•~--*^^=^-"
SOIL MOISTURE DEPIETION AND TEMPERATURE AFFECTED
BY SAND SHINNERY OAK (QUERCUS
HAVARDII RYDB,) CONTROL
PETER STEPHEN TEST, B,S. in Ag.
A THESIS
IN
RANGE SCIENCE
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of
MASTER OF SCIENCE
Approved
August, 1972 ACKNOWLEDGMENTS
I would like to extend my sincere appreciation to Dr, R, D.
Pettit whose continuous support, suggestions, and advice made this thesis possible. Also, I would like to thank Dr, J. R. Goodin,
Dr, B. E, Da.hl, Dr, R. E, Meyer, and Dr, D. A. Klebenow for their many comments and timely suggestions throughout this study.
Appreciation also goes to Dr. B. L, Allen for his help with several soil problems, and Dr, H. A, Wright and Mr, R, W, Wadley who helped with some of the data analysis problems.
Many other people deserve special thanks; among them are Mr,
D. W. Deering, Mr. R, E, Fagan, Mr, R, F, Paetzold, and Mr, M, A.
Smith, all graduate students at Texas Tech University, as well as
Mr. A, B. Bar bee and Mr, D, M. Hungerford, undergraduates who faithfully helped collect the field data.
li TABIE OF CONTENTS
ACKNOWIEDGMENTS ii
LIST OF TABLES v
LIST OF FIGURES vi
I. INTRODUCTION 1
II. REVIEW OF PREVIOUS RESEARCH 3
Vegetation Influence on Soil Water Depletion , 3
Plant Effects on Infiltration • • • 7
Vegetation Influence on Soil Temperature- Moisture Relationships 9
III. STUDY AREA 13
Physiography, Geology, and Soils 13
Climate 1^
Flora and Fauna 17
IV. METHODS 18
Soil Moisture Measurement and Analysis .... 18
Vegetation Analysis 23
V. RESULTS AND DISCUSSION 2^
Effect of Sand Shinnery Oak Removal on Soil Moisture --^
Effect of Sand Shinnery Oak Removal on Soil Temperature , , • ^0
Comparison of Two Soil Moisture Measuring Techniques ^?
lii Variability of Readings and Sensitivity . ^8
Data Collection and Analysis ,.,... 53
Calibration Methods 5^
IV, SUMMARY 56
LITERATURE CITED ^0
APPENDIX ^^
iv LIST OF FIGURES
Figure Page
1. Climatological data for Shinnery Oak study area near Plains, Texas; May, I970 to December, 1971. Minimiim- majcimum temperatures and monthly precipitation ... I6
2. Remove all vegetation treatment 19
3. Remove all oak treatment 19
k. Remove all vegetation except oak (leave all oak) , . 20 5, Leave all vegetation (control) 20 6, Neutron probe tube in relation to Coleman fiberglas cell series. Small can is over neutron probe tube and the large can sits on the hookup points of the cells 22
7, Neutron probe and Coleman soil cells being used simultaneously 22
8, Treatment 3 (control) soil moisture (% ^ipO by volume) at depths (15~75 cm) and precipitation (inches) for weekly intervals for May through December, 1971 ... 26 9, Treatment 2 (remove all vegetation) soil moisture {% H2O by volume) at depths (15-73 cm) and precipi tation (inches) for weekly intervals for May tbirough December, 1971 28
10, Treatment 1 (leave all oak) soil moisture (% H2O by volume) at depths (15-75 cm) and precipitation (inches) for weekly intervals for May through December, 1971 30
11, Treatment 4 (remove all oak) soil moisture {% H^O by volume) at depths (15-75 cm) and precipitation (inches) for weekly intervals for May through December, 1971 3^
vi Figure Page
12. Percent H2O by volume for depths (15-75 cm). Average for 1971 33
13. Soil moisture {% H^O by volume) by depths for treat ments. Depths to 165 cm at I5 cm intervals. Data collected April 22, 1972 35
14. Soil moisture {% KJd by volume) by depths (15-75 cm) for treatments. Eight month average in 1971 . . . , 37
15. Soil temperatures for all depths (15-75 cm) over all treatments, monthly 1970 and 1971 41
16. Temperature for depths (15~75 cm) over all treatments July, 1970 and June, 1971 42
17. Temperature for depths (15-75 cm) over all treatments December, 1970 43
18. Soil temperature average over 75 cm to monthly atmospheric extremes at 1 ft for June to December, 1970 and 1971 49
19. Comparison neutron probe {% H2O bv volume) to resistance units (ohms resistance). Depth over 8 months of 1971 50
vii CHAPTER I
INTRODUCTION
It may be more detrimental to the land's resources to control a species, believed to be undesirable, than to leave it alone. Thus, it is important to study the effects of the removal of a dominant organism on all ecological factors. Research of this type can reduce the probability of major environmental errors that cannot be corrected. The effects of brush control in the sand shinnery oak
(Quercus havardii Rydb.) ecosystem have received very little study.
We need documentation on the effects of brush removal on soil moisture ajid soil temperatures. These factors should be studied to determine possible beneficial and detrimental effects on the ecosystem.
An area dominated by a noxious or toxic brush species, such as sand shinnery oak, is not economically productive to the landowner because it may be detrimental to livestock and, in some cases, wildlife. Unwanted brush will also use soil moisture that would otherwise be available for more desirable range vegetation.
Thus, the objectives of this study were tlireefoldi
1, to study soil moisture changes as affected by oak removal
2, to study soil temperature changes as affected by oak removal 3. to compare the neutron probe and resistance block methods of soil moisture measurement. CHAPTER II
REVIEW OF PREVIOUS RESEARCH
Plants affect soil moisture in many ways. The three major areas of interest in this study are vegetation influence on:
(l) rates of soil water depletion, (2) water infiltration, and
(3) soil temperature-moisture relationships.
Vegetation Influence on Soil Water Depletion
All plants require moisture for growth and development, but
some species use water more efficiently than others, Rowe and
Reimann (1969) studied brush and grass communities in California
and concluded that brush used water for a longer period of time and
from greater depths than did grass. Klickoff (1967) found similar
results in the Upper Sonoran Desert of Arizona. In Israel, Hillel and Tadraor (I962) studied four sites and found that on rocky slopes,
individual shrubs subsisted on 3OO liters of water per growing
season. Loessial plains vegetation was found to use 200 liters of water per growing season. Wauii beds, with vegetation primarily of bermudagrass (Cynodon dactylon), had 25O to 5OO ^^ of water available for use, Tuereibe sands, which had the best water relations of the sites studied, had a grass-shrub type with 80 to
100 mm of water available for the growing season. Rickard (I967) found that big sagebrush (Artemisia tridentata) and greasewood (Sarcobatus vermiculatus) in southeastern Washington used approximately the same amount of water, but these species* water use differed according to season of use and soil depth. In
Arizona, soil water depletion by burroweed (Haplopappus tenuisectus) reduced the growth of the dominant perennial grass, Arizona cottontop
(Trichachne califomica) 25 percent, Burroweed depleted soil water faster than Arizona cottontop during the winter-spring growing period in this four year study (Cable, I969). Similar grass-shrub competition for soil moisture was noted in Texas by Stransky (I96I) and in Mississippi by Williston and McClurkin (I96I).
Soil moisture comparisons in Michigan on thinned and unthinned stands of red pine (Pinus resinosa) and on an open area, showed that soils under the unthinned stand contained less soil moisture than those of the thinned stand. In addition, the thinned stand soils contained less soil moisture than the open area. These soil moisture differences were greatest at the 6 inch depth (Della-Bianca and Oils,
1930). Similar results were obtained by McClurkin (I961) in a shortleaf pine (Pinus echinata) plantation in northern Mississippi.
