1. Overcoming the Limiting Factors Impairing Seeding Success of Cheatgrass-Invaded
Semi-Arid Rangelands: Supplemental Soil Testing on the North Rim Ranches
December 11th 2015
Sandra M. Dewitz
Aleydis Estrada
Tyler B. Franzen
Kelsey J. Jindra
Dawnylle M. Smith
Northern Arizona University
South San Francisco Street
Flagstaff, Arizona 86001

2. 1
Abstract
In a United States Department of Agriculture (USDA) – Agricultural Research Service study
entitled “Overcoming the Limiting Factors Impairing Seeding Success on Cheatgrass-
Invaded Semi-Arid Rangelands,” seed coating techniques were used on native grass seed
with the intention of increasing the germination success. This technique, in turn, may help
to combat the spread of the highly invasive Bromus tectorum, more commonly known as
cheatgrass. To supplement the Madsen et al.study, this study entailed a collection of soil
samples from 9 sites, each with an enclosure and exclosure plot. These sites are located
within the North Rim Ranches on the western side of the Kaibab-Plateau. The sites showed
a variety of landscapes with both high and low densities of biomass as well as differences in
plant height and vegetation diversity. The samples were used in conducting soil analyses to
identify soil color and to measure nitrate, phosphorus, potassium and pH levels. Results do
not indicate a significant difference between enclosure and exclosure soil tests. With the
aid of this study and continued research, better management techniques may be developed
to counter an incredibly time consuming and costly endeavor.

3. 2
Introduction
Southwestern grasslands are currently inundated by the exotic annual grass Bromus
tectorum, commonly known as cheatgrass, leading to the declining prevalence of native
perennial plant communities. Cheatgrass is native to Europe, southwestern Asia, and
northern Africa, but is invasive in a large portion of North America (Zouhar, 2003).
Cheatgrass’ wide spread success can be attributed to a variety of factors including seed
dispersal, decreased grazing, and a deep seedbed. Cheatgrass seed dispersal is facilitated by
accidental transport from human-induced processes such as grazing, transportation of
goods, and outdoor recreation. Additionally, these grasses have low forage quality and
palatability for livestock and other local granivores, resulting in decreased consumption.
Ungulates prefer to eat native grasses, leaving a higher abundance of cheatgrass compared
to native vegetation. (Pyke and Novak, 1994). Apart from these factors, cheatgrass is a
quick-burning fuel that can amplify the spread of fire and increase an area’s susceptibility
to environmental damage and native species loss (Pellant, 1994). Easily ignited, cheatgrass
produces a high-intensity, short-lived fire that damages native seedbeds without scorching
cheatgrass seeds. Consequently, cheatgrass has a competitive advantage over native plants.
Increases in the frequency of drought and wildfire events may result in shifted fire regimes.
Altered fire regimes, increased cheatgrass dispersal, easily ignitable foliage, and an
outlasting seedbed all contribute to the development of an adversely altered ecosystem
(Schwinning, 2008).
To potentially mitigate the predicted negative effects of cheatgrass, the Grand Canyon Trust
sponsored the USDA - Agricultural Research Service Madsen et al. study, “Overcoming the

4. 3
Limiting Factors Impairing Seeding Success on Cheatgrass-Invaded Semi-Arid Rangelands,”
a project consisting of planting fire-resistant native vegetation to create fire fuel breaks.
The objective of the Madsen et al. research is to find effective methods to potentially
restore native plant populations, reduce wildfire occurrence, and to find more cost-
effective methods to combat the spread of cheatgrass. The current cost of the rehabilitation
of cheatgrass-dominated land is approximately $250 per hectare with a 5% probability of
success. When factoring in the low 5% success rate, the total anticipated cost to rehabilitate
one hectare would be approximately $5,000. Seed technology developments may improve
the success of seed germination for native vegetation despite cheatgrass presence. Ideally,
the land rehabilitation success rate will increase to 50% with the use of seed enhancement
technologies (SET). It has been calculated that the cost per successful hectare could
decrease to $500 per hectare, a potential savings of $4,500 per hectare (Madsen et al.,
2013).
This supplemental study provides additional soil analysis to reduce variability in the
Madsen et al. study. Soil samples were collected from the semi-arid Kaibab-Plateau, and
these subsequent soil and statistical analyses may help to identify soil fertility limitations
of the seed enhancement technologies. Analyses include identification of soil color as well
as measurements of nutrient availability and pH level of 18 test plots. Soil nutrient tests
determine concentrations of phosphorus, nitrogen-nitrate, and potassium. The soil test
findings and effects of native plant seed augmentation can serve as a catalyst for continued
research into improved management practices of cheatgrass-invaded grazing lands to help
improve the conditions of native plant populations.

