TDOC

z TA245.7  .1  NIVERSITY iiEEiARY 3-1105
B873 "‘

ApflI1992
NO.1705

Texas Agricultural Experiment Station
J. Charles Lee, Interim Director

The Texas A&M University System
College Station, Texas

[Blank Page in Original Bulletin] '

a Descriptions and Uses of Soils of the
a f Texas Agricultural Experiment Stations
at Dallas and Prosper

by

Billy W. I-lipp, Tim C. Knowles, and Benny]. Simpson
Professor, Research Associate, and Research Scientist, respectively
Texas A&M University Research and Extension Center at Dallas
Texas Agricultural Experiment Station

in cooperation with

Billy R. Stringer
Soil Scientist
Soil Conservation Service, Terrell, TX

and

C. Tom Hallmark
Professor, Soil Genesis and Classification
Department of Soil and Crop Sciences
Texas A&M University, College Station, TX

Keywords: Morphology/ classification

Cover (clockwise from top): The Texas Agricultural Experiment Station at Dallas, research plot investigating fertilizer
n requirements of native ornamental shrubs, research on range and pasture fertilizer requirements.

This publication was edited by R. Marie Jones, and the cover was designed by Roxy A. Pike, Department of Agricultural
Communications, Texas A&M University, College Station, TX.

Contents

Summary ........................................................................................................................... .. 1
Introduction ...................................................................................................................... .. 1
Climate .............................................................................................................................. .. 2
Soils of the Centers ........................................................................................................... .. 2
Soil Series Descriptions .................................................................................................... .. 3
Laboratory Analyses of Selected Soil Profiles ................................................................ .. 9
Water Quality for Agricultural and Domestic Purposes ............................................. .. 12
Use and Management of Soils for Agriculture ............................................................. .. 13
Use and Management of Soils for Urban Purposes ...................................................... .. 14
Use and Management of Soils for Urban Landscapes .................................................. .. 15
Literature Cited ............................................................................................................... .. 18
Glossary ........................................................................................................................... .. 19

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Summary

Austin silty clay and Houston Black clay are the major soils on the Texas A&M
University Research and Extension Center at Dallas. Fairlie clay, Stephen silty clay, and
Eddy gravelly clay loam are present to a minor extent. Because of their complex patterns,
the Stephen and Eddy soils are shown as one unit in this survey.

Austin and Stephen soils are classified as Mollisols in the Comprehensive Soil
Classification System of the United States. Houston Black and Fairlie soils are classified
as Vertisols. Eddy soils are Entisols. Mollisols are dark-colored granular soils containing
more than 1 percent organic matter in the surface layer. Vertisols are referred to as self-
mulching soils or cracking clays. Entisols show little or no evidence of horizon
development.

The soils of the Dallas Center developed mainly from chalk and interbedded marl
under tallgrass and mid-bunchgrass vegetation. The relief is nearly level to gently
sloping with slopes ranging from 0 to greater than 3 percent.

Permeability of the Houston Black and Fairlie soils is very slow. The Austin, Stephen,
and Eddy soils have moderately slow permeability. All soils on the Dallas Center are
calcareous and have an average pH of 7.8. Montmorillonite is the major clay mineral,
which accounts for shrinking and swelling of the soils when drying and wetting. Austin
and Eddy soils contain more than 35 percent carbonate in the A horizon. The C horizons
of both the Austin and Houston Black soils approach a carbonate content of 75 percent.

Introduction

On September 1, 1972, the Board of Trustees of the
Texas Research Foundation, Renner, Texas, formally
presented to Texas A&M University the 380 acres and
facilities and buildings of Texas Research Foundation
for the purpose of creating the Texas A&M University
Research and Extension Center at Dallas. The remain-
ing 270 acres of the Foundation were given to The
University of Texas at Dallas.

The Texas Research Foundation was chartered on
April 11, 1946, as an independent, non-profit research
and educational institution. Business leaders in the
Dallas - Fort Worth area, concerned about the decline of
agricultural productivity of the Texas Blacklands, had
formed the Foundation.

For 125 years, Blacklands agriculture fostered
growth of cities and towns of Texas, which are insepa-
rable from the history of the state. These towns include
Paris, Sherman, Gainesville, Greenville, Denton,
McKinney, Dallas, Prosper, Celina, Fort Worth,
Hillsboro, Waco, Temple, Austin, San Antonio, and
many others. Agricultural production from the Black-
lands area passes through the ports of Galveston and
Houston to worldwide markets.

From the time of the first Spaniards some 400 years
ago to the coming of the railroads 100 to 120 years ago,
the Blacklands of Texas were covered with tallgrasses
and mid-grasses that produced wild game and sup-
ported cattle and sheep. Settlers relocating in the West

and hides of the diminishing bison provided early g

traffic for the railroads. With the arrival of the railroads
and their ability to transport principal crops such as
cotton, the plows turned the fertile grassland into vast

acreages of cultivated fields. Cotton became known as
“king." Small crops of corn and small grains were
produced, but in this early period of history they were
not commercially important. During this period, the
Blacklands were considered to be some of the richest
soils in America. This fertility was commonly assumed
to be inexhaustible.

The Texas Blacklands north of San Antonio ac-
count for only a small part of the land of the state, but
Blackland land resource areas are found extensively in
Arkansas, Alabama, and Mississippi. Before 1900,
nearly all the plowed land of Texas was in this belt.

In the early 1920's, a sharp drop in prices for farm
products focused attention on the declining fertility of
the Blacklands. Many efforts were made to restore soil
fertility, some of which in the early 1940's prompted the
establishment of Texas Research Foundation.

The excellent facilities and location of Texas Re-
search Foundation made it ideal for one of the Research
and Extension Centers being established in Texas by
Texas A&M University. Added to a continuation of
research and extension activities of the Texas Research
Foundation is an expanded program of research in all
agricultural areas, and especially in horticulture at the
Texas A&M University Research and Extension Center
at Dallas. Located in the urban area of the Dallas - Fort
Worth metroplex, the Dallas Center serves approxi-
mately 3.9 million people who reportedly control di-
rectly or indirectly the largest land ownership in the
state.

In 1986, the Dallas Satellite Farm at Prosper was
purchased from the sale of approximately 40 acres of
the Dallas Research and Extension Center land west of
Coit Road. The Prosper Farm consists of 161 acres that

were part of a 958-acre tract deeded to D. W. Light in
1873. It is located off State Highway 289 between the
towns of Prosper and Celina in Collin County. Research
at Prosper is centered around the needs of the agricul-
tural community of the north Texas Blacklands.

Future research and extension activities at Dallas
and Prosper will be directed toward the agricultural
and urban needs of the north-central Texas area. The
soil series of these facilities represent a large segment of
the total Blackland area. This bulletin details and
characterizes the uniqueness of the Blackland soils,
upon which the Center's research revolves.

Climate

The rolling hills of the area range from 500 to 800 ft
in elevation; the Center is about 700 ft above sea level.
The climate of the area is described as humid, subtropi-
cal with hot summers, and continental characterized by
a wide range in annual temperature extremes (National
Oceanic and Atmospheric Administration, 1977).

August, the hottest month of the year, averages a
high temperature of about 95 °F (Figure 1), but tempera-
tures above 100 "F are common in July and August.
January, the coldest month of the year, averages a
minimum temperature of 35 ‘F (Figure 1). The average
freeze-free period is 249 days. The last 32°F tempera-
ture occurs on March 16, and the first 32 °F clay in the fall
occurs on November 21.

Average annual rainfall at the Dallas Center is 35.1
inches with distinct rainy periods in April and May (4.5
inches/ month) (Figure 2a). This rainfall period is
extremely important for field crop production in the
area. Potential evapotranspiration (evaporation) reaches
its maximum from June through July (9.5 to 10 inches/
month). Actively growing plants often require supple-
mental irrigation between June and August. The prob-
ability of receiving more than five amounts of precipi-
tation within 7-day periods during the year is shown in
Figure 2b.

120
O-—O Mean Min. I--I Mean Max.
/\
100--
e \

a =0" -/ AH, ~ "t
D n   $ \
§ 6°" 0/‘ Q/ o I
m 1- / \
n‘ 4Q /o o\
5 an  o P
f_ lb
% 20"  Mean Annual Air Temperature 1- 63.8

i‘ Mean Annual Soil Temperature I 65.6 <>

0 4 ‘ ' ' ‘ ‘ ‘

iészsaaaéfofiiz
MONTH OF THE YEAR
Figure 1. Average monthly minimum (min.) and maximum

(max.) air temperature at the Center (recorded 1947 to 1983
at TAES-Dallas).

é 9-09“ I—-O Precipitation / Q "

1L I \ o
g 100-r: p \ 
E 7.00» / \o
c 0.00» o’ \
% 500" ’ q \

O "" / \
§ 4 001 o ./ \ o\
a ~ / / g o"; \
m 3.00" / . \ / \
o " Q/ i
G 2,001. Q... 0-0 +8 1
O. 1'00‘: Mean Annual Precipitation I 35.08 in.
0.00 ‘ ' ‘ ' ' ' '

léilssrfiérofifz
MONTH OF THE YEAR
Figure 2a. Normal monthly rainfall and potential evapo-

transpiration (PET) at the Center (recorded 1947 to 1983 at
TABS-Dallas).

PROBABILITY (x)

 

é. i s 0 1'01'1 1'21

é 5 l 5
MONTHOFTHEYEAR

Figure 2b. Probability of receiving at least the designated
amounts of precipitation in a 1-week period at TAES-
Dallas.

Climate determines the classification of soil mois-
ture and temperature regimes. Soils of the Centers are
in an ustic soil moisture regime and a thermic soil
temperature regime. An ustic moisture regime is typi-
cal of rainfed wheat lands. Soil moisture is limited
because the soil moisture control section (about 4 to 12
inches below the soil surface) is dry for more than 90
cumulative days when evapotranspiration exceeds pre-
cipitation but is not dry 90 consecutive days in most
years. A thermic temperature regime denotes a soil
having a mean annual soil temperature between 59'F
and 72°F at 20 inches below the soil surface.

The climate of the Dallas Center and the Prosper
Research Station is nearly identical, so the climatologi-
cal data presented previously also approximates that of
Prosper.

Soils of the Centers

Austin silty clay and Houston Black clay are the
major soils on the Texas A&M University Research and
Extension Center at Dallas. Fairlie clay, Stephen silty

O

clay, and Eddy gravelly clay loam are present to a minor
extent. Because of their complex patterns, the Stephen
and Eddy soils are shown as one unit in this survey.

Austin and Stephen soils are classified as Mollisols
in the Comprehensive Soil Classification System of the
United States. Houston Black and Fairlie are classified
asVertisols. Eddy soils are Entisols. Mollisols are dark-
colored granular soils containing more than 1 percent
organic matter in the surface layer and are moist more
than 3 months of the year. Vertisols are referred to as
self-mulching soils or cracking clays. Entisols are
relatively young soils that show little or no evidence of
horizon development.

The soils of the Center developed mainly from
Upper Cretaceous chalk and interbedded marl under
tallgrass and mid-bunchgrass vegetation (U. S. Depart-
ment of Agriculture, 1969). The relief is nearly level to
gently sloping with slopes ranging from 0 to 3 percent.
Weathering of the marl and chalk in low, nearly level,
slowly drained areas formed dark, plastic clay soils of
the Houston Black and Fairlie series. On steeper, higher
lying slopes, erosion exceeds soil formation, resulting
in shallow, poorly developed profiles typical of the
Austin, Eddy, and Stephen series. Thin, eroded profiles
of Stephen and Eddy soils commonly show up as white
spots in cultivated fields of the Blackland Prairies.