In 1953 Hoover et al., in a South Carolina study, showed that
loblolly pine (Pinus taeda) used water down to 5 ft during the maximum growth period of Kay to June. Moisture use below 30 inches was 5.60 inches of water, and 2,15 inches of that was taken from the
54 and 66 inch level. In another South Carolina study, Douglass (19^0) found that by thinning a loblolly pine forest witer use was decreased
in the areas between the trees. Thus thinning allowed the soil to store 3 inches more water for the first and second year after thinning
than in the unthinned stands. Patric, Douglass, and Hewlett (1965)1
also in South Carolina, found that early spring absorption from
uniformly damp soil was related to root density. Late summer
absorption tended toward equal extraction with depth even down to
20 ft. On the "piedmont-loblolly" and "mountain-oak" sites studied,
reduction of soil moisture was 17 inches by October due to
absorption and drainage,
McGinnies and Arnold (1939) conducted, in Arizona, one of the
few studies on the amount of water used by individual range plants.
In greenhouse conditions mesquite (Prosopis glandulosa) was shown
to use 1,725 lb of water/lb of dry matter produced, and catclaw
(Acacia sp.) 2,400 lb of water/lb of dry matter. On the other hand,
sideoats grama (Bouteloua curtipendula) used only about 705 lb of
water/lb of dry matter, Arizona cottontop used about ^1 lb of water/
lb of dry matter, and blue grama (Bouteloua gracilis) used 5^9 lb of
water/lb of dry matter. Weaver (l94l) conducted a similar study in
Nebraska with similar results.
In Ohio, Gaiser (1952) found that white oak (Quercus alba) on
Zaleski loajn soil used more water than thought ordinarily available
in the soil in dry years. The oak traaispired up to 25 inches of
water in a normal year. Tew (1966) working in northern Utah found
that Gam be 1 oak (Quercus gambelii) used 1 inch of water per foot of
soil. In western Colorado, Brown and Thomspon (1963) found that quaking aspen (Populus tremuloides) used an average of 19.2 inches. Engelmann spruce (Picea engelmannii) 14,9 inches, and grassland 5,9
inches of water per year over a three year period.
In 1961, Evans conducted a greenhouse study to evaluate the degree of competition for soil moisture between crested wheatgrass
(Agropyron desertorum) and downy brome (Bromus tectorum), Ke found
that moisture was depleted faster at a 2 to 3 inch depth with a
mixture of the brome and crested wheatgrass than with crested
wheatgrass alone.
Control of brush species in chaparral areas in California with
2,4-D, fire, and by hand clearing decreased soil moisture stress and
increased the chance of perennial grass establishment (McKell et al.,
1966; Goodin and McKell, I966; Perry et al,, 1967; McKell, Goodin,
and Duncan, I968; McKell, Goodin, and Duncan, I969). Hill and Rice
(1963) made similar conclusions in another California study. Tew
(1969a) in Utah found that by replacing Gambel's oak with grass, soil
moisture storage increased by 3.09 inches the first year and 2.35
inches in the second year after oak control. Savings of moisture
occurred primarily in the lower 4 ft of the 8 ft of soil measured.
Robertson (1947) found that removal of big sagebrush In Nevada
increased available water for grass production. Control of big
sagebrush with 2,4-D in Wyoming reduced the rate of soil moisture
use (Tabler, I968). Differences in soil moisture depletion due to
treatment occurred 75% of the time within the 3 to 6 ft soil iepth.
However, at the 2 ft depth less water was stored in the plot with
brush control than in those areas without brush. Increase! grass
growth caused this difference. Total evaporation loss was reduced 14% over the four month growing period the year after control.
Similar findings on sagebrush control as it affects soil moisture have been noted by other researchers (Meeuwig, I965; Fisser, I968;
Shown, Miller, and Branson, I969),
In Missouri four treatments were applied to a hardwood forest to determine the effects of various vegetation and litter cover on soil moisture storage. "Litter only" plots were wettest throughout the year, especially below 6 inches, and were the slowest to dry,
"Tree-litter" and "tree-only" plot soils were driest and had very little difference in moisture content. The "bare" plots had a moisture content mid-way between the other two extremes (Lull and
Fletcher, 1962; Fletcher and Lull, I963).
Plant Effects on Infiltration
A number of researchers have studied the impact of different range conditions and range types as they affect water infiltration.
Klemmedson (195^), in western Colorado, studied water infiltration rates into vegetative types with different range conditions. He found that the infiltration rate of 1 inch of water on good and fair range conditions were similar, 7.82 min on good and 8,71 min on fair ranges. The poor range site took 20,08 min for 1 inch of water to infiltrate. Rauzi (I96O) found that in North Dakota and Montana increased water infiltration was associated with better vegetative cover conditions. Also, standing vegetation facilitated the intake of water more than did mulches. Duley and Domingo (19^^) had similar results in Nebraska, Dune sands had especially high infil tration rates when supporting native grass. 8
The effect of grazing intensities on soil water infiltration has been the objective of much research. Duley and Domingo (1949), in Nebraska, found that under light grazing, infiltration rates were higher than in heavily used pastures. A later study, in
Saskatchewan, Canada, using similar techniques verified these results (Johnston, 19^2).
From infiltrometer studies in North Dakota, Rauzi and Smika
(1963) found that on plots dominated by sideoats grama, western wheatgrass (Agxopyron smithii), needle-and-thread grass (Stipa comata). and green needlegrass (Stipa viridula), grazing intensities were correlated with infiltration rates. In other words, higher grazing intensities decreased water infiltration rates. Similar conclusions were obtained from intake studies on Pratt loamy fine sand at the Southern Great Plains Experiment Range in northwestern
Oklahoma. The researchers concluded that the quantity of vegetation, both living aoid dead, and range condition were highly correlated with water intake (Rhoaides et al., 1964).
Box (1961) found that infiltration rates were influenced by- vegetation types in south Texas. In general higher infiltration rates occurred in soils covered with grass sod. Less water entered brushland and bare soils. Bluebunch wheatgrass (Agropyron spicatum) ranges of south central British Columbia were found to have high infiltration rates. This high rate WSLS possibly due to the "funnelling" effect of the aerial parts of the plant's canopy (Ndwalula-Senyimba,
Brink, and McLean, 1971). f
Dee, Box, and Robertson (1966) found that vegetation type
Influences water infiltration on Pullman soils in Texas, Infiltration rates for blue grama, silver bluestem (Andropogon saccharoides) and buffalograss (Buchloe dactyloides) types were 2,56, 2,51, and ,84 inches/hr, respectively. Infiltration rates were closely related to the successional stage of the community, amount of standing vegetation, and the amount of litter from previous year growth.
Vegetation Influence on Soil Temperature-Moisture Relationships
Berg (1938) concluded that plant cover had several effects on soil temperature. Plant cover shades the surface soil and decreases the inflow of heat and at night vegetation prevents re-radiation.
Plants dessicate the soil by evapotranspiration and they also hindered the turbulent mixing of air at the soils surface.
Quashu and Zinke (1964), working in California, concluded that vegetation reduced the mean annual soil temperature and introduced a temperature time lag in the profile. This was characteristic of each vegetation type and soil moisture regime studied.
Hide (1954) found the diurnal soil surface temperature to be highly variable in a Kansas study. In the same study, temperatures at a 12 inch soil depth were less variable. His results showed that daily temperature fluctuations were small and almost uniform throughout the year at deep soil profile depths. He found that cooling of soil can occur at or below the surface due to evaporation of soil moisture. The decrease in temperature variation with depth 10 has also been noted by other researchers (Rickard and Kurdock, I9631
Mueller, 1970; Mueggler, 1971).
Cable (1969) working on a sandy loam soil in an Arizona semi- desert rangeland found that soil temperature down to 6 inches responded to atmospheric temperature by reaching a minimum just before sunrise and a maximum about 2 PM, Minimum temperature at the 12 inch depth was reached at noon. There was relatively little daily temperature fluctuation at 24 inches. Maximum temperatures were reached between mid-June and mid-July, with the minimum in mid-
January. Absolute maximum and minimum for his study was l4l F and
29 F, respectively.
Soil temperatures also vary with altitude, low altitudes being warmest and high altitudes being coolest (Rickard and Murdock, I963;
Mueller, 1970; Mueggler, 1971). Exposure also caused variations in soil temperature (Mueggler, 1971).
