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Coarse Fragments

Coarse fragments

Use the appropriate coarse fragment modifiers according to the following table when adequate volumes are observed. Abbreviations provided in Attachment 1 are acceptable substitutes for the proper modifier. Misspelled modifiers are not awarded points.

Table 5. The course fragment modifiers are applied using the following volumes. These are volumes of course fraction in the volume of soil.

Coarse fraction        Modifier

< 15%           none needed

15-34%              modifier

35-60%          very modifier

60%       extremely modifier

For this purpose the terms “gravel” and “cobble” are defined as below:

“Gravel” – a fragment 2-75 mm diameter; any lithology and shape; as a modifier – gravelly.

“Cobble” – a fragment 75 to 250 mm diameter; any lithology and shape; as a modifier – cobbly.

“Stone”  – a fragment 250 to 600 mm diameter;  any lithology and shape; as a modifier – stony.

If gravels and cobbles occur in the same horizon, the largest coarse fragment modifier is used unless the smaller size fragment exceeds 2 times the volume of the larger.

Coarse fragment modifiers should be recorded in the column labeled “CF Mod.”

Recording in the “Class” column for the soil textural class is incorrect and if not recorded in “CF Mod” will result in loss of points for both “Class” and “CF Mod.”


The following is a quote from:

Soil Survey Division Staff. 1993. Chapter 3 – Examination and Description of Soils. In Soil Survey Manual, United States Department of Agriculture Handbook No. 18.

Rock Fragments

Rock fragments are unattached pieces of rock 2 mm in diameter or larger that are strongly cemented or more resistant to rupture. Rock fragments include all sizes that have horizontal dimensions less than the size of a pedon.

Rock fragments are described by size, shape, and, for some, the kind of rock. The classes are pebbles, cobbles, channers, flagstones, stones, and boulders (table 3-11). If a size or range of sizes predominates, the class is modified, as for example: “fine pebbles,” “cobbles 100 to 150 mm in diameter,” “channers 25 to 50 mm in length.”

Gravel is a collection of pebbles that have diameters ranging from 2 to 75 mm. The term is applied to the collection of pebbles in a soil layer with no implication of geological formalization. The terms “pebble” and “cobble” are usually restricted to rounded or subrounded fragments; however, they can be used to describe angular fragments if they are not flat. Words like chert, limestone, and shale refer to a kind of rock, not a piece of rock. The composition of the fragments can be given: “chert pebbles,” “limestone channers.” The upper size of gravel is 3 inches (75 mm). This coincides with the upper limit used by many engineers for grain-size distribution computations. The 5-mm and 20-mm divisions for the separation of fine, medium, and coarse gravel coincide with the sizes of openings in the “number 4” screen (4.76 mm) and the “3/4 inch” screen (19.05 mm) used in engineering.

The 75 mm (3 inch) limit separates gravel from cobbles. The 250-mm (10-inch) limit separates cobbles from stones, and the 600-mm (24-inch) limit separates stones from boulders. The 150-mm (channers) and 380 mm (flagstones) limits for thin, flat fragments follow conventions used for many years to provide class limits for plate-shaped and crudely spherical rock fragments that have about the same soil use implications as the 250-mm limit for spherical shapes.

Rock Fragments in the Soil

Historically, the total volume of rock fragments of all sizes has been used to form classes. The interpretations program imposes requirements that cannot be met by grouping all sizes of rock fragments together. Furthermore, the interpretations program requires weight rather than volume estimates. For interpretations, the weight percent >250, 75-250, 5-75 and 2-5 mm are required; the first two are on a whole soil basis, and the latter two are on a <75 mm basis. For the >250 and 75-250 mm, weighing is generally impracticable. Volume percentage estimates would be made from areal percentage measurements by point-count or line-intersect methods. Length of the transect or area of the exposure should be 50 and preferably 100 times the area or dimensions of the rock fragment size that encompasses about 90 percent of the rock fragment volume. For the <75 mm weight, measurements are feasible but may require 50-60 kg of sample if appreciable rock fragments near 75 mm are present. An alternative is to obtain volume estimates for the 20-75 mm and weight estimates for the <20 mm. This is favored because of the difficulty in visual evaluation of the 2 to 5 mm size separations. The weight percentages of 5-20 and 2-5 mm may be converted to volume estimates and placed on a <75 mm base by computation. The adjectival form of a class name of rock fragments (table 3-11) is used as a modifier of the textural class name: “gravelly loam,” “stony loam.”

Table 3-11. Terms for rock fragments

Shape and size1 Noun Adjective
Spherical, cubelike, or equiaxial:    
2-75 mm diameter Pebbles Gravelly
2-5 mm diameter Fine Fine gravelly
5-20 mm diameter Medium Medium gravelly
20-75 mm diameter Coarse Coarse gravelly
75-250 mm diameter Cobbles Cobbly
250-600 mm diameter Stones Stony
>600 mm diameter Boulders Bouldery
Flat:    
2-150 mm long Channers Channery
150-380 mm long Flagstones Flaggy
380-600 mm long Stones Stony
>600 mm long Boulders Bouldery
1. The roundness of the fragments may be indicated as angular (strongly developed faces with sharp edges), irregular (prominent flat faces with incipient rounding or corners), subrounded (detectable flat faces with well-rounded corners), and rounded (flat faces absent or nearly absent with all corners.

The following classes, based on volume percentages, are used:

Less than 15 percent: No adjectival or modifying terms are used in writing for contrast with soils having less than 15 percent pebbles, cobbles, or flagstones. The adjective “slightly” may be used, however, to recognize those soils used for special purposes.

15 to 35 percent: The adjectival term of the dominant kind of rock fragment is used as a modifier of the textural term: “gravelly loam,” “channery loam,” “cobbly loam” (fig. 3-17).

fig3-17_large

35 to 60 percent: The adjectival term of the dominant kind of rock fragment is used with the word “very” as a modifier of the textural term: “very gravelly loam,” “very flaggy loam” (fig. 3-18).

fig3-18_large

More than 60 percent: If enough fine earth is present to determine the textural class (approximately 10 percent or more by volume) the adjectival term of the dominant kind of rock fragment is used with the word “extremely” as a modifier of the textural term: “extremely gravelly loam,” “extremely bouldery loam.” If there is too little fine earth to determine the textural class (less than about 10 percent by volume) the term “gravel,” “cobbles,” ‘stones,” or “boulders” is used as appropriate.


 

CEC of the Clay and Fine Silt Fractions by Excess Salt Method

Background:  Read Chapter 5 in Jackson (2005) and this procedure.

Jackson, M. L. 2005. Soil chemical analysis: advanced course. Parallel Press, UW-Madison Libraries.

Objectives:  Measure CEC of the clay and fine silt fractions by the excess salt method.  Assess effects of pH on CEC.

Materials

  • Air-dry Na-saturated clay
  • Air-dry Na-saturated fine silt (2-20 µm)
  • 100 ml centrifuge tubes
  • 100 ml volumetric flasks with funnels
  • Plastic bottles with screw top lids for displaced solutions
  • 1.0 M CaCl2
  • 1.0 M MgCl2
  • 0.005 M CaCl2
  • 1 M NaOAc, pH 4
  • 1 M NaOAc, pH 7
  • Ethanol

Excess Salt Method

 

  1. Preweigh centrifuge tubes (to 0.0001 g) labeled with a Sharpie directly on the tube, no tape. Weigh about 0.2000 g of clay or fine silt into tubes.  Prepare four samples of each clay and fine silt (total eight tubes).  Weigh and record the weights of empty tubes and tubes plus clay or silt.

 

  1. To two tubes of each clay or silt, add 20 ml pH 4, 1 M NaOAc and to the other two tubes of clay or silt, add 20 ml pH 7, 1 M NaOAc. Sonicate in ultrasonic bath for 2 minutes to mix.  Centrifuge at 2000 RPM for 10 minutes.  Decant supernatant into clear beakers to insure that no sample is lost.  Discard supernatant.

 

  1. Repeat washing with 20 ml 1M NaOAc solutions, disperse (ultrasonic bath for 2 min +/- stirring with glass rod, but rinse stirring rod completely to avoid losing any sample) centrifuge, decant into beaker and measure pH with a pH meter, until supernatant pH is that of the added buffer (minimum of two washings, but this may be all that is needed).

 

  1. Add 20 ml 1.0 M CaCl2 to each tube, disperse with ultrasonic bath for 3 min (+/- stirring with glass rod).  Centrifuge at 2000 RPM for 10 min.  Discard supernatant.

 

  1. Wash, disperse, and centrifuge three times with 20 ml 0.005 M CaCl2 . Record the pH of the third wash.  We assume this brings the sample into equilibrium with the 0.005 M CaCl2.  Be careful that no sample is lost.

 

  1. Blot any large drops of solution in the tubes with Kim-Wipes and immediately weigh tubes plus wet samples (0.0001 g). Record weights.

 

  1. Add 20 ml 1.0 M MgCl2 to each tube. Disperse carefully and thoroughly (ultrasonic bath, 3 min.).  Centrifuge at 2000 RPM for 10 min.

