• .S of Soil Analysis Used in the Soil Testing Laboratory at Oregon State University
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IrG11) E111[41111111-9Y8L118R4A S 105 COMPACT .E55 no.321 rev.1978 cop.2 • .s of Soil Analysis Used in the Soil Testing Laboratory at Oregon State University Special Report 321 Revised September 1978 Agricultural Experiment Station Oregon State University, Corvallis CONTENTS Page Introduction General 1 Collection and Preparation of Soil Samples 1 Accuracy and Precision 2 Documentation of Methods. 2 Analytical Methods Soil Test Methods pH 3 Lime Requirement 5 Extractable Phosphorus Sodium Bicarbonate Method. 6 Dilute Acid-Fluoride Method 9 Extractable Potassium, Sodium, Calcium, and Magnesium 11 Water Soluble Boron 13 Organic Matter 15 Total Soluble Salts 17 Exchangeable Sodium 18 Cation Exchange Capacity-Ammonium Acetate Method 19 Total Nitrogen 21 Extractable Ammonium and Nitrate Nitrogen 23 Extractable Zinc 26 Exchangeable Hydrogen 27 Extractable Sulfate Sulfur 29 • Carbonate 33 Water Analysis Methods Calcium, Magnesium and Sodium 35 Boron 36 Carbonates and Bicarbonates 37 Organic Nitrogen and Ammonium Nitrogen 38 Nitrate Nitrogen and Ammonium Nitrogen 39 Total Salts... 40 Sulfate Sulfur. 41 Special Tests Calcium Carbonate Equivalent for Liming Materials and Highly Basic Soils. 42 Literature Cited 43 AUTHORS: M. G. Berg is a Research Assistant, and E. H. Gardner is an Extension Soils Scientist, Department of Soil Science, Oregon State University. ACKNOWLEDGEMENTS: The authors wish to acknowledge the contribution made by Drs. M. D. Kauffman, S. Roberts and Mr. R. V. Vodraska on the writing of the first and second editions of this publication. The authors also • wish to express their appreciation to the Soil Testing Laboratory per- sonnel for their suggestions and contributions to this manual. METHODS OF SOIL ANALYSIS USED IN THE SOIL TESTING LABORATORY AT OREGON STATE UNIVERSITY M. G. Berg, and E. H. Gardner INTRODUCTION General The chemical analysis of soil, sometimes referred to as "soil testing," is a means for evaluating the potential of soil to supply some of the essential plant nutrients. Deficiencies of several plant nutrients essential for commercial crop production occur in Oregon soils. In the Soil Testing Laboratory at Oregon State Unversity, major emphasis is placed on analyzing soil samples for some of the elements which are most likely to be deficient for the crops which are grown. Besides the diagnostic testing of soils in the laboratory, other analyses are conducted which provide useful data for soil characterization studies and other research projects. The purpose of this publication is to outline the methods of chemical analysis which are used in the Soil Testing Laboratory, and to supply information on the appropriate documentation of these methods. Numerous other methods for the chemical analysis of soil, some of which are not suited to Oregon conditions, are not covered in this summary. The Cascade Mountain Range is a natural boundary which separates Oregon into eastern and western sectors. Western Oregon has soil which tends to be well leached and acid in reaction, but much of the soil in eastern Oregon is either slightly acid or alkaline. In view of these and other major differences in soil chemical properties, not all of the soil testing methods included in this report are applicable or useful for the analysis of samples from all areas of the state. For example, two methods are used in analyzing soil for phosphorus. The phosphorus test for western Oref9n involves the use of the dilute acid-fluoride (Bray P 1 ) method (2)--, but the sodium bicarbonate method (15) is used for the analysis of samples from eastern Oregon. Although reference is made to the specific scientific supplies and instruments used in the Oregon State University laboratory, similar equipment from other manufacturers can serve the same purpose. Collection and Preparation of Soil Samples Collecting soil samples from the field is an integral part of the diagnostic testing program. Samples must be taken in a prescribed manner to fulfill the basic requirement: the soil sample is representa- tive of the soil in the field from which the sample is taken. Some suggestions on soil sampling are indicated on the soil sample bag ./ Underlined numbers in parentheses refer to Literature Cited, page 43. which is supplied to the grower by the Extension Service and more • detailed information is provided in Extension Circular 628, "How to Take a Soil Sample and Why" which is available on request. The Soil Testing Laboratory provides a standard bag in which to submit soil samples to the laboratory. Other containers should not be used. For example, contamination may be a serious problem for boron (B) and zinc (Zn) when samples are collected and stored in certain kinds of paper bags. Extreme care in the field is also necessary to avoid contaminating the soil sample with fertilizer or with extraneous materials from the sampling tools. When the soil samples arrive at the laboratory, they are placed on trays and dried in a forced-draft drying cabinet at a temperature not in excess of 35 C. The soil sample usually dries in about 24 hours. The 2/ sample is pulverized with a Custom Laboratory Equipment Co. soil crusher– and sieved by a Nasco-Asplin soil grinder.