Gardner (1955) reported that soil moisture tensions decreased approximately ,008 atm/deg rise in temperature within a range of 0 to 50 C, He concluded from this Colorado study that tension changes in soils due to temperature changes were too great to ignore. Tew
(1969b) suggested that the primary factor affecting growth and development of five Utah grasses was the difference in air and soil temperature regimes. He concluded that these differences would affect the water requirements of plants, as well as water and nutrient availability,
Daubenmire (1957) found that seasonal fluctuations of soil temperature resulted in raising soil field capacity in the spring 11
arid Icfrfering its wilting coefficient in the late summer. This
created a greater storage capacity for the soil than might be
expectM if the soil temperature was ignored. Wallace (1970), in
California, later found that evapotranspiration was affected more
"by Boil temperature than soil moisture content.
Wendt, Haas, and Runkles (I968), in Texas, found that water
abBorption by mesquite was directly affected by soil temperature;
the lElnimum absorption temperatxire was I3 C, Transpiration losses
increac.5d up to 29 C and ceased at 38 C,
Vegetation plays an important role in modifying soil
temperature changes. Shanks (1956), in Tennessee, found that
microclimatic temperature differences occur, induced by different
vegetation types, which create soil temperature changes equivalent
to 2,000 ft of altitudinal difference. Mueggler (l97l) found that
niaxlmum temperatures of shaded soil surfaces did not differ
appreciably between slope exposures. He also found that soil
temperatures in shaded areas were 4 to 10 F lower than the soil
temperatures on unshaded areas, Jeffery (1963) working on a white
spruce stand (Picea glauca), a balsam poplar stand (Populus
'balsamlffl-ra'\ ^ and a cut-over area in Canada found a variation in
times of maximum and minimum soil temperatures. A similar study was conducted in western Wyoming by Fisser (1968). He found that on
•t-wo vegetation types (i.e., a mesic foothill grassland and a cold ari.i desert shrub type) that the arid desert shrub type's soil temperature increased faster and was warmer throughout the sur-.mer than the mesic foothill grassland type. The mesic foothill irrassland 12 type went through cooling and warming cycles at a slowe>- ra. t e. Annual average temperature at all depths was 1 C higher on the cold arid desert shrub type than on the mesic type.
In general, most vegetation control methods increase >^ oil temperature, but unless the quantity of litter or mulch 1©,;. on the soil's surface changes drastically these temperature c^ *^.inges are minor (Army, Wiese, and Hanks, 1961; Hedrick et al,, 1VAZ.O\ CHAPTER III
STUDY AREA
Physiographv. Geologv, nnd Soils
This study was conducted on a typical Brownfield-Patricia soil
association. Study plots were nine miles north of Plains, Texas, in
Yoakum County, on the 2-B Ranch owned by Mr, Robert Beasley.
The study site is in the southwestern portion of the Llano
Estacado, a Spanish term describing that portion of the Great
Plains physiographic unit south of the Canadian River that lies in
eastern New Mexico and adjoining western Texas (Fenneman, 193l).
This area is also known, in Texas, as the High Plains Land Resource
Area (Gould, 1969; Rogers, I969). The Llano Estacado has few
striking topographic features except for playa lakes; however,
none are located near the study area. Elevation of the Llano
Estacado ranges from 2,500 ft in the southwest to 5,000 ft in the
northwest (Lotspeich and Everhart, 1962; Lotspeich and Goover, I962).
Elevation of the study area is 3»500 ft (u. S. Dep. of Agr,, 1964).
The Llano Estacado overlies the Ogallala geologic formation
which is composed of sediments of the Permian, Cretaceous, and
Triassic ages. The surface of the formation is overlain with a
thick layer of indurated caliche (Lotspeich and Everhart, 1962;
Rogers, I969).
13 14
The parent material of the present soils are aeolian deposits called "cover sands" and were deposited during the Illinoian glacial
period and the inter-glacial Sangamon (Frey and Leonard, I965).
The soil of the study area is a BrownfieId-Patricia complex
(see APPENDICES A and B for soil description and physical properties).
This sandy-textured soil has good water retention properties because
the top 18 to 24 inches is a very permeable sand overlying a "B"
horizon of sandy clay loam, which retains substantial quantities of
water for vegetative use (Lotspeich and Everhart, 1962; U, S, Dep,
of Agr., 1964). This soil is used for agricultural crops, peirticularly
sorghum, and rangeland (U, S. Dep. of Agr,, 1964), The soil has a
very high accumulation of calcium carbonate (CaCO-^) in the "B"
horizon (APPENDIX B).
Climate
The climate of the study area is a warm-temperate continental
climate characteristic of the southern High Plains, Temperature
extremes range from 112 F in August to a minimum of -23 F in February,
with the average for those months being 76.6 F and 42,1 F,
respectively. Frequent hourly and daily temperature fluctuations up
to 30 F may occur. The average temperature for summer nights is 60 F,
The mean annual number of frost free days, determined from the last
occurrence of 32 F in the spring to the first occurrence of 32 F in the fall, is 200 days. The first freeze commonly occurs around
November 1, and the last around April 1 (U. S, Dep, of Agr,, 1964), 15
More than B0% of the average precipitation occurs during the growing season. May through October, Between I96O and I970 the
U, S. Weather Bureau recording station in Plains, Texas recorded an average precipitation of I5.91 inches, with extremes of 6,00 inches to 22.98 inches. Monthly extremes have ranged from 0 to 11.52
inches. Afternoon convectional storms are commonly responsible for
these erratic and oftentimes intense storms. Snow occasionally
falls in the winter but is on the ground only for a short time.
Infrequent effective precipitation occurs in July and August due to
the low humidity and high temperatures (U, S. Dep, of Agr,, 1964;
U, S, Dep, of Com., I96I-I97I).
Monthly temperature extremes and precipitation are shown in
Fig, 1, These data were compiled from U, S. Department of Commerce,
Climatological Data 1961-1971 for Plains, Texas, Later a raingauge and minimum-maximum thermometers were installed on the study area.
Weather data are shown from the beginning of the study in May, 1970 to December, 1971. That data collected on the study area for
precipitation begins in November, 1970 and the study area temperature data were first collected in September, 1970. The last spring freeze
in 1970 was May 2 and the first fall freeze was October 2. The 1971 freeze dates were April 7 and November 2 (U. S. Dep. of Com., I96I-
1971). Extremes in temperature were 124 F and -6 F, Highest monthly rainfall was in August, 1971. No precipitation was received in
November, 1970 or March and May of 1971. 16
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LL o H CL 17
Flora and Fauna
The site's vegetation is composed of many species. Kajor brush species include sand shinnery oak, mesquite, sand sagebrush
(Artemisia filifolia), with some perennial broomweed (Gutierrezia sarothrae), and false tarragon (Artemisia glauca), Grasses include little bluestem (Schizachyrium scoparium), several perennial three awns (Aristida sp,), fall witchgrass (Leptoloma cognatum), sand dropseed (Sporobolus cryptandrus), sideoats grama, sand paspalum
(Paspalum setaceum var, stramineum), Many forbs also occupy the study site. Annual wild buckwheat (Eriogonum annuum), plains black- foot (Commelina erecta), Fendler euphorb (Euphorbia fendleri), James rushpea (Caesalpinia .iamesii), narrowleaf gromwell (Lithospermum incisum), and Russian thistle (Salsola kali) are most common. A complete list of study site vegetation, percent canopy cover of each and frequency data are in APPENDICES C and D.
The regions major faunal species are rodents including kangaroo rats (Pipodomys sp.), gophers (Geomys sp.), ground squirrels (Citellus sp,), and small mice (Peromyscus sp., Neotoma sp., and Sigmodon sp.),
A small herd of approximately 25 antelope (Antilocapra americana) are present in the general vicinity. Many species of birds are present at various times of the year, the major game species being scaled quail (Callinepla squaJiata) and mourning dove (Zenaidura macroura), with smadl populations of bobwhite quail (Colinus virginianus) and lesser prairie chicken (Tympanuchus pallidicintus), CHAPTER lY
METHODS
Soil Moisture Measurement and Analysis
After examining several BrownfieId-Patricia soil associations,
where sand shinnery oak dominates, a typical area was selected for
study. Vegetation on the site indicated that no herbivores had
heavily used the area for some time.