 

  1. Decant supernatant into 100 ml volumetric flasks. Repeat three more times (total of four washes with 1.0 M MgCl2), each time collecting the supernatant in the 100 ml volumetric flask.  Bring flask to volume with 1.0 M MgCl2

 

  1. Mix flask contents thoroughly and transfer to plastic bottles. Ca to be determined by AA or ICP.

 

  1. Disperse samples with 20 ml ethanol and sonicate for 3 min. Centrifuge at 2000 RPM for 10 min.  Decant into clear beaker to ensure that no dispersion has occurred.  Discard clear supernatant.  Blot any large drops of solution in the tubes and weigh tubes immediately (0.0001 g).  Record weights.  Compare to weight in step 6.

 

  1. Oven-dry tubes overnight at 105 °C, cool in a desiccator, and weigh (0.0001g). Record weights. 

 

  1. Rinse and acid wash the volumetric flasks.

 

  1. Calculate CEC of clay and fine silt fractions. Total Ca is exchangeable Ca plus Ca in the 0.005 M CaCl(i.e., the excess salt)­­.  Ca in the liquid is calculated from the mass (hence, volume) and Ca concentration in the solution.  Solution mass is calculated from difference in tube weights:  step 6 minus step 11.  Sample mass on an oven-dry basis is calculated from step 11 minus original tube mass.

 

Cation Exchange Capacity by Barium Saturation – Calcium Replacement Method

CATION EXCHANGE CAPACITY

Barium Saturation – Calcium Replacement Method

Source: University of California Division of Agriculture and Natural Resources

Scope and Application

The method determines the cation exchange capacity (CEC) of soil as described by Rible and Quick (19601) and Janitzky (19862). The soil is quantitatively displaced of all exchangeable cations with Ba, followed by four deionized rinses to remove excess Ba. A known quantity of calcium is then exchanged for Ba and excess solution calcium is measured. CEC is determined by the difference in the quantity of the Ca added and the amount found in the resulting solution. The method has a detection limit of approximately 1.0meq l00g-1 (soil basis) and is generally reproducible within ±7%.

Equipment

  1. Analytical balance: l000g capacity, resolution ±.0.01g.
  2. Mechanical shaker.
  3. Repipette dispenser(s), calibrated to 10 and 15mL.
  4. 150mL glass beakers.
  5. Whatman No. 2 filter paper.
  6. Heating plate or steam table (90° C).
  7. Atomic Absorption Spectrometer (AAS), Perkin Elmer 2380.
  8. Peristaltic (Istamac) two channel pump diluter with variable speed, 0-100rpm.

Reagents

  1. Deionized water, ASTM Type I grade.
  2. Barium Acetate Reagent, 1.0 N pH 7.0. Dissolve 1280g of reagent grade barium acetate (Ba(C2H3O2)2 in 9000mL of distilled water. Adjust pH to 7.0 with acetic acid or barium hydroxide.
  3. Calcium Sulfate Reagent. Dissolve 10.0g of reagent grade calcium sulfate (CaSO4.2H2O) in 1 0L of deionized water and place on magnetic stir plate with stir bar for one hour. Settle for twelve hours.
  4. Standard calibration solution, calcium. Prepare six calibration standards, concentration range 0.5-400mg L-1 of calcium made up in 5% nitric acid (v/v) made from 1000mg L-1 standard solution.

Procedure

  1. Weigh out 4.00±0.05g of air dry soil into a 150mL beaker. Add 15.0mL of 1.0 N Barium acetate reagent using repipette dispenser (see comments #1 Р#3).
  2. Place extraction vessel(s) on a steam table for 30 minutes.
  3. Immediately filter, refilter if filtrate is cloudy.
  4. Leach with 10.0mL Barium acetate reagent and then wash with four 50mL increments of deionized water. Allow to drain between increments.
  5. Air dry filtrate and filter for twelve hours on lab bench or dryingoven for two hours at 50ºC.
  6. Transfer to second extraction rack vessel and add 100.0±0.1mL of Calcium sulfate reagent. Place on mechanical shaker for twenty minutes.
  7. Filter and collect extract. Analyze Ca in both soil filtrate and Calcium sulfate reagent by atomic absorption spectrometry and pump diluter in accordance with standard instrument operating protocol using the prepared standard working solutions and report results as mg L-1 calcium in solution.

Calculations

Cation Exchange Capacity can be calculated by:

CEC meq/l00g = [(Calcium Sulfate Ca – Soil Filtrate Ca) x 0.1 L x 100]/4

Record CEC results to three significant digits.

Comments

  1. Check calibration of repipette dispenser, recalibrate using analytical balance as necessary.
  2. For samples having CEC concentrations (>60meq 100g-1) decrease soil sample size to 2.0g. Cation exchange capacity can also be reported as cmol kg-1 which equal to meq 100g-1.
  3. Soils containing large quantities of gypsum, should be washed extensively with 0.01 N NaCl to remove calcium sulfate.

Literature

Soil Factors – FFA Land CDE

Soil Factors – FFA Land CDE

By Donald G. McGahan, Ph.D.
Revised: April 9, 2017


There really is no concrete right or wrong method to determine soil texture in the field. We use laboratory methods to “truth” ourselves as professionals.

The flow diagram in the Land Judging in Oklahoma manual is pretty good. I teach collegiate students at a different level and compare the FFA high school five (5) textural class determination to the three (3) class and twelve (12) class methods.

I have made the blog post comparing the three (3), five (5), and twelve (12) class methods available on this web log at http://bionicprofessor.com/future-farmers-of-america-ffa/soil-apparent-texture-class/

There really is little substitute for lots of practice.

Interpretation of Soil Factors – FFA Land CDE

Questions about Interpretation of Soil Factors

By Donald G. McGahan, Ph.D.
Revised: April 9, 2017


Previously Texas had it’s own guide to FFA Land Career Development Events, but the Texas FFA Board of Directors (BOD) have decided to use the Land Judging Manual for Oklahoma. This decision might have been driven by a desire to adopt the State Manual where the National FFA events have been customarily been hosted.

In an instance where the surface soil texture is moderately coarse and the subsoil texture is course. The Texas and Oklahoma Guides seem to have a contradiction with respect to permeability. I have heard over the last few years that Oklahoma rules trump Texas rules. What do I do?

Texas Guide said on page 6 “permeability should be based upon the most limiting horizon regardless of its position in the soil profile.” The Oklahoma Guide says in the second paragraph of Permeability on page 5 left hand column, and in the shaded box on page 5 at the top of the right hand column:

 ...the subsoil texture sample in the box will be used to determine permeability.

Trust that the Event Steward would have liked to choose a different site that makes their efforts less stressful. However, with the time investment necessary to get permission to excavate from Texas811locate and the excavation time itself it is often logistically unsound to move the site when these conditions present themselves.

The career soil scientists chooses the most limiting horizon as stated in the Texas Guide. However, Texas no longer uses the Texas Guide. It is retired by the Texas FFA BOD regardless of it being more correct. The FFA Land CDE in Texas FFA now uses the Oklahoma guide. Therefore, the marked subsoil texture sample in the box, bag, or bucket is to be used to determine the permeability.

Soils influenced by over-banking of water courses –either in the past or presently– are not uncommon in many parts of Texas. Often this results in a surface texture that is finer –heavier– than the subsoil texture. This one is not going away. Event sites will continue to be excavated on these landscapes.

Please have patience with the professionals who are stewards at these excavations. It is difficult to adjust to recording incorrect information for the sake of an FFA Event.

My question involves permeability. Again, in the Oklahoma guide, permeability is defined as a function of texture. Coarse texture has rapid permeability, moderately coarse and medium textured soil has moderate permeability, moderately fine soil has slow permeability, and fine soil has a very slow permeability. Is this how we determine permeability in our Texas State contest? As I read the Oklahoma book, it does not mention soil structure in determining permeability. The permeability is strictly based upon the soil texture. I was hoping you could clarify this for me.

Since adoption of the Land Judging in Oklahoma manual by the FFA BOD structure is no longer considered for the FFA Land CDE. Collegiate judgers do account for structure. Professional judgers also do account for structure. NOT the highschool FFA Land CDE. Just subsoil texture that is presented and marked in the bag, box, or bucket by the Event Steward.

Other Factors – FFA Land CDE

By Donald G. McGahan, Ph.D.
Revised: April 9, 2017


I have always been taught and told that wetness as a factor makes a site a land class 3. However, I cannot find that written in any manual. Is this correct?
No. Wetness keeps the land out of Class I. Installing drainage systems on wet Class V land is typically not economical and is not recommended for the FFA Land CDE. Under Other Factors on page 8 of the Land Judging Manual Oklahoma under Wetness it mentions a category of “moderately-wet” as if it was a Wetness Class. Coaches and the high school kids likely do not have any idea what that is or how to determine moderately-wet from any other. For simplicity sake, if you see the site (or field) conditions having  Wetness, you can proceed using practice 18 under treatments unless it is a Deep soil as determined in Part 1. For Deep soils that have Wetness the condition sheet will have to provide an alternate Surface Runoff term. It is probably self evident that a soil with Wetness might have Very Slow Surface Runoff but this may not be the case! All slopes classes are allowed in Table 5. Therefore, Deep soils with Wetness will have to have a Surface Runoff given to modify the Wetness as follows:

Wetness: Mod. Wet
Wetness: Wet
Wetness: Flooding

The wording in the Land Judging Manual Oklahoma is contradictory, but this is perhaps the best way to handle this. This does not get the student out of the box of having contradictory and conflicting Surface Runnoff terms used in Part 1 and Part II. To further reduce confusion the official might consider adding to the condition sheet the desired response for Surface Runoff in Part I. For more information not specific to the FFA Land CDE, but for edification 🙂 Wetness is actually a term used in describing Drainage Class, and the Classes —or categories– of Drainage Class are used in arable and non-arable soils. I have a thumbnail description of the Soil Drainage Categories at http://bionicprofessor.com/soil-drainage-classes/ From the National Soil Survey Handbook

618.16  Drainage Class

A.  Definition.—“Drainage class” identifies the natural drainage condition of the soil.  It refers to the frequency and duration of wet periods.

