BASIC SOIL SURVEY – FIELD AND LABORATORY UNDERSTANDING THESOIL SURVEY LABORATORY DATA SHEET Michael WilsonResearch Soil Scientist Soil Survey Research and Laboratory
ObjectivesUpon completion of this module, the student should be able to: • Query the on-line KSSL characterization database • Navigate to locate specific data on the KSSL datasheet • Find references for method codes, units, etc. • Distinguish between measured and calculated laboratory data • Evaluate quality of laboratory data based on comparison with other data elements within or between horizons.
REFERENCES • Burt. R. (ed.) Soil Survey Laboratory Methods Manual. 2014. Soil Survey Investigations Report No. 42. Version 5.0. U.S. Govt. Print. Office, Washington, DC. • Soil Survey Laboratory Staff. 2011. Soil Survey Information Manual. Soil Survey Investigative Report No. 45. ver. 2.0. U.S. Govt. Print. Office, Washington, DC. http://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/research/lab/guide/ • Soil Survey Laboratory Characterization Database http://ncsslabdatamart.sc.egov.usda.gov/
METHOD OF INSTRUCTION • Review basic features of the SSL internet data site • Review datasheet with lecture/ discussion format • Questions (handout) on specific data elements for review • Evaluate/discuss worksheet answers
Order of Presentation • Section 1: Introduction, PSDA and Rock fragment tier, Bulk Density and Moisture Tier • Section 2: Cations and Extractions Tier, pH and Carbonates Tier • Section 3: CEC and Bases Tier, Salts Tier • Section 4: Clay Mineralogy Tier, Sand-Silt Mineralogy Tier, Supplemental Tiers
SECTION 1 Introduction
Introduction • Lab data = Point (pedon) data • Analytical, not subjective • Method based (consistency with time important) • Measured and calculated data used
Laboratory Data and Use --Importance • Quantitative • Operationally defined • Multifaceted usage – interpretation, genesis, taxonomy, geomorphology • Best use of data occurs when analytical methodology and reporting of data well understood
Advanced Query Page Click to get more information
Tiers on the SSL Data Sheet • Primary Characterization Data Output • PSDA and Rock Fragments • Bulk Density and Moisture • Water Content • Carbon and Extractions • CEC and Bases • Salt • pH and Carbonates • Clay Mineralogy • Sand Silt Mineralogy • Geochemistry • Supplementary Characterization Data • Four Tiers • Taxonomy Characterization Data • Two Tiers
Caribou Pedon ID (Field assigned) (Calendar year, State/County FIPS codes, consecutive pedon sampled in county that year): S1988WA003001 Lab Project ID and Name (Assigned by fiscal year) Lab assigned Sample numbers Good calculations for ST if control section is correct
PREPARATION CODES ON DATASHEET • S = Standard air- dried preparation • M = Standard moist preparation • H = histic or organic soil preparation • K = crush 2-20 mm coarse fragments to < 2-mm (e.g., SK prep) • GP = mix and crush <20mm soil material (<2mm soil plus coarse fragments) to < 2-mm
SECTION 1: PSDA and Rock Fragment Tier Bulk Density and Moisture Tier
Caribou Total Clay = Silicate clay + carbonate clay Units Method Codes Prep codes ST Loamy/Silty Criteria Rock fragments wt%
Particle size analysis • Soils are chemically and physically dispersed; • Peroxide treatment for OM • Washed to remove soluble salts • Shaken overnight with Na hexameta-phosphate
1500 kPa (15 bar) water – • the permanent wilting point for agronomic plants • Represents water in pores <0.2 µm and on particle surfaces • Greatest proportion of surface area in soil related to clay Check for dispersion: ROT: Most soils have 1500kPa/clay ratio=0.4 to 0.6
Caribou Possible Vertic if > 0.06 Ratios to Clay BDod> BD33 WC33 > WC15m > WC15d
