LAND UTILIZATION IN RELATION TO SOIL TYPES AND SOIL RATINGS

iElmer G. Fitzpatrick

Numerous valuable studies of land usehave been made by economists and others hav-ing no special knowledge of soils or soiltypes. It appears to the soils student thata great many of the variations in land useare closely allied with variations in soils.It may be inferred from this that a study ofland use, if it is to be on a firm founda-tion, needs to be correlated with a detailedsoil survey map or similar map which deline-ates the soil boundaries and soil types. Aninventory.of the soils is of basic impor-tance in the understanding of variations inland use and in judicious land planning. Con-siderable attention has been directed recent-ly toward the retirement of submarginal landfrom cultivation. Work of this nature needsto be based on a knowledge of the soil andits suitability for crops.

Soil Survey field men have an excel-lent opportunity to study the utilization ofeach soil type within their respective areas.In fact, they are called on to provide suchinformation in the soil survey reports. Inmost instances, this information is includedin notes gathered during the progress of thesurvey, and is very generalized. The authorhas found this method rather unsatisfactory,because the information on land utilizationgathered in this manner is not very specificand not very accurate. Most field men areinclined to be somewhat lax in taking notes.This peculiar trait of human nature can bealtered to some extent by persistent applica-tion of will power. Few will admit that theyare successful in following this course tosuch an extent that it becomes habitual. Bystudying his own notes, the author has foundthat it is difficult to avoid exaggeration ofthe percentage of land occupied by the domi-nant crop on each soil type. It is also dif-ficult to keep from exaggerating the percent-age of crops which are grown on only a fewsoil types. Often the percentage of land inpasture on the better types of land is under-estimated, and it is overestimated on thepoorer types of arable land. It is necessarythat these more important or more noticeablecharacteristics of land use be emphasized in

the report, but they should not be exaggerat-ed. The increasing importance of studies onland utilization make it imperative thatstatements regarding land use be as accurateas possible.

The author has found that the prepa-ration of crop maps of representative areasin the county is of considerable value in ob-taining more specific information regardingthe land use of each soil type. The crop mapis constructed on the same scale as the soilsurvey map, and both crop and soil maps arecross lined in pencil in such a manner thateach ten acres on the crop map may be com-pared with the corresponding ten acres on thesoil map. By this means it is possible toobtain a reasonably accurate estimate of thenumber of acres of each soil that is utilizedfor each of the various crops in the areacovered by the crop maps. The percentage ofa particular soil type devoted to each of thevarious crops may then be calculated. Thisis tedious work and requires several days ofoffice work in the average-sized county.

Crops may be mapped in large blocksor sections of land, or they may be mappedin a narrow strip adjoining the roads. Map-ping crops in narrow strips along each sideof the road is more rapid and, therefore,more satisfactory, except where nearness tothe road influences utilization of the soil.A general knowledge of the county as a wholeis desirable in selecting the areas to be cov-ered by crop maps. The crop maps are moreeasily constructed if made during the seasonwhen crops are growing on the land. Aerialphotographs may be of value in this work, butit w6uld be necessary to compare the photo-graphs with actual conditions in the field,because the photographs will not, in everyinstance, reveal the type of the crop.

Using both the block system and thenarrow-strip system, a soil survey party hasmade crop maps of representative areas inseveral counties of Oklahoma during theprogress of the soil survey. Included inthis paper are the results of these studiesin Pontbtoc County, the mapping of which wascompleted in 1936. Most of the crop mapping

1United States Department of Agriculture.483

484 SOIL SCIENCE SOCIETY PROCEEDINGS 1937

was done by Orville Stout of the Oklahoma Ag-ricultural Experiment Station. The soils inthe county covered toy crop maps were surveyedby Orville Stout, Lonnie E. Rose, and.theauthor. The crop mapping covers approximate-ly 100,000 acres in the county.

