Water Requirements for Establishing
Native Atriplex Species During Summer
in Southern Arizona
M. Carolyn Watson
Bruce A. Roundy
Steven E. Smith
Hossein Heydari
Bruce Munda
and water catchment methods. Supplemental irrigation has
been a promising tool in revegetation of mine sites (Ries
and Day, 1978) and of non-mine sites, such as abandoned
farmlands. Thacker and Cox (1992) recommended that for
the arid conditions in southern Arizona, a permanent vegetative cover be established on farmland before farmland
is retired to take advantage of existing irrigation systems.
The line-source sprinkler irrigation gradient system
(LSSIGS) has been utilized extensively to evaluate the effects of variable water deficits on crop plants and to screen
cool-season grass and legume genotypes for responses to different levels of moisture stress under field or greenhouse
conditions (Hanks and others, 1976; Johnson and others,
1982; Rumbaugh and others, 1984; Asay and Johnson, 1990;
Johnson and others, 1990). This irrigation technology is
designed to give uniform application at the same distance
along the line-source and decreasing application with increased distance from the irrigation line. The LSSIGS has
been mostly used to study post-establishment plant responses and has not yet been extended to measure water
requirements during seedling establishment of desertadapted plants.
The use of Atriplex shrub transplants may facilitate revegetation of rangelands where seed germination and seedling
establishment may be low and in critical areas (Springfield,
1970; Aldon, 1972; Van Epps and McKell, 1980; McKell,
1986; Roundy and Call, 1988). In many instances, transplanting adapted shrubs may be the only viable revegetation
strategy. Although the use of container-grown transplants
provides more flexibility in timing of planting, supplemental
water may be required to ensure survival. Aldon (1972)
indicated that soil moisture availability after planting was
a factor in successfully establishing A. canescens transplants.
Direct-seeding would generally be more economical in establishing perennial shrubs than using transplants. Studies have shown that the optimum temperature for germination and establishment of Atriplex shrubs native to the
western United States is at relatively low temperatures
and that high temperatures frequently suppress germination and survival. Although optimum germination temperatures may vary both among and within species (Mikhiel
and others, 1992), the temperatures most favorable for germination of A. lentiformis, A. polycarpa and A. canescens
range from 10 to 25 °C, 9 to 15 °C, and 13 to 24 °C, respectively (Cornelius and Hylton, 1969; Springfield, 1969;
Sankary and Barbour, 1972; Young and others, 1980; Potter
Abstract—Germination and establishment characteristics of
11 perennial Atriplex accessions belonging to four species were
determined during the summer of 1992 and 1993 under field
conditions in southern Arizona. Meteorological, soil moisture,
soil temperature, irrigation and plant performance data of seedlings or transplants were used to estimate water requirements
for establishment under a line-source sprinkler irrigation gradient system. Under natural rainfall conditions during the summer, establishment of plants by transplanting was greater than
that by direct seeding. Transplant survival varied within and
among species and was generally lower in A. linearis, which was
heavily grazed by rabbits. Germination and emergence of plants
were greater at the highest irrigation level than under natural
rainfall conditions. Supplemental irrigation increased the probability of seedling establishment both years.
Disturbed desert plant communities can be improved
by reseeding forage-producing and soil-stabilizing grasses,
forbs, shrubs or trees that are adapted to the environmental
conditions of the area (Roundy and Call, 1988). Vegetation
recovery on direct-seeded disturbed lands depends largely
on the amount and seasonal distribution of precipitation
during the period when temperatures are favorable for germination and establishment. Since soil moisture availability during establishment is a primary factor determining
the success of plantings in arid and semiarid lands, revegetation projects have focused on the use of water catchment
and mulching methods, and of supplemental irrigations.
Jackson and others (1992) evaluated the establishment of
perennial shrubs on disturbed lands in the lower Sonoran
Desert that had shown no signs of natural recovery. They
were able to establish Atriplex polycarpa and A. canescens
on abandoned farmland in central Arizona under average
to above-average winter rainfall by using organic mulches
In: Roundy, Bruce A.; McArthur, E. Durant; Haley, Jennifer S.; Mann,
David K., comps. 1995. Proceedings: wildland shrub and arid land restoration symposium; 1993 October 19-21; Las Vegas, NV. Gen. Tech. Rep.