1. Caribou pedon: a. What is the size of fine clay particles? < 0.0002 mm b. What is the size range of particles classified as very fine sand? 0.05 to 0.10 mm c. What weight basis is used for column 16 on the PSDA and Rock fragments Tier? % < 75 mm d. For what purpose is that data column (16) listed on the SSL data sheet (i.e., where is it used)? (Consult the text, pg 55). Soil Taxonomy family particle size classification: Loamy (> 15% particles fine sand sized or coarser, including rock fragments up to 7.5 cm) vsSilty (<15%)
1e. What tier and column is the oven dry bulk density (Db) found? “Bulk Density and Moisture” tier, Column 2. f. Which has a greater density (higher value), the oven dry or 1/3 bar Db? Bulk density is weight of the <2-mm soil material divided by the volume of the clod. Oven dry Db is greater than third bar Db due to the expected decrease in volume of the clod when it shrinks. The weight of soil material used for both moisture states is the oven dry < 2-mm soil. g. COLE (Coefficient of Linear Extensibility) can be used to infer (predict) what other soil properties? (consult the text, pg. 81-82). See pg. 81; shrink-swell, clay mineralogy
SECTION 2 Carbon and Extractions Tier pH and Carbonates Tier
TOTAL CARBON ANALYZER (C, N, AND S) Analysis performed on all soils (acid, alkaline, organic) in SSL • Determines C representing both organic and inorganic carbon • Decomposed organic matter, charcoal, coal, carbonates, wood • Does not necessarily approximate organic C by Walkley Black Sample combustionSpecific adsorption columnsThermal conductivity detection
ORGANIC CARBON (OC)by Walkley Black Method • Formerly performed in SSL (now obsolete) • Excludes fresh roots, charcoal, carbonates • May have incomplete oxidation >8% OC • Acid Potassium Dichromate Digestion • Indirect determination of organic matter • Assumes 58% OC in organic matter • Correction factor 1.724 “Van Bemmelen factor” Chromium Waste down the drain. UGH! Organic Matter = % Organic C X 1.724
Most soils have 1500kPa/clay ratio=0.4 to 0.6 Rule in Soil Taxonomy for Particle Size Family: For soils having majority of control section: 15 bar/clay ratio < 0.25 or > 0.6 ; use the following: %clay = (1500 kPa water retention – Organic C) X 2.5 This means: 40% water retention X 2.5 = 100% clay (if no organic C) Remember: Total C =Organic C+ inorganic C Inorganic C is carbonates %CaCO3 reported on datasheet (Current) Combustion Analyzer (Current) Walkley Black Method (Defunct)
Organic C = Total C – Inorganic C Carbonates • Inorganic C in soils • Reported as %CaCO3 • composed of 12% C based on atomic weights • . C/CaCO3 = 12/100 %C as CaCO3 = %CaCO3 X 0.12
Caribou • Selective Dissolutions • Citrate Dithionite- Total pedogenic Fe oxide/oxyhydroxides= • Crystalline, Noncrystalline, Organo-metallic • Use in Family Mineralogy (Ferritic, Parasesquic) • Acid oxalate = Noncrystalline, Organo-metallic • Use in Andic, spodic materials definitions • Ratio with CD Fe = Feo/Fed = fraction of noncryst. pedogenic Fe • Sodium Pyrophosphate = Organo-metallic • No longer used in Soil Taxonomy, but good indicator of organically bound material (subtract from acid oxalate)
pH in dilute salt solution pH water Caribou NaF pH – performed on soil with noncrystalline component – isotic, andic, vitrandic pH in 1N KCl for Acid soils pH from Saturated Paste Extract (Salts) Oxidized pH – performed on possible Sulfidic soils (Fe sulfideSulfuric Acid)
END SECTION 2 ANSWER QUESTIONS
2. Read the section on 15-bar water retention/clay in the SSIR 45 (pg. 84). • a. In the upper three horizons of the Caribou pedon, the 15 bar/clay ratio > 0.6. Does this ratio suggest poor dispersion is occurring during particle size analysis or is it related to high water retention of the organic C? What is the range of organic C in the upper three horizons? • Poor dispersion may be occurring, but organic matter is responsible for increased water retention in the surface horizons. Organic carbon ranges from 2.28 to 0.93 percent.