Table 1 lists the various soil typesmapped in the county, together with the aver-age yields of the principal crops on eachsoil, the crop productivity rating for eachsoil, and the percentage of each soil typeutilized for each crop and for forest and pas-ture. The percentages of forest and pastureland are not separated because so much of theland in this county is used simultaneouslyfor both purposes. The yield of each soiltype listed in this study represents theauthor's estimate of the average annual yieldand is based on interviews with farmers, onextensive study of yields reported in AAA con-tracts, on detailed study of the various soilprofiles, and on observation of crops grownon the soils.

The rating of each soil for each cropis based directly on the estimated averageannual yield. A simple linear equation wasused in converting the yields into ratings. Agraph was constructed for each crop in such away that a yield of 0 gives a rating of 0 andthe average annual yield of the best soil inthe county for the crop in question gives arating of 100. For example: Teller veryfine sandy loam is the best corn soil In thecounty and produces an average annual yieldof twenty-six bushels per acre. This is giv-en a rating of 100. Riverwash, being thepoorest corn soil, producing an average an-nual yield of 0 bushels per acre, is given arating of 0. Therefore, Crawford silt loam,with an average annual yield of thirteenbushels of corn per acre, would receive a rat-ing of 50. The highest average annual acreyield of other crops included in the studyare as follows: cotton, 175 pounds of lint;oats, fifty bushels; and sorghums, three tons.The rating for pasture is based on the annualcarrying capacity of the native pasture. Therating for sowed pasture would be approxi-mately the same as for sorghums, which is muchhigher than the rating for native pasture onthe forested soils. An annual carrying ca-pacity of three acres per cow is given a rat-ing of 100, and of twenty-five acres per cow,a rating of 0. These figures represent thecarrying capacity of the best and poorest pas-ture land in the county. Pasturing continuesthroughout the year in this county, but somesupplemental feeding of cottonseed cake ispracticed during the winter.

These ratings may be converted readi-

ly to a state-wide, national, or internation-al basis by the use of simple proportion. Forinstance, if the best corn soil in the UnitedStates produced an average annual yield offifty bushels per acre, the ratings for Ponto-toc County could be converted to a nationalbasis by multiplying the corn ratings in thispaper by the fraction S6/50. These ratingsare for the soils in Pontotoc County. Thesame soil type in other counties would havedifferent ratings because of factors externalto the soil such as climate.

Such an imposing array of figures asare shown in Table 1 is apt to be very con-fusing; therefore, a series of graphs hasbeen prepared which show these data for eachcrop in a more simplified manner. In thesegraphs the location on the vertical axis in-dicates the percentage of land utilized forthe crop and the location on the horizontalaxis indicates the soil rating. Each dotrepresents one soil type as listed in Table 1.In other words, it is a graphic representa-tion indicating the relationship or degree ofcorrelation of the soil ratings with the per-centage utilization of the soil for the prin-cipal crops of the county. Another graph(graph No. 4) indicates the average soil rat-ing for all crops on the horizontal axis andthe percentage in cultivated crops on thevertical axis. This shows the correlation ofthe average soil rating with the percentageof land in cultivation. This average soilrating is the arithmetical mean of the cropratings for the principal crops grown in thecounty. In instances of a soil with an ex-ceptionally high rating for a special cropand a relatively low rating for other crops,this may be considered an unfair basis for ar-riving at an average soil rating. It appears,however, that a soil probably should be suit-ed to more than one or two crops before it isdeserving of a high average rating. It ap-pears that the special crop rating can betterexpress this condition. The present utiliza-tion of the soils has not been considered inthe process of rating soils for various crops,except that ratings have been prepared onlyfor those crops which are important in the.county at the present time.

A study of the graphs indicates thatthere is some correlation between the ratingfor each crop and the percentage of the soilutilized for the crop. There is considerablepositive correlation between the average rat-ing for crops and the percentage in cultivat-ed crops. In other words, the higher theaverage rating the higher the percentage ofthe soil type in cultivation. There are,however, several discrepancies in the graphs.