5. 4
Materials and Methods
On the west side of the North Rim Ranches, soil cores were collected from 9 sites, each
containing an enclosure and an exclosure (see Appendix C). The samples were extracted
from October 23 - 25th, 2015 and analyzed from November 3rd to November 24th. Utilizing
augers, soil cores of 10 cm in length were obtained. The 10 cm soil profiles were assumed
to lack the “O” horizon due to the nature of the land from previous observation. In general,
the majority of the semi-arid grass and shrub land “A” horizon soil profile contained
minerals and small amounts of organic matter. On each plot, the most central Control
Transect South (CTS) point out of four CTS points was selected and located via GPS
navigation. A point 5 meters south of the central CTS point was selected as the start point;
soil samples were then collected from 2 meters north, south, east, and west of the start
point. The soil from each of the four cardinal directions were combined into a single sterile
sample bag which was later dehydrated in the Northern Arizona University soil lab for 24
hours to prepare the samples for soil chemistry tests. Samples were then tested for soil
color, nitrogen-nitrate via the cadmium reduction method, potassium exchangeable in soil
via the turbidimetric tetraphenylborate method, phosphorous via the PhosVer3 (ascorbic
acid) method and pH level obtained via the electrode method. For the potassium soil
analysis, three dipstick measurements were taken and averaged for each soil sample.
Derived from the Hach SIW-1 soil and irrigation water manual conversion chart, the fitted
equation, ŷ =18779x-1.043 with an R2 value of 0.9986 converted the dipstick measurements
from mm to units of Kg/Ha.

6. 5
Results
Final measurements for soil color, pH, nitrogen-nitrate, phosphorus and potassium content
in enclosure (EN) and exclosure (EX) plots of all sites are recorded in Appendix B. To
compare the findings of the enclosure plots to those of the exclosure plots, the mean values
of the tests are graphed using standard deviation for error bars. A two-tailed test statistic,
assuming constant variability, and the corresponding p-value (Table 2), were calculated to
evaluate if there is a significant difference between the mean values of the enclosure and
exclosure plots for each assessment performed.
Three soil color hue categories were identified across the samples; 10 YR, 7.5 YR and 5 YR.
See appendix B for further soil color classification results.
Mean pH values for enclosure and exclosure plots are 7.64 and 7.69, respectively. The
standard deviation for the enclosure plots is 0.49, while exclosure plots have a standard
deviation of 0.43 (Figure 1). The test statistic comparing the enclosure group to the
exclosure group is 0.84 (p-value=0.42).
The enclosure plots have an average nitrogen availability of 4.30 ppm with a standard
deviation of 0.85 ppm. Exclosure plots have an average nitrogen-nitrate value of 3.67 ppm
and a standard deviation of 1.37 ppm (Figure 2). A t-test was performed to yield a test
statistic of 0.40 (p-value=0.69).

7. 6
The mean phosphorus content of enclosure plots is 7.64 mg/L; the exclosure plot values
averaged to 7.69 mg/L. The standard deviation value for the enclosure group is 34.79 mg/L
and 23.04 mg/L for the exclosure (Figure 3). The t-test statistic is 0.16 (p-value=0.88).
The mean potassium availability of the plots is 258.75 kg/Ha and 256.72 kg/Ha for the
enclosures and exclosures respectively. Standard deviation values are 49.50 kg/Ha for the
grouped enclosures and 88.54 kg/Ha for the exclosure group (Figure 4). A t-test produced a
0.95 test statistic (p-value= 0.37).
Discussion
Nitrogen-nitrate, phosphorus, potassium, and pH analyses incorporated t-tests to calculate
if there are significant differences between the enclosure and exclosure measurements. The
p-values for each t-test (Table 2) concluded that there is not sufficient evidence to indicate
a significant difference between soil results of the enclosure plots and those found in the
exclosure plots. Plot 6 EX had a value of 0 ppm for nitrogen-nitrate content and was
excluded from the graph due to an error when conducting the test. We can ascribe errors to
the following reasons: multiple people conducting soil tests at different times, systematic
errors in reading measurements from soil test apparatuses, and contamination of soil
samples in the field.
Exotic grasses have spread throughout vast areas of North America, degrading
approximately 60 million acres of land. Previous attempts to reestablish native vegetation
have fallen short despite the funding of millions of dollars to implement restoration
projects, which have had success rates of less than 5% (Madsen et al., 2013). To counter the

8. 7
arid growth conditions, cheatgrass competition, and herbicide treated soil, SET’s have been
implemented in experimental plots across the North Rim Ranch rangelands. SET plots will
be evaluated to improve seedling germination with a goal of producing a more cost-
effective approach for restoring lands degraded by cheatgrass (Madsen et al., 2013).
Our soil analyses of samples collected from the SET plots will help to identify soil fertility
limitations on the seed enhancement technologies. Additional research on the ideal soil
conditions for native species and cheatgrass could be utilized to inform future results of the
Madsen et al. (2013) study. Future investigations should also incorporate t-tests to
measure possible differences in soil nutrient content between enclosure and exclosure
sites. It is likely that the additional soil analyses will supplement this innovative approach
to manage the devastating effects of cheatgrass and ultimately influence policy and land
management practices.
Acknowledgements
We would like to thank Cerissa Hoglander and Ed Grumbine from the Grand Canyon Trust
as well as Kaitlyn Elkind from Northern Arizona University for being our invaluable
mentors throughout the time spent collecting and testing soil samples. We would also like
to extend our gratitude toward the Grand Canyon Trust as well as the Mangum & North
Rim Ranches for hosting us during our research. Additional thanks to Professor Robert
Sanford Jr. for his guidance and support throughout the entirety of the research project. We
would also like to thank the School of Earth Sciences and Environmental Sustainability at
Northern Arizona University for the opportunity and funding for us to work on this study.
Lastly, a very special thank you goes to Matthew Madsen and Lauren Porensky from the