15bar/clay ratio increases with depth for the first three horizons, while the organic carbon decreases. This indicates that the dispersion is becoming increasing poor in the upper horizons with depth. • The 15bar/clay ratio is >0.6 in over one half of the control section (25-100 cm). According to the rules of Soil Taxonomy, you would estimate %clay (for most soils) by the rule: • (1500 kPa water retention - % org. C) X 2.5 Control Section
2b. What is the reason for the elevated 15 bar/clay ratio in the 3Bqkm horizon of the Wildmesa?
Possibly secondary, non-crystalline silica • But the sample preparation treatment is “GP”, meaning the entire < 20 mm fraction was ground to < 2-mm. • “GP” is done within the laboratory for horizons in which the rock fragments can not be successfully separated from the soil materials, or the horizons is almost entirely rock fragment, such as a Cr or R horizon. • This treatment would alter or violate any standard relationships. • There is little interpretive meaning in particle size data on a horizon that has been “GP”ed.
3.On the Caribou pedon, which horizon has the highest acid oxalate-extractable Fe? Is this reasonable based on your knowledge of horizon suffixes and pedogenesis? Bs. Reasonable since non-crystalline or organically-chelated Fe is translocated in spodic type soils and accumulates in the Bs horizon.
SECTION 3 CEC and Bases Tier Salt Tier
CEC and Bases • Variable charge (pH dependent charge) • Clay: edge hydroxyls mineral surfaces • Sesquioxides and noncrystalline minerals • To small degree, crystalline minerals (octrahedral, kaolinite) • Humus: carboxyls, hydroxyls, phenols • Permanent charge • Clay (isomorphic substitution) • Al+++ substitutes for Si++++ in tetrahedral • Mg++ substitutes for Al+++ in octrahedral • Leaves net negative charge, cation adsorbed (CEC)
CEC and Bases • NH4OAc (pH7)—buffered neutral salt • Extracts adsorbed exchangeable cations • Also extracts soluble salts, and some carbonates and gypsum. • Saturate soil with NH4+--Bases are removed and 4 most concentrated bases analyzed • Exchange NH4+ with KCl – NH4 analyzed to determine CEC-7 • Sum of Bases = Ca+Mg+Na+K • CEC7= direct measurement of NH4+ adsorbed at pH7
KCl- extractable Al • active acidity • immediate lime requirement at existing CEC • Trivalent Al – primary exchangeableAl in soil • Solubility is function of soil pH • Trivalent Al drops off pH > 5.5 Relative distribution of the forms of soluble aluminum as a function of pH. (FromMarion, et al., 1976, used by permission of the Williams and Wilkins Company.)
Acidity • H extracted by BaCl2-TEA (pH 8.2) • Extractable acidity = potential acidity
Caribou ECEC= effective CEC = sum bases + KCl-Al (natural pH of soil in KCl) CEC-7= direct measurement of charge at pH 7 pH 7.0 – reference point – neutrality CEC8 (sum cats) = sum bases + acidity (charge at pH 8.2) pH 8.2, all hydroxyl Al neutralized pH 8.2, upper pH of soil if free CaCO3 ROT: Sum Bases < CEC-7 ECEC < CEC7 < CEC8.2
Predict Electrical Conductivity • Used to determine is soils are saline and require saturated paste • 5 g soil: 10 ml H2O; stand overnight • If EC > 0.25 dS m-1; do saturated paste • ROT: Predict EC < Sat Paste EC
Exchangeable Sodium Percentage (ESP) ESP = 100 [Naex – (Naws x (H2Ows/1000))] __________________________ CEC-7 where: ESP = Exchangeable sodium percentage Naex = Extractable Na (NH4OAc extractable Na+, cmol/kg) Naws = Water soluble Na (mmol/L) H2Ows = Water saturation percentage CEC-7 = CEC by NH4OAc, pH 7.0 (cmol/kg) Based on Na adsorbed on exchange sites
Sodium Adsorption Ratio SAR = [Na+] [Ca2+] + [Mg2+] where: SAR = Sodium Adsorption ratio Na+ = Water soluble Na+ (mmol (+) L-1) Ca2+ = Water soluble Ca2+ (mmol (+) L-1) Mg2+ = Water soluble Mg2+ (mmol (+) L-1) 1/2 2 Based on Na to Ca and Mg in Saturation Extract