Some Soil Classification and Mapping Problems in theWisconsin Drift Area of Iowa1

F. F. RIECKEN, W. H. ALLAWAY, AND GUY D. SMITH2

THE classification of the soils of the Wisconsindrift area of Iowa has been an evolutionary pro-

cess since first surveys were initiated in the area near-ly 5'o years ago. All counties of this area but one,namely, Humboldt County, have been mapped, fieldwork ranging in date from about 1914 to 1935.

In the past decade or so, a re-examination of theclassification and mapping of the soils of this area hasbeen initiated. These efforts are primarily being as-sociated with the program of Soil Conservation Dis-tricts, and with suggestions by land appraisers, frommanagers, and county agents that the classification ofthe Carrington series in one or two counties of thearea should be re-examined. Although no basic soilsurveys are in progress in the area concerned, it isbecoming evident that re-classification of a numberof soil types is necessary, and also that re-mapping ofa number of counties is highly desirable. The presentpaper, which is in the way of a preliminary report, isbeing presented at this time to indicate some of theprogress made and to discuss some of the problemsencountered.

SOIL-FORMING FACTORS OF THE AREA

The area under consideration is outlined in Fig. i.The climate of the area is continental in character,ranging in annual rainfall from About 30 to 35 inches.The mean annual temperature is about 45° to 50° F.Tall prairie grasses were the dominant native vege-tation, although trees occurred in' small areas on themore rolling morainic areas and along rolling lands

FIG. I.—Location of Mankato and lowan substage areas inin Iowa, with profile and till-sampling sites indicated.

bordering streams. In both areas the topographyranges from level to rolling, although level to mod-erately sloping topography is dominant.

An important factor accounting for differences insoils occurring in the Wisconsin drift area is thereforeto be expected to be due to variations in the characterof the drift as well as to differences in the age of theMankato and lowan drifts. Both outwash and tilloccur in the area, although till is dominant. Prior tothe present study no investigations had been made ofthe mechanical and consistence characteristics of eith-er of the glacial drift sheets or of variations withineach area.

PREVIOUS SOIL CLASSIFICATION STUDIESOF THE WISCONSIN DRIFT AREA

The earliest classification of ;soils formed from Wisconsindrift were made by Morean and Jones (7)3 and Ely, Coffey,and Griffin (3) in 1904 and 1905, 'in making reconnaissancesoil maps of Story and Tama counties. In common with theconcept of that period, the undulating dark-colored soils wereclassified with the Marshall series. No distinction was madein regard to the character of the glacial material, whetherloessial, outwash, or till in origin. In 1911, Stevenson (12)recognized that . the different glacial drift sheets, as well asvariations in loessial materials, influenced the character of thesoils.

By the time the Iowa Experiment Station and the Bureauof Soils initiated a cooperative soil survey program in 1914,the Carrington series had been established, including dark-colored soils derived from young drift. It was at about thistime that the Carrington series was introduced into Iowa andmany of the "Prairie Region" states, although the name-placeis Carrington, North Dakota (9).

From about 1915 to 1920, the Carrington series wasmapped extensively in Iowa in counties located in both theMankato and lowan glacial substage areas. No recognitionwas given to the importance of the degree of leaching of car-bonates, or to mechanical and consistence characteristics ofthe drift materials. About 1923, the Clarion series was sub-divided from the Carrington series in Iowa, the differentiatingcharacteristic from the Carrington series being the depth tocarbonates. From 1923 to about 1930 both the Clarion andCarrington series were mapped in the Mankato area. How-ever, the Clarion series was not mapped in the lowan areaduring this period. .From about 1930 op, the Clarion serieswas mapped in the Mankato area and the Carrington series inthe eastern lowan drift area. Thus, in the most recent surveysin the Wisconsin drift area, namely, in Cerro Gordo (2) andFranklin (10) counties, field work .being completed in about1936, the Clarion series is mapped on Mankato till and theCarrington series on lowan till.

In the preceding discussion reference has been made onlyto the Carrington and Clarion series. These soils belong to thePrairie Great Soil Group, and' represent the undulating togently rolling upland soils of the area. These series comprisethe most extensive part of the landscape and therefore theyseemed logically to be the most important ones to.' study first." ' • " ' ' ~ •

Contribution from Soils Subsection, Iowa Agricultural Experiment Station, Ames, Iowa, and Division1 of Soil' Survey, Bureauof Plant Industry, Soils, and Agricultural Engineering, U. S. Dept, of Agriculture, cooperating. Journal Paper No. Ji495. Project635-

"Research Professor, Research Associate Professor of Agronomy, and Senior Soil Correlator, respectively:'Figures in parenthesis refer to "Literature Cited", p. 440.

432

RIECKEN, ET AL. I SOIL CLASSIFICATION AND MAPPING PROBLEMS 433

PLAN OF STUDY

The general plan of study was to, make morphologicalstudies in the field of areas shown as Clarion and Carringtonon the published county maps. Carefully selected profile sam-ples were taken, and properties were determined in the labora-tory as seemed likely to be of value in characterizing thesoils. In this study six profiles in all will be reported upon.