INT-GTR-315. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Intermountain Research Station.
M. Carolyn Watson and Hossein Heydari are Graduate Students, School
of Renewable Natural Resources, and Steven E. Smith is Associate Professor, Department of Plant Science, all at the University of Arizona, Tucson.
Bruce Munda is Manager of USDA-SCS Plant Materials Center, Tucson,
AZ. Bruce A. Roundy is Professor, Department of Botany and Range Science, Brigham Young University, Provo, UT.
119
and others, 1986). In general, the best time for native
Atriplex seedling establishment appears to correspond to
the cooler winter periods in the southwestern and western
U.S. arid and semiarid lands (Wilson, 1928; Parker and
McGinnies, 1940; Cornelius and Hylton, 1969; Sankary
and Barbour, 1972; Thacker and Cox, 1992; Munda, 1993).
Tucson, Arizona has a bimodal rainfall pattern which
provides the opportunity to evaluate establishment under
both summer and winter rainfall patterns. In the summer
of 1992, field studies were initiated to measure water requirements for establishment and survival of desert-adapted
grass, shrub, and tree species that were direct-seeded. Because high soil temperatures associated with summer conditions are potentially unfavorable for establishing Atriplex
from direct seeding, transplants were evaluated as an alternate method of establishment. The main objectives of the
summer field studies were to: 1) evaluate direct seeding
and transplanting methods for establishing plants under
a LSSIGS and, 2) utilize meteorological, soil temperature
and moisture levels, irrigation amounts and plant performance data to determine water requirements for successful establishment.
weather station was installed to record windspeed, temperature, solar radiation, relative humidity and precipitation.
In three replicates, soil moisture and temperature sensors were buried at five depths (1-3, 8-10, 18-20, 38-40 and
58-60 cm below soil surface) and at four distances (1.5, 6,
10.5, 16.5 m) from the irrigation line. Soil temperatures
were measured with thermocouples; gypsum blocks were
used to measure soil water tension. Hourly averages of
soil water tension and temperature, air temperature, relative humidity, total and net radiation and windspeed were
recorded with Campbell CR-10 microloggers.
Species that were evaluated either as direct-seeded
plants or as transplants are listed in Table 1. The three
direct-seeded species and one of the transplant sources
were cultivars or collections maintained at Tucson Plant
Materials Center (TPMC). The remaining sources were
from seed collections made during the fall and winter of
1992 and 1993 from populations in central and southern
Arizona, and coastal northern Mexico. The subspecies
classification of A. canescens accessions were based on descriptions and site information provided by S. Sanderson
and H. Stutz (USDA, Shrub Lab and Brigham Young
Univ., Provo, UT).
Methods and Materials
Direct Seeding
Site Description and Plant Sources
Germination was counted in four replicates of 25 seeds
each placed on filter paper in petri dishes in a Conviron
incubator under a gradual diurnal fluctuating temperature regime from 20 to 40 °C. Bulk seeding rates were
based on mean percent purity, seed germination percentage and individual seed weight for each seed lot. A seeding rate of 33 pure live seed (pls) per meter was used for
the direct-seeding trials when germination percentages
were greater than 50%. Seeding rates were adjusted to
66 pls/m and a germination percentage of 10% was used
to calculate bulk seeding rates when actual germination
was <10%. Seed was sown using a Kincaid No-Till Plot
drill at a depth of 1.3 cm on 14 July in 1992 and 20 July
in 1993. Irrigation water was applied daily for 9 to 11 successive days to maintain high soil moisture in the upper
3 cm of the soil profile nearest the irrigation line. After
initial seedling emergence, irrigation water applications
The 1992 and 1993 summer experiments were conducted
at the USDA-SCS Tucson Plant Materials Center (TPMC),
Tucson, AZ. The soil was an Anthony sandy loam (coarseloamy, mixed, calcareous, thermic typic Torrifluvent). For
both years, the soil profile was wet from either natural rainfall or from supplemental irrigations prior to planting.