B.  Classes.—The eight natural drainage classes are listed below.  Chapter 3 of the Soil Survey Manual provides a description of each natural drainage class.

(1)  Excessively drained
 (2)  Somewhat excessively drained
 (3)  Well drained
 (4)  Moderately well drained
 (5)  Somewhat poorly drained
 (6)  Poorly drained
 (7)  Very poorly drained
 (8)  Subaqueous

C.  Significance.—Drainage classes provide a guide to the limitations and potentials of the soil for field crops, forestry, range, wildlife, and recreational uses.  The class roughly indicates the degree, frequency, and duration of wetness, which are factors in rating soils for various uses.

D.  Estimates.—Infer drainage classes from observations of landscape position and soil morphology.  In many soils the depth and duration of wetness relate to the quantity, nature, and pattern of redoximorphic features.  Correlate drainage classes and redoximorphic features through field observations of water tables, soil wetness, and landscape position.  Record the drainage classes assigned to the series.

E.  Entries.—Enter the drainage class name for each map unit component.  Use separate map unit components for different drainage class phases or for drained versus undrained phases, where needed.”

End


In Land on the additional info of the condition sheet if it were written occasional flooding would it be a major factor and class V. I believe flooding is flooding. I can’t find anywhere in the land section where it states what occasional or frequent means.
I am going to use the USDA-NRCS National Soil Survey Handbook  Part 618 (Subpart A) at 618.30 as part of the information to address this. First, contradictions do exist in the Land Judging Manual Oklahoma.

strong>Flooding is an "Other Factor" that can be added to the FFA Land CDE condition sheet for a field and on page 8 it states:
Flooding is not considered on slopes over 3 percent. Flooding would place an area in Class V. Practices 14 and 20 would be possible treatments.

A contradiction for Deep soils is that the guide also has Flooding listed as a Surface Runoff within Table 5 on page 11. It is likely that a judger will be confused here because on page 5 the guide states:

Four classes of runoff are recognized in Oklahoma land judging.

These four classes of runoff listed on page 5 are Rapid, Moderate, Slow, and Very Slow. There is no mention of the Runoff Classes of Mod. Wet, Wet, and Flooding listed in Table 5. Furthermore, in Table 5 it states that “All” slopes might fit in a “Surface Runoff” of Flooding. As a career soil judgers treat Drainage Class (often confused with Wetness) and Flooding separately even though they are –like so many things– related.

Flooding Frequency Class.—Flooding frequency class indicates the number of times flooding occurs over a period of time.

The Flooding Frequency Class of “Frequent” is:

Flooding is likely to occur often under usual weather conditions; more than a 50 percent chance of flooding in any year (i.e., 50 times in 100 years), but less than a 50 percent chance of flooding in all months in any year.

The Flooding Frequency Class of “Occasional” is:

Flooding is expected infrequently under usual weather conditions; 5 to 50 percent chance of flooding in any year or 5 to 50 times in 100 years.

The “Land Judging in Oklahoma” states “or frequent flooding” as one of the limitations that might place it in Class V and “unsuitable for cultivation. However, in Table 5 no mention of “Flooding Frequency Class” are evoked. Just occasional flooding alone is not enough to place it into Class V for the FFA Land CDE. But, note that if it were deemed to have “very poor surface and internal drainage” that can also place it in Class V for the FFA Land CDE. Perhaps where Land and Homesite CDE’s are separated, as they often are in Texas, there is a disservice to the student. Try reading Page 18 in the Homesite CDE section for more on what the Guides authors were intending. What is internal drainage? Drainage class” identifies the natural drainage condition of the soil. It refers to the frequency and duration of wet periods. “Very poorly drained” is a class within the “Drainage Class” classification.

618.16  Drainage Class

A.  Definition.—“Drainage class” identifies the natural drainage condition of the soil.  It refers to the frequency and duration of wet periods.

B.  Classes.—The eight natural drainage classes are listed below.  Chapter 3 of the Soil Survey Manual provides a description of each natural drainage class.

(1)  Excessively drained
 (2)  Somewhat excessively drained
 (3)  Well drained
 (4)  Moderately well drained
 (5)  Somewhat poorly drained
 (6)  Poorly drained
 (7)  Very poorly drained
 (8)  Subaqueous

C.  Significance.—Drainage classes provide a guide to the limitations and potentials of the soil for field crops, forestry, range, wildlife, and recreational uses.  The class roughly indicates the degree, frequency, and duration of wetness, which are factors in rating soils for various uses.

D.  Estimates.—Infer drainage classes from observations of landscape position and soil morphology.  In many soils the depth and duration of wetness relate to the quantity, nature, and pattern of redoximorphic features.  Correlate drainage classes and redoximorphic features through field observations of water tables, soil wetness, and landscape position.  Record the drainage classes assigned to the series.

E.  Entries.—Enter the drainage class name for each map unit component.  Use separate map unit components for different drainage class phases or for drained versus undrained phases, where needed.”

For edification you might want to see my web blog on soil drainage classes at http://bionicprofessor.com/soil-drainage-classes/. End


 

Mechanical Land Treatments – FFA Land CDE

By Donald G. McGahan, Ph.D.
Revised: April 9, 2017


In contests, officials marks control brush and trees on land classes 5-7 on any size brush. In the Oklahoma manual, it only mentions 1-4. Do you control brush and trees for non-cultivated soil?

I assuming you meant non-cultivated to be non-arable. Where arable is Class I to IV (1 to 4) lands. Specifically, I interpret the question to be asking for the possible Classes of Lands that Number 14 “Control Brush or Trees” under “Mechanical Land Treatment” on the judging card is a possible choice.

See the Land Judging Manual Oklahoma. Quickly scan the Tables (for instance Table 1 on page 9) and identify that rows on the table that have Capability Class VI (6) have number 14 as a “possible mechanical treatment.”

While Class I through IV (4) are considered arable land, non-arable land may benefit from removal of woody vegetation to increase grass growth for livestock, and to decrease woody shrubs from competing for water and nutrients in Timber production or post lots.

Your question did not specifically address a nuance in the paragraph on page 7 of the Land Judging Manual in Oklahoma. “The purpose is to improve the desirable negative cover by removing or killing undesirable brush and trees (Class I to IV).” That passage curiously makes no mention of how one is to determine the size, but the following passage does. “… should not be used when bushy plants and trees are less than two inches (2”) in diameter at 5 feet above ground (Class I to VI).” Note the second passage includes up to Class VI (6) land.

It is an admittedly confusing paragraph.

For simplicity sake if woody (brushy plants and trees is the terminology used in the guide here) is present, is equal to or greater than 2 inches in diameter at five feet above the ground, and the factors Desires Post or Wood Lot or Timber production are not on the condition sheet for that field, number 14 under mechanical land treatments must be considered up to Class VI (6).

This contest does not have guidance for Class VIII land and you can expect to not see it at an FFA Land CDE event. Note also that there is no guidance to use number 14 on Class VII land.

 

A question arose on class 5 land -or- higher, do you control dewberry (or ANY other brush for that matter) when it is so small that you cannot even see it (smaller than the surrounding grass, clover and vetch)?

The argument presented by the coaches to the steward was that since the field is non-arable, that ANY woody (including woody vines) should then receive brush control.

“Control Brush or Trees” under “Mechanical Land Treatment”

Presumably this would be by both mechanical and chemical means of control at the non-arable sites (Class V and VI).

Since the dewberry was smaller than the surrounding clover, vetch, ryegrass, and rescue grass (and did not have any blooms), the steward did not see it during the set-up of the contest.

The stewards argument was that if the dewberry was taller and plainly visible, then you would consider control. Many stewards have heard the teacher’s argument before on Class V or higher.

Typically, stewards try to include some trees or other brush in the field to make it plainly clear.

The way the Land Judging in Oklahoma manual is structured it leaves ambiguity on page 7:

The purpose is to improve the desirable negative cover by removing or killing undesirable brush and trees (Class I to IV).”

That passage curiously makes no mention of how one is to determine the size, but the following passage does.

 “…should not be used when bushy plants and trees are less than two inches (2”) in diameter at 5 feet above ground (Class I to VI).”

Note the second passage includes up to Class VI (6) land.

For consistency sake using the latter passage for Land and Classes I to VI (1 to 6) and not using it for less than 2 inch woody species is desirable.

For terrace and farming on a contour, you mark when slopes are greater than 1% except when course textured soil is present. Is this if the top soil or subsoil is coarse?

It is the surface soil texture that is used.