Permeability of the Houston Black and Fairlie soils
is very slow. The Austin, Stephen, and Eddy soils have
moderately slow permeability. All soils atthe Center
are calcareous and have an average pH of 7.8. Montrno-
rillonite is the major clay mineral, which accounts for
the shrinking and swelling of the soils when drying and
wetting. Austin and Eddy soils contain more than 35
percent calcium carbonate (lime).

Soils at the Dallas Center are typical of about 6.75
million acres, or 53 percent, of the Blackland Prairie
regions of Texas. The Austin series, the most extensive
soil at the Dallas Center, accounts for about 70 percent
of the soils at the Center. Other soils at the Dallas Center
are Houston Black, Fairlie, Stephen, and Eddy series.
The Prosper Farm consists entirely of the Houston
Black series on O to 1 percent slopes. Austin, Houston
Black, Stephen, and Eddy soils are found throughout
the Blacklands. The Fairlie soils are extensive in other
areas outside Dallas and Collin Counties. Maps of the
soils and topography at the Dallas Center are shown in
Figure 3. Tables 1, 2, and 3 show characteristics of the
soils, their moisture relationships, topography, and ca-
pability class. Detailed descriptions of typical profiles
for each of the soils are presented in the next section.

Soil Series Descriptions

This section describes the soil series and mapping
units at TABS-Dallas. Five series are recognized at the
Dallas Center, representing three groups within three
soil orders. Only one series, the Houston Black, is
recognized at TAES-Prosper. Each soil series contains
both a brief nontechnical and a detailed technical de-

scription of the soil profile, or the sequence of layers
beginning at the surface and continuing down to depths
beyond which most plant roots do not penetrate.
Sample sites were selected after preliminary soil
cores were taken from loca tions considered to be repre-
sentative of mapping units defined after the survey was
made. Soils were sampled from freshly dug pits.
Morphological descriptions of each horizon were made
and samples were collected for laboratory analyses
(Soil Survey Staff, 1951). Soil mapping units were
delineated by soil scientists of the U. S. Department of
Agriculture, Soil Conservation Service. Map delinea-
tions and soil descriptions were confirmed by soil
scientists on the state staff of the Soil Conservation
Service. The detailed high-intensity survey was com-
pleted in November 1973, then updated in 1991.

A: Austin silty clay (fine-silty, carbonatic,
thermic, Udorthentic Haplustoll)

The Austin series is a moderately deep, well-
drained, moderately slowly permeable, fine-textured,
calcareous soil on nearly level to gently sloping up-
lands. The soil formed in chalky limestone. n

Type location: 800 ft east of headquarters along north
end of plots, 100 ft south into cultivated
field (200 ft southwest of east barn).

Typifying pedon: Austin silty clay - cropland (Figure 4,
inside back cover).

Very dark grayish brown (1 OYR 3/2) silty
clay, very dark brown (IOYR 2/2) moist;
moderate fine subangular blocky struc-
ture; hard, firm, sticky, and plastic; few
roots; few soft CaCOa masses and fine
concretions; calcareous, moderately al-
kaline; abrupt smooth boundary.

Dark grayish brown (10YR 4/2) silty clay,
very dark grayish brown (1 OYR 3 / 2) moist;
moderate medium subangular blocky
structure; hard, firm, sticky, and plastic;
few roots; few worm casts; few fine
CaCOs concretions; calcareous, moder-
ately alkaline; gradual wavy boundary.

Ap 0-5"

A 5-13"

AuA Austin silty clay, 0 to 1 percent slopes

AuB Austin silty clay, 1 to 3 percent slopes

FaA Fairlie clay, O to 1 percent slopes

FaB Fairlie clay, 1 to 3 percent slopes

HoA Houston Black clay, O to 1 percent slopes
HoB Houston Black clay, 1 to 3 percent slopes
SeC Stephen-Eddy complex, 1 to 3 percent slopes,

eroded

(Aerial photograph taken by Dallas Aerial Surveys, Dallas,
TX, and topographic map compiled by the architectural
firm of Wheeler and Stefoniak.)

Figure 3. Legend for soil maps (see following pages).

.. "4

/’-—‘\\ ‘I

‘-\ HoB
\

HeB \
x

 e__--____1_____._l

Figure 3a. Soil map of the Texas A&M University Research and Extension Center at Dallas (approximate scale: 1 inch = 720 ft).

 as  
  first


.\

{L

R  

.“' \

ea

l;

 

/'/l/ "'/7/\.

Figure 3b. Contour map of the Texas A&M University Research and Extension Center at Dallas (approximate scale: 1 inch =
400 ft with a contour interval of 2 ft).

Table 1. Characteristics of soils at TAES-Dallas.

Map Soil

symbol series Surface Subsoil Substratum

AuA, Austin silty Dark grayish brown clay silty Brown silty clay; moderate and White platy chalk with brown

AuB clay clay; fine subangular blocky fine subangular blocky structure; silty clay in crevices. At depth
and granular structure, hard hard when dry, firm when moist; of 20-40 inches.
when dry, firm when moist, 10-30 inches thick.
10-20 inches thick.

FaA, Fairlie clay‘ Very dark-gray clay; fine angu- Very dark-gray clay; fine angu- White chalk, platy in the upper

FaB lar blocky structure, very hard lar blocky structure, extremely 6 inches, massive below. At
when dry, very firm when hard when dry, very firm depth of 20-40 inches.
moist, 16-30 inches thick. when moist, 12-34 inches thick.

HoA, Houston Black Very dark-gray clay; fine an- Grayish brown silty clay with Pale-brown and gray marly

HoB clay gular blocky structure; very olive and gray mottles; angu- clay; massive; very hard when
hard when dry, very firm lar blocky structure, very hard dry, very firm when moist.
when moist; 6-50 inches thick. when dry, very firm when

moist; 10-50 inches thick.
SeC Stephen-Eddy Dark-brown silty clay, suban- Dark-brown silty clay with White platy chalk, at depths of
Complex’ gular blocky structure; hard 60% platy chalk fragments, 7-20 inches.
Stephen - when dry, firm when moist; 0-6 inches thick.
(80% of unit) 7-20 inches thick.
Eddy - Brownish gray gravelly clay White platy chalk with brown- White partly cemented
(20% of unit) loam; fine granular structure; ish gray clay loam in crevices; marine chalk, at depths of

35% chalk fragments, 0-5 inches thick 3-15 inches.

3-10 inches thick.

‘The Fairlie series at the center is 4 to 8 inches thicker than normal.

‘These soils occur in a complex pattern and are not mapped separately.

Table 2. Characteristics of soils at TAES-Dallas.

Percentage
Map Moisture Capability Acres at of the
symbol relationship classification Setting the Center Center
AuA, AuB Well drained, surface runoff AuA - l Nearly level to gently sloping AuA-21 6
is medium to rapid; permea- AuB - lle uplands, slopes are 0-3%. AuB-227 62
bility is moderately slow.
FaA, FaB Well drained, surface runoff slow FaA - ll Gently undulating uplands, FaA-4 1
to medium; very slow permeability. FaB - lle slopes are 0-3%. FaB-5 1
HoA, HoB Moderately well drained, HoA - ll Nearly level to gently sloping HoA-27 7
surface runoff is slow to rapid; HoB - lle uplands, slopes are 0-3%. HoB-82 22
very slow permeability
SeC Well drained, surface runoff SeC - lVe Gently sloping uplands with SeC-4 1
is medium to rapid; permea- convex surfaces, slopes are 2-5%. ‘
bility is moderately slow.
Table 3. Some physical properties of soils at TAES-Dallas.
Available
water-holding Potential Erosion
Soils capacity Permeability vertical rise factors Corroslvity
(inches water/ (inches/hour) (inches) K T Steel Concrete
inch soil)
Austin 0.13-0.16 0.2-0.6 > 2 0.32 2 high low
Houston Black 0.12-0.15 < 0.06 > 2 0.32 4 high low
Fairlie 0.12-0.15 < 0.06 > 2 0.32 3 high low
Stephen 0.13-0.16 0.2-0.6 0.5-1 .3 0.32 1 high low
Eddy 0.17-0.19 0.2-0.6 < 0.25 0.24 _1 high low

Bw 13-26"

Bk 26-33"

Cr 33"+

Grayish brown (10YR 5/ 2) silty clay, dark
grayish brown (10YR 4/ 2) moist; moder-
ate fine subangular blocky and angular
blocky structure; hard, firm, sticky, and
plastic; few fine roots; few worm casts;
few fine CaCOa soft masses and chalk
fragments; calcareous, moderately alka-
line; diffuse boundary.

Pale-brown (10YR 6/3) silty clay, brown
(10YR 5/3) moist; medium subangular
blocky and angular blocky structure; hard,
firm, sticky, and plastic; few fine roots;
common soft CaCOs masses, few fine
chalk fragments; calcareous, moderately
alkaline; clear wavy boundary.

White (10YR 8/2) and yellowish brown
(10YR5/ 6) platy chalk hardness of 2 Mohs’
scale; fractures in upper part filled with
Bk material.

Range in characteristics: Solum thickness is 26 to 37

inches. The dry color of the A horizon is

dark brown (10YR 3/2) or dark grayish i

brown (10YR 4/2). Texture is silty clay or
silty clay loam. Thickness is 11 to 19
inches. The dry colors of the B horizons
are dark grayish brown (10YR 4 / 2), pale
brown (10YR 6/ 3), brown (10YR 5/ 3), or
light yellowish brown (2.5YR 6/ 4). Faint
mottles of yellowish brown (1 OYR 5/ 6) or
light yellowish brown (10YR 6/ 4) range
from none to few. Texture is mainly silty
clay but ranges to clay. The substratum is
platy chalk interbedded with marl and
clay in some pedons.

B: Houston Black clay (micro high) (fine,
montmorillonitic, thermic, Udic Pellustert)

Houston Black series is a very deep, moderately
well-drained, very slowly permeable, fine-textured,
calcareous soil on nearly level to gently sloping up-
lands. The soil formed in calcareous marl and clay.

Type location: 200 ft east of Coit Road, 100 ft south of

intersection of Coit Road and St. Louis
Southwestern Railroad.

Typifying pedon: Houston Black clay (micro high) -

Ap 0-5"

pasture (Figure 5, inside back cover).

Nery dark gray (10YR 3/1) ranging in

texture from silty clay to clay, black (10YR
2/1) moist; moderate medium angular
blocky and subangular blocky structure;
very hard, very firm, very sticky, and
plastic; many fine roots; few fine soft
CaCOa masses; calcareous, moderately
alkaline; abrupt smooth boundary.

A

5-14"

Bssl 14-46"

Bss2 46-63"

C

63-80"

Dark gray (10YR 4/ 1) ranging in texture
from silty clay to clay, very dark gray
(10YR 3/ 1) moist; moderate medium an-
gular blocky structure; very hard, very
firm, very sticky, and plastic; common
fine roots; few fine CaCOs soft masses
and concretions; calcareous, moderately

alkaline; clear wavy boundary.