In addition to the profile samples, numerous samples ofMankato and lowan till were collected and analyzed formechanical composition.

PROFILE SAMPLESClarion loam (P49)SWSW-S6-T82N-R24W, Story Co.,

IowaCollected in weed-covered road cut, slope 4%, by R. W. Si-

monson in 1939O-6 inches Dark brown loam; friable soft crumb grading

into6—14 inches Brown to dark yellowish brown loam; colors

are variegated; worm holes are frequent; gradual changeto lighter color with depth

14-19 inches Variegated yellow brown loam to heavyloam; no • sharp boundary to layer above or below

19-29 inches Light yellowish brown heavy loam; lowerboundary fairly distinct

30-60 inches Calcareous grayish yellow loam till; pebblesand stones are common but not plentiful

Clarion loam (Pp;) SESENE-Sy-TgSN-RssW, DickinsonCo., Iowa

Collected in r.oadcut bank, bluegrass sod, slope 3 to 5%, byF. F. Riecken, M. B. Russell, and H. L. Hoegh in 1944

0-8 inches Dark brown granular loam8-16 inches Dark brown grading into dark yellow brown

in lower part, with some variegation of these colors;texture is loam; weakly developed subangular blockystructure

16—28 inches Dark yellow brown heavy loam, with weaklydeveloped subangular blocky structure

28-60 inches Dark yellow brown grading into dusky yel-" low or light yellow brown at about 40 inches; some faintolive mottlings at lower depths; structure is massive;calcareous; texture is medium loam

Sac silty clay loam (Pus) SWSWSW-Sso-ToSN-Rj/W,Dickinson Co., Iowa

Collected in roadside bluegrass sod in middle of 2 to 3%slope l/4 mile long by F. F. Riecken, W. B. Russell, andH. L. Hoegh in 1944. This area was classified as Carring-ton silt loam in the county survey. The parent material isa thin blanket of loess-like material, 20 to 40 inches thickon slightly to medium plastic till.

0-12 inches Brownish black light silty clay loam withgranular structure

12-20 inches Brownish black grading into dark brownlight silty clay loam; structure particles are indistinctlydeveloped subangular blocky

20-28 inches Dark yellowish brown medium silty clayloam, with weakly developed subangular blocky structure

28-40 inches Dark to moderate yellowish brown mediumto light silty clay loam; weakly developed coarse sub-angular blocky structure particles; faint mottlings of paleolive begin at 32 to 35 inches; some fine to coarse sandpresent

40-52 inches Mixed yellow brown and olive colors, with. strong secondary lime streaks; heavy loam to light clay

loam of slight to medium plasticityCar r ing ton si l t loam (P52)SWSW-S27-T8pN-Ri6W

Grundy Co., IowaCollected in corn stubble field, slope 2%, by R. W. Simon-

son and R. W. Pearson, 1938.0-16 inches Dark brown silt loam, with some dark yellow

• brown in the lower part; the upper part has granular tocrumb structure, and lower has tendency to weakly de-veloped subangular blocky

16-26 inches Dark yellowish brown loam

26-40 inches Dark yellowish brown sandy clay loam tosandy clay; some pockets of sand occur in this layer aswell as some I- to 3-inch cobbles

40-60 inches Yellowish gray sandy clay or clay loamwhich has slight to medium plasticity; splotches of orangeand black indicate iron and iron-manganese concretionsare present

Carrington loam (P22)NWSWSW-Si2-TQiN-Ri6W But-ler Co., Iowa

Collected on a 5% slope by W. H. Allaway and F. F.Riecken

0-12 inches Dark brown loam with fine granular structure12-18 inches Transition from dark brown to dark yellow

brown color; structure is weakly developed subangularblocky; texture is loam

18-28 inches Dark to moderate yellow brown loam grad-ing into medium clay loam in lower part of layer; struc-ture is medium weak angular to subangular blocky; somefaint olive gray mottlings in the lower part of the layer

28-50 inches Variegated yellow brown and olive gray col-ors, with medium contrasts mottles of strong brown anddull orange; structure is medium to coarse blocky, withmedium clay loam texture

50-62 inches About as above layer except that carbonatesare present as secondary lime

Carrington loam, plastic till phase (Pii4)NWNWNW-S27-T99N-R27W, Howard Co., Iowa

Collected in sod stubble near fence, slope 2 to 3%, by F. F.Riecken, Kirk Lawton and H. R. Meldrum in 1944.

0-9 inches Dark brown granular loam9-17 inches Weak to dark brown loam, with a weakly de-

veloped subangular blocky or coarse crumb structure17-26 inches Dark yellow brown loam, with faint mot-

tlings of strong brown and pale olive; structure is weak-Iv developed subangular blocky; medium plastic clayloam

26-36 inches Pale olive to light olive gray medium plastic- clay loam, with high contrast strong brown mottlings;

Coarse blocky structure36 -̂60 inches Pale olive to light olive gray medium plastic

clay loam, with strong brown mottlings; coarse blocky;carbonates at 55 inches

TILL SAMPLES

Samples of till were collected generally whenever otherstudies were being made in the area. The sampling is not com-plete by any means, and the data are presented at this timeonly to give some idea of the variations encountered thus far.