9. 8
USDA - Agricultural Research Service as well as Elizabeth Leger from the University of
Nevada and Matt Williamson from the Grand Canyon Trust for their previous time spent
creating and heading the “Overcoming the Limiting Factors Impairing Seeding Success on
Cheatgrass-Invaded Semi-Arid Rangelands” research study.

10. 9
Literature Cited
Madsen, M., L. Porensky, E. Leger, M. Williamson. 2013. Overcoming the limiting factors
impairing seeding success on cheatgrass-invaded semi-arid rangelands. A proposal
to the Kane and Two Mile Research and Stewardship Partnership.
Pellant, M. 1994. History and applications of the Intermountain greenstripping program.
General Technical Report INT-GTR-313. USDA Forest Service, Intermountain
Research Station, Ogden, UT.
Pyke, D. A., and S.J. Novak. 1994. Cheatgrass demography-establishment attributes,
recruitment, ecotypes, and genetic variability. General Technical Report INT-GTR-
313. USDA Forest Service, Intermountain Research Station, Ogden, UT.
Schwinning, S., J. Belnap, D. R. Bowling, and J. R. Ehleringer. 2008. Sensitivity of the
Colorado Plateau to change: climate, ecosystems, and society. Ecology and Society
13(2): 28
Zouhar, Kris. 2003. Bromus tectorum. U.S. Department of Agriculture, Forest Service, Rocky
Mountain Research Station. Available from
http://www.fs.fed.us/database/feis/plants/graminoid/brotec/all.html (accessed
December 2015)

11. 10
Appendix A
Figure 1: A comparison of average pH levels between the enclosure and exclosure plots
with a line indicating standard deviation.

12. 11
Appendix A
Figure 2: A comparison of average Nitrogen-Nitrate concentrations between the enclosure
and exclosure plots measured in parts per million, with a line indicating standard
deviation.

13. 12
Appendix A
Figure 3: A comparison of average Phosphorus concentrations between the enclosure and
exclosure plots measured in milligrams per liter, with a line indicating standard deviation.

14. 13
Appendix A
Figure 4: A comparison of average Potassium concentrations between the enclosure and
exclosure plots measured in kilograms per hectare, with a line indicating standard
deviation.

15. 14
Appendix B
Table 1: Soil Chemistry Results
Site Soil Color pH
Nitrate
(ppm)
Phosphorus
(mg/L)
Potassium
(Kg/Ha)
6 EN 10 YR 2/2 8.0 5.34 66.00 262.87
6 EX 7.5 YR 2.5/2 7.8 -- 46.20 166.47
7 EN 7.5 YR 2.5/2 8.3 4.00 48.40 279.02
7 EX 5 YR 8/3 8.0 4.00 26.40 341.61
8 EN 10 YR 2/2 7.8 5.32 132.00 341.69
8 EX 10 YR 2/2 8.3 4.00 103.29 369.38
9 EN 7.5 YR 4/3 6.8 4.00 46.20 218.46
9 EX 10 YR 3/6 7.3 2.72 48.38 186.66
11 EN 7.5 YR 3/3 7.5 4.00 105.60 248.49
11 EX 5 YR 3/4 7.9 5.33 50.59 354.84
13 EN 10 YR 4/3 8.2 4.00 127.54 162.82
13 EX 7.5 YR 2.5/2 8.0 4.00 74.79 203.59
15 EN 10 YR 3/6 7.7 2.67 41.79 279.02
15 EX 10 YR 3/4 7.0 5.33 77.00 175.66
16 EN 7.5 YR 2.5/2 7.2 5.33 96.80 248.49
16 EX 7.5 YR 2.5/2 7.7 2.67 75.90 329.39
23 EN 5 YR 3/4 7.3 4.00 74.79 287.85
23 EX 5 YR 3/4 7.2 1.33 50.59 182.84

16. 15
Appendix B
Table 2: Soil Chemistry Results Statistics
pH N (ppm) P (mg/L) K (Kg/Ha)
EN Average 7.64 4.30 82.12 258.75
EN St. Dev. 0.49 0.85 34.79 49.50
EX Average 7.69 3.67 61.46 256.72
EX St. Dev. 0.43 1.37 23.04 88.54
t-test 0.84 0.40 0.16 0.95
p - value 0.42 0.70 0.88 0.37

17. 16
Appendix C
Figure 5: Map of sample site locations from each enclosure (EN) and exclosure (EX) at nine
study sites from the Kaibab Plateau West Side.