Grayish brown (10YR 5/2) ranging in
texture from silty clay to clay, dark gray-
ish brown (10YR 4/2) moist; few fine faint
brown (10YR 5/ 3) mottles; moderate
medium angular blocky structure; very
hard, very firm, very sticky and plastic;
common intersecting slickensides below
20 inches; few fine roots; few soft CaCOa
masses; calcareous, moderately alkaline;
gradual wavy boundary.

Lightbrownish gray (10YR 6/ 2) silty clay,
grayish brown (10YR 5/2) moist; few fine
faint yellowish brown (10YR 5/ 6) and
very pale-brown (1 OYR 7/ 3) mottles; mod-
erate medium angular blocky structure;
very hard, very firm, very sticky, and
plastic; few intersecting slickensides and
vertical streak of very dark gray (10YR 3/ 1)
from horizons above; few roots; few soft
powdery masses of CaCOa; calcareous;
moderately alkaline; gradual wavy
boundary.

Very pale-brown (10YR 7/3) and yellow-
ish brown (10YR 5/ 6) silty clay loam;
massive; very hard, very firm, very sticky
and plastic; few fine CaCOs concentra-
tions and soft powdery masses; calcare-
ous, moderately alkaline.

Range in characteristics: Solum thickness is 62 to 78

inches. Gilgai microrelief is indistinct;
microknolls are 4 to 8 inches higher than
microdepressions. Distance from the cen-
ter of the microridge to the center of
microdepression ranges from 9 to 14 ft,
and this cycle is closer on more sloping
areas. Texture of the control section is
clay or silty clay with clay content typi-
cally 50 to 60 percent. The A horizon dry
colors are very dark gray (10YR 3/1) or
dark gray (10YR 4/ 1). Thickness is 13 to
41 inches, and the A horizon is thickest in
microdepressions. The Bss horizons dry
colors are dark grayish brown (10YR 5/ 3),
yellowish brown (10YR 5/ 6), or very pale
brown (1 OYR 7/ 3). Thickness of the Bss
horizon is 17 to 58 inches. The C horizon
is mottled with colors of dark grayish

brown (10YR 4/2), brown (1 OYR 5/ 3),
very pale brown (10YR 7/3), or yellowish
brown (10YR 5/6). Texture is clay or silty
clay and mar].

C: Fairlie clay (fine, montmorillonitic,
thermic, Udic Pellustert)

The Fairlie series is a member of the fine, montmo-
rillonitic thermic family of Udic Pellusterts. It is a deep,
moderately well-drained, very slowly permeable cal-
careous soil on nearly level to gently sloping uplands.
These cyclic clayey soils have black A horizons and
dark-gray or very dark-brown B horizons that rest on
chalk about 46 inches below the surface.

Type location: 150 ft north and 50 ft east of southwest
comer of the Center.

Typifying pedon: Fairlie clay, micro low - cropland.

Ap 0-5" Very dark-gray (10YR 3/ 1) clay, black
(10YR 2/1)moist; moderate fine and
medium subangular blocky structure;
very hard, very firm, very sticky, and
plastic; common roots; few fine CaCOa
soft masses and concretions; calcareous,
moderately alkaline; abrupt smooth
boundary.

Very dark-gray (10YR 3/1) clay, black
(10YR 2/ 1) moist; moderate medium an-
gular blocky structure; very hard, very
firm, very sticky, and plastic; common
fine roots; few fine CaCOs concretions
and chalk fragments; few intersecting
slickensides below 20 inches; calcareous,
moderately alkaline; gradual wavy
boundary.

Bss 23-40" Very dark-gray (10YR 3/ 1) clay, black
(10YR 2/ 1) moist; strong, medium, angu-
lar blocky structure; very ha rd, very firm,
very sticky, and plastic; few fine roots;
common intersecting slickensides and
parallel-epipeds;fewfinechalkfragments;
calcareous, moderately alkaline; gradual
wavy boundary.

A 55-23"

 Bk 40-47" Gray (10YR 5/ 1) clay, dark gray (10YR

4/ 1) moist; strong fine angular blocky
structure; very hard, very firm, very sticky,
and plastic; common fine soft CaCOa
masses and chalk fragments; calcareous,
moderately alkaline; diffuse boundary.

Cr 47-55" Very pale-brown (1 OYR 7/ 3) chalky marl,
becomes platy chalk below 54 inches with
hardness less than 3 on Mohs’ scale.

Range in Characteristics: Solum thickness to chalk is 43
to 54 inches. Texture of the control sec-
tion is clay; clay content is 4O to 50 per-
cent. Dry color of the A horizon is black
(10YR 2/1) or very dark gray (10YR 3/1).
Thickness is 12 to 40 inches, and subsoil
lows and highs occur each 12 to 15 ft. Dry
color of the Bss horizon is very dark grey
(10YR 3/ 1), very dark grayish brown
(10YR 3/2), dark gray (10YR 4/1), dark
grayish brown (10YR 4/ 2), or grayish
brown (10YR 5/ 2). Some pedons have
mottled Bk horizons that are very dark
grayish brown (10YR 3/ 2) and grayish
brown (10YR 5/ 2, 2.5YR 5/ 2). Mottles of
brown (10YR3 / 3), yellowish brown (10YR
5/4), or brown (10YR 5/ 3) range from
none to few. The Cr horizon is platy chalk
or chalky marl. The chalky marl occurs in
the subsoil lows. Texture is silty clay with
common chalk fragments. Colors are
mottled with shades of browns and yel-

lows.

D: Stephen silty clay (clayey, mixed,
thermic, shallow, Udorthentic Haplustoll)

The Stephen series is a member of the fine, mixed,
thermic, shallow family of Typic Haplustolls. It is a
shallow, well-drained, moderately slowly permeable
soil on nearly level to gently sloping uplands. These
calcareous soils have a dark grayish brown silty clay Ap
horizon, brown silty clay Bw horizon, and platy chalk
at a depth of 13 inches.

Type location: Part of the Stephen-Eddy complex found
350 ft west of east property line and 1,200
ft south of St. Louis Southwestern Rail-
road.

Typifying pedon: Stephen silty clay - cropland.

Ap 0-7" Dark grayish brown ( 10YR4 / 2) silty clay,
very dark grayish brown (1 OYR 3/ 2) moist;
moderate medium subangular blocky
structure; hard, firm, sticky, and plastic;
common fine roots; 5 percent chalk frag-
ments less than 0.5 inch in diameter; cal-
careous, moderately alkaline; clear,
smooth boundary.

Brown (7.5YR 5/ 4) silty clay, dark brown
(7.5YR 4 / 4) moist; moderate fine suban-
gular blocky and granular structure; few
fine roots; common chalk fragments finer
than layer above; calcareous, moderately
alkaline; abrupt wavy boundary.

Bw 7-13"

D

Cr 13-20" White (10YR 8/2) platy and massive
chalky limestone with hardness of 2 on
Mohs’ scale, interbedded with very pale-
brown (10YR 7/3) marly silty clay in up-
per 5 inches.

Range in characteristics: Solum thickness to chalk or marl
is 9 to 18 inches. Chalk fragments in the
solum range from 3 to 15 percent and in
size from 0.25 to 1 inch. Texture is silty
clay. Dry color of the A horizon is dark
grayishbrown(10YR4/2)orbrown(10YR
4/3). Dry color of the Bw horizon is dark
brown (7.5YR 4/2, 4/ 4). Moist chroma
and values are less than 3 in at least one-
third of the solum depth. The C horizon
is white platy chalk interbedded with
very pale-brown (10YR 7/ 3) marly silty
clay.

E: Eddy very gravelly clay loam
(loamy-skeletal, carbonatic, thermic,
shallow, Typic Ustorthent)

The Eddy series is a member of the loamy skeletal,
carbonatic thermic family of Typic Ustorthents. It is a
shallow, well-drained, moderately permeable soil.
These calcareous soils have grayish brown gravelly clay
loam A horizons, very pale-brown gravelly silty clay
loam C horizons, and white platy chalk at depths of 11
inches.

Type location: Part of the Stephen-Eddy complex found
350 ft west of east property line and 1,200
ft south of St. Louis Southwestern Rail-
road.

Typifying pedon : Eddy very gravelly clay loam - crop-
land.

Ap 0-5" Grayish brown (10YR 5/2) very gravelly
clay loam, dark grayish brown (10YR
4/ 2) moist; moderate fine granular struc-
ture; hard, firm; few roots; 35 to 40 per-
cent chalk fragments 0.5 to 1 inch in diam-
eter; calcareous, moderately alkaline;

abrupt wavy boundary.

CA 5-11" Very pale-brown (10YR 7/ 3) very grav-
elly silty clay loam; structureless; hard,
firm; 50 percent by volume of chalk frag-
ments 1 to 3 inches in diameter; calcare-
ous, moderately alkaline; abrupt wavy

boundary.

White (10YR 8/ 2) and very pale-brown
(10YR 7/ 3) platy and massive chalky lime-
stone.

Cr 11-18"

Range in characteristics: Solum thickness is 4 to 14 inches
over chalk. The soil contains 35 to 50
percent by volume of platy chalk frag-

ments ranging from 0.5 to 3 inches in
diameter. Dry color of the A horizon is

grayish brown (10YR 5/2) and brown
(10YR 5/ 3, 7.5YR 5/ 2). Texture is very
gravelly clay loam with 18 to 35 percent
clay. The C horizon is very pale-brown
(10YR 7/3) and white (10YR 8/2) platy
limestone interbedded with silty clayloam
in the upper 4 to 7 inches. The chalk
becomes harder and plates become coarser
with depth.

Stephen-Eddy complex,
2 to 5 percent slopes (SeC)

Stephen-Eddy complex soils are shallow and very
shallow, gently sloping, calcareous, clayey, and loamy.
The soil area is long and narrow and is slightly less than
4 acres in size (Figure 6, inside back cover). A represen-
tative area is 350 ft west of the east property line and
1,200 ft south of the St. Louis Southwestern railroad.

This soil area is 80 percent Stephen and 20 percent
Eddy soils. Eddy soils occur as slightly steeper areas
less than 1 / 4 acre in size within larger areas of Stephen
soils.

Stephen soils have surface layers of very dark
grayish brown silty clay about 7 inches thick. Below this
to a depth of l3 inches is brown silty clay. Below 13
inches is platy white chalk interbedded with very pale-
brown marly clay.

The Eddy soils have dark grayish brown clay loam
surface layers about 5 inches thick that contain about 35
percent flattened chalk fragments less than 2 inches in
diameter. Below this to a depth of 11 inches is a very
pale-brown silty clay loam with about 70 percent flat-
tened chalk fragments. Below 11 inches is very pale-
brown and white platy chalk.

Included with these soils and shown on the map are
small spots less than about 1 / 6 acre of soil similar to the
Stephen with chalk 20 to 26 inches below the surface.

The permeability is moderately slow and surface
runoff is medium to rapid. The available water capacity
is low. The water erosion hazard is moderate to severe.
Terracing and crop residue managed near the soil
surface has reduced the erosion that normally occurs on
these soils.

The capability unit is IVe-4. Pasture group is 13A.

Laboratory Analyses of
Selected Soil Profiles

Soil samples representing each horizon from both
the Austin and Houston Black soils were taken from
freshly dug pits atTAES-Dallas in November 1989. The
Texas A&M University Soil Characterization Labora-
tory performed soil analyses using standard proce-
dures (Hallmark et al., 1986).