LABORATORY STUDIES AND PROCEDURES

Laboratory studies of the profile samples have been con-fined to determinations of particle size distribution, replace-able cations, pH, and organic carbon. On the till samples, par-ticle size distribution alone was determined. Standard pro-cedures reported in the literature have been used throughout.

Particle size distribution, data were obtained by the pipettemethod, using H2Oa to destroy organic matter. NaPOs-NaaCOa mixture was used as dispersing agent for profilesP-49, Pus, Pi 14, and P22, but HC1 pretreatment and NaOHas dispersing agent for profiles P-97 and P-52. These dis-persing agents give comparable results for these types of soils,the advantage of the HCl-NaOH method being that analysisfor the 0.0002 mm clay fraction can be made on the samesample.

Replaceable bases were determined by leaching the sam-ples with neutral normal NH4Ac, and the individual ions de-termined in this extract by standard volumetric and colorimet-ric procedures. Replaceable H+ was determined by leachingthe samples with neutral Ba(Ac)2 and titrating the leachatewith phenolphthalein. The pH determinations were made withglass electrode pH-meters, using a i: i soil and water ratio.Organic carbon was determined by dry combustion.

434 SOIL SCIENCE SOCIETY PROCEEDINGS

RESULTS OF FIELD AND LABORATORY STUDIESThe data from the profile samples are shown in

Table I. The data for the till samples are shown inFig. i and Table 2. The locations of the profiles with-in the Wisconsin drift area are given on Fig. i.

REPLACEABLE CATIONS OF THE PROFILES

An examination of the replaceable cation data inTable I shows that the two Clarion profiles, P-49and P-97, have a higher base saturation than thethree Carrington profiles, P~52, P-22, and P-II4.

The pH data, plotted in Fig. 2 for a Clarion profile,P-4$, and a Carrington profile, P—114, confirm thereplaceable base data that the Clarion profiles are lessleached than the Carrington profiles. The replaceableH*,' pH, as well as percentage base saturation datashown on Fig. 3 and Table I confirm that the Car-rington soils require a rather heavy lime applicationof about 4 to 5 tons per acre to neutralize the acidity,whereas the Clarion soils have a rather low or no limerequirement. . - • . . ; . •

Of the replaceable bases, the data show.that-Ca isthe dominant base in all the profiles^ with- Mg^nextand then E. The content of replaceable. K 'is''ratherlow for the Clarion and Carrington profiles''.even inthe surface layers. It;., isia- rather ̂ common experiencein Iowa to find that dark-colored loess-derived soilsof';simiTar stage of development' to: the1: Clarion''andCarrington soils have a rather high" content of replace-able, K.. Profile P—115, which is derived from loess-like material overlying lowan till, illustrates this pointwhere the surface layers, according to Table i, haveabout'o.S.'rrile. of replaceable K, whereas the Clarionand Carrington profiles have only about O.2 to, ,0.4m.e. of replaceable K in the surface layers.

ORGANIC CARBON

As is to be expected, the organic carbon content ishighest,in the,,immediate surface layer and decreaseswith depth in each of,the profiles. Using the factor of1.72 to convert carbon to organic matter, it is seenthat the surface layers of the Clarion and Carringtonprofiles have about 3.25 to 5.85% organic matter. TheClarion profile, P^49, has the lowest, content of or-ganic matter, naitiely, 3.25%, the low value possiblybeing explained by the fact that this site was,a formercultivated field through which a road had been re-cently cut. Profile P—115 has the highest organic mat-ter content, about 8.32%, of any of the surface layers,although this profile occurs on a more favorable slopethan the other profiles for the accumulation of organicmatter.

MECHANICAL ANALYSIS DATA OF THE PROFILES

The mechanical analysis data for the two Clarionprofiles, P—49 and P-97, show that the parent ma-terial till at depths of 30 to 60 inches is fairly low inclay, about 15 to 17%, and medium in sand content,about 35 to 50%. The texture is a loam, and it is offriable consistence. In the B horizons, the clay con-tent is about 22 to 26%, indicating perhaps that some

pH5.0 s'.'s &.o TO TS e.o e.s

5

10

V5

20

25

IP -30Ul1(J-352

55

P-II4-

FIG. 2.—The pH values for Clarion loam P 49, Carrington: loam Pii4, and Sac silty clay loam Pus.

clay has formed during profile development. The sur-face textures of both profiles are in the loam class.