Grass, tree and shrub species were planted perpendicular
to a line-source sprinkler into field plots with rows 16.5 m
long spaced 41 cm apart. Plots were replicated six times,
three on each side of the irrigation pipe. Six water application levels were designated within the 16.5 m distance from
the irrigation line, with one level receiving only natural
rainfall. The amount of water applied at each irrigation
was measured with catch cans placed at 1.5, 4.5, 7.5, 13.5
and 16.5 m from the line-source sprinkler. An electronic
Table 1—Atriplex accessions evaluated under the line-source irrigation system during the
summer of 1992 or 1993 at Tucson, Arizona.
Species
A. linearis
A. linearis
A. linearis
A. canescens
A. canescens
A. canescens
A. canescens
A. polycarpa
A. polycarpa
A. polycarpa
A. lentiformis
Subspecies/
cultivar
Collection
locality/source
—
—
—
Toltec, AZ
Tucson, AZ
Puerto Penasco, MX
angustifolia
grandidentatum
occidentalis
Tucson, AZ
Puerto Penasco, MX
Willcox, AZ
Tucson Plant Materials Center, AZ
cv. Santa Rita
—
—
—
Tucson, AZ
Casa Grande, AZ
Tucson Plant Materials Center, AZ
cv. Playa
Tucson Plant Materials Center, AZ
120
were scheduled according to evapotranspiration data obtained from a AZMET weather station located approximately 3 km from the experimental site. Irrigations were
then adjusted to maintain the mean cumulative catchment
of water at the 1.5 to 4.5 m line source distance approximately equal to 75% of the cumulative reference evapotranspiration. Irrigation was conducted in the early morning
to minimize wind interference.
Over a period of 3 months, seedling plant counts (plants
per linear meter) were recorded at five to seven dates and
at six distances from the line-source sprinkler (1.5-2.5,
4.5-5.5, 6.0-7.0, 7.5-8.5, 10.5-11.5, and 13.5-16.5 m). Within
28 days after sowing seed in 1993, the field planting was
fenced to exclude rabbits.
Transplants
Seedlings were started under greenhouse conditions and
juveniles were hardened-off in a lath-house for 2 weeks
and cut back to approximately 18 cm height prior to transplanting. Transplants were of 3 months and 5 months of
age for the 1992 and 1993 planting dates, respectively.
In both years, spacing of the transplants within rows was
76 cm. Transplants were planted during the first 10 days
of August, the root ball being placed within a 10 cm (1993)
or 20 cm (1992) depth. The 1992 trial contained four rows
of each accession in each plot and the 1993 trial contained
one row of each accession per plot.
Transplant survival was determined approximately every
20 days until the end of November by counting the number
of live plants in each row. Survival and persistence of the
1992-established plants that had received no supplemental
irrigation over the winter season were evaluated at the beginning of the 1993 summer season. In the 1993 planting,
mortalities were classified as being caused by rabbit predation, as determined by less than 2.5 cm of plant remaining
above the soil line, or being due to natural causes, when
plants were greater than 15 cm tall at time of death. Survival percentage data were arc sine transformed prior to
analysis of variance.
Figure 1—Daily rainfall (bars) mean daily air temperature (lines) for 80 days after commencement
of line-source irrigation for direct seeding and transplant trials of Atriplex species at Tucson, Arizona.
Direct Seeding
Laboratory seed germination of A. canescens, A. polycarpa
and A. lentiformis was 0%, 0 to 4% and 7 to 53% for the
1992 and 1993 trials, respectively.
Between the 1.5 to 10.5 m line-source distance, species
plant counts 23 or 24 days after seeding were generally less
than 1 plant per meter (Fig. 3). During the study period,
none of the direct-seeded accessions became established with
only natural precipitation. In general, seed germination and
emergence of plants were greater at the highest irrigation
level than under natural rainfall conditions. Direct-seeded
plants established in 1992 survived the mild wet winter
and persisted through the first year.
Results and Discussion
Climatic Data and Irrigation Amounts
In both summers, mean air temperatures during the first
month averaged 30 °C for the direct-seed planting and 29 °C
for the transplants (Fig. 1). In 1993, most of the precipitation occurred within 40 days after seeding, while in 1992
most of the precipitation fell within a 25 day period after
seeding. Total rainfall for the first 80 days after irrigation
during 1993 (76.9 mm) was slightly less than that of 1992
(85.1 mm). In both summers, rain fell within 1 day after
transplanting and was followed by a series of storms that
essentially kept the soil profile wet.