 

 

 

Questions asked by FFA Coaches

By Donald G. McGahan, Ph.D.
Revised: April 9, 2017

FFA Land CDE Questions

The questions and answers presented are not a comprehensive list.
Limited posting of questions and answers are presented here and mostly as a reference since these are frequent, or troublesome, questions.
Often the answers go beyond the actual FFA Land CDE event. The more flushed answers are meant to help as edification for the coaches and to show that there is so much more to Land Evaluation that what is presented in the FFA Land CDE. That is not to limit the information to coaches eyes only, it is just to state that it is not written to address the high school judger directly though there is no reason the high school judger might not want to try to approach this material. Finally, little effort is invested in editing these for clarity and proper grammar or spelling.

Soil Factors
Interpretation of Soil Factors

Part II – Mechanical Land Treatments
Other Factors

 

Organic Carbon – modified Tiurin’s Method

Wet Oxidation Soil Organic MatterOrganic Carbon by Tiurin’s Method (modified) a wet oxidation

Donald G. McGahan, Ph.D.

Reference: Mebius, L.J. 1960. A Rapid Method for the Determination of Organic Carbon in the Soil. Analytica Chimica Acta. 22: 120-124.

This determination of soil organic matter is by oxidizing it with potassium dichromate (K2Cr2O7). The reaction generates heat when oil of vitriol (sulfuric acid: H2SO4) are added to potassium dichromate.

3 C + 2 K2Cr2O7 + 8 H2SO4 → K2SO4 + 2 Cr2(SO4)3 + 8 H2O + 3 CO2

Instructions

  1. Weigh out 0.3 g of soil.
  2. Transfer the sample into the 100 ml Erlenmeyer flask.
  3. Pipette pour 10 ml of 0.4 N potassium dichromate (K2Cr2O7) into the flask.
  4. Put 2-3 glass boiling pellets into the flask, put funnels on the flasks (reciprocal evaporating dish).
  5. Put the flask on a beating plate under the ventilating hood and boil for 5 minutes taking care not to overheat the sample (timing from the beginning of the boiling).
  6. After 5 minutes of boiling, cool the samples to room temperature.
  7. Transfer the sample quantitativly into a 300 ml Erlenmeyer flask.
  8. Add 2 ml of 85% orthophosphorus acid (H3PO4) and 5 drops of of N-phenylanthranilic acid dissolved in a 0.2% Na2CO3 solution (fenylenediamina).
  9. Titrate the sample with 0.1 Mohr’s salt [ferrous sulphate – FeSO4⋅(NH4)2] until a green color develops.
  10. Conduct the same procedure with the blank.
  11. Repeat with two more replicates of the sample.

 6 Fe(NH4)2SO4 + K2Cr2O7 + H2SO4 → 3 Fe2(SO4)3 + Cr2(SO4)3 + K2SO4 + 7 H2O + 6 (NH4)2SO4

Results

Calculation to percentage of organic carbon (OC) formula:

% OC = (a–b) x 0.0003 x 100 / n

where:

  • a = ml of Mohr’s salt titrated in blank
  • b = ml of Mohr’s salt titrated in sample
  • n = weight of the sample (g)

presume that 1 ml of 0.1 N Mohr’s salt equals 0.0003 g of organic carbon.

To calculate % organic matter (% OM) from % organic carbon (% OC) used the “Van Bemmelen factor” of 1.724.

μ of % OC x 1.724 = % OM

Clay Percentage

For the Region IV SASES[1] Collegiate Soil Judging Contest Clay Percentage

(See Chapter 3, Soil Survey Manual)

Clay content:
as a weight percentage of the soil fines should be recorded in the “Clay%” column.

Actual %Allowed Deviation %
< 20+/- 2
20 to 40+/- 3
> 40+/- 4

The textural class and % clay for each horizon will be determined by the judges and supported by laboratory data. Soil textural classes as defined in the Soil Survey Manual Chapter 3 (1993) and their official abbreviations (supplied to contestants as part of Attachments 1 and 2) are to be used. Deviation from standard nomenclature will be incorrect (i.e., sandy silt or silty loam instead of the proper silt loam).

Credit for sand, loamy sand, and sandy loam textures will NOT be given if sand modifiers are required and not provided (i.e. very fine, fine, coarse, or very coarse).

Textural class:
record in the “Class” column.

 

TextureAbreviationTextureAbreviation
Coarse sandCOSFine sandy loamFSL
SandSVery fine sandy loamVFSL
Fine sandFSLoamL
Very fine sandyVFSClay loamCL
Loamy coarse sandLCOSSiltSI
Loamy sandLSSilt loamSIL
Loamy fine sandLFSSilty clay loamSICL
Loamy very fine sandLVFSSilty claySIC
Coarse sandy loamCOSLSandy clay loamSCL
Sandy loamSLSandy claySC
ClayC

 


The following is a quote from:

Soil Survey Division Staff. 1993. Chapter 3 – Examination and Description of Soils. In Soil Survey Manual, United States Department of Agriculture Handbook No. 18 pp136-143. [last visited May 8, 2016]

Particle Size Distribution

This section discusses particle distribution. The finer sizes are called fine earth (smaller than 2 mm diameter) as distinct from rock fragments (pebbles, cobbles, stones, and boulders). Particle-size distribution of fine earth or less than 2 mm is determined in the field mainly by feel. The content of rock fragments is determined by estimating the proportion of the soil volume that they occupy.

Soil Separates

The United States Department of Agriculture uses the following size separates for the <2 mm mineral material:

Name Size (mm)
Very coarse sand: 2.0-1.0 mm
Coarse sand: 1.0-0.5 mm
Medium sand: 0.5-0.25 mm
Fine sand: 0.25-0.10 mm
Very fine sand: 0.10-0.05 mm
Silt: 0.05-0.002 mm
Clay: < 0.002 mm

Figure 3-14 compares the USDA system with others.

fig3-14_large

Figure 3-15 illustrates classes of soil particles larger than silt.

fig3-15_large

Soil Texture

Soil texture refers to the weight proportion of the separates for particles less than 2 mm as determined from a laboratory particle-size distribution. Field estimates should be checked against laboratory determinations and the field criteria should be adjusted as necessary. Some soils are not dispersed completely in the standard particle size analysis. For these, the field texture is referred to as apparent because it is not an estimate of the results of a laboratory operation. Apparent field texture is a tactile evaluation only with no inference as to laboratory test results. Field criteria for estimating soil texture must be chosen to fit the soils of the area. Sand particles feel gritty and can be seen individually with the naked eye. Silt particles cannot be seen individually without magnification; they have a smooth feel to the fingers when dry or wet. In some places, clay soils are sticky; in others they are not. Soils dominated by montmorillonite clays, for example, feel different from soils that contain similar amounts of micaceous or kaolintic clay. Even locally, the relationships that are useful for judging texture of one kind of soil may not apply as well to another kind.

The texture classes (fig. 3-16) are sand, loamy sands, sandy loams, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay. Subclasses of sand are subdivided into coarse sand, sand, fine sand, and very fine sand. Subclasses of loamy sands and sandy loams that are based on sand size are named similarly.

fig3-16_large

Definitions of the soil texture classes follow:

Sands.—More than 85 percent sand, the percentage of silt plus 1.5 times the percentage of clay is less than 15.

Coarse sand. A total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand.

Sand. A total of 25 percent or more very coarse, coarse, and medium sand, a total of less than 25 percent very coarse and coarse sand, and less than 50 percent fine sand and less than 50 percent very fine sand.

Fine sand. 50 percent or more fine sand; or a total of less than 25 percent very coarse, coarse, and medium sand and less than 50 percent very fine sand.

Very fine sand. 50 percent or more very fine sand.

Loamy sands.—Between 70 and 91 percent sand and the percentage of silt plus 1.5 times the percentage of clay is 15 or more; and the percentage of silt plus twice the percentage of clay is less than 30.

Loamy coarse sand. A total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand.

Loamy sand. A total of 25 percent or more very coarse, coarse, and medium sand and a total of less than 25 percent very coarse and coarse sand, and less than 50 percent fine sand and less than 50 percent very fine sand.

Loamy fine sand. 50 percent or more fine sand; or less than 50 percent very fine sand and a total of less than 25 percent very coarse, coarse, and medium sand.

Loamy very fine sand. 50 percent or more very fine sand.

Sandy loams.—7 to 20 percent clay, more than 52 percent sand, and the percentage of silt plus twice the percentage of clay is 30 or more; or less than 7 percent clay, less than 50 percent silt, and more than 43 percent sand.

Coarse sandy loam. A total of 25 percent or more very coarse and coarse sand and less than 50 percent any other single grade of sand.

Sandy loam. A total of 30 percent or more very coarse, coarse, and medium sand, but a total of less than 25 percent very coarse and coarse sand and less than 30 percent fine sand and less than 30 percent very fine sand; or a total of 15 percent or less very coarse, coarse, and medium sand, less than 30 percent fine sand and less than 30 percent very fine sand with a total of 40 percent or less fine and very fine sand.

Fine sandy loam. 30 percent or more fine sand and less than 30 percent very fine sand; or a total of 15 to 30 percent very coarse, coarse, and medium sand; or a total of more than 40 percent fine and very fine sand, one half or more of which is fine sand, and a total of 15 percent or less very coarse, coarse, and medium sand.