Particle-size distribution, also called soil textural
analysis, measures the size distribution of mineral soil
particles less than 2 mm in diameter. Soil particle
fractions normally determined include sand (0.05 to 2
mm diameter), silt (0.002 to 0.05 mm diameter), and
clay (<0.002 mm diameter). The pipette method of
measuring suspended solids was used to estimate par-
ticle-size distribution (Tables 4 and 5).

Most of the soil horizons tested have a silty clay
texture. Although the control section of the Houston
Black series is silty clay, silt percentages less than 4O
percent result in a clay textural class. Thus, the Houston
Black soil borders between a silty clay and a clay
texture. Soils that are primarily silt have intermediate
nutrient-holding capacity but are easily eroded by
water and have medium to rapid runoff potential. Clay
soils are also sticky and heavy when wet and can be
difficult to till but have a high nutrient-holding capacity.

Bulk density was determined from core samples
taken horizontally within each pit with a double cylin-
der sampler. This reflects the density of an undisturbed
volume of soil solids plus pore space. Bulk density is
used primarily for converting water percentage by
weight to content by volume and for estimating the
weight of a volume of soil too large to weigh, such as
tons per acre foot.

Soil reaction (pH), a measure of the hydrogen ion
activity in soil, is a routine measurement determined on
1:1 soil-to-distilled-water suspensions. Soil pH greatly

. affects the availability of plant nutrients. The observed

range of pH values between 7.6 to 7.9 reflects the
calcareous nature of Austin and Houston Black soils
(Table 6). Major effects of the slightly basic pH often are
to reduce the solubility of iron (Fe) and zinc (Zn) and to
reduce the availability of soil phosphorus (P).

Total carbon was determined by dry combustion.
Organic carbon (Table 6) was calculated as the differ-
ence of total carbon and inorganic carbon determined
in calcite (CaCOa) equivalent analyses. Organic carbon

Table 4. Particle size distribution of TAES-Dallas soils.

was multiplied by a factor of 1.724 to obtain an estimate
of soil organic matter.

Organic matter content of the surface 12 inches of
Austin and Houston Black soils exceeded 2 percent
(Table 7). Concentrations in these two cultivated soils
ranged from4.5 to 4.6 percent in the plow layerbut were
considerably lower (<0.03 percent) in subsoil. Organic
matter changes are extremely slow in Blackland soils;
therefore it is economically feasible to increase soil
organic matter for production agriculture only by in-
corporating plant residues. Laws (1961) found that
about 1.8 tons/ acre/ year of crop residue must be re-
turned to Blackland soil to maintain organic matter
levels. Smith et al. (1954) determined that Blackland
soils under corn reached an equilibrium of about 2
percent organic matter.

Bases extractable in 1 M ammonium acetate
(NH 4OAc, pH 7.0) and cation exchange capacity (CEC)
using 1 M sodium acetate (NaOAc, pH 8.2) were also
determined for the two soils (Table 6). Extractable bases
measured included calcium (Ca), magnesium (Mg),
sodium (Na), and potassium (K). An abundance of free
lime (CaCOa) in these soils resulted in high concentra-
tions of extractable Ca. The ability of a soil to absorb
cations, or plant nutrients, is quantified by its CEC.
Soils containing high levels of organic matter and / or
montmorillonitic clay have relatively high CEC values;
but the presence of sand and silt tends to lower CEC
values.

Critical levels suggested by the Texas A&M Soil
Testing Laboratory are 0.9, 0.42, and 0.32 meq/ 100 g for
extractable calcium, magnesium, and potassium, re-
spectively, in Texas soils. Fertilizer additions are rec-
ommended when soil nutrient concentrations are be-
low these critical levels. Thus, plants would not be
expected to benefit from applications of Ca, Mg, or K
fertilizers at these two sites. Sodium can affect plants by
changing the physical properties of soil when extract-
able Na concentrations exceed 4.35 meq/ 100 g or when

Sand Silt Clay
Very Very Coarse Fine Coarse

Depth coarse Coarse Medium Fine line (0.1 - (0.02- (0.002- Fine

Soil from (2.0 - (1.0 - (0.5 - (0.25- (0.1- 0.02 0.002 0.0002 (<0.0002
series Horizon surface 1.0mm) 0.5mm) 025mm) 0.1mm) 0.05mm) mm) mm) mm) mm)

inches percentage

Austin Ap 0-5 0.5 0.6 0.7 3.0 4.9 13.0 33.0 32.6 1 1.7
a A 5-13 0.2 0.4 0.2 1.2 3.2 10.0 34.1 30.7 20.0
' Bw 13-26 0.5 0.4 0.4 2.3 3.1 8.5 37.4 28.1 19.3
Bk 26-33 0.4 0.3 0.4 2.1 3.2 8.2 42.2 27.4 15.8
Cr 33-60 0.1 0.3 0.3 2.8 4.3 7.0 49.3 31.2 4.7
Houston Black Ap 0-5 0.3 0.4 0.5 1.4 2.9 16.8 28.3 44.5 4.9
(micro high) A 5-14 0.3 0.8 0.7 1.5 2.9 8.9 32.2 32.7 20.0
Bss1 14-46 0.5 1.2 0.7 1.2 2.5 9.1 33.2 27.5 24.1
Bss2 46-63 0.6 0.9 0.5 1.0 2.6 10.3 32.1 45.3 6.7
C 63-72 0.3 0.6 0.8 4.2 5.4 4.9 42.2 40.9 0.7

1O

9X“

Table 5. Texture and bulk density of TAES-Dallas soils.

’ Depth Sand Silt Clay Moist

’ Soil from (2.0- (0.05- (<0.002 Coarse bulk

series Horizon surface 0.05mm) 0.002mm) mm) fragments Texture class density

Q inches ............................. .. percentage ............................. .. g/cm‘
Austin Ap 0-5 9.7 46.0 44.3 1 silty clay 1.00
A 5-13 5.2 44.1 50.7 0 silty clay 0.99
Bw 13-26 6.7 45.9 47.4 0 silty clay 1.02
Bk 26-33 6.4 50.4 43.2 0 silty clay 1.05
Cr 33-60 7.8 56.3 35.9 0 silty clay loam 1.09
Houston Black Ap 0-5 5.5 45.1 49.4 0 silty clay 1.08
(micro high) A 5-14 6.2 41.1 52.7 0 silty clay 1.07
Bss1 14-46 6.1 42.3 51.6 0 silty clay 1.08
Bss2 46-63 5.6 42.4 52.0 0 silty clay 1.20
C 63-72 11.3 47.1 41.6 0 silty clay 1.39

Table 6. Soil reaction, organic carbon, and extractable bases (ammonium acetate extractable) of TAES-Dallas soils.

Depth pH Cation Exchangeable
Soil from (H2O Organic Extractable bases exchange sodium
series Horizon surface 1:1) carbon Calcium Magnesium Sodium Potassium capacity percentage
inches % ................................... .. meq/100g* ................................ .. %
Austin Ap (>5 7.6 2.59 68.0 1 .3 0.1 1.3 39.5 0.2
o A 5-13 7.8 1.94 75.5 1.5 0.1 0.8 42.7 0.2
Bw 13-26 7.8 1.23 67.8 0.7 0.2 0.3 37.3 0.5
Bk 26-33 7.9 0.70 58.2 0.4 0.2 0.2 28.6 0.7
Cr 33-60 7.9 0.18 50.6 0.4 0.2 0.2 1 1.3 1.8
Houston Black Ap 0-5 7.6 2.66 85.4 2.1 0.2 0.9 47.5 0.4
‘(micro high) A 5-14 7.8 1.20 79.7 1.1 0.4 0.4 44.3 0.9
Bss1 14-46 7.8 0.83 83.6 0.9 0.5 0.4 45.1 1.1
Bss2 46-63 7.8 0.44 70.8 0.9 0.4 0.4 42.0 0.9
C 63-72 7.9 0.01 50.7 0.5 0.3 0.2 16.4 1.8

‘Calcium (ppm) = calcium (meq/100 g) x 200
Magnesium (ppm) = magnesium (meq/100 g) x 120
Sodium (ppm) = sodium (meq/100 g) x 230
Potassium (ppm) = potassium (meq/100 g) x 390

Table 7. Water soluble anions (saturated paste), lime equivalent, and organic matter of TAES-Dallas soils.

Depth
Soil from Soluble anions Calcite Organic
series Horizon surface Carbonate Bi-carbonate Chloride Sulfate Calcite Dolomite equivalent matter
inches ............. .. ..... .. parts per million percentage ........................... ..

. Austin Ap 0-5 0.0 299 63.0 77 40.5 0.8 41.5 4.5
A 5-13 0.0 159 3.5 24 35.8 0.1 35.9 3.3

Bw 13-26 0.0 159 3.5 34 46.8 0.0 46.8 2.1

Bk 26-33 0.0 165 3.5 34 61.4 0.7 62.2 1.2

Cr 33-60 0.0 134 7.0 82 76.0 0.9 77.0 0.3

fi Houston Black Ap o-s 0.0 177 28.0 sa 22.7 0.4 23.2 4.6
A (micro high) A 5-14 0.0 195 3.5 48 29.5 0.8 30.4 2.1
Bss1 14-46 0.0 128 0.0 101 28.8 0.3 29.1 1.4

Bss2 46-63 0.0 153 3.5 1 10 36.0 0.0 36.0 0.8

C 63-72 0.0 128 53.0 77 72.2 0.0 72.2 0.0

11

exchangeable sodium percentage (ESP) exceeds 15 per-
cent, resulting in a sodic (alkali) soil. Sodium is nor-
mally low in Blackland soils, although a few areas
contain saline seeps that result in excessive total salts
and/ or sodium.

Many compounds that are readily soluble in
NH,OAc areonly slightly soluble in water (e.g., CaCOa).
Therefore, concentrations of soluble salts often repre-
sent solute concentrations in the soil solution more
accurately than extractable bases. Electrical conductiv-
ity (EC) and soluble cation (base) plus anion concentra-
tions to include Ca, Mg, Na, K, carbonate (CO3), bi-
carbonate (HCOQ), chloride (Cl), and sulfate (S0,) were
determined on a saturated paste extract. Final distilled
water content was noted at saturation (Tables 7 and 8).
Electrical conductivity was multiplied by a factor of 640
to obtain an estimate of total salt content expressed in
parts per million.

The EC of a saturated soil extract is directly related
to the concentration of soluble salts in the soil solution.
High soluble salt concentrations lower the availability
of soil water for plant uptake. Saline (salty) soils have
EC’s exceeding 4 mmhos/ cm. When EC exceeds 2
mmhos/ cm, salt damage may occur on salt sensitive
plants such as beans, corn, clovers, roses, photinia, and
holly. Typical ranges of EC measured at the Center
were between 0.4 and 1.3 mmhos/ cm (Table 8), indicat-
ing low potential for salt damage to cultivated plants.

The Texas A&M Soil Testing Laboratory suggests
a critical level of 25 ppm sulfate (S0,) in Texas soils.
Plants growing on soils testing below 25 ppm soluble
S0, could benefit from sulfur (S) fertilizer applications.
Typical ranges of S0, measured at the Center were
between 24 to 110 ppm, reflecting adequate supplies of
soil sulfur.