Three blocks consisting of four treatments each: (a) remove
all vegetation, (b) remove all oak, (c) remove all vegetation except
oak (leave all oak), and (d) control (leave all vegetation) were
established to measure soil moisture depletion rates and soil
temperature fluxes (Fig, 2-5), These treatments were applied by
hand using hoes and clippers; the vegetation was uprooted and cut
at or below the soil surface, leaving litter in place. Treatments
were reapplied when any unwanted vegetation reappeared on the plots.
The perimeter of each treatment plot was encircled by a trench,
15 cm wide and 2 m deep, to sever any plant root system which
entered or exited the plot boundary. This should minimize errors
resulting from water utilization by plants outside the treatments. 2 Each treatment was replicated three times on 10 m plots. Within each plot two series of Coleman fiberglas soil moisture and temperature cells were placed at I5 cm increments to a depth of 75 -ni. A post
18 19
Fig, 2, Remove all vegetation treatment.
Fi^. 3. Remove all oak treatment. 20
Fig, 4. Remove all vegetation except c=k (leave all oak),
•,:-T7:.", _ >v:
Fi.?:. 5. Leave all vegetation (centre!). 21 hole digger was used to form the access holes for placement of the soil cells. The cells were oriented vertically into the undisturbed side of the access holes to minimize errors which might result because of a modified soil structure. Soil was replaced into the access hole by horizon and was tamped to simulate its original density. Cells were allowed three weeks to equilibrate with the surrounding soils before the first readings were taken on June 23,
1970, Thereafter, weekly readings were taken throughout the 1970 growing season with a Soil Test Soil Moisture Ohmmeter, and twice a month during the non-growing season of 1970 to May, 1971. Weekly readings were resumed in May, 1971 and carried on through December,
1971.
Two neutron probe access tubes were placed in each treatment plot into holes which had been formed with a hydraulic soil corer.
The tubes were placed into the soil to a depth of 2 m and were located within 1,5 ni of each series of soil cells (Fig. 6). They were monitored for 30 sec, at I5 cm soil depth increments with a
Troxler neutron probe, model I255 S/N 713t beginning May 18, 1Q71.
These samples were taken on the same dates as were the resistance readings (Fig, 7).
Atmospheric maximum and minimum temperatures and precipitation data were recorded weekly during the growing season and biweekly when the vegetation was dormant. Atmospheric temperatures were sensed at
123, and 4 ft levels above the soil surface using maxir.ur.- minimum thermometers. The precipitation was collected in an official
U. S. Weather Bureau rain .^auge located on a site near the plots. 22
Fig, 6, Neutron probe tube in relation to Coleman fiberglas cell series. 3-all can is over neutron probe tube amd the large can sits on the hookup points of the cells.
Fi.c;, 7. ^'eutr on pro'oe and Cole^.m soil cell? be inc used s'. ".jltar.eouslv. 23
The experimental design used was a randomized complete block design and the data were analyzed with a split-plot factorial analysis. The factors compared were dates, depths, and treatments.
Significant differences within these factors were partitioned using
Duncan's Multiple Range Test,
Field readings were converted, by computer, to ohms resistance,
and temperature in degrees F, Neutron probe field data were converted
from counts to percent moisture by volume.
Vegetation Analysis
Species frequency and canopy coverage percentages were taken
in October, 1971, on the control, remove all oak, and leave all oak
plots,
Oak canopy cover was measured using a variation of Canfield's
(1941) line intercept method. Eight lines, 1 m apart and 10 m long,
were stretched across each leave all oak and each control plot.
Interception of the line by any portion of the oak canopy was recorded
to the nearest inch. The mean oak coverage per treatment was then
calculated. 2 Foliage cover of all other species was estimated from ten, 2,4 m
circular quadrats per treatment plot. The quadrats were randomly
placed in remove all oak and control plots. Frequency and foliage
cover data were then calculated for each of these treatn:ents.
APPENDIX C lists the common and scientific names of all plar.t species
found on the study area. Cover and frequency data for all major
species are presented in API^NDIX D. CHAPTER V
RESULTS AND DISCUSSION
Effect of Sand Shinnery Oak Removal OILJ^II Moisture
When this research project was initiated in May, 1970, Coleman fiberglas resistance units were uiiod to measure soil moisture. In
May, 1971f neutron probe access tubes were installed to compare the neutron probe soil moisture rea;iln^s with the resistance units. Data from the probe indicated that tYifi resistance unit data were not reliable for several reasons (see Discussion of Techniques, p, 48),
Thus, the neutron probe data are the only information used to discuss the effect of sand shinnery oak removal upon soil moisture,
Paetzold (1972) studied the Irydxaulic conductivity of the
Brownfie Id-Pa-, ricia soil within L^/J m of our study area. He found the hydraulic conductivity to "c^ very high in the soil profile,
especially in --he upper 30 cm of ?i4.nd. After applying 26 cm of
water onto the surface of a clear%> plot, he found 50^ of the water
to move throusii the upper 90 ex viX',in two days after application.
The depths belrj- 90 cm initially r;iir.ed water and then began to
lose it slowly. Using Paetzold'^ 'i:-72) data it was estimated that
the upper level of available ws.-«rr — field capacities (F.C.) of
the soil's sarr. and sandy clay l-.^ subsoil to be 20^ and 35* b>'
volume, respec-.ively. The lower _^r»i of available water or 25 permanent wilting point (P.W.?.) far the surface sand and finer textured subsoil was ^% and \% by volume, respectively (APIVNDIX B) At field capacity there was approximately 5./.0 inches of available water in the upper 75 cm of soil.
Throughout 19711 five intervals of adequate precipitation caused a recharge of soil moisture u^ig. 8), In the control treatment at least 1,50 inches of precipitation were required to incrt^v^^e soil water at the 60 and 75 cm depths. Showers of lesser intensity seemed to replenish only the upper portion of the profile. Since most of
1970 and early 1971 were extremely dry, the soil moisture content at the beginning of these data was near the wilting point.
Sufficient rainfall was received to replenish subsoil moisture during the weeks of June 1 and August 11, 18, 25, and Septembor 25,
Soil water was rapidly depleted fran August 25 through September 16,
This reduction in soil moisture was caused by very vigorous ^rass
and oak growth following a period of semi-dormancy throughout most
of the summer. An additional 3,12 inches of precipitation war.
received during the weeks of September 25 and 30, however thin was
inadequate to fully recharge the 60 and 75 cm depths. Apparently
the grass and oak were utilizing the available water readily \n the
upper 45 cm of the soil. Similarly when 1.25 inches of water were
received during the week of October 21, no increase in soil wnter
was noted below 45 cm.
After the oak lost its leaves and the grasses became fully
dormant in late November, .97 inch of water caused a slight Increase
in soil water storage below the 45 cm depth. These data show -v,,,^ 26
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In the control plots soil moisture in the sandy siirface soil exceeded its field capacity during the weeks of August 1, 18, 25, and September 25. This excess in surface soil water may have resulted from the differential hydraulic conductivities of the surface sand and subsurface sandy clay loam. This "perching" of water immediately above the finer textured subsoil is ecologically
important. At the sand-sandy clay loam interface, large numbers of fine oak roots are present. They undoubtedly use large quantities
of this water for growth. In addition, this "perched" water also
allows grass roots an opportunity to utilize the water before it
reached deeper soil depths.
The pattern of soil water storage in the denuded plots was
similar to the control plots (Fig, 9). After the major periods of
precipitation, however, soil water content at the two deeper depths
exceeded or was near field capacity after August, This "perching"
of water again reflects a change in soil texture below 75 cm.