The mechanical analysis data for the three Carring-ton profiles, P—22, P-52, and P—114, are somewhatmore variable than were the data for the Clarion pro-files. The distribution of clay in three Carrington pro-files is plotted in Fig. 4. Profiles P-22 and P-H4 areapparently about equal in clay content in all layers. Inprofile P—22 the maximum clay content of about 31%is reached in the B horizon at a depth of about 30inches, ,In profile P-H4, the clay content of the Bhorizon is about equal to the clay content in the C

',.:-. . - • • • . . • . PERCENT BA.=.E •SA.TUR.A.TJOM-••• '• 10 .ao 30 40 50 &o TO eo so \oo

1 1 1 1 1 fi ' ') '\ \\ Vz^ P- >=

1

9T

u)

\5

20

i 25|

' 30

i-QA3

50

- H-4-

FIG. 3.—Percentage base saturation of Clarion loam Pp7and Carrington loams P52 and Pii4.

RIECKEN, ET AL.: SOIL CLASSIFICATION AND MAPPING PROBLEMS

TABLE i.—Replaceable cations, pH, organic carbon, and mechanical analysis of the soil profiles studied*

43 S

SampleNo.

Depth,inches pH

Replaceable cations, m.e. per 100 grams soil

Ca . Mg K H

Basesatura-tion, %

Organiccarbon,

%

Totalsands,

%

2 Mclay,%

P49—Clarion LoamP49-iP49-2P49-3P49-4P49-5P49-6P49-7P49-8P49-9P49-IOP49-IIP49-I2P49-I3P49-HP49-I5

0-66-99-12

12-1515-18

• 18-2121-2424-2727-3030-3333-3636-3939-4239-4245-51

5-45-75-75-9—6.26.36-77-77-98.18.18.08.18.1

n-5

"•S

ii-9II .O————————

2-9

2.8—3-5

3-0

———————

0.14—

O.II—

0.25—0.18——0.08——0.07——

4-6

3-42.O

i1.0

————— :

———

———

———

———

———

76

81—80—94———— •———

. 1.89—1-36

o-950.62——

0.25—————

47-947-748.848.448-9-50.251.053-550.050.048.649.050.650-149-4

21.8

23-122.9

'22.522.5'21.920.718.9I7.I-15-415-5I5-II5-I14-515.3

P97 — Clarion LoamP97.-IP97-2P97-3P97-4P97-5P97-6P97-7P9Z-8?97~9?97-ioP97-iiP97-I2P97-I3P97-HP97-I5

O-44-8,8-12

1 2-1 616-2020-2424-2828-3232-3636-4040-4444-4848-5252-5656-60

6.15-95-85-86.0—7-47-98.17-97-97-98.08.07-9

16.714.613-713-313-7

15-9—

37-2——————

5-34-94.84-85-o

5-2— '4-3

4-3

4-74.0

0-390.340-390-350.36—

0.44

0-390.27

0.31

0.28

4-35-95-34-32-5

0.8———

" —————

8477788188——————————

3-002.481.881.380.92—

0.53——' —————

39-037-240-7'41.943-1

44-339,8 .38-0, ;36.737-437-o39-539-040.0

24.826.225-526.225.8

18.020.917-917-917-517-417.016.817.0

Pi 1 5 — Sac Silty Clay LoamPi I5-IPi 1 5-2Pi 1 5-3Pi 1 5-4Pi 1 5-5Pi 1 5-6Pi 15-7Pi 1 5-8Pi 1 5-9Pii5-ioPiiS-iiPII5-I2Pii5-i3

0-44-88-12

12— 1 616-2020-2424-2828-32,32-3636-4040-4444-4848-52

. 5-4'' 5-5.; 5-5. : 5-6

. 5-45-55-6

. 5-96.26.77.87-77-9

2O.621.3

, 19.817.717.115-414-5

. 14.616.4————

4-44.0

• 3-9 • •

5-45-25-i4-75-0

———

• " ' • 0.78••'• • 0.52

0.400.390.360.360.420.400.38—0.44

0.40

9-39-68.08.07-4:"6-92-52-5

————

747375

76' •758989— • .———

4-833-93

' 3-332.65— •I-5I——————

9-97.07-4

n-39-59-5

1 1. 2II . I12.526.625-326.424.2

31-63i-732-03i-531.230.4

.28.526.5,26.830.827.826.0

' 25-5P52 — Carrington Silt Loam

P52-IP52-2P52-3P52-4P52-5P52-6P52-7P52-8P52-9P52-IOP52-IIP52-I2P52-I3P52-I4P52-I5P52-I6P52-I7

P52-I.8P52-I9

O-66-99-12

12-1515-1818-2121-2424-2727-3030-3333-3636-3939-4242-4545-4848-5151-5454-5757-6o

4-54-64.84-64-64-64-74-74-85-05-25-3

s5-55-45-55-55-55-75-8

9-8—ii. i——Ji-5——8.1

—8.1

——9-9

——10.7—

3-o

3-5——4-3

——3-o—2-3

—3-3——3-5

. 0.37

0.35—

0-39——0.31—O.2I

————

O.22—— :

———

——

O.2O——

,8.2—6-4

5-94-94-o—2.0

——

0-9

i-51.2

——i-70.8

61—70—

• 77—84

9i———

' ————

2.402.281-751-43I .IO0.820.56o-34O.22O.22O.I I0.140.130.12

————————

17-616.914.118.315-323.831-646.957-767.074-564.25i-3 .53-348.949-5——

25-126.929.521.52O.222 .026.4I7.I19-313-015-722.727.928.521-4

. 28.9—————

"Laboratory data for profiles P-49 and P-52 obtained under the direction of Dr. R. W. Simonson.