Soils containing calcium carbonate (CaCO3) are
called calcareous soils. The presence of CaCO3 in soil
influences the soil pH, the availability of phosphorus,
iron, and zinc, and the fate of applied phosphorus
fertilizers. Percentages of calcite (CaC0,) and dolomite

(CaCO3-MgC03) were determined by gasometric analy-
sis using a Chittick apparatus. The calcite equivalent
(total lime content) was calculated from the sum of
CaCOa and CaCO3-MgC03 percentages.

The importance of CaCO3 in controlling soil pH is
emphasized by the requirementof about 3 tons of sulfur
(or 10 tons of sulfuric acid) per acre to neutralize every
1 percent CaCOa to a depth of 6 inches. The presence of
CaC03 can be determined qualitatively by efferves-
cence in the presence of cold, dilute hydrochloric acid
(HCl). Austin and Houston Black soils contained 23 to
4O percent CaCOa in the surface 12 inches and 72 to 76
percent CaCOs in the subsoil (Table 7). Large-scale
sulfur applications to decrease alkalinity are not prac-
tically or economically feasible for these soils.

Water Quality for Agricultural and
Domestic Purposes

Water used at the Dallas Center is primarily sur-
face water from Lake Lavon purchased from the city of
Richardson. Two water samples were taken in Febru-
ary 1990 at the greenhouse facilities and the turfgrass
sprinkler irrigation lines for chemical analysis at the
Texas A&M University Soil Testing Laboratory. Simi-
lar laboratory results were obtained from both samples;
therefore their mean chemical concentrations are pre-
sented (Table 9).

Principal uses of water at the Center include drip
and sprinkler irrigation and consumption by humans
and livestock. Concentrations of Ca, Mg, Na, K, C03,
HCOQ, Cl, S0,, and nitrate (N03) are well below Texas
Department of Health and U. S. Environmental Protec-
tion Agency (1975) limits for drinking water (Table 9).
Total soluble salt concentration was well below recom-
mended limits of 1,000, 1,300, and 2,000 parts per
million (ppm) proposed for drinking, irrigation, and
livestock waters, respectively (Texas Department of
Health). No danger of boron toxicity to plants or
animals exists, and negligible quantities of elements

Table 8. Salinity and water soluble bases (saturated paste extract) of TAES-Dallas soils.

Depth
Soil from Electrical Water Soluble bases Total
series Horizon surface conductivity content Calcium Magnesium Sodium Potassium salts
inches mmhos/cm % ................................. .. parts per million ................................ ..
Austin Ap 0-5 0.8 73 140 2.4 4.6 12.0 512
A 5-13 0.3 79 56 1.2 4.6 3.9 192
Bw 13-26 0.4 66 72 1 .2 6.9 0.0 256
Bk 26-33 0.4 59 72 1 .2 9.2 0.0 256
Cr 33-60 0.4 58 62 0.0 16.0 0.0 256
Houston Black Ap 0-5 1.3 81 250 25.0 14.0 3.9 832
(micro high) A 5-14 0.4 75 70 13.0 16.0 0.0 256
Bss1 14-46 0.4 89 70 1 1 .0 25.0 0.0 256
Bss2 46-63 0.4 93 68 1 1.0 23.0 0.0 256
C 63-72 0.4 63 58 6.0 21 .0 0.0 256

12

Table 9. Analytical data ot TAES-Dallas water used tor ornamental
plant irrigation and human and animal consumption.

O

Pounds applied Recommended
Parts per acre limit in parts

Analysis per million inch water per million
Calcium 25.8 5.8 75"
Magnesium 2.0 0.4 1 25°
Sodium 9.0 2.0 100°
Potassium 5.5 1.2 340‘
Carbonate 0.0 0.0 ——
Bi-carbonate 73.1 17.0 150°
Chloride 7.5 1.7 250“
Sulfate-S 6.2 1 .4 250'
Nitrate-N 0.2 0.0 10'
Phosphate-P 0.0 0.0 —-
Boron 0.0 0.0 1'
Total salts 142.0 32.0 1000'
Other unlts

Electrical conductivity (mmhos/cm) 0.30

pH 8.10

Sodium absorption ratio (SAR) 0.46

Hardness (grain/gallon) 1.66

Leaching requirement (%) 0.0

Sulfuric acid requirement (gal. of 95% H2804 per

acre inch to neutralize bi-carbonate) 0.5
Gypsum requirement (lbs/ac inch) 0.0

' Based on upper limits for drinking water established by the EPA
(1975).

i’ Proposed upper limit for drinking water tor which Ca and Mg contribute
to water hardness.

° Proposed upper limit for drinking water for persons on a low-sodium
diet

° Proposed upper level tor drinking water for disagreeable taste.

' Proposed upper limit for potable water tor detrimental scale formation
on pipes and fixtures.

' Proposed upper level tor irrigation of ornamental plants sensitive to
salts.

essential for plant growth are applied in irrigation
water. Although fluoride concentration was not deter-
mined, the low concentration of total dissolved solids
could reflect low concentrations of this mineral. In fact,
livestock would benefit from mineral supplements be-
cause of the low salt content of this water.

The presence of calcium and magnesium made this
water slightly hard. Water hardness can be reduced
with a water softener; however soft water can be corro-
sive and often contains excessive quantities of chloride
and sodium from the softening process. Overall, no
restrictions exist for irrigation, livestock, or domestic
uses of this water.

Use and Management of
Soils for Agriculture

Research conducted on the soils at TAES-Dallas
have wide application because results and findings can
oftenbe expanded to include most soils of the Blackland

13

Prairie. The primary crops grown in the Texas Black-
land are cotton, grain sorghum, oats, wheat, corn,
alfalfa, clover, and forage grasses.

The Blackland Prairie soils are subject to erosion by
water and wind. These soils have inherently low
permeabilities, which increase surface runoff and soil
losses. Soil erosion is the major concern on about two-
thirds of the cropland and pasture in Dallas and Collin
Counties. If the slope exceeds 1 percent, erosion poten-
tial is high. When Austin and Stephen soils lose topsoil
material to erosion, productivity is drastically reduced
because chalky, limestone subsoil becomes the newly
exposed surface layer. This bedrock layer restricts the
rooting zone of plants and has low fertility. Addition-
ally, soil erosion can result in sedimentation and pollu-
tion of surface waters.

Erosion control measures reduce runoff from soils
and increase water infiltration. This may be accom-
plished by maintaining a vegetative cover on the soil
through crop residue management. Terraces and di-
versions that reduce the length of slopes also reduce
runoff and erosion. Contour farming is a common
erosion control practice in Dallas and Collin Counties.

Well-maintained livestock pastures reduce ero-
sion on sloping soils, provide nitrogen, and improve
tilth for succeeding crops. Commonly grown pasture
grasses include coastal bermudagrass, kleingrass,
lovegrass, King Ranch bluestem, and Harding grass.
Alfalfa and clovers and silage sorghum are also grown
to some extent. Native rangeland vegetation suited to
grazing includes big and littlebluestem, silver bluestem,
Indiangrass, switchgrass, sideoats grama, Texas
needlegrass, Texas bluegrass, and vine mesquite.

Proper range management minimizes erosion and
controls grazing so that vegetation can be about the
same in kind and amount as the potential natural plant
community for that site (Table 10). Overgrazing and
mismanagement has depleted much of our native grass-
land, which is now covered with mesquite, weeds, and
annual grasses. Carrying capacity should be evaluated
as range conditions change and as cross fencing is
installed to control free-ranginglivestock. Most ranches
require supplemental grazing crops such as small grains
or silage sorghum. Hay and concentrates are also fed
to range animals in winter months.

Houston, Fairlie, and Austin soils can be produc-
tive agricultural soils with proper management prac-
tices. The clay content results in very low water infiltra-
tion rates. Without contour farming, terracingfand
proper tillage, soil erosion can be a problem. Plant
residue should be managed so that water intake by the
soil will be maximized and erosion will be prevented.
This can be accomplished by shredding stubble with a
rotary mower, incorporating the residue into the top 2
to 4 inches of soil, and leaving it in this manner as long
as possible for soil and water conservation (Simpson,
1964).

Table 10. Potential native plant communities of soils at TAES-
Dallas (dry welght basis)!

Houston
Common plant name Austin Black Fairlie Stephen Eddy

(percentage composition)

little bluestem 40 50 50 30 30
big bluestem 15 10 10
silver bluestem 5 5 5
lndiangrass 15 25 25 15 15
switchgrass 5 5 5

sideoats grama 5 5 5 10 10
Texas wintergrass 5 5
Texas needlegrass 5

hairy grama 5 5
vine mesquite 5 5

other perennial grasses 10 10
other perennial iorbs 5 5 5
other annual forbs 5 5

other half shrubs 5 5 5

other trees 5 5
Potential production (lbs/ac)

favorable years 6500 7000 6000 4500 4500
normal years 5000 6000 5000 3500 3500
unfavorable years 3000 3500 3500 2000 2000

' Modified from Dallas County Soil Survey (1980, Range Productivity
and Composition).

Field plots were in the same location and undergo-
ing the same treatment practices each year from 1947 to
1982 at the Dallas Center. These plots, designated as the
"Renner Plots," provided valuable soil chemical and
physical data under equilibrium conditions with con-
tinuous, rotated, fertilized, and nonfertilized systems.
Crops in the Renner Plots included cotton, corn, grain
sorghum, wheat, and I—Iubam clover. One group of
plots received a yearly application (5 tons/ acre) of
manure (Hipp and Simpson, 1988).

The Renner Plots have shown that under
nonfertilized continuous cropping, Houston, Fairlie,
and Austin Soils have the nutrient-supplying capacity
to yield about 200 pounds of cotton lint, 23 bushels of
wheat, 1,500 pounds of grain sorghum, or 26 bushels of
corn per acre. Applications of nitrogen (N) will nor-
mally increase yields of these crops, and phosphorus
(P) applications will benefit some crops if N is applied
in adequate amounts. Cool-season crops such as small
grains normally respond to fertilizer P applications.
Split applications of fertilizer are seldom required for
maximum economic yield of annual rainfed crops.
When fertilized, Houston, Fairlie, and Austin soils can
yield about 750 pounds of cotton lint, 60 bushels of
wheat, 5,500 pounds of grain sorghum, or 100 bushels
of corn per acre. These three soils will mineralize (make
N available from organic N forms) about 40 to 100
pounds of N per year, depending on soil moisture,
temperature, and organic N level. Crops in nonfallow
rotations (such as wheat after sorghum) require higher
N application rates than if a fallow period has occurred

14

between crops (for example, sorghum after wheat).
Cotton grown in rotation with sorghum or corn and
wheat results in lower incidence of cotton root rot than
does cotton grown continuously.

Other soils studies at TAES-Dallas involve deter-
mining fertilizer requirements of various crops grown
on soils of the area, contribution of legumes to fertilizer
requirements of other crops, and varietal interactions
of field and forage crops with fertility and moisture
needs. Continuous studies are in progress involving
energy and soil conservation through soil manage-
ment, fertilizer efficiency, moisture conservation, resi-
due management, and supplemental irrigation.

Research with field crops, small grains, and forage
crops involves variety selection and cultural practices
for the various soil types of the Center. The variety of
soils on the Dallas Center provides opportunity for
interdisciplinary approaches to research on all the soil
types. For example, crop and soils scientists evaluate
varieties and breeding lines for adaptation to various
soils through drought, disease, and insect tolerance.