Mechanical analysis of the 45 to 105 cm soil depths indicated a clay
texture (APPENDIX A). Thus, this unique characteristic of this
Brownfield-Patricia soil association provides favorable soil moisture
conditions for that vegetation whose effective rooting depth is in
the upper 75 cm of soil.
Water loss from the upper 30 cm in the bare plots were similar
to all other treatments. The very rapid hydraulic conductivity 28
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through the sand along with high evaporation rates provide desert
like conditions for those plants with a shallow rooting habit.
Ephemeral plant species in the area have apparently adapted to this
environment ajid complete their life cycles in a very short time period.
In late 1970 and early 1971 few annual plants were found in the area.
Additionally, the perennial fall witchgrass died in several areas
which was possibly due to its shallow rooting characteristics.
The remove all oak and leave all oak treatments had soil water
storage levels intermediate to the other treatments (Fig. 10 and ll).
The significance of removing oak to enhance soil moisture storage
at deeper soil depths is apparent in Fi^. H. In both treatments
where oak was removed, significantly more water was found at the 75
cm depth.
Water use or depletion in the upper 30 cm of all treatments was similar. That water which entered the sand had three possible uses; (a) evaporation back into the atmosphere, (b) utilization by shallow rooted plants, and (c) when sufficient hydraulic heads develop, it could move downward into the subsoil. This confounding of pathways which the water might take after entering the soil, makes positive interpretations of water use difficult.
Statistical analysis of these data using a split-plot factorial indicated there were significant differences in the total water stored in the treatments (APPENDIX E), To see which treatments differed, Duncan's Multiple Range Test was used. Table 1 shows that the remove all vegetation plot had significantly more water than the control and leave all oak plots. Similarly the control plot had 30
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Table 1, Duncan's Multiple Range Test of Factor C (Treatments).
C3* Cl^ C^° 02^
17.98® 18.98 19.65 20.57 f
^Treatment mean for control. T*reatment mean for leave all oak, ^Treatment mean for remove all oak, treatment mean for remove all vegetation. ^% water by volume. Lines connect like means (.05 level). the least water of aill treatments. No water storage differences were found between the leave all oak and remove all oak treatments.
The water content at all depths was significantly different
(APPENDIX E). Figure 12 shows that as depth increased soil moisture content by vol\me increased. These data are averaged over eight months and do not reflect weekly or monthly variations. Also these data clearly show that most of the soil's stored water is found below
I4.5 cm. However, the differences in water available to plant growth in the surface 30 cm and lower ^5 cm may not be substantially different,
Paetzold's (1972) data showed that after 26 cm of water were applied to this soil, over one half the water passed into the subsoil. At the completion of his study (289 hours after water 33
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33f and 32% by volume soil water. At the 90 and IO5 cm depths, the percent water by volume increased to 35?S and 365S, respectively.
These differences reflected differing soil textures with depths.
The remaining factor in the split-plot analysis (dates) proved to be highly significant (APPENDIX E), Weekly precipitation varied from 0 inches throughout most of July to 2.58 inches the week
preceding August 18, The 4.5^ inches of water received in early and
late August were the only period during this study that a sufficient
hydraulic head was obtained to recharge the 75 cm depth.
Since the heavy late summer and fall rains saturated the 75 cm
depth in the remove all vegetation treatment, it was desirable to
take readings at the deeper depths to see how far water had penetrated
the profile. Figure I3 indicates that the remove all vegetation
treatments subsoil was recharged to a depth of I65 cm. Below I05 cm
the leave oak and remove oak treatments had decreased water contents.
In these treatments, 3^ less water was found at I65 cm than at IO5 cm.
Surprisingly, the soil water content in the control or leave all
vegetation plot continued to increase to the deepest depth, We
expected the control treatment to have least water at the deeper
depths, but it was only surpassed by the denuded treatment. This
phenomenon may have occurred because we cm Id not get below the 120
cm depth on half of the six access tubes that were in the three
control treatment plots. While all other treatments were an average
of the measures of all six access tubes.
Evidently from Fig. 13, in April, 1972 those treatments from which the grasses and forbs were left contain less water in the top o 35
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120 cm of the soil. The eight months data averaged across dates and depths provide similar conclusions (Fig. Ik), Because of the extensive effects of drought upon the study area, the differences between treatments were not as was expected early in the study.
Probably treatment differences would have been observed if the late
1971 summer precipitation had not fallen. Early field observations in 1972 show treatment vegetation effects to be more marked than throughout 1970 and 1971.
Table 2 shows neutron probe moisture data that was converted to inches of available water, July 6 was a week of very low soil moisture following four weeks of no effective precipitation and
September 25 represents a week of hi^ soil moisture following a week
of beneficial precipitation. During the week preceding July 6 almost all the available water in the first ^5 cm was used by the vegetation
treatments, with the lower 60 and 75 cm depths having much less water
than the same depths from the remove all vegetation treatment. The
control contained an inch less available water in the overall 75 cm
than the remove all vegetation plot, while the remove all oak and
leave all oak contained an intermediate amount of available water.
The week of September 25, representing a wet period showed similar
results in treatment relationships. Striking differences in use of
water in the upper ^5 cm are noted between the vegetative treatments
versus the bare treatment. The data in this table again indicates
the vegetation's ability to take almost immediate advantage of added available water in the surface ^5 cm of soil. The benefit of the clav layer's "perching" ability to keep more water available at the 37
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Table 2. Inches of available water for treatments on July 6 and September 25. 1971.
July 6, 1971 September 25, 1971
TREATMENT 1 (leave all oak)
Depth Inches Inches H2O Depth Inches Inches H-0 cm H2O Available cm H2O Available
15 ,06 0 15 .9^ ,6/+
30 .31 .01 30 1.^8 1.18 ^5 .78 0 ^5 2.01 1,11
60 1.11 .21 60 2.19 1.29
75 1.30 .^0 75 1.97 1,07
Total 3.56 ,62 Total 8.59 5,29
TREATMENT 2 (remove all vegetation)
15 .1^ 0 15 .90 ,60
30 M .15 30 1.^2 1,12 ^5 .96 .06 ^5 1.97 1,07
60 1.^9 .59 60 2.26 1,36
75 1.50 .60 75 2.30 1.^0
Total 4,5^ 1.^0 Total 8.85 5.55
TREATMENT 3 (Control)
15 0 0 15 1.11 ,81 30 .1^ 0 30 1.33 1.03
^5 .56 0 ^5 1.8^ .9^
60 1.00 .10 60 1.78 ,88
75 1.16 .26 75 1.91 1.01
Total 2.86 .36 Total 7.97 3.77 39 Table 2. Continued
July 6, 1971 September 25, 1971
TREATMENT ^ (Remove all oak)
Depth Inches Inches H2O Depth Inches Inches H2O cm HgO Available cm H2O Available
15 .03 0 15 1.28 .90
30 .35 .05 30 1.82 1.52
45 .99 .09 45 2.04 1.14
60 1.18 .28 60 1.80 .90
15 1.36 .46 75 1.78 .88
Total 3.91 .88 Total 8.72 5.34 40 sand-sandy clay loaim subsoil interface are seen in the bare plot having 5.55 inches of available water, which is more than would be available at field capacity (5.40 inches).
Effect of Sand Shinnery Oak Removal on Soil Temperature
Soil temperature measurements were taken using Coleman fiberglas resistance units containing a thermister. According to the manufacturer of the units, the thermisters have a nominal resistance of 1000 ohms at 77 F with individual thermisters having resistances within 10^ of this value (Coleman, 1964). Each unit, because of nonuniformity in construction was given a correction factor. To check the manufacturer's specifications, five of the units were allowed to equilibrate in a constant water bath set at 77 F. All were found within 1 F of the temperature bath. Conversion of ohms resistance to temperature was accomplished using a computer,
A sinusoidal soil temperature curve was found in the Brownfield-
PSitricia soil association (Fig. I5). As would be expected, the 75 cm depth was coolest in the summer and slightly warmer in mid-winter.