Very fine sandy loam. 30 percent or more very fine sand and a total of less than 15 percent very coarse, coarse, and medium sand; or more than 40 percent fine and very fine sand, more than one half of which is very fine sand, and total of less than 15 percent very coarse, coarse, and medium sand.

Loam.—7 to 27 percent clay, 28 to 50 percent silt, and 52 percent or less sand.

Silt loam. 50 percent or more silt and 12 to 27 percent clay, or 50 to 80 percent silt and less than 12 percent clay.

Silt. 80 percent or more silt and less than 12 percent clay.

Sandy clay loam. 20 to 35 percent clay, less than 28 percent silt, and more than 45 percent sand.

Clay loam. 27 to 40 percent clay and more than 20 to 46 percent sand.

Silty clay loam. 27 to 40 percent clay and 20 percent or less sand.

Sandy clay. 35 percent or more clay and 45 percent or more sand.

Silty clay. 40 percent or more clay and 40 percent or more silt.

Clay. 40 percent or more clay, 45 percent or less sand, and less than 40 percent silt.

The texture triangle (fig. 3-16) is used to resolve problems related to word definitions, which are somewhat complicated. The eight distinctions in the sand and loamy sand groups provide refinement greater than can be consistently determined by field techniques. Only those distinctions that are significant to use and management and that can be consistently made in the field should be applied.

Groupings of soil texture classes.—The need for fine distinctions in the texture of the soil layers results in a large number of classes of soil texture. Often it is convenient to speak generally of broad groups or classes of texture. An outline of soil texture groups, in three classes and in five, follows. In some areas where soils are high in silt, a fourth general class, silty soils, may be used for silt and silt loam.

General Termsa Texture Classes
Sandy soil materials:
Coarse-textured Sands (coarse sand, sand, fine sand, very fine sand) Loamy sands (loamy coarse sand, loamy sand, loamy fine sand, loamy very fine sand)
Loamy soil materials:
Moderately coarse-textured Coarse sandy loam, sandy loam, fine sandy loam
Medium-textured Very fine sandy loam, loam, silt loam, silt
Moderately fine-textured Clay loam, sandy clay loam, silty clay loam
Clayey soils:
Fine-textured Sandy clay, silty clay, clay
a. These are loamy, and clayey texture groups, not the sandy, loamy, and clayey particle-size classes defined in Soil Taxonomy.

Organic Soils

Layers that are not saturated with water for more than a few days at a time are organic if they have 20 percent or more organic carbon. Layers that are saturated for longer periods, or were saturated before being drained, are organic if they have 12 percent or more organic carbon and no clay, 18 percent or more organic carbon and 60 percent or more clay, or a proportional amount of organic carbon, between 12 and 18 percent, if the clay content is between 0 and 60 percent.

The kind and amount of the mineral fraction, the kind of organisms from which the organic material was derived, and the state of decomposition affect the properties of the soil material. Descriptions include the percentage of undecomposed fibers and the solubility in sodium pyrophosphate of the humified material. A special effort is made to identify and estimate the volume occupied by sphagnum fibers, which have extraordinary high water retention characteristics. When squeezed firmly in the hand to remove as much water as possible, sphagnum fibers are lighter in color than fibers of hypnum and most other mosses.

Fragments of wood more than 2 cm across and so undecomposed that they cannot be crushed by the fingers when moist or wet are called wood fragments. They are comparable to rock fragments in mineral soils and are described in a comparable manner.

Muck (sapric) is well-decomposed, organic soil material. Peat (fibric) is relatively undecomposed, organic material in which the original fibers constitute almost all of the material. Mucky peat (hemic) is material intermediate between muck and peat.


Date last modified: May 7, 2016.
Donald G. McGahan, Ph.D.
Work of Authorship


[1]Students of Agronomy, Soils, and Environmental Sciences

Graduate Assistantship: Soil Science

Position Announcement:
Starting Summer/Fall 2016

Graduate Research Assistant: Soil

Position Summary:
The Department of Wildlife, Sustainability, and Ecosystem Sciences at Tarleton State University at Stephenville, Texas, is seeking a graduate student at Masters of Science level in Natural Resources with a focus on soil. Responsibilities will include duties as a teaching assistant and will also include the learner spearheaded research into landscape distribution relationships of soils, specifically a catena.

Qualification:
The candidate(s) should have degree/s in soils / agricultural /environmental / natural resources / civil, environmental, or related engineering discipline with strong background in soils. Fluency in English, and the ability to work in an interdisciplinary team are further essential requirements.

Salary:
The salary/stipend is $1,200 per month for a 9 month academic calendar. Subsequent summers a stipend may be possible if extramural research funds are identified. To receive summer support the student must demonstrate successful academic progress, attainment of candidacy (committee and Graduate College approved student written research proposal), and identification / availability of extramural research funds.

Anticipated Starting Date:
June 1, 2016 or the commencement of the Fall 2016 semester (August 16, 2016). Suggested application deadline to the College of Graduate Studies is ASAP for summer, and June 15 for Fall term.

Interested qualified applicants are encouraged to send their resume, unofficial transcripts, a writing sample, and contact information for three professional references to:

Dr. Donald G. McGahan
Department of Wildlife, Sustainability, and Ecosystem Science
Tarleton State University
1333 W. Washington
T Box 0050
Stephenville, TX 76402
Phone: 254–968–9701
E-mail: mcgahan@tarleton.edu

Soil Drainage Classes

Soil Drainage Class

Soil drainage class is a way of communicating internal soil drainage conditions together with the depth in the soil that reducing conditions were/are prevalent (as determined by soil morphological features). There are seven such classes.

The Seven Soil Drainage Classes

Excessively drained:
Water is removed very rapidly (gravelly or coarse sand textures). The occurrence of free water is very deep (> 150 cm [or 60 inches]). Free of redoximorphic features related to wetness.
Somewhat excessively drained:
Water is removed from the soil rapidly (sands and loamy sand textures). The occurrence of free water commonly is very deep (> 150 cm [or 60 inches]). Free of redoximorphic features related to wetness.
Well drained:
Water is removed readily but not rapidly. Free water occurrence is deep (> 150 cm [or 60 inches]). Well drained soils are generally free of redoximorphic features related to wetness in the upper 150 cm (or 60 inches). There may be redoximorphic features deeper in the soil profile.
Moderately well drained:
Water is removed from the soil somewhat slowly during some periods of the year. Free water occurrence is moderately deep (50 cm to 100 cm) and transitory (1 to 3 months) to permanent (continuous). The soils are wet for only a short time within the rooting depth during the growing season. Moderately well drained soils may have redoximorphic features below a depth of 50 cm (about 20 inches). It is common for moderately well drained soils to have a slowly permeable layer within or immediately beneath the solum or a relatively high water table.
Somewhat poorly drained:
Water is removed slowly so that the soil is wet at a shallow depth for significant periods during the growing season. The occurrence of free water is shallow (25 cm to 50 cm [or 10 to 20 inches]) and transitory (1 to 3 months) or common (present 3 to 6 months). Wetness markedly restricts the growth of many common crop plants unless artificial drainage is provided. They commonly have a high water table, and redoximorphic features occur below a depth of 25 cm (about 10 inches). These soils often have thick dark A horizons high in organic matter.
Poorly drained:
Water is removed so slowly that the soil is wet at shallow depths periodically during the growing season or remains wet for long periods. The occurrence of free water is shallow or very shallow (< 25 cm [about 10 inches]) and common (3 to 6 months) or persistent (6 through 12 months). Free water is commonly at or near the surface long enough during the growing season so that mesophytic crops cannot be grown without artificial drainage. These soils are commonly gleyed rather than redoximorphic features because they remain anoxic for long periods.
Very poorly drained:
Water is removed from the soil so slowly that free water remains at or very near the ground surface during much of the growing season. The occurrence of free water is very shallow and persistent or permanent.

References

  1. Soil Survey Division Staff. 1993. Soil survey manual. Soil Conservation Service. U.S. Department of Agriculture Handbook 18.

Citations, blog posts, and WordPress

When adding citations to blog posts the bibliography as an endnote seems untenable. The very nature of web pages promotes a non-linear approach to content.

Browser tabs help quickly switching between pages, but the reader has to get to the page with the endnotes (bibliography). It is annoying to know the author is referring to a scholarly work, a clarification, or another web page and not have a ready hyperlink to what is referred to.

Bloggs and web pages are actually fairly straightforward links to add in WordPress. If either of these are from you’r own site it is relatively easy, if you’re good at the page or post titles.

Academic writing frequently uses inline citations and Reference lists  or Bibliographies at the end of Articles. Books are another story. When a book has multiple authors and compiled by editors each Chapter is self contained with respect to the inline citations and bibliography or reference list. It would not be uncommon to direct a citation back to a specific Chapter.

Increasingly, Books, and Book Chapters are available online.

This weblog post chronicles a glimpse of my approaching citations to Books and Book Chapters using WordPress in the least cumbersome and most coherent manor. I would like my site to have some coherency and reflect scholarly norms by including citations. Wikipedia is also moving down this path of documenting the citations on a per-page basis.