- The part of the sample which passes through the 14-mesh sieve is returned to the original sample bag and stored ready for analysis. The remainder of the sample is discarded. The samples usually are analyzed within one to two days after they are received at the laboratory. The soil test results are released immediately after sample analysis, and the soil samples are stored for future reference. Three months after analysis, the samples are discarded unless there is some reason for retaining them. Accuracy and Precision • The laboratory instruments are calibrated by standard solutions of the nutrient elements, and the accuracy of the determinations is cross- checked by evaluating the quantitative recovery of measured amounts of the nutrients which are added to sample extracts. Selected soil samples also are maintained as reference samples in evaluating the day-to-day precision of the analytical results. Documentation of Methods The analytical methods used in the laboratory are outlined in the following section under the following subheadings: Reagents, Procedure Calculation (when required), and Comments. The appropriate literature citation for each method is indicated along with the title of the method. Any modification of the published method with respect to change in reagents or in procedural detail is indicated under the subheading of Comments. In view of the limited distribution and availability of this summary of soil testing methods, specific reference to this report is not recommended for use in scientific publications. 2/Distributed by Custom Laboratory Equipment, Inc., Orange City, FL. 1/Distributed by Nasco, Fort Atkinson, WI. -3- ANALYTICAL METHODS pH - 1:2 Soil to Solution Ratio and Glass Electrode pH Meter (9) A. Reagents Buffer reagents may be purchased or prepared as described (8). 1. Potassium biphthalate, 0.05M, gH 4.005 at 25°C - Dry KE- phthalate for two hours at 110 C. Dissolve 10.21 g of KH- phthalate in distilled water, and dilute the solution to 1 liter with distilled water. As a preservative, add 1.0 ml of chloroform or a crystal (about 10 mm in diameter) of thymol, per liter of the buffer solution. o HPO pH 6.860 at 25 C - 2. Phosphate, 0.025M KH 2PO4, and 0.025M Na 2 4 ' o Dry the two phosphate salts for two hours at 110 C. Dissolve 3.40 g of KH 2PO4 and 3.55 g of Na2HPO4 in distilled water, and dilute the solution to 1 liter with distilled water. As a preservative, add 1.0 ml of chloroform or a crystal (about 10 mm in diameter) thymol per liter of the buffer solution. Borax, 0.01M Na B 0 -10H 0, pH 9.177 at 25 C 3. 2 - Dry the 2 4 7 o . 10 H 0 for two hours at 110 C. Dissolve 3.81 g in distilled B 0 2 water4 7 and dilute the solution to 1 liter. • B. Procedure 1. Weight or scoop 20 g of soil into a 3-ounce paper cup. 2. Add 40 mis of water and stir thoroughly. 3. Let stand at least 30 minutes, stirring two or three times. 4. Standardize the pH meter in accordance with instructions for the instrument using two of the prepared buffer solutions. After standardization of the instrument, rinse the electrodes with distilled water to remove the film of buffer solution. 5. After the soil has settled to the bottom of cup (around 15 minutes after last stirring) read the pH by placing the pH meter electrodes in the supernatant solution. Record the pH to the nearest 0.1 unit. Rinse the electrodes with distilled water prior to each pH determination, and when not in use immerse the electrodes in distilled water. C. Comments The method outlined here is a modification of method 3-26 described by Jackson (9). The modifications are the following: (1) A 1:2 soil- solution ratio is used instead of . a 1:2.5 ratio. (2) The pH reading is taken in the supernatant solution instead of in the soil suspension. These modifications were made for convenience and to minimize the errors introduced by liquid junction potential and the settling of the soil particles during the time the pH measurement is being made. It is advisable to prepare fresh buffer solutions at least once a month, and to check the standardization of the pH meter periodically when making a series of determinations. Greweling and Peech (8) indicate that the measured pH value may shift slightly with each change in the soil-to-water ratio used in preparation of the soil sample and that seasonal fluctuations in pH may also be anticipated.