Figure I6 show the weekly variations in soil temperature by depths
in a summer period of 1970 and 19711 while Fig. 17 shows that for the winter month of December, 1970. These figures better emphasize the
changes in temperature from one soil depth to another and that the
75 cm depth remain warmer in the winter and cooler in the summer.
The drop in soil temperature after July 9 for the I5 cm level is
Quite puzzling. It could have been due to overcast weather caused by convectional storms that occurred on the days data were collected. 41
J A MONTHS(197a MONTHS(1971) Fig, 15. Soil temperaturaa for all depths (15-75 cm) over all treatments, monthly 1970 and 1971, ^ 42
80 -
F
AlScm D30cnn 045cnn oeocm v75cm
•-v-^ 4 70 1 ^y T^ i2 2'9 -t 15 ^ JULY 1970 JUNE19:n Fig. 16. Temperature for depths (15-75 cm) over all treatments July, 1970 and June, 1971. 43 55
50
45
A 15cm DBOcm 045cm O60cm V7 5cm
40 2 16 30 DECEMBER 1970 Fig. 17. Temperature for depths (15-75 cm) over all treatments December, 1970, 44
Daily variations and declining soil temperature can be expected in
the upper sandy levels of this soil on days without direct sunlight.
Contrary to some published data (Baver, I956, Kohnke, I968) the time
lags required for the transfer of heat downward in the profile are
not readily apparent in this soil (Fig. 15).
Although the graphical representation of the soil temperature
data seem similar at all depths, statistical analysis show them
to be different in 1971 at the .05 level (APPENDIX F). Significant
temperature differences also occurred among dates and treatments.
Non-significance was found between depths in I970 (APPENDIX G),
At the .05 level, the Duncan's Multiple Range Test showed the
temperature at I5, 60, and ^'^ cm depths to be similar (Table 3). In addition the 30 and 45 cm depth temperatures were not different.
This array of mean soil temperatures by depths appears atypical to textbook data (Baver, I956; Kohnke, I968). Possible explanations for these atypical data were (a) different soil texture between 30 and
Table 3. Duncan's Multiple Range Test of Factor B (Depths). 1971.
30 cm 45 cm 15 cm "J^ cm 60 cm
60,40* 60.80 61.18 6I.58 61,88 b
temperature degrees F, iiines connect like means (,05 level). ^5
45 cm depths, (b) water or air relationships in the surface and subsoil, (c) differential shading or organic matter accumulations which would affect the thermisters, and (d) slight variations in the time of day that sensors were read. It is believed that the soil texture as related to hydraulic conductivity was of paramount importance in this study. The sands surface became exceedingly hot when solar radiation was intense. This heat could be used for the following purposes: (a) be conducted downwaxd into the soil,
(b) heat the air adjacent to the soil surface, or (c) cause intense evaporation from the soil's surface. The moisture held in the soil apparently provided an ideal conductor for heat to travel to the
75 cm depth. This coupled with the rapid to very rapid hydraulic conductivity could explain the transfer of heat to the low depths.
Also when the heat was transferred to the finer textured subsoil its rate of transfer would decrease. In addition temperatures in the subsoil should be more stable than in the sandy surface soil.
Since weekly and not daily soil temperature readings were taken, the dynamic and very rapid surface soil temperature changes were not recorded. Data in Fig, 15 reflect this dynamic soil surface temperature characteristic, as do Figs, l6 and 17. The 30 cm depth is warmer in mid-summer than the 15 cm depth. Apparently heat is leaving the system at the shallower depth and is being conducted downward or back into the atmosphere.
Soil temperatures in 1971 showed no difference between the leave all oak and remove all vegetation treatments (Table 4). Those treatments without prass and forbs removed; the control and the 46 Table 4. Duncan's Multiple Range Test of Factor C (Treatments) 121U
C3* C4^ Cic 02^
60.64® 60.91 61.34 61.77 f
I'reatment mean for control, treatment mean for remove all oak. ^Treatment mean for leave all oak, treatment mean for remove all vegetation, ^Temperature degrees F, Lines connect like means (,05 level).
remove all oak, were also not different. The treatments with grass
remaining, however, were significantly cooler than those with grass
removed. Less than 1 F difference was noted between all treatments.
The effect of treatments on soil temperatures then was possibly of
little biological significance. Soil temperature differences within
treatments should become more marked when the vegetation in the
respective plots becomes more dense. The effects of drought in relation to plant vigor have minimized temperature differences.
To obtain an index of reliability of soil temperature measurements, coefficients of variation have been calculated for the dates, depths, and treatments (Table 5)* These data show that little variability between thermisters was present. The 1970 and
1971 data both were consistent in reporting the variation. 47
• (0
1 rn • • • CM OS
•a vO a &; o ix •^ O iH OS vO vO NO
U O u -P o O -p o pq o ce
05 e
(D O o vO CM O • O -H ^ n5 o 0) > O o
ON ON 00 o CO CO • CM CM CM o (0 iH -P •P
o 0) OU I c -P o •a c (d cd "•—-' o 0) -p (0 E vf> n m SI +> U o -P (D o a> 1 -p (X a rH •p o o <6 Q> .o o u cd 0) 0) xjp O TD ® t-l &H 48
The relationship between maximum and minimum air temperatures at the 1 ft height as they affect the overall soil temperatures has been examined (Fig. 18). These data show that the average monthly soil temperatures of the Brownfield-Patricia soil association are intermediate between the maximum-minimum air temperature in June,
August, November, and December. Regarding the "new" soil classification system which utilizes average soil temperature data, this study indicated that maximum-minimxim air temperatures can closely predict the soil temperature (U. S. Dep. of Agr., I960),
Comparison of Two Soil Moisture Measuring Techniques
Two indirect methods were used to measure soil moisture levels in this study. Coleman fiberglas resistance \inits and a Toxler model
1255 neutron scattering device were the sensors used. These methods were compared using the following criteria: (a) variability in readings and sensitivity to differing soil water levels, (b) ease of data collection ajid analysis and, (c) calibration characteristics.
Variability of Readings and Sensitivity
Figure 19 shows the I97I eight month average resistance and percent water by volume data. This data for each I5 cm increment of soil depth is depicted by ohms resistance in the upper portion while the neutron probe data are below. The data collected from the neutron probe and resistance units are contradictory throughout the soil profile. That is, the resistance units showed most water to be present at the I5 cm depth while the probe data indicates most water 49
120
110
lOOl-
90
80
70
60
50
40
30
20
10 Alft High Temp. 0 DAvg Soil Temp. -10 V 1ft Low Temp. ^ L. _1 L. J 1 i 1 I ' ' JJASOND JJASOND 1970(MONTHS) 1971(MONTH9 Fig. 18, Soil temperature average over 75 cm to Monthly atmospheric extremes at 1 ft for June to December, 1970 and 1971, 50
30^ 5 2 0 OHMS 10^
30-
20 °/c WATER BY VOL.
10
15 30 45 60 75 DEPTH(cm)
Fig. 19, Comparison neutron probe (% H2O by volume) to resistance units (ohms resistance). Depth over 8 months of 1971.
a i a »^
was at 75 cm. Similarly the probe data at 60 cm was comparable to resistance readings at 30 cm.
This relationship was highly negative with a correlation coefficient of -.82. When comparing the treatment resistance value; with probe data, a negative relationship was also found. However, this correlation of -.58 was not as clearly unassociated as for the depth comparisons. It was obvious from these data that the methcxis were not measuring soil water similarly.
Data show that the resistance units gives erratic readings whe; soil moisture decreased below 10^ by volume. At or near ^% soil water, no readings were observed. In the lower 45 cm of the soil, the units were even more unreliable. Since these sensors are measuring matric potential, the divergent textural changes in the profile have caused erroneous readings of water. The drought which affected the area until mid 1971 has apparently magnified the uselessness of this technique.
The neutron probe, on the other hand, records hydrogen atoms within a confined area regardless of state or form. Thus soil texture changes or high soil moisture tensions have not altered data recording.