Another issue is that I reuse Book and Book Chapter citations and it would be handy to have them ready made in WordPress similar to how pictures. Another example that I have found is the TablePress plugin for reusing tables.

Where I am at

The current list of webpages that I am looking at to help with this is below.

Limited time keeps me from attacking this in one chunk. I expect this list to grow and this post get refreshed and updated.

Unconsolidated Horizons, Layers, Lithic, and Paralithic Contact Depth Interpretations

Unconsolidated Horizons, Layers, Lithic, and Paralithic Contact Depth Interpretations

Should the excavation not extend to a depth of 150 cm the last horizon, or unconsolidated layer (interpret this as all non-root restrictive layers or horizons) should be extrapolated to 150 cm for interpretations for the Region IV SASES[1] contest. The last horizon depth should be the specified judging depth with a “+” added.

Thus, if the pit sign states “Describe 5 horizons to a depth of 140 cm”, the fifth lower depth designation should be “140+”.

Lithic contact: the upper contact should be considered in evaluating hydraulic conductivity, effective soil depth, and water retention difference. When a lithic contact is encountered the “+” is dropped from the depth recorded.

Paralithic contact: occurs within the specified depth, the contact should be considered as one of the horizons to be included in the description, and the appropriate horizon nomenclature should be applied (i.e., Cr). When a paralithic contact is encountered the “+” is dropped from the depth.


[1]Students of Agronomy, Soils, and Environmental Sciences

Lower Depths of Horizons and Boundaries

Lower Depths of Horizons and Boundaries

The depth of the lower boundary as measured from the soil surface should be recorded in centimeters (cm).  Alternately, the depth of both the upper and lower boundary may be given, but only the depth to the lower boundary will be graded.  For example, a Bt1 horizon occurring from 30-45 cm may be recorded as “45 cm” (preferred) or “30-45 cm”.

Depth measurements should be made between the tapes in the restricted area on the pit wall using the mounted tape measure provided.  A range for the lower depth considered correct will be based on the boundary’s distinctness according to Table 3. Where one horizon grades into another, the location of the boundary will be specified at the bottom of the transition zone.

The transition will be part of the overlying horizon for the Region IV SASES[1] land judging.

No horizon less than 8 cm thick will be described.  If a horizon less than 8 cm thick occurs, it should be combined with the adjacent horizon that is most similar for the depth measurement purposes.  When two horizons combine to a total thickness of 8 cm or more, the properties of the thicker horizon should be described.  If lamellae are encountered that are thinner than 8 cm, then the convention is to describe the eluvial and illuvial horizons as a unit (i.e., E&Bt) and the thickest horizon’s morphology would be described.


[1]Students of Agronomy, Soils, and Environmental Sciences

Horizons and Layers

Designations for Horizons and Layers

Horizon Designations (Chapter 18, Keys to Soil Taxonomy, Twelfth Edition 2014 – available online).

Horizon designations will follow standard procedures, including a master, transitional or combination horizon symbol to be recorded in the “Master” column, and when needed, a lower case symbol in the suffix/subordinate distinction column labeled “Sub”, and an Arabic numeral in the “No.” column.  Arabic numerals should be used in the “Prefix” column preceding the “Master” column to indicate lithologic discontinuities.  Prime symbols to distinguish otherwise identical designations should be placed in the “Master” column.  All B horizons must have a suffix/subordinate distinction.  If no designation is necessary for a cell, contestants may leave the cell blank or record a dash (-) to indicate no designation.  Only mineral horizons will be described for the contest, and students should be especially familiar with the master horizons A, E, B, C, and R layer designations, and the appropriate application of transitional and combination horizons.  Contestants are expected to be familiar with suffix symbols, vertical subdivisions and discontinuities. Special clarification will be communicated to your coach/instructor concerning special guidance when appropriate, or will be added as an addendum if necessary.

Thumbnail Descriptiond of Soil Horizons

Nomenclature to describe soil horizons

Example = Bt2 horizon

1. Capital letters – master horizons

2. Lower case letters – specific characteristics or subdivisions of the master horizon (see handout)

3. Arabic numerals – further subdivision of horizons with similar features

O horizon

A surface layer dominated by organic materials (> 20% organic carbon)

Oi – slightly decomposed organic matter; can still identify the original plant and animal remains

Oe – intermediately decomposed

Oa – highly decomposed; can not identify the original source of the organic material

A horizon

mineral horizon (<20% organic C) which forms at the surface or beneath an O horizon

characterized by a darker color than the rest of the profile due to the accumulation of organic matter; high biological activity

eluvial horizon (loss of materials such as iron/aluminum oxides and clays)

E horizon

an intensively leached eluvial horizon in which organic matter along with iron/aluminum oxides and clay have been removed; most commonly found in forest soils.

typically white or light gray in color due to the lack of coatings on the mineral surfaces

B horizon

horizon formed beneath an A, E or O horizon and is a zone of accumulation (illuvial horizons). May accumulate clay, iron/aluminum oxides, organic matter, carbonates, etc.

C layer

a layer of unconsolidated material showing little weathering (alteration) and biological activity (e.g., beach sand, alluvium deposited by rivers, glacial till deposited by glaciers).

R layer

consolidated rock that can not be dug with a shovel and shows little evidence of weathering (e.g., granite, sandstone).

Transition horizons

horizons that contain properties of two types of master horizons

Example = AB horizon

An AB horizon has a dark color due to organic matter (A-like), plus red color due to accumulation of iron (B-like).

Common transition horizons: AB, BA, BC, CB. The dominant horizon is listed first.

Not every soil contains all of the master horizons.

O horizons form preferentially under forest vegetation; often absent under grass vegetation

Soils that have been eroded may be missing their O or A horizon

A horizon may be missing in some forest soils (e.g., O-E-B-C)

B horizon may be missing in young soils (e.g., A-C); B horizons take a long time to form.

Additional Terminology

Solum – the zone of active soil formation; comprised of the A, E, and B horizons

Topsoil – the surface layer of the soil – the layer manipulated by tillage; typically the upper 10-25 cm

Subsoil – the soil layers beneath the topsoil (does not include the C horizon)

Boundary Distinctness

 Soil Horizon Boundary Distinctness

For the Students of Agronomy, Soils, & Environmental Sciences (SASES) Region IV Collegiate Soil Judging

C. Boundary Distinctness

Boundary Distinctness Ranges

Distinctness class nameDistinctness classRange for grading
Abrupt (A)< 2 cm thick± 1 cm
Clear (C)2-5 cm thick± 3 cm
Gradual (G)5-15 cm thick± 8 cm
Diffuse (D)> 15 cm thick± 15 cm

 

The boundary distinctness of the deepest horizon will not be described and should be left blank or with a dash (-) recorded in the cell.

Boundary topography will not be described for the SASES[1]

contest. Be sure to use horizon and layer depths measured at the restricted area of the pit wall since wavy and irregular boundaries may exist. Where wavy or irregular boundaries exist in restricted area the median of the maximum and minimum is the official depth.

Obviously some compromises must be made for the Collegiate SASES[1] contest. The professional practitioners guidance is quoted below from:

Soil Survey Division Staff. 1993. Chapter 3 – Examination and Description of Soils. In Soil Survey Manual, United States Department of Agriculture Handbook No. 18 pp133-134. [Last visited January 29, 2014]

Boundaries of Horizons and Layers

A boundary is a surface or transitional layer between two adjoining horizons or layers. Most boundaries are zones of transition rather than sharp lines of division. Boundaries vary in distinctness and in topography.

Distinctness.—Distinctness refers to the thickness of the zone within which the boundary can be located. The distinctness of a boundary depends partly on the degree of contrast between the adjacent layers and partly on the thickness of the transitional zone between them. Distinctness is defined in terms of thickness of the transitional zone:

Abrupt: Less than 2 cm thick

Clear: 2 to 5 cm thick

Gradual: 5 to 15 cm thick

Diffuse: More than 15 cm thick

Abrupt soil boundaries, such as those between the E and Bt horizons in many soils, are easily determined. Some boundaries are not readily seen but can be located by testing the soil above and below the boundary. Diffuse boundaries, such as those in many old soils in tropical areas, are most difficult to locate and require time-consuming comparisons of small specimens of soil from various parts of the profile until the midpoint of the transitional zone is determined. For soils that have nearly uniform properties or that change very gradually as depth increases, horizon boundaries are imposed more or less arbitrarily without clear evidence of differences.

Topography.—Topography refers to the irregularities of the surface that divides the horizons. Even though soil layers are commonly seen in vertical section, they are three-dimensional. Topography of boundaries is described with the following terms:

Smooth: The boundary is a plane with few or no irregularities.

Wavy: The boundary has undulations in which depressions are wider then they are deep.

Irregular: The boundary has pockets that are deeper than they are wide.

Broken: One or both of the horizons or layers separated by the boundary are discontinuous and the boundary is interrupted

Date last modified: January 29, 2014.


[1]Students of Agronomy, Soils, and Environmental Sciences

Soil Morphology Judging

Soil Morphology – Judging

The field observable attributes of the soil within the various soil horizons and the description of the kind and arrangement of the horizons.[cite num=”1″]

Students of Agronomy, Soils, and Environmental Sciences (SASES) is the undergraduate student program of the American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and Soil Science Society of America (SSSA).