43 6 SOIL SCIENCE SOCIETY PROCEEDINGS 1947

TABLE i.—Concluded.

SampleNo.

Depth,inches PH

Replaceable cations, m.e. per 100 grams soil

Ca Mg K H

Basesatura-tion, %

Organiccarbon,

%

Totalsands,

%

2 yuclay,%

P22—Carrington LoamP22-IP22-2P22-3P22-4P22-5P22-6P22-7P22-8P22-9P22-IOP22-IIP22-I2P22-I3

O-66-12

12-1515-1818-2121-2424-2828-3232-3838-4444-5050-5656-62

5-55-25-i5-i5-o5-04-94-95-i5-35-87-57-6

. 11.78.59.27-98-59-5

H-712.3—13.6

42.4

2.52.O2.O1-92.12.12.22-3 '—1.8

—"2.O .—

0.470.27—

0.26—

. 0.27—

0-35—0.36—

0.24—

7-78.7

7-4

S-1—4-3—3-2

——

6855

58

• 70—78

83——

2.861.89—

'1.04—

0-59——————

38.337437-736.540.640.437-838.64'-536.841.942.143-7

22.822.223-224.424.226.930-732.431.630.129-527.226.8

Pi 14 — Carrington LoamPi 14-1Pi 14-2Pi 14-3Pi 14-4Pi H-5Pi 14-6Pi 14-7Pi 14-8Pi 14-9Pi 14-10Pi 14-1 1Pi 14-12Pi 14-13Pi 14-14-

O-66-99-i3

13-1717-2121-2626-3131-3636-4141-4646-52 .52-5656-6060 +

5-2S-'5-o5-o4-9

4-75-05-36.26.16.16.87-9

14.413.2II .O9-1

9-19-3

10.611.712.3

13.2——

•4• 7.2.1.6

. .62-32.82.6

—2.8———

O.22O.220.240.28

——0.29—

O.29—

0.31——

0.27—

ii. i10.69-38-56.8

—4-93-63-8

1.2———

5959595561—738080—93——

3-412.922.221.460-73

' ———————————

22.825.525-424.833-5

35-635-6 •34-133-633-434-o,36.236-4

24.824-525-425.024.826.829.830.129.830.629.229.628.530.1

horizon at 45 to 60 inches. There is a suggestion thatthe C horizon, or till, of profile P-H4 has a slightlyhigher clay content than the C horizon, or till, of pro-

10PE.KC.E.WT CLA.V

15 Zo GS -30 "M5

5

10

15

20-

25-

•3C-

ul1400

63

TO

P-22

P- 114-

FIG. 4.—Distribution of 2-micron clay in three Carringtonloam profiles, P-22, P-II4, and P-52.

file P—22. For profile P-52, the mechanical analysisdata suggest that the parent material has some strati-fication. The sharp decrease in clay content and inincrease in sand content at 25 to 35 inches is especial-ly to be noted. At 40 to 50 inches the clay contentincreases to about 28 to 30%, a value equal to aboutthat of the till in profile P-22. The apparent stratifiedfeatures .of profile P-52, as contrasted to the un-stratified character of profiles P-22 and P-H4, willbe discussed in more detail in a subsequent part ofthis paper.

The mechanical analysis data for profile P—115show that this profile has some textural features notpresent in either of the Clarion profiles or any of theCarrington profiles. In profile P—115 the low sandcontent, about 8 to 10%, of the first 36 inches isreadily apparent, whereas below 36 inches the sandcontent increases sharply to about 25%. These dataconfirm the field observation that the upper 3 feet is aloess-like material, but the lower material, belowabout 3 feet, is till. This situation is of rather commonoccurrence in a number of counties of northwest Iowawhere the Peorian (lowan) loess is present as a rath-er thin mantle overlying lowan 'drift (11).

MECHANICAL ANALYSIS OF TILL SAMPLES

The mechanical analysis data of the till samples aregiven in Table 2, and also in part on Fig. i. On Fig.I the clay content of the samples is given by groups.

RIE.CKEN, ET AL. 1 SOIL CLASSIFICATION AND MAPPING PROBLEMS

TABLE 2.—Mechanical analysis of some lowan and Mankato till samples.

