only that portion of the elements which are water soluble in the soil or mix will be determined.

PLANT TISSUE SAMPLES

Plant tissue samples are dry ashed at 500 °C for 4 hours and analyzed for 12 elements on the ICP emission spectrograph. Nitrogen is determined by a combustion method using thermal conductivity for detection. Sulfur and carbon are determined by a combustion method using an infrared detection system.

OTHER SAMPLES

Drinking water samples as well as fish pond water, and waters from lakes and streams are analyzed for 16 elements on the ICP emission spectrograph. This includes both primary contaminant elements and secondary contaminant elements on drinking water samples. Lead in drinking water samples is determined by graphite furnace atomic absorption spectroscopy. The hardness of the water is calculated, based on the mineral analysis. Dissolved and suspended solids are determined by standard analysis procedures. Mercury is analyzed by atomic fluorescence using a cold vapor technique. Flouride, chloride, nitrate, phosphate, and sulfate are analyzed using an ion chromatography instrument.

Litter and sludge samples are analyzed for 16 elements on an ICP emission spectrograph, using a nitric-perchloric acid digestion procedure.

Fertilizer, limestone, and nutrient solutions can be analyzed for their elemental content. The procedures for fertilizer samples are not official AOAC procedures. Such analysis may be obtained on request. Hydroponic nutrient solutions are analyzed for their element content.

Other substances can be analyzed in the laboratory. Spectrographic analysis of various animal tissues provide elemental composition values for substances such as milk, blood, bone, serum, kidney and liver.

QUALITY ASSURANCE

It is desirable to have quality control samples that are the same type and have the same general composition as the samples being analyzed. This laboratory uses four National Institute of Standards and Technology Standard Reference Material (NIST SRM) standards and five NIST traceable standards as outside source quality control samples. All outside source quality control samples must have a certificate of analysis for the elements being analyzed. Additionally this laboratory has developed three in house quality control standards. In house quality control samples are validated by analyzing them in conjunction with NIST SRM's.

The laboratory participates in the following performance evaluation studies: North American Proficiency Testing program, for soils and plant tissue, United States Geological Survey for water, and the Environmental Protection Agency for water.

REFERENCES

Various manuals and reference methods of analysis are given in the following publications. They are used by this laboratory as a source of methods and techniques.

  1. Cunniff, P.A. (ed), 1990. Official Methods of Analysis of AOAC International, 16th edition, Washington D.C.
  2. American Public Health Association, 1995, Standard Methods for the Examination of Water and Wastewater, 19th edition, Washington D.C.
  3. Environmental Protection Agency, 1983, Methods for Chemical Analysis of Water and Wastes, Cincinnati, Ohio.
  4. Jackson, M.L., 1958, Soil Chemical Analysis, Prentice-Hall Inc., Englewood Cliffs, New Jersey.
  5. Hesse,P.R., 1971, A Textbook of Soil Analysis, Chemical Publishing Co. Inc., New York, New York.
  6. Westerman, R. L. (ed), 1990, Soil Testing and Plant Analysis, third edition. Soil Science Society of America, Madison, Wisconsin.
  7. Sparks, D. L. (ed), 1996, Methods of Soil Analysis: Chemical Methods, Part 3, Soil Science Society of America, Madison, Wisconsin.
  8. Walsh, L.M., 1971, Instrumental Methods for Analysis of Soils and Plant Tissue, Soil Science Society of America,Inc. Madison, Wisconsin.
  9. Barnes, R.M. (ed), 1983, Plasma Spectrochemistry, Spectrochemica ACTA, Vol. 388, Nos. 1/2.
  10. Gorsuch, T.T., 1970, The Destruction of Organic Matter, Pergamon Press, Oxford, England.
  11. Garner, W.Y., Barge, M.S., Ussary, J.P. (eds), 1992, Good Laboratory Practice Standards, American Chemical Society, Washington D.C.