The quantity of irrigation water applied was generally
higher in 1992 than in 1993 (Fig. 2). During the 1992 and
1993 seasons, there were a total of 16 or 11 irrigation events,
respectively, during the first 32 days after direct seeding.
Transplants received two irrigations after planting in 1992
and no supplemental water in 1993.
Figure 2—Total irrigation water applied at different distances from a line-source sprinkler during
summer 1992 and 1993 revegetation trials of
Atriplex species at Tucson, Arizona.
121
Figure 4—Soil water tensions (1-3 cm depth) at
four distances from a line-source sprinkler after direct seeding Atriplex species during the summers
of 1992 and 1993 at Tucson, Arizona.
Figure 5—Soil water tensions (8-10 cm depth)
at four distances from a line-source sprinkler
after transplanting Atriplex species during the
summers of 1992 and 1993 at Tucson, Arizona.
Plant count (plants/linear meter)
Figure 3—Plant counts of three Atriplex species
at six distances from a line-source sprinkler 23
days after initial irrigation during the summers of
1992 and 24 days after initial irrigation during
1993 at Tucson, Arizona.
For the first 13 days (1993) and 21 days (1992) after seeding, soil moisture availability was high at all distances from
the line-source sprinkler except for the non-irrigated area
(Fig. 4). After the initial dry period, all positions had generally similar patterns of soil moisture availability as a result of continued storms. Between rainstorms, there were
brief drying-out periods resulting in relatively high (greater
than 0.3 MPa) soil water tensions, especially in 1993. After
the initial dry period, soil moisture tensions were less than
0.4 MPa for at least 16 days in the non-irrigated area, but
no germination occurred. Results of these studies indicate
that except for an initial dry period, soil moisture levels
were generally adequate for seed germination in the nonirrigated area. However, soil water tension at the depth of
seeds may have been greater than that at the sensor depth
of 1 to 3 cm as presented in Figure 4.
Until the rainy season began, daylight soil temperatures
were 5 to 15 °C lower at the highest irrigation level (1.5 m)
when compared to the non-irrigated area (Fig. 5). After a
series of rainstorms, differences in temperatures between
the two levels were not as extreme. Maximum germination
rates for A. canescens occurred between –0.2 to –0.8 MPa
122
(Briede and McKell, 1992) and between –0.1 to –0.8 MPa
osmotic potentials when temperatures were low (12-17 °C)
(Potter and others, 1986). Springfield (1966) reported that
limited water availability decreased and delayed germination of A. canescens, with an osmotic potential of –0.3 MPa
being the effective limit for germination at high temperatures. In these studies, the relatively low plant counts in
the irrigated areas and the absence of seedling establishment under natural rainfall conditions may have been
caused by the combination of high soil temperature and
low soil moisture availability.
Transplants
During 1992, irrigation applications after transplanting
did not have an effect on survival since planting was followed
by a series of rainstorms. Within 15 days after planting in
1992 and 1993, transplants had received 51 and 28 mm of
rainfall, respectively, resulting in soil water tensions below
0.3 MPa (Fig. 6).
Aldon (1972) found that survival of A. canescens transplants was at least 80% when soil moisture tension was
between 0.03 and 0.2 MPa. The recommended time for
transplanting was when the probability for sizable summer
thunderstorms exceeded 50%. Soil moisture conditions of
this study were comparable to those suggested by Aldon
(1972) for successful transplant survival. The occurrence
of continued storms after transplanting allowed soil moisture to be relatively high during the first 15 days of establishment. In this study, the soil profile was wet at the time
of transplanting. Transplant survival may have been much
lower if the soil profile had been initially dry.