437

SampleNo. Location (county) Sample depth,

inches

Mechanical analysis

Clay, % Sand, %

Mankato Till48549 1

3067309130923069308930743088

Wright, NES2-Tgi-R24Hamilton, Ei4-T8g-R24Hamilton, SE26-T88-R.25Hamilton, NW5-T86-R25Hamilton, SE34-T8g-R25 'Kossuth, SE2i-Tioo-R3oKossuth, SW2i-Tioo-R30Calhoun, SE36-T87-R34Buena Vista, W3i-Tg2-R37

504045404060405040

181946251515241722

34155

352848

83233

lowan Till483484486487488495502505

307030763078308130843085489499490501

30733077307930863087476477482492493506

307130723083475481497500504498

3051305230563053305430553°573064*3075

Howard, SW2o-Tg9-Ri3Howard, NW29-T99~Ri3Howard, SEi3-T96-Ri4Howard, Ei9-T99-Ri2Howard, SEs-T97-Ri3Howard, NE23-Tg8-Ri2Howard, SW2o-Tioo-Ri3Howard, SWn-TgS-RnHoward, NW27-Tg9-Ri4Howard, SW25-Tioo-Ri3Howard, NEio-T99-Ri3Howard, SEi9-T99-Ri2

. Howard, SW3-Tg7-Ri4Howard, NW^-TcjS-RuBremer, SW25-T93-Ri3Bremer, NW36-Tg2-Ri3Mitchell, NEii-T99-Ri7 .Mitchell, NEii-T99-Ri6Mitchell, NE35-Tioo-RisMitchell, SW20-T98-Ri8Mitchell, Ws-TgS-RiSMitchell, N35-Tioo-Ri3Mitchell, N26-Tg8-Ri6Mitchell, SWi6-T94-RnMitchell, SWio-T94-RnMitchell, NW29-Tg2-Ri6Chickasaw, SE2i-T97-RiiChickasaw, SWs-Tgs-RiiChickasaw, NWii-Tgs-RlsChickasaw, NW3i-T97-Ri3Chickasaw, SW8-T96-Ri2Chickasaw, SE8-T96-Ri2Floyd, NWi4-Tg5-Ri7Floyd, SE2i-T97-Ri6Floyd; NEi4-T94-Ri7Floyd, SWii-Tge-RiSFloyd, NW26-Tg7-Ri5Butler, SW36-T93-RI7Clay, SEI4-T97-R37Blackhawk, Ei6-T88-Ri4Blackhawk, Ei6-T88-Ri4Cedar, SW-7~T82-RiWDickinson, NW29-T98-R37Grundy, SWi6-T87-Ri8Fayette, NWig-Tgs-RioSioux, NW29-T95-R45Worth, SW2I-T98-R20

45404040404040404040404045405°4540454040404040404040 -40406560404040404540405060-5540505550457050

282425312O

- 3034193i303i3122283°23211631193134192624222729172722222222182O233126191939273i3i3221

3938443950243656363440355036364830—353734354546424635—544348462646445143193044512830 .32362445

*The sample taken below the Peorian (lowan) loess mantle.

•Group I, shown on Fig. i by a cross, have from 15to 19% less than 2 \i clay; group 2, shown on Fig. iby closed circles, have from 20 to 26% 2 \i clay;group 3, shown by closed triangles, have from 27 to35% clay; and group 4, shown by closed squares,

from 36 to 50% clay. These group limits are usedmerely to facilitate the graphical presentation of thedata.

From Table 2 and Fig. i it is seen that the Man-kato till samples fall for the most part in group i, or

SOIL SCIENCE SOCIETY PROCEEDINGS

have 15 to 19% clay. The sand content is medium,ranging from about 25 to 50%. From the data givenand from other field observations, it is thought that alarge percentage of the Mahkato till in Iowa will haveabout 15 to 20% clay and a medium content of sand.It should be noted that till underlying the two Clarionprofiles, P-49 and P-97, falls within these limits.From Table 2 it is seen that one sample of Mankatotill has about 46% clay. This situation is thought tobe minor in the Mankato area, and soils formed fromthis high clay material should be classified as a newseries.

Data given in Table 2 and on Fig. i show that thelowan till is quite variable in clay content. The con-centration of till samples with clay content of about27 to 33% in the Howard County area is to be noted.However, till samples with equally high clay content-were found in other parts of the lowan area, as forexample in Bremer, Grundy, and Cedar counties. Ingeneral, the lowan till has more clay than the Man-kato till.

GENERAL DISCUSSIONThe basic differences between the Clarion and Car-

rington series, as expressed in the more recent map-ping in Cerro Gordo and Franklin counties (2) (10),was the degree of leaching of carbonates and acidity.Data presented for several Clarion and 'Carringtonprofiles confirm that depth to carbonates was a validfield mapping criterion when used in a broad separa-tion of soils formed from Mankato or lowan driftmaterials, the degree of leaching associated with theage of the drift sheet. In these two counties the sepa-ration was essentially regional, the boundary coincid-ing with the division between the Mankato and lowandrift sheets. Furthermore, it seems that it is correctto conclude that Mankato till-derived soils are lessleached than lowan till-derived soils of eastern Iowa.This criterion, the degree of leaching, is importantenough by itself to warrant separation of soils of theMankato drift area from those of the lowan driftarea. However, other differences occur also which canbe used as criteria in their identification and sepa-ration.