LAND UTILIZATION IN RELATION TO SOIL TYPES AND SOIL RATINGS 485

Table 1

AVERAGE ANNUAL YIELD, SOIL RATING, AND PERCENTAGE OF EACH SOIL UTILIZED FOR EACH OF THEPRINCIPAL CROPS GROWN IN PONTOTOC COUNTY, OKLAHOMA

Teller very fine sandy loamLincoln fine sandy loamSummit clay loamOsage clay loamVerdigris clay loamParsons very fine sandy loamDenton clay loamDurant very fine sandy loamStratford fine sandy loamBrewer fine sandy loamDurant fine sandy loamVerdigris fine sandy loamBuckhorn fine sandy loamRoff gravelly loamCrawford silt loamDougherty fine sandy loamConway fine sandy loamStidham fine sandy loamCrawford clayDenton clay loam, shallowphase

Hanceville fine sandy loamDurant very fine sandy loam,shallow phase

Stidham fine sandy loam,rolling phase

Dougherty fine sandy loam,shallow phase

Chigley fine sandy loamStidham fine sandChigley gravelly loamRoff gravelly loam, shallowphase

Lincoln fine sandTalihina very fine sandy loamCrawford stony loamDenton stony loamRough stony land (Hancevillesoil material)

Rough stony land (Dentonsoil material)

Riverwash

Gen-eralRat-ing

1009190888778787465656362.60555453515138

3634

33

32

31302623

1912000

0

00

Corn

YieldBush-els

26232421201720181615152014131312.111111

98

8

8

8876

65000

0

00

Rat-ing

100889280766576696258587654505046424242

3530

30

30

30302723

2318000

0

00

PerCent

4040161427201514214030401016520201414

77

10

15

148

K>9

#•-*-*•*#

#

#*

Cotton

YieldLbs.

1751501501451451401401301301301201001151009010510010065

6575

60

65

65605550

4030000

0

00

Rat-ing

100858583838080747474685665565160565637

3743

34

37

37343028

2216000

0

00

PerCent

35302116720222532202025152353530238

1014

13

25

2016206

####*

*

##

Oats

YieldBush-els

5045454545453735"3031302527252925252520

2015

18

15

12111010

80000

0

00

Rat-ing

100909090909074706062605054505850505040

4030

36

30

24222020

160000

0

00

PerCent

1510301011301614101015*595*5*4

88

7

4

74*2

##**#

#

##

Sorghums

YieldTons

3.03.02.83.03.02.32.52.52.02.02.02.02.02.01.71.71.71.71.0

1.01.0

1.0

1.0

1.01.0.8.7

.5

.2000

0

00

Rat-ing

10010092100907683836666666666665656565633

3333

33

33

33332623

166000

0

00

PerCent

55712810101113105551751010184

58

8

5

1111•*5

*•H-

*

#

*

#

•fr

X

Nat

ive

Pas

ture

Rat-ing

1504010040409090807070703040709030303075

8030

70-

30

30201520

6015107080

30

700

• od•\

<D -.H-^3 W (U-p CD -PT3W h W CjCD O CO COdnliH &J

PerCent

552642392037362010252560308030304470

7062

60

48

41536076

100100100100100

100

100100

Note: Yield refers to the average annual yield for the particular crop and soil in question.Rating is based directly on yield, the highest average annual yield in the county being rated 100.General rating is the average rating of the soil for the principal crops grown in the county.Per Cent is the percentage of each soil that is cropped to each of the important crops.

*Less than 1 per cent.

486 SOIL SCIENCE SOCIETY .PROCEEDINGS 1937

Utilizat

$ 50

40g.gg iU

a> 105

c

Utilizat

* 5°

"S 40

§Vj 30

fu 20

0 10sft 0

Graph No. 1 Graph No. 3ion of soils for cotton in relation to soil Utilization of soils for oats in relation to soil rat-

ratings ings

_._ J •

•i

•

i

•

.