To document the precision of the two techniques, coefficients of variation were determined for each technique (Table 6), Precisl of data obtained with the resistance units were low. For most comparisons the coefficient of variation exceeded 100^ with this method. However, the neutron probe data had coefficients of variations near 50^ or lower. When considering this variation witl (0 CN- +> C7N C O 0> ^ ^ O o O o o o r^ ^ C^ 00 CN- iH cd O
-p o o VO O VO O VO -p r-t r> ^ NO (^ 1 1 1 1 1 T-l CM .d- u o O u cd < PQ PQ pq PQ PM pq u o O o o o M a (0 o -p e V) o 0) o CM O -p H C CM c c ON o VO H
Calculations of technique efficiencies indicate the probe to be
3.6 and 2,4 times more efficient in measuring water at different depths and between treatments, respectively. At the 75 cm soil depth the probe is 5•4 times more efficient than the resistance units while at 15 cm it is 2,4 times more efficient.
Data Collection aJid Analysis
More time is required to install the resistance units than is
required of an equal number of aluminum access tubes for the probe.
Of particular concern in the installation of the units is the chance
of soil structural changes near the unit. It is obvious that if the
soil horizons were not replaced and packed to the original density
that inaccurate data would be obtained.
The resistance units are also subject to wire breakage, rodent
damage, or calibration changes in some soils. This unreliability of
the units make them of lesser value in determining soil moisture
changes or content. No mechanical failures in permanent field
equipment to obtain neutron probe data were noted.
Time utilized to record data in the field is similar for both techniques, A 30 sec counting time was used for the probe after 5^ consulting Hewlett, Douglass and Clutter's (1964) and Rogerson's (1970) data. Experiences with the ohmmeter used to record resistances in the study were also less than desirable. Breakage of electrical components or dust in the meter required that two meters be available for each recording date.
Transcription of field data onto computer cards is also easier
with neutron probe data than with resistance readings. The computer
programs utilized in this research converted neutron probe counts
directly into percent water by volume and subsequently inches of
available water. Manufacturer's of the resistance units indicated
that no computer program was available to transfer resistance
readings into soil moisture and temperature values. Thus, a program
was developed to transform resistance directly into degrees F. No
satisfactory method is available to obtain soil water content, other
than corrected ohms resistance, from raw field data.
Calibration Methods
Calibration poses a problem in both techniques, but once
calibrated to a specific soil, the neutron probe readings vary only
slightly at the same soil water content. Resistance units, however,
have been reported to change as a result of mineral concentrations
on the units (Baver, 1956; Kramer, I969). An attempt was made to
calibrate the resistance units used in this study. So much variability
in data was obtained at specific resistance readings that calibration
attempts were terminated.
Besides mineral accumulations on the resistance units, corrosion
of wires which affects electrical currents were apparent. In 55 summary, it is believed that more variables are uncontrollable when using resistance units than when using the probe. It is suggested, then, that resistance units should have alternative uses or be used in more mesic environments. CHAPTER VI
SUMMARY
Four treatments, remove all vegetation except oak, remove all vegetation, control, and remove all oak, were applied to 10 m^ plots in a sand shinnery oak community, on a Brownfield-Patricia soil association. Soil moisture and temperature data were collected at
15 cm intervals to 75 cm depths. Two methods were used to collect soil moisture data, Coleman fiberglas resistance units and a Troxler model 1255 neutron scattering device, or neutron probe. Soil temperatures were recorded with thermisters in the Coleman fiberglas resistance units. The data were used to determine the effect of sand shinnery oak, a noxious and poisonous brush species, removal on soil moisture and soil temperature. The moisture data were also used to compare the two indirect methods of soil moisture measurement.
Several soil properties became evident as the study proceeded that made interpretation of the results easier. The soil had a very high hydraulic conductivity particularly in the upper sandy textured
30 cm depths. Upper levels of available water were estimated to be
20% and 35% while lower levels of available water were S^ and 15^, respectively in the sand and sandy clay loam textural classes of the study area's soil. At field capacity 5,40 inches of water were available in the upper 75 cm of the soil. Most water storage occurred
56 below the 45 cm depth. To recharge the soil to the 60 and 75 cm depths approximately 1,5 inches of precipitation were required. Effective
recharge of the soil was directly related to growth characteristics
of above ground vegetation. A water "perching" effect was observed
at the sand-sandy clay loam sub-surface interface, which may be
ecologically important by holding available water longer for plant use.
The soil's moisture properties favored plants with effective
rooting depths of 75 cm. Although 1970 and 1971 were mostly dry
years, (i.e., weekly precipitation ranging from 0 or less than ,5
inches in most cases, to 2,85 inches) five monthly periods of
adequate precipitation were noted. Only one of the five intervals
(August, 1971) was capable of recharging the lower 60 and 75 cm
depths, The vegetation of the area readily uses available water in
the upper 45 cm of the soil, and depletion to 30 cm was the same for
all vegetation treatments. Recharge of soils at the I65 cm depth
occurred in the bare-ground treatments while treatments with grass and
forbs remaining had less water in the 120 cm depth. Oak removal
treatments had increased water available at the 75 cm depths when
compared to the vegetation treatments, which indicates that oak
removal releases water for more desirable vegetation to use or to go
to deep storage.
The many pathways of water use coupled with the dry years durinc
which this data was collected did not allow the difference between
treatments that was first expected at the beginning of this study and
made positive interpretation impossible. With the late summer and 58 early fall precipitation of 1971, early vegetation changes in 1972 indicate that the treatment relationship will become more distinct as this project is carried on.
Soil temperature studies resulted in a typical sinusoidal temperature curve. Although lag of heat's downward movement in the profile was not apparent, the 75 cm depth remained cooler in the summer and warmer in the winter, as was expected. Temperature seemed to relate to the hydraulic conductivity of the soil and moisture content, with the sandy clay loam sub-surface area's temperatures more stable than the sand's. The maximum and minimum soil temperatures recorded at all depths were 84 F and 40 F, which proved to be almost
perfectly intermediate of the atmospheric extremes, in many cases.
After testing data collected with the thermisters, they were considered to be very accurate and indicated good precision.
Grass and forb treatments were significantly cooler than all
other treatments. Vegetation seemed to have little physical or
biological effect on soil temperatures of this area, which may have
been due to the drought years' effect on plant vigor. Temperature differences between treatments are expected to become more pronounced when the vegetation recovers from the drought conditions.
The two indirect soil moisture methods (i.e,, Coleman fiberglas resistance units and neutron probe) were compared. After tests were run to correlate the data collected from both methods it became evident they were not giving the same relative information. Upon calculation of coefficients of variation for the two methods it was found that, in most cases, resistance unit data had coefficients of 59 variation over 100%, while neutron probe data was near 50% or less.
The high coefficients of variation for the resistance unit technique were due to its inability to measure consistently at the 10% by
volume moisture level and not measure below 5% by volume water
contents. Because resistance units measure matric potential we
believe that water at these levels was held too tightly for the
resistance units to record. The neutron probe method of soil moisture
measurement measures water regardless of the tension in the soil or
in what phase. Efficiency calculations, using coefficients of
variation, showed the neutron probe to be 3'6 and 2.4 times more
efficient for depth and between treatment measurements, respectively.
Installation, data collection and preparing data for analysis
were easier using the neutron probe. Also breakage of field and
recording equipment was not as common with the neutron probe as with
the resistance unit technique. Calibration posed a problem with both
techniques, but the probe, once calibrated to a soil, seldom changes,
whereas the resistance units, in most soils, do change over time.
It was, therefore, concluded there are more uncontrollable variables
when using resistance units than with the neutron probe and that
resistance units should have alternate uses or be used in more mesic
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A, Description of study area's Brownfield-Patricia soil association.
B, Physical properties of study area soil; soil separates, calcium carbonate equivalent, bulk density, field capacity, permanent wilting point.
C, List of plant species observed on study area. Nomenclature from Gould (1969) and Correll and Johnston (1970).