Participation in the SASES National Soil Judging Contest (USA) requires qualification at the Regional level.  Region IV (Arkansas, Mississippi, Texas, Louisiana, Oklahoma) Collegiate Soil Judging is an experiential event to practice application and develop skills associated with scholarly learning.

Back to Soils


  1. Buol, S. W., Southard, R. J., Graham, R. C., & McDaniel, P. A. (2003). Soil Genesis and Classification, 6th Edition. Ames Iowa: Iowa State Press, A Blackwell Pub. Co. p. 494. ISBN 9780813807690.

Cation Exchange Capacity (CEC) by Buchner Funnels

CATION EXCHANGE CAPACITY (CEC)

Ammonium Replacement Method(Buchner funnels vacuum flasks)

Tarleton State University Environmental Soils and Biogeochemistry Characterization Laboratory

Dr Donald G. McGahan

 The following is adapted from Soil Survey Laboratory Methods Manual – Soil Survey Investigations Report No. 42 Ver. 4.0. USDA-NRCS and much text is lifted directly from their and then adapted where necessary for our local laboratory conditions.

Scope and Application

Cation exchange capacity(CEC) is the measure of a soil to retain readily exchangeable cations which neutralize the negative charge of soils. This method involves saturation of the cation exchange sites with ammonium, equilibration, removal of the excess ammonium with ethanol, replacement and leaching of exchangeable ammonium with protons from HCl acid (Horneck, et al. 1989). This method may be poorly suited to soils containing carbonates, vermiculite, gypsum and zeolite minerals. The procedure is time consuming and labor intensive. The speed at which samples filter depends on the strength of the vacuum applied and sample makeup. If using a water aspirated generated vacuum, some samples may never filter because of clogged filter paper. The method detection limit is approximately 1.0 cmol kg-1 (or meq/100 gm on a dry soil basis) and is generally reproducible within ± 10%.

Equipment

  1. Analytical balance: 250 g capacity, resolution 0.01 g (greater resolution is acceptable and often desirable).
  2. Reciprocating horizontal mechanical shaker, capable of 180 oscillations per minute.
  3. Repipette dispensers (or pipets), calibrated to 20 ± 0.1, 8.0 ± 0.1 mL and 5.0 ± 0.1 mL.
  4. Whatman No. 1, No. 2 or equivalent filter paper.
  5. Buchner funnels vacuum flasks and source of vacuum
  6. Auto analyzer or Kjeldahl distillation equipment.

Reagents

  1. Deionized water ASTM Type I Grade.
  2. Ammonium acetate (1.0 N) extraction solution neutral: Add 570 mL of glacial acetic acid CH3COOH (99%) to 8000 mL of deionized water. Add 680 mL of concentrated ammonium hydroxide adjust pH to 7.0 with 3.0 N glacial acetic acid or 3.0 N ammonium hydroxide and dilute to 10 L final volume.
  3. Ethanol, 95%
  4. Hydrochloric acid, 0.1 N HCl – Dilute 8.3 mL of concentrated HCl reagent to 1000 mL with deionized water.
  5. Standard calibration solutions of NH4-N. Prepare six calibration standard solutions of 1.0 – 20 mg L-1 of NH4-N mg L-1 from 1000 mg L-1 stock solutions. Dilute calibration solutions with 0.1 N HCl solution.

Procedure:

  1. Weigh 10.0 ± 0.1 g of air dry soil pulverized to pass 10 mesh sieve (< 2.0 mm) soil into a 125 mL Erlenmeyer flask. Add 50 mL of ammonium acetate solution (See Comment #1) and place the flask reciprocating shaker for thirty (30) minutes. Include a method blank.
  2. Connect a 1L vacuum extraction flask to a Buchner funnel fitted with a Whatman No. 5 or equivalent filter paper. Moisten the filter paper with 2 mL deionized water (See Comment #2).
  3. Transfer the soil suspension into the Buchner funnel and leach the sample with 175 mL of 1 N ammonium acetate. The soil extract may be analyzed for extractable K, Ca, Mg, and Na.
  4. Rinse the excess ammonium acetate from the soil sample in the Buchner funnel by leaching with a total volume of ethanol and discard the leachate. Note: Be sure to gently fill funnel to remove all excess ammonium and allow it to drain until only damp soil remains. Continue adding ethanol in this manner until 200 mL of solution has been used.
  5. Change to a clean 500-mL suction flask and leach the soil sample with 225 mL of 0.1 NHCl to replace the exchangeable ammonium. Bring leachate to a final volume of 250 mL volumetric flask using deionized water.
  6. The concentration of ammonium-N in the final leachate can be determined. The determination can be made using the Kjeldahl distillation method (See Comment #3 and #4). See Berthelot Reaction below for non-automated standard laboratory method which relies on ammonium to complex with salicylate to form indophenol blue. This color is intensified with sodium nitroprusside and measured at 660 nm.]

Calculation

CEC in meq per 100 g of soil = (mg L-1 of NH4-N in leachate) x (0.25 / 14) x (100 / sample size (g)) mg L-1 NH4-N in leachate is determined using a standard curve.

Comments

  1. Check repipette dispensing volume calibration using an analytical balance.
  2. Check filter paper supply for possible contamination of and NH4-N. If contamination is greater than 0.2 mg L -1on a soil extract basis, rinse filter paper with 0.1 N HCl solution.
  3. Samples having ammonium concentrations exceeding the highest standard will require dilution and reanalysis.
  4. This procedure used is essentially the same as that of Schollenberger (1945) except that determination of NH4-N is done spectrophotometrically rather than Kjeldahl distillation and titration. To determine the NH4-N content using the Kjeldahl distillation method, follow steps 1 through 5 above, then proceed to Kjeldahl distillation. Care must be taken not to allow soil to dry and crack between ethanol leaching, as this could result in incomplete removal of excess NH4-N. A similar procedure is described by Rhoades (1982).

Literature

Horneck, D.A., J.M. Hart, K. Topperand, B. Koespell. 1989. Methods of Soil Analysis used in the soil testing laboratory at Oregon State University. Ag. Expt. Station SM 89:4.

Rhoades, J.D. 1982. Cation exchange capacity. In: A.L. Page, R.H. Miller, and D.R. Keeney (eds.) Methods of soil analysis. Part 2. Agron. Monogr. 9, Am. Soc. Agron., Madison, WI. p. 149-157.

Schollenberger, C.J. andR.H. Simon. 1945. Determination of exchange capacity and exchangeable bases in soils-ammonium acetate method. Soil Sci. 59:13-24.

Thomas, G.W. 1982. Exchangeable cations. In A.L. Page (ed.). Methods of soil analysis, Part 2, 2nd ed. Agronomy Monograph 9, American Society of Agronomy, Madison, WI.


Ammonium (NH4+) Determination

Berthelot Reaction

Berthelot reaction, salicylate analog of indophenol blue. Ammonia reacts with hypochlorite to form chloramine, which couples with two non-para-substituted phenols. Citrate and tartrate are included to avoid precipitation of Ca, Mg, and other hydroxides.

Example References:

Forster JC. 1995. Soil nitrogen. In: Alef K and Nannipieri P (eds.) Methods in Applied Soil Microbiology and Biochemistry. Academic Press, San Diego. pp. 79-87.

Kempers AJ, Kok CJ. 1989. Re-examination of the determination of ammonium as the indophenol blue complex using salicylate. Anal. Chim. Acta. 221:147-155.

Verdouw H, van Echteld CJA, Dekkcrs EMJ. 1977. Ammonia determination based on indophenol blue formation with sodium salicylate. Water Res. 12:399-402.

-The procedure below most closely matches Forster 1995.

Reagent A: in 100 ml water

  • 6.5 g sodium salicylate
  • 5 g sodium citrate
  • 5 g sodium tartrate
  • 0.025 g sodium nitroferricyanide (sodium nitroprusside)

This reagent is somewhat sensitive to light. It may be stored cold. Discard if dark.

Reagent B: in 100 ml water

  • 6 g sodium hydroxide
  • 2 ml bleach (5.25% sodium hypochlorite) or equivalent

Quantities in reagent preparation need not be exact.

  • In semimicro cuvets mix sample, then A, then B, in the appropriate amounts. Cap and invert to mix. Read absorbance at 650 nm against a reagent blank after 50-60 minutes.
  • For 1-20 ppm NH use 40 µl sample, 500 µl A, 500 µl B.
  • For 1-10 ppm use 80 µl sample, 500 µl A, 500 µl B.
  • For 1-5 ppm, LISC 140 µl sample, 400 µl A, 400 µl B. (to ~0.1)
  • For less than 1 ppm*. use 600 µl sample, 150 µ1 A, 150 µl B. Working lower limit is approximately 0.025 ppm N.
  • For 5-60 ppm*, use macrocuvets, 45 µl sample, 1500 µl Ω x A, 1500 µl Ω x B. (lower limit ≈ 1 ppm)

Primary amines e.g. amino acids) and certain other N compounds may interfere slightly when present in large amounts (more than 10-20 times the ammonia concentration). It is usually not a problem with soil extracts and water samples. For reducing such interference substitute sodium 2-phenylphenolate for sodium salicylaic (Rhine et al Soil Sci. Soc. Am. J. 62:473-480).