Use and Management of Soils for
Urban Purposes

Interest in urban-related soil problems is increas-
ing. The location of the Texas A&M University Re-
search and Extension Center at Dallas has brought an
awareness of the needs of urban people. Much of the
research done for agricultural purposes can be adapted
to urban situations. Many of the management practices
for agriculture are directly applicable to the manage-
ment needed for urban lawns, gardens, construction
sites, and landscapes.

Some urban uses of the soils, however, are not
closely related to agriculture. Most of the soils on the
Center are poorly suited for building foundations and
other structures. Metal pipelines corrode rapidly when
buried in Blackland soils. The shrinking and swelling
of the clays, the fine texture of the soil, and the depth to
chalk layers are all factors that should be considered in
the design and construction of urban structures. These
problems do not prohibit the use of the soil, but they do
need special consideration before building.

Table 11 lists some selected urban and agricultural
uses of the soil and soil factors that need to be considered.

Common practices used on shrink-swell soils are
application of stabilization materials (commonly hy-
drated lime at high rates) to streets and roads during
construction and irrigation of soils around houses and
buildings. Maintaining moist soil around slabs and
foundations partly prevents soil cracking and conse-
quent cracks in the foundation and walls. Rapid estab-
lishment of turfgrass is important on new homesites to
prevent erosion of topsoil onto streets and sidewalks.

Use of Austin, Houston, and Fairlie soils for recre-
ational areas (parks, playgrounds, etc.) is hampered by

$1‘.

0'

U‘

D



Table 11. Use Interpretation oi soils at TAES-Dallas.

Streets Gardening

Soil and and Sanitary

series Buildings roads Recreation landscaping landfill Pasture Cropland
Austin Poor Poor Poor Fair Poor Good Good

High shrink-swell High shrink-swell Clayey texture Clayey texture Depth to rock
Clayey texture
Fairlie Poor Poor Poor Poor Poor Good Fair
High shrink-swell High shrink-swell Clayey texture Clayey texture Clayey texture Clayey texture
Very slow
permeability
Houston Poor Poor Poor Poor Poor Good Fair
Black High shrink-swell High shrink-swell Clayey texture Clayey texture Clayey texture Clayey texture
Very slow
permeability
Stephen- Poor Poor Poor Poor Poor Poor Poor
Eddy Shallow to rock Shallow to rock Shallow to rock Shallow to rock Shallow to rock Shallow to rock Shallow to rock
Sloping

the slow water infiltration rate, which results in stand-
ing water for long periods. The sticky nature of these
soils limits use during wet weather. These problems
can be partly offset by maintaining a ground cover and
providing adequate drainage.

A major urban use of soils such as those found at
TAES-Dallas is for gardening and landscaping. All
these soils pose some particular problem, but certain
management practices decrease the problems enough
to permit their use. For gardening and landscapes, the
primary problem with Houston Black and Fairlie soils
is the high clay content and low water infiltration rates.
The water infiltration rate is moderate when dry, but as
soils become wet, the infiltration rate is reduced to very
low (about 0.06 inches per hour). Water must be applied
slowly by sprinkler or drip (trickle) irrigation systems
to avoid runoff and erosion or standing water.

Associated with low permeability and high clay
content is slow oxygen diffusion to plant roots. This is
particularly a problem when soils remain wet for long
periods and is deleterious to plant growth. Establishing
a ground cover such as grass increases permeability of
soils to water and air. Addition of peat moss, compost,
or mulch is beneficial to home gardens because it
improves tilth and physical properties. The Houston
and Fairlie soils are inherently fertile, but additional
nitrogen and phosphorus are normally needed for
gardens and most landscape plants. Problems with
permeability of Austin soils are similar to those encoun-
tered with Houston and Fairlie but to a lesser extent.

Stephen-Eddy and eroded Austin soils are com-
mon in new’ home developments. Establishment of
vegetation is difficultbecause of poor water infiltration,
low water-holding capacity, and poor root growth in
the bedrock. Trees and shrubs normally require appli-
cation of peat moss, mulch, or topsoil material at the
time of transplanting. Established plants and grass
roots can penetrate the subsoil to some extent, and

15

water infiltration is greatly increased after establish-
ment. Severely eroded areas may require a thin appli-
cation of topsoil before grass can be established.

Soils such as these require slow irrigation (e.g.,
sprinkler or drip) and must be watered frequently
because of the low water-holding capacity. Successful
gardening requires the addition of peat moss or other
suitable sources of organic matter and / or topsoil (mixed
in the surface soil if possible). These soils require
frequent but low application rates of nitrogen and
phosphorus, and for some plants, iron or zinc applica-
tions may be beneficial.

Selection of adapted plants is an important consid-
era tion in establishing landscapes on soils such as those
found at TAES-Dallas.

Use and Management of Soils for
Urban Landscapes

The Center is on a part of the Blackland Prairie,
which stretches from near the Red River in northern
Texas to the Rio Grande Plains in southern Texas and
from the Post Oak Savannah in the east to the East Cross
Timbers in the west. It is a part of the Tallgrass Prairie
of the midcontinental grasslands of North America
(Collins et al., 1975). Climax vegetation is tallgrass;
little bluestem is the climax dominant, and other
tallgrasses are a part of any particular association de-
pending on depth of soil, rainfall, etc. Woody plants
occupied the well-watered valleys and thin hillsides
where fire could not occur because of lack of fuel
material on the rocky slopes and excess moisture in the
valleys. Once the land became settled, the prairie
broken by the plow, and fires more or less controlled,
trees and shrubs established in fence lines and aban-
doned areas. Thebestplace to observe whatmighthave
been part of the climax vegetation is along fenced-in
railroad tracks (Simpson, in press).

Although Blackland soils present drawbacks such
as high CaCOa, root pruning by the shrink-swell nature
of montmorillonitic clays, high incidence of cotton root
rot, poor internal drainage, and a waxy, sticky nature,
a rather extensive plant palette exists (Table 12), which
is suitable for aesthetic landscaping (Baker, 1987; Gar-
rett, 1975; George, 1991). Specialized lists of Texas
native plants (Native Plant Society of Texas, 1990),
drought-tolerant plants (Simpson and Hipp, 1984), and
plants having urban erosion control potential are avail-
able (Hipp et al., 1991; Simpson and Hipp, 1986).

A well-adapted plant to this area will meet a
minimum set of requirements, i.e., grow in a pI-I range
of 7.0 to 8.3, be adapted to USDA Plant Hardiness Zones
7b to 8a (average annual minimum temperatures of 5°
to 15 'F), and able to withstand sustained readings of

more than 100'F in the summer. These criteria are not
readily controlled or easily manipulated by the
homeowner or grower (Hipp and Simpson, 1986).
Other aspects of landscape gardening such as fer-
tility requirements, pest control, water requirements,
uses of mulch, organic matter enhancement, and im-
proved internal drainage of the soil, while perhaps not
simple, can usually be satisfactorily accomplished.
Correct plant selection will go a long way toward
solving most garden problems. If plants are adapted to
the soil type and the climatic conditions of the area,
other facets of gardening become easier. Some Black-
land soils are low in phosphorus and in most areas in
nitrogen. Some flowering plants and many native
plants require low inputs of fertilizer (Hipp et al., 1988,
1989). Potassium is normally available in adequate

Table 12. Landscape plants adapted to the soils and climate at TAES-Dallas.

Houston Black and Fairlie

Austin

Stephen-Eddy
and eroded Austin

Trees, shade

Trees, flowering

Trees, decorative

Trees, conifer

Shrubs

bigtooth maple’, Texas ash’,
escarpment live oak’, Caddo
maple’, cedar elm’, American
elm’, Shumard red oak’, Texas
red oak’, chinkapin oak’, bur
oak’, Chinese pistache,
lacebark elm, pecan’,
sweetgum’, sugar hackberry’

desert willow’, crape myrtle,
goldenrain tree, Texas redbud’
(esp. the cv's Oklahoma and
white Texas), Mexican redbud’,
Mexican plum’, southern
magnolia’, ornamental pear,
Wright acacia’, mesquite’,
eastern redbud’, Eve's
necklace’, rusty blackhaw’

yaupon holly’, deciduous
holly’, southern waxmyrtle’,
prairie flameleaf sumac’, redtip
photinia

bald cypress’, Japanese black
pine, deodar cedar, eastern red
cedar’, ashe juniper’, Arizona
cypress’, alligator juniper’

barberry, crape myrtle, abelia,
Japanese boxwood, dwarf and
shrub junipers (many cv's),
elaegnus, burford holly,
Chinese holly, dwarf nandina
(several cv's), compact
nandina, nandina, dwarf yaupon
holly, Nellie R. Stevens holly,
flowering quince, spirea,
smooth sumac’, fragrant
sumac’, red yucca’, false
indigo’, flame acanthus’, Texas
barberry’, agarito’, American
beautyberry’, cenizo’, white
bush honeysuckle’, dwarf
waxmyrtle’, mockorange’,
autumn sage’, mountain sage’,
Arkansas yucca’, silver dalea’

All the trees that grow in

Houston Black and Fairlie. If
grown on thin Austin soil, will
need supplemental irrigation.

All the trees that grow in

Houston Black and Fairlie. If
grown on thin Austin soil, will
need supplemental irrigation.

All the trees that grow in

Houston Black and Fairlie. lf
grown on thin Austin soil, will
need supplemental irrigation.

All the trees that grow in

Houston Black and Fairlie. If
grown on thin Austin soil, will
need supplemental irrigation.

All the shrubs that grow in
Houston Black and Fairlie. If
grown on thin Austin soil will
need supplemental irrigation
during drought.

16

Texas ash’, escarpment live
oak’, cedar elm’, Texas red
oak’, bur oak’, Chinese
pistache, bigelow oak’, sugar
hackberry’

goldenrain tree, Texas redbud’,
Mexican redbud’, Mexican
plum’, Wright acacia’,
mesquite’, Eve's necklace’

deciduous holly’, prairie
flameleaf sumac’

ashe juniper’, alligator
juniper’, eastern red cedar’

abelia, barberry, Japanese
boxwood, most junipers,
elaeagnus, all nandina cv's and
species, smooth sumac’,
fragrant sumac’, red yucca’,
flame acanthus’, Texas l6
barberry’, agarito’, cenizo’,
white bush honeysuckle’, dwarf
waxmyrtle’, mockorange’,
autumn sage’, mountain sage’,
Arkansas yucca’, silver dalea’

f“

Table 12. (Continued)

Houston Black and Fairlie

Austin

Stephens-Eddy
and eroded Austin

Vines

Ground covers

Flowering plants, herbaceous
perennials



Flowering plants, annuals

Tu rfg rass

Landscape grasses, cool
‘ season

Landscape grasses, warm

$898800

Carolina jessamine’, English
ivy, coral honeysuckle‘,
trumpet vine’, Madame Galen
trumpet vine, cross vine’,
climbing prairie rose’, wisteria,
Boston ivy, Lady Banks rose,
summer grape’, sweet
mountain grape’, mustang
grape’, seibel 9110 grape

creeping junipers (many cv's),
Asiatic jasmine, purpleleaf
honeysuckle, English ivy,
greater periwinkle (Vinca
major’), common periwinkle (V.
minor), liriope cv's, monkey
grass, purpleleaf euonymus,
artemesia’, Virginia creeper’,
wood fern’

Mexican hat’, columbine’,
butterfly weed’, chocolate
daisy’, blackfoot daisy’,
Barbara's buttons’, winecup’,
lantana’, Lantana cv's, black
sampson’, purple ooneflower’,
Engelmann daisy’, Maximillian
sunflower’, Jerusalem
artichoke’, Turk's cap’, pink
evening primrose’, mealy blue
sage’, pavonia’, dogweed’,
Aster’ spp., Pensfemon’ spp.,
Wright skullcap’, blue
baptisla’, chrysanthemum,
canna, daffodil, daylily, iris,
thrift

alyssum, begonia, caladium,
candletree, ooleus, copperleaf,
dianthus, shasta daisy,
geranium, impatiens, Joseph's
coat, kale, marigold,
nierembergia, pansy,
periwinkle, petunia, portulaca,
snapdragon, tulip (act as
annual), zinnia, Texas
bluebonnet’, Indian blanket’,
black-eyed Susan’

common Bermuda, ‘tit’
Bermuda, buffalo’, ‘prairie’
buffalo’, St. Augustine, tall
fescue, Zoysia cv's

Canadian wild rye’, Virginia
wild rye’, Texas bluegrass’,
junegrass’, western
wheatgrass’, threeflower
melic’, blue fescue

big bluestem’, little bluestem’,
season bushy bluestem’,
Springfield bluestem’, splitbeard
bluestem’, indiangrass’, seep
muhly’, sideoats grama’,
eastern gamagrass’,
switchgrass’, pampasgrass

All the vines that grow in
Houston Black and Fairlie.
During drought, will need
supplemental irrigation.