•

*

•

) 50 1CSoil rating for cotton

Graph No. 2Lon of soils for corn in relation to soil

ratings

. • •

.

•

• •

•0 40 | ———8.8 in -

+*808 20<dS° 10 -o

£ o •0

0

Utilizatl

100

90

P. 80

b 70.9•g 60

^ 50•8« 40

•g 30

fc ZOP<

10

O

on

•

•

• »

. '

50 WO

Soil rating for oats

Graph No. 4of soils for crops in relation to general

soil ratings

.

•

•

'•

1

. .•

•

1 I

50

Soil rating for corn

100 O 50 100

General rating of soils for crops

LAND UTILIZATION IN RELATION TO SOIL TYPES AND SOIL RATINGS 487

These discrepancies, in most instances, arethe result of factors other than the inherentproductivity of the soils. One of the mostpotent factors in determining the utilizationOf a soil, aside from the character of thesoil profile, is the type or types of soilwith which it is associated. For example,Crawford silt loam has a very low percentageof utilization for crops in comparison to itsrating. This is explained by the fact thatit is a good grass soil and is associatedwith and intimately intermingled with areasof Crawford stony loam, which is unsuited forcrops. This association of soils in mostplaces is utilized for grazing purposes, be-cause cultivated fields necessarily would bevery small and irregular in shape.

A somewhat different picture of theinfluence of associated soils on utilizationof a soil is presented by Chigley fine sandyloam. This soil has a low rating, yet nearlyone-half of it is in cultivation. This is avery poor pasture soil and is associated withChigley gravelly loam, which also is a poorpasture soil and a very poor soil for crops.In attempting to utilize the region occupiedby this association of soils the farmers grad-ually have been forced by economic pressureto abandon the Chigley gravelly loam type andhave continued to farm the Chigley fine sandyloam. Had these soils been suited to grass,it is likely that they both would be largelyin pasture.

The selection of specific crops to begrown on the soil is influenced by many fac-tors besides the suitability of the soil forparticular crops. In the first place, a farm-er finds it advisable to grow more than onecrop, in order that he may have a cash crop aswell as concentrates and roughages for feed.Also, it is found advisable to change thecrops grown on the soil from time to time. Inregions where farming has been established fora long time it is customary to follow a fair-ly definite plan of crop rotation. In regions

where this practice is common it is evidentthat the nature of the rotation would have amarked influence on the utilization of thesoils. In this particular county a definitecrop rotation is practiced by only a few farm-ers. The common practice is to vary the cropon each field occasionally, without any fixedplan or rotation. Legumes are seldom grownexcept on alluvial soils.

Associated soils also influence thespecific crop grown on some soils. Conwayfine sandy loam has a moderately low ratingfor corn, but twenty per cent of this soil iscropped to corn. This is not a very extensivesoil and is associated with Hanceville finesandy loam, which is a poor corn soil in thiscounty. If corn is to be grown in the sectionof the county where this association of soilsoccurs, it must be planted on Conway finesandy loam.

The utilization of inextensive soilscannot be considered very significant in astudy of this kind, because crop maps coveronly a small area of such soils.

The results of this study indicatethat farmers pay some attention to the gener-al value of the soils in deciding whetherland shall be in crops or in pasture. It isevident, however, that a great deal of land oflow productivity is in cultivation. Farmersattempting to cultivate such land must workunder a serious handicap at all times. Suchland rarely pays enough to cover the expensesof the crop, and the farmer must be contentwith a bare subsistence. If land is to be re-tired from cultivation under government super-vision, such programs can be directed most ad-vantageously to those poor land areas contain-ing soils of low productivity. Knowledge ofthe relative productivity of various soiltypes and the present utilization of thesesoils would prove extremely useful to agen-cies responsible for the selection of landsto be retired from cultivation.