During both years, transplants became established with
only natural rainfall (Table 2). Except for A. linearis, whose
survival was generally low both years, survival rates were
above 90%. During 1992, transplant survival was highest
in A. canescens cv. Santa Rita compared to A. linearis, and
by the next summer season, plant densities had not significantly declined. Most of the mortality in A. linearis accessions was due to rabbit predation, with the ecotype from
Mexico being the most highly preferred. Although not
Figure 6—Soil temperature at 1 to 3 cm depth
at 1.5 and 16.5 m from a line-source sprinkler
during the summers of 1992 and 1993 at
Tucson, Arizona.
monitored during 1992, it is likely that transplants of A.
linearis were also affected by rabbit predation. Variations
in the browsing preferences exhibited by rabbits to different collections of A. canescens have been reported (Nord
Table 2—Transplant survival of Atriplex accessions on a sandy loam soil during summer of 1992 and 1993 at Tucson, Arizona.
Species
Subspecies/cultivar
Source
Sept. 1992
Survival (percent)
June 1993
Sept. 1993
Rabbit predation
% of mortalities
1992
A. linearis
A. canescens
—
cv. Santa Rita
Mexico
Tucson Plant
Materials Center
74 a1
93 b
67 a
88 b
—
—
—
—
Tucson
Toltec
Mexico
—
—
—
—
—
—
83 a
77 a
76 a
25 abc
47 bc
87 d
Mexico
Willcox
Tucson
—
—
—
—
—
—
92 b
97 cd
99 d
20 abc
0 ab
17 abc
Tucson
Casa Grande
—
—
—
—
94 c
98 d
0 ab
17 abc
1993
A. linearis
A. linearis
A. linearis
A. canescens
A. canescens
A. canescens
A. polycarpa
A. polycarpa
1
—
—
—
grandidentatum
occidentalis
angustifolia
—
—
Means within a column followed by the same letter are not significantly different (P<0.05).
123
Table 3—Summary of cumulative rainfall, applied irrigation and total rainfall plus applied irrigation at different distances from a line-source
sprinkler for direct seeding and transplant revegetation trials with Atriplex species during the summer of 1992 and 1993 at Tucson,
Arizona.
Cumulative
rainfall
Cumulative
applied water
1.5 m
10.5 m
1.5 m
Total rainfall plus applied water
10.5 m
16.5 m
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - mm - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Direct seeding
1992
23 days after seeding
30 days after seeding
60 days after seeding
1993
24 days after seeding
60 days after planting
18
28
84
236
280
280
109
139
139
254
308
364
127
167
223
18
28
84
35
77
217
217
118
118
252
294
153
195
35
77
51
53
62
29
29
29
17
17
17
80
82
91
68
70
79
51
53
62
28
71
0
0
0
0
—
—
—
—
28
71
Transplant
1992
15 days after planting
30 days after planting
60 days after planting
1993
15 days after planting
60 days after planting
and Stallings, 1975; Young and others, 1981; Sanderson
and others, 1987). Springfield (1970) and Van Epps and
McKell (1980) indicated that many successful seedings of
A. canescens have been severely damaged or destroyed by
rabbit predation.
to fill the soil profile prior to transplanting and by adding
a minimal amount of supplemental irrigation water, even
in the absence of precipitation.
Acknowledgments
Conclusions
This paper is dedicated to the late A. K. Dobrenz, Department of Plant Science, University of Arizona, Tucson.
Applied irrigation and rainfall amounts totaling a range
of 223 to 364 mm for 1992 and 195 to 294 mm for 1993 resulted in at least some establishment of Atriplex seedlings
(Table 3). These studies indicate that for a summer planting, supplemental irrigation will increase the probability
of plant establishment after direct seeding. Results suggest that establishment of perennial Atriplex seedlings is
restricted to those conditions when the environmental criteria of soil moisture availability and soil temperatures are
met. Criteria for successful establishment of Atriplex from
direct seeding during the summer include long periods of
high soil moisture in combination with relatively low soil
temperatures favorable for germination.
In contrast, transplants required only natural rainfall
for establishment, with amounts ranging from 62 to 71 mm
(Tables 2, 3). With the exception of A. linearis, transplant
accessions which originated distant from the planting site
were equally adapted for establishment when compared
to the germplasm collected nearest to the site. Assuming
that over a three month period soil moisture remains relatively high from natural rainfall, or irrigation, transplants
may be a more efficient method of establishing plants than
using seed. Available moisture at lower depths in the soil
profile probably increased transplant establishment under
natural rainfall conditions but had less effect on directseeding establishment. This study suggest that Atriplex
transplants may be fairly easily established by irrigating
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