All the ground covers that
grow in Houston Black and
Fairlie. During drought, will
need supplemental irrigation.

All the flowering plants that
grow in Houston Black and
Fairlie. During drought, will
need supplemental irrigation for
all non-natives and for
columbine’ and Maximilian
sunflower.’

All the flowering plants that
grow in Houston Black and
Fairlie. Non-native will need
supplemental irrigation.

All the grasses that grow in
Houston Black and Fairlie.
Tall fescue, St. Augustine, 'tif'
Bermuda, and Zoysia cv's will
need supplemental irrigation.

All the grasses that grow in
Houston Black and Fairlie.
During drought, will need
supplemental irrigation,
especially during heat of
summer.

All the grasses that grow in
Houston Black and Fairlie
except bushy bluestem.
During drought will need
supplemental irrigation.

coral honeysuckle’, trumpet
vine’, climbing prairie rose’,
sweet mountain grape’

creeping junipers, purpleleaf
honeysuckle, artemesia’,
virginia creeper’

All will grow except non-natives
(Lantana cv's will grow) and
columbine’ and Maximilian
sunflower.’

Except for Texas bluebonnet’,
all these annuals need

special bed preparation
(compost, peat moss, etc.) and
supplemental irrigation.

common bermuda, buffalo’,
‘prairie’ buffalo’

None is adapted unless planting
areas are amended with organic
matter.

little bluestem’, Springfield
bluestem’, seep muhly’,
sideoats grama’

’Native Texas plants.

17

amounts and does not need to be added to Blackland
soils for urban landscape maintenance. Organic matter
is vitally important and canbe obtained from composted
leaves, grass, and other organic materials. These mate-
rials can be used as mulch in droughty conditions of
midsummer and then incorporated into the soil at least
2 inches deep in the fall. Turfgrass should be mowed
regularly, leaving all clippings on the lawn as fine
organic matter (Knoop, 1988).

In most Blackland areas, plants benefit from raised
flower and shrubbery beds. These need to be elevated
only 6 to 12 inches but 18 inches is better. Native soil of
the area should fill the bed, and composted organic
matter (2 to 6 inches deep) should be added and thor-
oughly tilled in. This should give excellent drainage.
For transplanted trees, special beds are not necessary,
but the trees should be planted slightly higher than
previously planted. Many transplanted trees are lost
because they are planted too deeply and watered exces-
sively.

Beds and trees should be watered only when
needed, which might be once per week in a hot, dry
summer, or possibly only once every 2 weeks for well-
established trees in summers with normal rainfall.
However, when plants are watered, apply at least 1 inch
of water. Drip irrigation is an excellent way to water
beds and trees (Duble and Welch, 1985; Parsons et al.,
1985). Inexpensive drip irrigation kits can be purchased
at most nurseries or hardware stores. The pressure
gauge should be set to apply about 2 gallons per hour
at each emitter. About 62 gallons of water per 100 ft’
equals an inch of surface water. Sprinkler irrigation is
the mostcommonly used method of irrigating turfgrass.
Sprinklers should be operated in short enough time
frames that runoff does not occur. If ru noff begins, stop
the irrigation and allow standing water to soak in, then
apply subsequent waterings until the desired amount
has been applied.

Literature Cited

Baker, M. L. 1987. Trees, shrubs, vines and ground covers for north
central Texas. TX Agri. Ext. Serv. Mimeograph. Dallas.

Collins,O. B., F. E. Smeins, and D. H. Riskind. 1975. Plant communities
of the Blackland prairie of Texas. In M. K. Wali (ed.). Prairie: a
multiple view. Univ. North Dakota, Grand Forks, 320 pp.

Duble, R. L., and W. C. Welch. 1985. Texscape for conservation. TX
Agri. Ext. Serv. B-1498. Texas A&M Univ., College Station.

Garrett, Howard. 1975. Plants of the metroplex. Lantana Press. Dallas,
TX, 90 pp.

George, Steven. 18991. Recommended landscape plant materials for
north central Texas. TX Agri. Ext. Serv. Mimeograph. Dallas.

Hallmark, C. T., L. T. West, L. P. Wilding, and L. R. Drees. 1986.
Characterization data for selected Texas soils. TX Agri. Exp. Sta.
MP-1543. Texas A&M Univ., College Station, 239 pp.

18

Hipp, B. W., and B. J. Simpson. 1986. Influence of sulfur on soil pH and

growth of cenizo [Leucophyllum frutescens (Berl.) I. M. Johnst.]. J. f, \‘

Environ. Hort. 4(4): 142-144.

Hipp, B. W., and B. J. Simpson. 1988. Thirty-five years of farming
systems research in the Texas Blackland. TX Agri. Exp. Sta. B-
1604. Texas A&M Univ., College Station, 24 pp.

Hipp, B. W., B. J. Simpson, and P. S. Graff. 1988. Influence of nitrogen
and phosphorus on growth and tissue N and P concentration in
Salvia greggii. J. Environ. Hort. 6(2):59-61.

Hipp, B. W., B. J. Simpson, and P. S. Graff. 1989. Influence of phospho-
rus on nitrogen fertilizer requirement of Melampodium leucanthum
(blackfootdaisy) grown in perlite-vermiculite medium. J. Environ.
Hort. 7(3): 83-85.

Hipp, B. W., M. C. Engelke, and B. J. Simpson. 1991. Use of resource
efficient landscape plants to reduce urban runoff. In Ric Jensen
(ed.). Symposium on water quality of the upper Trinity River.
Texas Water Res. Inst. Texas A&M Univ., College Station, 274 pp.

Knoop, Bill. 1988. Don't bag it. Lawn care plan for north central and
central Texas. TX Agri. Ext. Serv. L-2456. Texas A&M Univ.,
College Station.

Laws, W. D. 1961. Farming systems for soil improvement in the
Blacklands. Texas Res. Found. Bull. 10. Renner Research Founda-
tion, Renner, TX, 26 pp.

National Oceanic and Atmospheric Administration. 1977. Local cli-
matological data, Dallas - Ft. Worth, TX, and Asheville, NC.

Native Plant Society of Texas. 1990. A beginner's list, native plants for
landscape use in Dallas and Fort Worth. Georgetown, TX.

Parsons, J., S. Cotner, and R. Roberts. 1985. Efficient use of water in the
garden and landscape. TX Agri. Ext. Serv. B-1496. Texas A&M
Univ., College Station.

Simpson, B. J. 1964. Wheat production in farming systems for north
central Texas. Texas Research Foundation Bulletin 19. Renner
Research Foundation, Renner, TX, 31 pp.

Simpson, B. J. In press. The modern urban Blacklands, from tallgrass

 prairie to soccer fields. In O. T. Hayward and Joe C. Yelderman
(eds.). The Texas Blacklands: a land, its history, and its culture.
Blackland Symp. Baylor Univ., Waco, TX.

Simpson, B. J., and B. W. Hipp. 1984. Drought tolerant Texas native
plants for amenity plantings. In M. A. Collins (ed.). Water for the
21 st century: Will it be there? Southern Methodist Univ., Dallas,
869 pp.

Simpson, B. J., and B. W. Hipp. 1986. Native Texas flora with urban
erosion control potential. Proceedings of Conference XVII. Inter-
national Erosion Control Assoc, Dallas, 303 pp.

Smith, R. M., D. O. Thompson,J. W. Collier, and R. J. Hervey. 1954. Soil
organic matter, crop yields, and land use in the Texas Blackland.
Soil Sci. 77:377-388.

Soil Survey Staff. 1951. Soil survey manual. U.S. Department of
Agriculture - Soil Conservation Service Handbook 18. U.S.
Government Printing Office, Washington, D.C., 503 pp., illus.

Soil Survey Staff. 1987. Keys to soil taxonomy (third printing). SMSS
Tech. Monograph No. 6. Cornell Univ., Ithaca, NY, 280 pp.

U. S. Department of Agriculture. 1969. Soil survey of Collin County,
Texas. U. S. Department of Agriculture - Soil Conservation
Service. U.S. Government Printing Office, Washington, D.C., 55
pp., illus.

U. S. Environmental Protection Agency. 1975. Maximum contaminate
levels. Federal Register, V. 40, No.,248, pp. 59566-59588.

Glossary*

- Aggregate. Many fine soil particles held in a single
mass or cluster, such as a clod, crumb, block, or
prism.

 Alkaline soil. Generally, a soil thatis alkaline through-
out most or all of the part occupied by plant roots.
Precisely, any soil having a pH value greater than
7.0; practically, a soil having a pH above 7.3.

Anion. Any ion carrying a negative charge. Common
soil anions are bicarbonate, sulfate, chloride, and
nitrate.

Available water capacity (availab le moisture capac-
ity). The capacity of soils to hold water available for
use by most plants. It is commonly defined as the
difference between the amount of soil water at field
capacity (-1 / 3 Bar) and the amount at wilting point
(-15 Bars).

Calcareous soil. A soil containing enough calcium
carbonate (often with magnesium carbonate) to
effervesce (fizz) visibly when treated with cold,
dilute hydrochloric acid.

Cation. Any ion carrying a positive charge. Common
soil cations are calcium, magnesium, sodium, and
potassium.

Cation exchange capacity. The total amount of ex-
changeable cations that can be held by the soil,
expressed as milliequivalents per 100 grams of soil.

I

Chalk. A soft, white or light-gray, unindurated lime-
stone consisting principally of skeletons of Fora-
minifera in a matrix of finely crystalline calcite.

Clay. Individual mineral soil particles less than 0.002
millimeter in diameter. As a textural class, soil
material that is 40 percent or more clay, less than 45
percent sand, and less than 40 percent silt.

Clay film. A thin coating of clay on the surface of a soil
aggregate; clay coat, clay skin.