*Note: When using <1 ppm range with high Ca/Mg samples (e.g. soil extracts), use 700 µl sample, 300 µl 2.5 x A*, 200 µl B. 2.5 x A: in 100 ml, 17 g sodium salicylate, 12.5 g each sodium citrate and tartrate, 62 mg sodium nitroprusside.


Direct Distillation of Adsorbed Ammonia, Kjeldahl

Example References:

Soil Survey Staff. 2004. Soil Survey Laboratory Methods Manual – Soil Survey Investigations Report No. 42 Ver. 4.0. USDA-NRCS. Lincolin, Nebraska, USA. [Online WWW] URL: http://soils.usda.gov/technical/lmm/, [Accessed 8 March 2016]. (p 619-620)

Peech, M., L.T. Alexander, L.A. Dean, and J.F. Reed. 1947. Methods of soil analysis for soil fertility investigations. U.S. Dept. Agr. C. 757, 25 pp.

Reagents

  • Sodium chloride (NaCl).
  • Antifoam mixture. Mix equal parts of mineral oil and n-octyl alcohol.
  • Sodium hydroxide (NaOH), 1 N.
  • Hydrochloric acid (HCl), 0.2 N, standardized.
  • Boric acid (H3BO3), 4-percent.
  • Mixed indicator. Mix 1.250 g methyl red and 0.825 g methylene blue in 1 liter 95-percent ethanol.
  • Brom cresol green, 0.1-percent, aqueous solution.

Procedure

  • Transfer the soil plus filter paper from CEC7 method to a Kjeldahl flask. Add 400 ml water and about 10 g NaCl, 5 drops antifoam mixture, a gram or two of granular zinc, and 40 ml 1 N NaOH. Connect the flask with the condenser and distill 200 ml into 50 ml 4-percent H3BO3 solution. Titrate the distillate to the first tinge of purple with 0.2 N HCl, using 10 drops mixed indicator and 2 drops brom cresol green.

Calculations

  • CEC(meq/100 g) =(A/B) x N x 100

where

A = Volume HCl (mL)

B = Sample weight (g)

N = Normality of acid

Report on ovendry (OD) basis.

Thursday, August 1, 2013

Cation Exchange Capacity-Buchner funnels vacuum flasks.pages

Soil Acre Furrow Slice

Soil Acre Furrow Slice

By Donald G. McGahan

Two values that are handy to calculate when managing land are the pore space in the soil and the mass of soil in any given volume of soil. The volume of the pores is important because the total pore space, together with the pore size distribution, influences water retention and soil atmosphere exchange with the above ground atmosphere. The mass of soil is critical to determine exchange capacities and nutrient buffering capacities.

To calculate many things on the basis of an acre furrow slice of soil we must have more information about the soils bulk density, or alternately we can estimate the bulk density. Since soils have varying densities we are not quite sure about the bulk density unless it is physically measured.

To calculate the mass of soil by using an estimate of the bulk density of the soil we proceed as follows, and if the actual bulk density is known the calculation remains the same. Simply substitute the measured bulk density for the assumed bulk density.

afs = acre furrow slice; or the volume of soil to the nominal depth of plowing over one acre (ac).

The nominal plowing depth can be something like 0.5 ft, or 15 cm, depending on the way the question is asked.

For this segment I will address the total volume of the acre furrow slice then the mass.

Since the bulk density is not given I will assume a bulk density of 1.475 Mg / cubic m or 1.475 g / cubic cm. Bulk density is nearly always reported in metric terms. The exception to this is with engineers. Producers in the USA also often use lb so we must be able to calculate and convert.

Remember that a megagram (Mg) is 1,000,000 g.

1 cubic m = 1.31 cubic yd. Where m = meter.

You could proof this, right?

1 lb = 454 g, or 0.454 kg, or 0.000454 Mg.

1 ac. = 43,560 sq. ft.

You memorized this previously, right?

Going to the nominal plowing depth, 0.5 ft., for an acre furrow slice (afs):

(43,560 sq. ft. / ac.) x (0.5 ft / fs) = 21,780 cu. ft. / afs

[where furrow slice is fs and this example fs = 0.5 ft – two dimensional]

1 cu. yd. = 3 ft. x 3 ft. x 3 ft., or 27 cu. ft.

(21,780 cu. ft. / afs) x (1 cu. yd. / 27 cu. ft) = 806.667 cu. yd. / afs

[cubic yard (cu. yd.) is a common volumetric unit used when unconsolidated materials are transported. That that once was soil is included in these unconsolidated materials. Any volumetric unit can be used and calculations by scientist frequently use metric whereas engineers commonly use cubic feet.]

Now we use the assumed density to calculate the weight of an afs.

(1.475 Mg / cubic m) x (1 cu. m / 1.31 cu. yd.) x ( 1 lb. / 0.000454 Mg) = 2480 lb. / cu. yd.

Therefore the mass of an afs is:

(2480 lb. / cu. yd.) x (806.6667 cu. yd. / afs) = 2,000,516 lb.

Obviously if you assume (but alway better if you have an emperical measurement) a different density you get a different mass.


Reviewing Molecular Weight and Valence

By Dr. Donald G. McGahan
Published: September 15, 2008
Modified: March 11, 2016

Go to Chemistry Refresh list page.


An element consists of two basic parts, the nucleus and the electrons which orbit the nucleus. The nucleus primarily contains uncharged neutrons and positive charged protons, while the negative charged electrons orbit the nucleus. In the uncombined or free state, an element has the same number of protons as it has electrons, hence it had no overall electrical charge. Examples of this are metallic iron and copper, and flowers of sulfur.

While elements in an uncombined state are uncharged, most elements have a tendency to gain or to lose electrons. Elements tend to gain or lose electrons until they obtain a stable or noble gas electron configuration (s2p6). The number of electrons that an element gains or loses is its valence. The valence of an element can be thought of as the number of hydrogen ions (H+) that it will replace or combine with in a chemical reaction. You may also think of the valence as the charge on element when it gains or losses electron(s).

A. Major nutrients

Major nutrients valence examples
Major Nutrient Valence Example
Calcium +2 CaCO3
Magnesium +2 MgCO3
Potassium +1 KCl
Phosphorous* +5, +3, -3 H3PO4
Sulfur* -2, +4, +6, +2 H2S, SO2, SO3
Nitrogen* -3, +3, +5, +4, +2 NH3, HNO2, HNO3

B. Minor nutrients

Minor nutrients valences
Minor Nutrient Valance Example
Manganese* +2, +4, +7, +6, +3 MnSO4, MnO2, KMnO
Iron* +2, +3 FeSO4, Fe2O3
Copper* +1, +2 Cu2O, CuO4
Zinc +2 ZnSO4
Boron +3 H3BO3
Molybdenum +3 MoO3

C. Nutrients mainly from water or the atmosphere

Nutrients mainly from water or the atmosphere
Nutrients from water or atmosphere Valance Example
Carbon* -4, 0, +4, +2 CH4, CH12O6, CO2
Hydrogen* (usualy in a soils course) +1 H2O
Oxygen* (usually -2 in a soils course) -1, -2 H2O2, H2O

D. Other miscellaneous elements

Other miscellaneous elements
Element Valance Example
Sodium +1 NaCl
Silicon +4 SiO2 (Quartz)
Aluminum +3 Al2O3
Chlorine -1 NaCl
Fluorine -1 CaF
Silver +1 AgCl

*These elements commonly show variable valences and the valence will usually be calculated from the other elements in the compound.

Naming Ions and Ion Radicals

By Dr. Donald G. McGahan
Published: September 15, 2008
Modified: March 11, 2016

Go to Chemistry Refresh list page.


A single element (or a group of elements) with an electrical charge is called an ion. Ions which are positively charged are called cations, while those ions with a negative charge are anions. If an ion is not a single element but a group of elements such as (SO42-) this may be spoken of as a radical. 

Naming of radicals and compounds

Three suffixes are commonly used to denote the chemical state. These suffixes and rules for names of the compounds follow and should be learned.

  1. “ide” – Refers to the lowest negative valence state of an element. The negative ion in this case is always a single element, and is not combined with oxygen. Examples are H2S (hydrogen sulfide) and NaCl (sodium chloride).
  2. “ite” – Refers to the valence of some element combined with oxygen to form an ion but this element is not in its highest possible valence. For example, SO33-, has sulfur in a +4 valence but S can in some instances have a +6 valence. So this anion with S in a +4 valence is named “sulfite.”
  3. “ate” – Refers to some element combined with oxygen to form an anion. The particular element is in its highest valence state. (Example, SO42-, sulfate has sulfur in a +6 state, its highest oxidation).
  4. For cations (positive ions) having two valence states, the higher valence is “ic” and the lower valence is “ous”. Thus Cu+ is cupprous and Cu++ (or Cu2+) is cupric or Fe++ (or Fe2+) is ferrous and Fe+++  (or Fe3+) is ferric.
  5. To name compounds, use the element name of the cation plus the name of the anion.
    • NaNO3 is sodium nitrate
    • CuS is cuppric sulfide or Cu (II) sulfide
    • CaO is calcium oxide
    • Na2SO3 is sodium sulfite
    • NCl is ammonium chloride
    • FeO is ferrous oxide or Fe (II) oxide
    • K2CO3 is potassium carbonate