Therefore, in classifying the soils derived fromWisconsin till in Iowa, great significance must begiven to the age differences of the two Wisconsin sub-stages, the Mankato and lowan. Each of these sub-areas can be studied as separate units for they arequite large and distinctly separated as is indicated byFig. i. Within each area it is then necessary to studythe variability, or homogeneity, of the drift. In boththe Mankato and lowan drift areas, till is the domi-nant condition with outwash relatively minor. There-fore an important next step would seem to be a studyof the till of each area and obtain information on rela-tionship of morphology and other soil properties totill variations. That this might prove profitable is sug-gested by the studies of Winter and Wascher (13)and Odell (8) where it has been shown that mor-phology and productivity are different for differentkinds of Wisconsin till.

SOILS DERIVED FROM MANKATO TILL

Data given in Table 2 for two profiles, P-49 andP-97, show that the Mankato till from which thesesoils have developed is very similar in textural com-position, with about 15 to 17% clay and about 40 to50% sand. From data on mechanical composition ofmiscellaneous till samples shown in Table 2, and fromother field observations, the Mankato till in Iowa isapparently dominantly of the mechanical compositionfound under profiles P-49 and P-97- As indicated bysample No. 3067 (Table 2), till of high clay contentis present, although such conditions are thought tobe minor. Field observations have shown that minorareas of sandy till are also present.

Therefore, it seems that on the basis of presentknowledge, the Clarion series, especially the loamtype, can be defined as having properties as indicatedby profiles P-49 and P-97- This kind of Clarion loam,it is believed, will be the dominant so called "normal"grassland soil of the Mankato area in Iowa. Soilsformed under grass and derived from sandy-till andsilty-clay till, or other varieties of till, should be clas-sified as new series and not with the Clarion catena orwith any of the catenas of this bio-sequence.

Although some studies in the field and laboratoryhave been made on catena associates of Clarion andon the forest and grass-forest transition catenas, ad-ditional studies are needed to characterize these otherseries. It seems worthwhile, however, to present atthis time the possible relationships of the Clarionseries to other catena members and to associatedcatenas of this bio-sequence. This is presented inTable 3. Several of the series are of recent establish-ment and relatively little experience in their mappingin Iowa is available. It is of interest to note that theHayden catena occurs on published county mapsmostly as either the Lindley, Conover, or Miami ser-ies. In Iowa the Nicollet series has been includedwith the loam member of the Webster series on anumber of published maps. The Storden series, whichis a Lithosol, has been mapped with a slope or shal-low phase of the Clarion series. It is readily apparentthat the introduction of many of these new series is anarrowing of the permissible range in properties ofthe series.

SOILS DERIVED FROM IOWAN TILL

If the till, excluding outwash, in the eastern lowandrift area was of uniform composition, there wouldbe a repeating pattern of soil types, varying withtopography and vegetation. The so-called "normal"soil of the area formed under grass might be classedas a single series. If one consults the published coun-ty soil reports, or other publications on the subject(i, 6), it would be found that the Carrington series,particularly the silt loam and loam types, was indi-cated as being the dominant Prairie series of thisarea. If the reader is prepared to accept a rather •broad concept of series, then this classification is per-haps satisfactory. In that case, however, the readermust expect to find that Carrington silt loam andloam have a wide range of productivity, even under

RIECKEN, ET AL.: SOIL CLASSIFICATION AND MAPPING PROBLEMS 439

TABLE 3.—Showing proposed classification and catenary relationships of soils derived from Mankato friable loam till in Iowa.

Nativevegetation

Grasses

Trees

Transition(Grass-Trees)

Catena

Clarion

Hayden*

Lester*

Slope

Catena members

Level

Webster(Wiesenboden)

Ames(Plamosol)

Dundas*

Nearly level

Nicollet< — Intermediate — >

Moderate

Clarion(Prairie)

Strong

Storden*(Lithosolic)

Hayden*(Gray Brown Podzol)

Lester*

*Soil series named proposed in Minnesota by Dr. P. R. McMiller and Dr. Iver Nygard.

constant management, and that the published soilmaps will not differentiate between moderately pro-ductive areas of Carrington, and Carrington areas oflow productivity.

The alternative to a rather broad concept of theCarrington series is to re-examine the classification ofthe soils derived from lowan till. Under this alterna-tive, a somewhat narrowed concept of series can beutilized and therefore a number of sub-divisions ofthe Carrington series can be established as progressin the re-classification is made. As for soils derivedfrom Mankato till, study of the lowan till-derivedsoils has been initiated by collection of several profilesand a number of miscellaneous till samples. Data forthree profiles, P-22, P-52, and P-II4, are given inTable i. Data for a number of till samples are givenin Table 2.