D, Canopy cover and frequency of major plant species on treatment plots,
E, Analysis of variation table for neutron probe soil moisture data (percent by volume, 1971). F, Analysis of variance table for temperature data (1970),
G, Analysis of variance table for temperature data (1971).
66 Tr*'
67 APPENDIX A: DESCRIPTION OP STUDY AREA'S BROWNFIELD-PATRICIA SOIL ASSOCIATION.
Horizon Inches (cm)
Al 0-6 Dark brown {7,Si^ 4/4) sand, dark (0-15) ^own (7.55fR 3/2) moist; weak subangular blocky structure; soft, clear smooth boundary
A2 6-15 Brown (7.5YR 5/4) sand, dark brown (15-37) {7.5 YR 4/4) moist; weak subangular blocky structure; slightly hard, abrupt wavy boundary;
B21t 15-36 Yellowish red (5YR 5/6) sandy clay (37-90) loam, (5YR 4/6) moist; yellowish red moderate prismatic and moderate subangular blocky structure; very hard; clear smooth boundary
B22t 36-50 Yellowish red (5YR 4/8) sandv clay (90-125) loam, yellowish red (5YR 4/6) moist; weak prismatic and moderate subangular blocky structure; hard; abrupt irregular boundary
B23tca 50-70 Pinkish white (5YR 8/2) clay, pink (125-175) (5YR 7/4) moist; massive structure; moderately cemented; clear wavey boundary; some krotovinas present
B24t 70-77 Reddish yellow (5YR 6/6) sandy clay (175-192) loam, yellowish red (5YR 4/6) moist; weak subangular structure; very hard; abrupt wavey boundary; ped surfaces coated with CaCOo, discontinuous horizon
B25xca 77-115 , Yellowish red (5YR 5/6) and pinkish (192-287) grey (5YR 7/2) sandy clay loam, yellowish red (5YR 4/6) and light reddish brown (5YR 6/4) moist; sub- angular blocky structural remains; very hard; diffuse boundary; CaCO-*; reticulated appearance
Reddish yellow (5YR 6/6) sand, yellowish 115^- (287+) red (5YR 4/8) moist; granular structure ^:omplled with the help of Dr. B, L, Allen, Professor of Agronomy, Texas Tech University, Lubbock, Texas, 68
APPENDIX Bi PHYSICAL PROPERTIES OF STUDY AREA SOIL; SOIL SEPARATES, CALCIUM CARBONATE EQUIVALENT, BULK DENSITY, FIELD CAPACITY, PERMANENT WILTING POINT,
Sand* Silt* Clay^ CaC03»* Horizon Texture class %
Al 93.90 4,10 2,00 ,28 Sand
A2 93.90 2,20 4,00 .25 Sand
B21t 62.22 10,49 27,29 ,68 Sandy clay loam
B22t 69.22 8.21 22,57 .65 Sandy clay loam
B23tca 35.79 22.07 42,14 62,54 Clay
B24t 57.52 12.14 30,34 4,94 Sandy clay loaon
B25tca 67.68 10,10 22,22 13.23 Sandy clay loaun
C 92,00 2,00 6,00 1.52 Sand •^Mechanical analysis. Hydrometer method (Black, I965). **CaC0^ equivalent: Acid neutralization method (Richards, 1954).
Bulk Density Horizon F.C, P,W,P, gm/cm-^ % by volume Al Ave. 1.345' 20.0 5.00 A2
B21t 1.430 35.00 15.00 ^Bulk density: Core method (Black, I965)• 69
APPENDIX C: LIST OF PLANT SPECIES OBSERVED ON STUDY AREA, NOMEN- GUTURE FROM GOULD (I969) AND CORRELL AND JOHNSTON (1970),
Scientific name Common naone
Brush:
Artemisia filifolia Torr. Sand sagebrush
Chrysothamnus pulchellus (Gray) Southwest rabbitbrush
Opuntia englemannii Parry Englemann pricklypear
Prosopis glandulesa Torr. var. glandulosa Honey mesquite
Quercus havardii Rydb. Shinnery oak
Schrankia uncinata Willd. Catclaw sensitive briar
Xanthocephalum sarothrae (Pursh) Shinners Broom snakeweed
Yucca campestris McKelvey Plains yucca
Forbs:
Ambrosia psilostachya D,C, Western ragweed
Artemisia caudata Michx, Threadleaf sagewort
Asclepias pumila (Gray) Vail Plains milkweed
Commelina erecta L. Hierba Del Pallo
Calylophus serrulatus (Nutt,) Raven, Yellow evening primrose
Eriogonum annuum Nutt, Annual wildbuckwheat
Euphorbia fendleri T, and G, var fendleri Fendler euphorb
Caesalpinia iamesii (T, and G.) Fisher James rushpea
Hymenopappus flavescens Gray var, flavescens Yellow woolywhite
Lithospermum incisum Lehm, Narrowleaf gromwell
Mirabilis linearis (Pursh) Heimerl Linearleaf four-o'clock
Mollugo verticillata L, Indian chlckweed
Palafoxia sphacelata (Torr,) Gary, Rayed palafoxl 70 APPENDIX Ci GontiTi»»H
Scientific name Common name
Paronychia jamesii T. and G, James nailwort
Petalostemum purpureum (Vent.) Rydb, Purple prairie clover Polygonum sp,
Portulaca pilosa L, Shaggy portulaca
Salsola kali L. Russian thistle Thelesperma megapotamicum (Spreng.) Ktze. var, megapotamicum Colorauio greenthread Grass:
Andropogon hallii Hack. Sand bluestem
Aristida purpurea Nutt. Purple threeawn
Bothriochloa barbinodus (Lag.) Herter Cane bluestem
Bouteloua curtipendula (Michx.) Torr, Sideoats grama
Bouteloua hirsuta Lag. Hairy grama
Ghloris cucullata Birsh. Hooded windmill grass
Digitaria sanguinalis (L,) Scop, Hairy crabgrass
Eragrostis oxylepis (Torr.) Torr. Red lovegrass
Leptoloma cognatum (Shult.) Chase Fall witchgrass
Munroa squarrosa (Nutt.) Torr. False buffalograss
Paspalum setaceum Michx, Thin paspalum
Schizachyrium scoparium (Michx,) Nash. Eastern little bluestem
Sporobolus cryptandrus (Torr.) Gray SaJid dropseed 71
APPENDIX D: CANOPY COVER AND FREQUENCY OF MAJOR PLANT SPECIES ON TREATMENT PLOTS. Control Remove all Oak Type Canopy Canopy and Frequency Cover Frequency Cover Species %
Brush:
A, filifolia 3.7* 2.3 3 1,6 £, havardii 12.3 5.5 0 0 X. sarothrae 3.3 2.2 4.3 2.5 Other brush 3.0 .7 .7 .8
Forbs: A, psilostachya ,1 .1 1.3 1.0
A* caudata 0 0 3.7 1,0 0. erecta 4,3 1.2 4.5 1.7 E. fendleri 3.7 1.5 4,7 1.7 c. iamesii 3.0 1.3 2.3 .4 Polygonum sp. 0 0 4,0 1.0 s. kali 4.0 1.0 5*7 2,6 Other forbs 23.7 2,6 7.5 4,2
Grasses: 2.6 A. purpurea 10.3 4,7 6.3
B. curtipendula 3.7 1,0 6,0 1.3 1.4 B, hirsuta 1.7 ,7 5.0 L, cognatum 4.7 1.8 1.7 2.7
P. setaceum 0 0 6,0 1,1 72
APPENDIX D: Continued
Control Remove all Oak Type Canopy Canopy and Frequency Frequency Species Cover Cover %
S, scoparium 8.7 6.7 9.0 3.5
S, cryptandrous 12.0 5.6 10.5 4.0 Other grasses 6.4 2.0 3.3 .8
Total 40.8 38,0 * % taken by quadrats
Canopy cover on control and oak only plots. Control Oak only Canopy cover {%) 3.7* 9.7
• % taken by line intercepts.
X at at
3 3 3 73
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