Concretions. Grains, pellets, or nodules of various
sizes, shapes, and colors, consisting of concentra-
tions of compounds or of soil grains cemented
together. The composition of some concretions is
unlike that of the surrounding soil. Calcium car-
bonate and iron oxide are examples of material
commonly found in concretions.

U"

Consistence, soil. The feel of the soil and the ease with
which a lump can be crushed by the fingers. The
following terms are used to describe consistence:

Loose. Noncoherent; will not hold together in a
mass.



‘Adapted from Soil Survey Manual (1951).

19

Friable. When moist, easily crushes under gentle
pressure between thumb and forefinger and
can be pressed together into a lump.

Firm. When moist, crushes under moderate pres-
sure between thumb and forefinger, but resis-
tance is distinctly noticeable.

Plastic. When wet, readily deforms by moderate
pressure but can be pressed into a lump; will
form a wire when rolled between thumb and
forefinger.

Sticky: When wet, adheres to other material; tends
to stretch and pull apart rather than to pull free
from other material.

Hard. When dry, moderately resistant to pressure;
can be broken with difficulty between thumb
and forefinger.

Soft. When dry, breaks into powder or individual
grains under slight pressure.

Cemented. Hard and brittle; little affected by mois-
tening.

Depth, soil. In soil descriptions, the following depth
classes are used:

Very shallow. 3 to 10 inches of soil over bedrock or
another impervious layer that severely restricts
growth of roots.

Shallow. 10 to 20 inches of soil over bedrock or
another impervious layer that severely restricts
growth of roots.

Moderately deep. 20 to 40 inches of soil over bedrock
or another impervious layer that restricts
growth of roots.

Deep. 40 to 60 inches of soil over bedrock or another
impervious layer.

Very deep. More than 60 inches of soil over bedrock.

Gilgai. Typically a succession of microbasins and
microknolls in nearly level areas; similar to hog-
wallow land.

Horizon, soil. A layer of soil, approximately parallel to
the surface, that has distinct characteristics pro-
duced by soil-forming processes. These are the
major soil horizons:

Ap horizon. A plowed surface horizon. The plow
layer of agricultural soils.

A horizon. The mineral horizon at the surface or just
below an Ap horizon. Living organisms are
most active in this horizon, and it is therefore
marked by the accumulation of humus. The
horizon may have lost one or more soluble
salts, clay, and sesquioxides (iron and alumi-
num oxides).

B horizon. The mineral horizon below an A horizon.
The B horizon is partly a layer of change from
the overlying A to the underlying C horizon.
The B horizon also has (1) distinctive character-
istics caused by accumulation of clay,
sesquioxides, humus, or some combination of
these; (2) prismatic or blocky structure; (3)
redder or stronger colors than the A horizon; or
(4) some combination of these. The combined
A and B horizons are usually called the solum,
or true soil- If a soil lacks a B horizon, the A
horizon alone is the solum.

Specific types of soil horizons:

Bk - Indicates the accumulation of calcium
carbonate in the B horizon.

Bss - Indicates the presence of slickensides in
the B horizon.

Bw - Indicates the development of color and / or
structure with little or no apparent illuvial
accumulation of material in the B horizon.

C horizon. The weathered rock material immedi-
ately beneath the solum. In most soils, this
material is presumed to be like that from which
the overlying horizons were formed. If the
underlying material is known to be different
from that in the solum, an Arabic numeral
precedes the letter C. Difficult to excavate.

Cr horizon. Root restrictive layers of soft bedrock.
Excavation difficulty is low or moderate.

R layer. Consolidated rock beneath the soil. The rock
typically underlies a C horizon but may be
immediately beneath an A or B horizon. Diffi-
cult to excavate.

Loam. The textural class name for a soil that is 7 to 27
percent clay, 28 to 50 percent silt, and less than 52
percent sand.

Marl. A mixture of clays and calcium carbonate.

Matrix. The natural material in which a fossil, metal,
gem, crystal, or pebble is embedded.

Microrelief. Minor surface configurations of the land.

Mohs’ scale. A scale of hardness for minerals in which
1 represents the hardness of talc; 2 of gypsum; 3 of
calcite; and on up to 10 of diamond.

Mottled. Irregularly marked with spots of different
colors that vary in number and size. Mottling in
soils normally indicates poor aeration and lack of
drainage. Descriptive terms are as follows: abun-
dance - few, common, and many; size - fine, me-
dium, and coarse; and contrast - faint, distinct, and
prominent. The size measurements are these: fine -
less than 5 millimeters (about 0.2 inch) in diameter
along the greatest dimension; medium - ranging

from 5 millimeters to 15 millimeters (about 0.2 to
0.6 inch) in diameter along the greatest dimension;
and coarse - more than 15 millimeters (about 0.6
inch) in diameter along the greatest dimension.

Munsell notation. A system for designating color by
degrees of the three simple variables hue, value,
and chroma. For example, a notation of 10YR 6/4
designates a color with a hue of 10YR, value of 6,
and a chroma of 4.

Parent material. The disintegrated and partly weath-
ered earthy material from which a soil has formed.

Ped. An individual natural soil aggregate, such as a
crumb, a prism, or a block, in contrast to a clod.

Permeability or hydraulic conductivity. The quality of
the soil that enables water to move downward
through the profile, expressed as inches per hour
through saturated soil. The following terms de-
scribe permeability:

Very slow . . . . . . . . . . less than 0.06 inches/ hour
Slow . . . . . . . . . . . . . . 0.06 to 0.20 inches/ hour
Moderately slow . . . . . . 0.2 to 0.6 inches/ hour
Moderate . . . . . . . . . . . 0.6 to 2 inches/ hour

pH value. A numerical means for designating rela-
tively weak acidity and alkalinity in soils. A pH
value of 7.0 indicates precise neutrality; a higher
value, alkalinity; and a lower value, acidity.

Potential evapotranspiration. The rate at which water,
if available, will be removed from the soil surface.
Expressed as a depth of water.

Profile, soil. A vertical section of the soil through all its
horizons and extending into the parent material.

Reaction, soil. The degree of acidity of alkalinity of a
soil expressed in pI-l values. A soil that tests to pH
7.0 is precisely neutral in reaction because it is
neither acid nor alkaline. In words, the degrees of
acidity or alkalinity are expressed thus:

PH PH
Extremely below 4.5 Neutral 6.6 to 7.3
acid
Very strongly 4.5 to 5.0 Slightly 7.4 to 7.8
acid alkaline
Strongly acid 5.1 to 5.5 Moderately 7.9 to 8.4
alkaline
Moderately 5.6 to 6.0 Strongly 8.5 to 9.0
acid alkaline
Slightly acid 6.1 to 6.0 Very strongly 9.1 and higher
alkaline

Relief. The elevations or inequalities of a land surface,
considered collectively.

Runoff. The part of the precipitation upon a drainage
area that is discharged from the area in stream
channels. The water that flows off the surface

t‘

6“



f)

without soaking in is called surface runoff; water
that enters the ground before reaching surface
streams is called ground-water runoff.

Sand. Individual rock or mineral fragments in soils
having diameters ranging from 0.05 to 2.0 millime-
ters. Most sand grains consist of quartz, but they
may be of any mineral composition. The textural
class name of any soil that is 85 percent or more
sand and not more than 10 percent clay.

Shale. A sedimentary rock formed by the consolidation
(hardening) of clay deposits.

Silt. Individual mineral particles in a soil that range in
diameter from the upper limit of clay (0.002 milli-
meter) to the lower limit of very fine sand (0.05
millimeter). Soil of the silt textural class is 80
percent or more silt and less than 12 percent clay.

Slickensides. Polished and grooved surfaces produced
by one mass sliding past another. In soils, slicken-
sides may occur at the base of a slip surface on a
relatively steep slope; in swelling clays they may
occur where moisture content changes markedly.

Soil separates. Mineral particles less than 2 millimeters
in equivalent diameter and rangingbetween spec-
ified size limits. The names and sizes of separates
recognized in the United States are as follows: Very
coarse sand (2.0 to 1.0 millimeter); coarse sand (1.0 to
0.5 millimeter); medium sand (0.5 to 0.25 millime-
ter); fine sand (0.25 to 0.10 millimeter); very fine sand
(0.10 to 0.05 millimeter); silt (0.05 to 0.002 millime-
ter); and clay (less than 0.002 millimeter). The
separates recognized by the International Society
of Soil Science are as follows: I (2.0 to 0.2 millime-
ters); II (0.2 to 0.02 millimeter); III (0.02 to 0.002
millimeter); and IV (less than 0.002 millimeter).

Solum. The upper part of a soil profile, above the parent
material, in which the processes of soil formation
are active. The solum in mature soil includes the A
and B horizons. Generally, the characteristics of the
material in these horizons are unlike those of the
underlying material.

Stratified. Composed of or arranged in strata, or layers.
The term is confined to geological material. Allu-
vium is commonly stratified, and its strata inherit
characteristics of the parent material. Layers that
are the result of the soil-forming processes are
called horizons.

Structure, soil. The arrangement of primary soil par-
ticles into compound particles or clusters that are

i)

21

separated from adjoining aggregates and have
properties unlike those of an equal mass of
unaggregated primary soil particles. The principal
forms of soil structure are platy (laminated), pris-
matic (vertical axis of aggregates longer than hori-
zontal), columnar (prisms with rounded tops), blocky
(angular or subangular), and granular. Structure-
less soils are (1) single grain (each grain by itself, as
in dune sand) or (2) massive (the particles adhering
without any regular cleavage, as in many claypans
and hardpans).

Subsoil. Technically, the B horizon; roughly, the part of
the profile below the plow depth.

Substratum. Any layer beneath the solum, either con-
forming (C or R) or unconforming.

Surface layer. Technically, the A horizon; roughly that
part of the profile above the subsoil; includes the
plow layer.

Surface soil. The soil ordinarily moved in tillage or its
equivalent in uncultivated soil, about 5 to 8 inches
in thickness; the plowed layer.

Terrace. An embankment, or ridge, constructed across
sloping soils on the contour or at a slight angle to
the contour. The terrace intercepts runoff so that
the water soaks in the soil or flows slowly to a
prepared outlet. Terraces in fields are generally
built so they can be farmed. Terraces intended
mainly for drainage have a deep channel that is
maintained in permanent sod.

Terrace (geological). An old alluvial plain, ordinarily
flat or undulating, bordering a river or lake. Stream
terraces are frequently called second bottoms, as
contrasted to flood plains, and are seldom subject to
overflow.

Texture, soil. The relative proportions of sand, silt, and
clay particles in a mass of soil. (See also Clay, Sand,
and Silt.) The basic textural classes, in order of
increasing proportion of fine particles, are sand,
loamy sand, sandy loam, loam, silt loam, silt, sandy
clay loam, clay loam, silty clay loam, sandy clay,
silty clay, and clay. The sand, loamy sand, and
sandy loam classes may be further divided by
specifying ”coarse,” ”fine," or ”very fine.”

Well drained. Water is removed from the soil readily
but not rapidly. Moisture is available to plants
throughout most of the growing season, and wet-
ness does not inhibit root growth for significant
periods during most growing seasons.

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4-.
~’< v
a t»: . » , :1-  *
_. M, .4 ,.,

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Figure 4. Typical profile of Austin silty clay at TAES-
Dallas.

Figure 6. Typical profile of the Stephen-Eddy complex at
TAES-Dallas.

Figure 5. Typical profile of Houston Black silty clay at
TABS-Dallas.

Q

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