These data, as well as preliminary field studies,show that the parent material factor is quite variablein this area. For example, the condition representedby profile P-52 is a rather common feature in thelowan drift area. In this profile, the upper horizonshave moderate permeability, but the lower section,especially that below 36 to 40 inches, is of slowerpermeability. This situation seems to be related to anapparent stratification of the till. Kay (5) has re-ferred to this condition on the lowan till and hascalled attention to the "pebble band", in some in-stances considering the material overlying the pebbleband to be loessial in origin. However, this materialoverlying the pebble band is poorly size sorted, therebeing present pebbles and fine gravel, as well as sandsand silts, suggesting that an agency other than windis responsible for its origin. It seems that the condi-tion referred to above has some of the features of thebasal till and superglacial till referred to by Flint (4),although geologists have not suggested that the ma-terial above the pebble band in the lowan drift areais superglacial till. Observations made in this studysuggest that the material below the pebble band iscompact and dense, a feature characteristic of basaltill (4). However, whatever the origin of the pebbleband the overlying material, it is evident that a betterunderstanding of its distribution and extent is neces-sary before satisfactory progress can be made in theclassification of lowan till-derived soils.

Another problem in the lowan till 'area is the de-

velopment of profiles like P-22 and P-II4 from com-pect plastic till where the pebble band is absent. Dataon mechanical analysis given in Table I and on Fig.4 and on replaceable cations in Table I do not sug-gest that these profiles are greatly different. Prelimi-nary investigations indicate that these two soils arequite similar in regard to the mineralogical constitu-tion of their clay fraction. However, present informa-tion indicates that soils with a profile like P-H4,common to the Howard County area, are of ratherlow productivity. A careful examination of the mor-phology of these two profiles reveals that P-U4 hasmottlings and olive colors at a shallower depth thanP—22, suggesting that profile P-H4 is somewhat lesswell aerated or less "well drained" of the two. Per-haps studies on physical properties, including per-meability, pore size distribution, and density will in-dicate wherein these soils differ other than in mor-phology.

Mechanical analysis data on lowan till do not seemto offer conclusive evidence that the till with higherclay content is found beneath the least productivePrairie soils, as some of the samples with higher claycontent were collected in areas of productive soils.

At the present stage of the study it seems that it isnot possible to draw any definite conclusions regard-ing the variations in the existing Carrington series.That variations are present is recognized, and it isbelieved that the Carrington series as formerlymapped in Iowa will have several sub-divisions, pos-sibly four or five in all. Two of these sub-divisions,both of low productivity, occur in the Howard Coun-ty area, one being represented by profile P-U4. Twoother sub-divisions, both moderately productive withone represented by profile P-52 and the other byprofile P—22, are considered to be important varietiesin the central and southern part of the area. Anothervariety, developed from a till with about 20 to 25%clay, may also be of considerable extent, possiblydominant in Worth and Mitchell counties. Soilsformed from other lowan drift phases, such as out-wash- or thin loess over till near lowan till borderareas, have also been classified with the Carringtonseries. However, in future classification studies suchconditions will be established as new series.

Inasmuch as no conclusions seemed possible at thepresent time on the classification of the Prairie series

440 SOIL SCIENCE SOCIETY PROCEEDINGS 1947

in this area, it did not seem advisable to devote muchtime to the Wiesenboden and Gray Brown Podzolicassociates.

NOMENCLATURE OF IOWAN TILL-DERIVED SOILS

It has been stated above that the existing Carring-ton series in Iowa has been a rather broad concept.Add to this the areas of Carrington series recognizedin other states and the soil conditions designated bythis series become indeed diverse. As redefinition ofthe former Carrington series progresses in the nextfew years, a decision will need to be made as to whichsub-division or variety shall be designated as Car-rington. From the point of view of acres included withthis series, Iowa will rank among the first. But thenwhich variety shall be designated as Carringtonseries ? If research data are published on soil fertility,soil productivity, or soil conservation, to which of themany varieties of Carrington series will the data re-fer — the redefined Carrington, or to the Carring-ton which is.described in one of the many older coun-ty soil survey reports which many individuals willhave in their files? Therefore, it seems that in thecase of the Carrington series name, it would be betterpolicy to abandon the name entirely in favor of new

'names as sub-divisions are recognized and estab-lished. This policy will cause less confusion and errorthan if some segment of the former series is retainedunder the name Carrington.

SUMMARY

A discussion has been given of the classification ofWisconsin till-derived soils in Iowa, including ashort history of the development of the present taxo-nomic units.

Based on data given here and from other field ob-servations, it is concluded that the soils derived fromtill of Mankato glacial sub-age are less leached thansoils derived from till of lowan sub-age. The Mankatotill is a more recent deposit than the lowan till, thusdifferences in degree of leaching and acidity are dueto the time factor.

From data on two profiles, from a number of mis-cellaneous till samples, and from field observations, itseems that the Mankato till is dominantly of loamtexture and of friable consistence. Therefore, theClarion series, which is a well-drained, "normal"Prairie soil derived from Mankato till, will remain asone of the most important taxonomic units of theMankato area. The Clarion catena will be the domi-nant catena of the area, with Webster, Nicollet andStorden series important members.

From data on three profiles, from a number of mis-cellaneous till samples, and from field observations, itseems that the lowan till of eastern Iowa is quitevariable in composition. It seems likely that severalwell-drained, "normal" Prairie soil series will prob-ably need to be established to replace the existingCarrington series.