Project Title: Morphological and Physiological Response of Bermudagrass and Zoysiagrass to
Soil Moisture and Mowing Height
Principle Investigators: Gerald Henry, Ph.D. and Jared Hoyle, Ph.D. – University of Georgia
Justification:
Water conservation efforts have intensified in the Southeastern U.S. due to increases in
urbanization and local drought conditions which resulted in reduced amounts of water available
for irrigating turfgrass. Legislature concerning water use is often drafted and implemented with
little regard for short- or long-term effects on managed turfgrass environments. Reductions in
turfgrass quality and plant health in response to water restrictions not only affect the playability
of turf, but may significantly reduce golf course revenue. Investigation into methods for reducing
water consumption in turfgrass while maintaining quality may provide a partial solution to this
specific problem.
Bermudagrass (Cynodon spp.) and Zoysiagrass (Zoysia spp.) are two of the primary
warm-season turfgrass species utilized for home lawns, athletic fields, and golf courses in the
southern U.S. Previous research examining the response of bermudagrass and zoysiagrass to soil
moisture has predominantly focused on irrigation intervals or short-term drought conditions.
Mowing is the most basic cultural practice performed on turfgrass environments and can have a
major impact on water use efficiency. The periodic removal of a portion of shoot growth causes
a lot of stress on turfgrass plants. Mowing causes a temporary cessation of root growth, a
reduction in carbohydrate production and storage, a temporary increase in water loss from cut
leaf ends, and a reduction in water absorption by the root system. Minimal to no research has
examined the simultaneous effect of soil moisture and mowing height on bermudagrass and
zoysiagrass growth and turf quality.
Studies that investigate the response of plant species to soil moisture have been
conducted with a variety of experimental approaches, each of which has its limitations. Pot
studies based on frequency or volume of watering, or irrigation triggered by sensors (e.g.
gypsum blocks) have been employed for many years. However, pot studies have been criticized
for problems associated with rooting depth and volume, and unnatural soil moisture profile and
root distribution. A classic study that employed an approach that reduces these shortcomings was
conducted by Mueller-Dombois and Sims (1966). This approach utilizes water table depth
gradient tanks that allow for natural capillary action (soil water) as well as surface irrigation to
simulate rainfall. However, these tanks require a fairly large amount of greenhouse space, labor,
and materials to construct and house. Water table depth is regulated by a standpipe while
capillary rise keeps the low end of the tank near field capacity. Plants growing at higher
elevations are subjected to progressively lower soil moisture levels and greater depth to the water
table. This methodology allows investigators to measure reductions in turfgrass quality/growth
caused by irrigation restrictions and mowing height on native Georgia soil within a controlled
environment.
Experimental Design:
Four water table depth
gradient tanks were constructed at
the Crop and Soil Sciences
greenhouse complex at the
University of Georgia from March
through May of 2013. Each tank
(Fig. 1 and 2) was steeply sloped
and has a volume of nearly 33 ft3.
Tanks were oriented to the south
and measured 8 ft long, 4 ft wide,
and were 1 ft high at one end and 6
ft high at the other end. Tanks were
lined with a double layer of 3-mil
plastic and had a 4 inch base of pea
gravel to provide a uniform
substrate for water movement.
Tanks were filled with a 2:1 mixture Figure 1: Water table depth gradient tank construction.
of a Pacolet sandy clay loam (fine,
kaolinitic, thermic Typic
Kanhapludults) and course sand.
The pea gravel was covered with 1.5
inches of coarse sand to reduce soil
movement into the pea gravel.
Tanks were then filled with soil. A
valve at the high end of the tank
regulated water inflow, while a
standpipe at the low end of the tank
regulated the water table height.
Tank surfaces were divided into 9
levels ranging in depth to the water
table (DWT) of 10.6 inches (level 1)
to 59.4 inches (level 9). Soil
Figure 2: Pea gravel at the base of each tank is used to create the water
moisture measurements were taken table.
at time of final harvest by probing
the soil profile at each level and measuring percent volumetric water content (%VWC) with a
TH2O Theta Probe. Moisture measurements from each tank were combined and averaged to
determine the capillary fringe of the tanks.
One year old ‘Tifway 419’ hybrid bermudagrass and 'Zeon' zoysiagrass sod were
established on the soil surface of two tanks, respectively, on June of 2013 and allowed to grow-in
until September of 2013 (Fig. 3). A starter fertilizer (7 N-7 P2O5-7 K2O) was applied at sodding
and monthly thereafter at a rate of 1 lb N/1000 ft2. Surface irrigation was employed daily (0.2
inch/day) during sod establishment to give a greater opportunity for uniform recruitment and
occasionally thereafter to alleviate permanent wilting. Natural light was supplemented with
artificial light at 1840 W/ft2 photosynthetic photon flux in a 12-h day to approximate summer
light intensity and photoperiod. Greenhouse conditions were maintained at day/night
temperatures of 90/78 °F. Bermudagrass and
zoysiagrass were mowed using sheep shears once a
week during establishment to a height of 1 inch to
simulate conditions similar to a golf course rough.
Two weeks prior to moisture treatment initiation
each box was divided vertically in half. One side was
maintained at 1 inch and the other at 2 inches.
Turfgrass quality ratings were assessed every
two weeks using a 0 to 9 numerical scale, where 9 is
considered to be optimal turf quality and 6.5 the
minimum acceptable level. Plant stress was
determined every two weeks using a normalized
difference vegetation index (NDVI) meter. Turfgrass
canopy temperature was evaluated prior to each
mowing and at the termination of the study with an
infrared (IR) thermometer. Cores (4 inch in
Figure 3: Sodding ‘Tifway 419’ bermudagrass and
‘Zeon’ zoysiagrass during June of 2013.
diameter) (3 per level) were removed at
trial termination (90 days after initiation)
(Fig. 4). Cores were washed and root
tissue was separated for further analysis.
Total root biomass was determined via
Figure 4: Growing in sod over a 3 month period prior to trial
initiation.
loss of ignition testing. Roots were oven
dried at 221 °F for
4 d and weighed. Once dry, roots were
placed in a muffle furnace at 842°F for 4
h. The remaining ash was weighed and subtracted from the initial oven dry weight to determine
total root biomass (grams).
Results:
Turfgrass quality, turfgrass vigor/health (NDVI), root biomass, and canopy temperature
were recorded for both turfgrass species three months after soil moisture treatments were
initiated. These measurements were recorded for each mowing height and soil moisture level.
TH2O Theta Probe soil moisture measurements of the upper 6 inches of soil (Fig. 5) revealed
that the capillary rise of each gradient tank extended approximately 30 to 35 inches from the
water table (Fig. 6).
Zoysiagrass maintained turfgrass quality above acceptable levels (> 6.0) for levels 1
through 3 at the 2-inch mowing height and levels 1 and 2 for the 1-inch mowing height (Fig. 7).
Although turfgrass quality was significantly below acceptable levels when zoysiagrass was
subjected to drought (levels 7 through 9), increasing mowing height from 1 to 2 inches did have
a positive impact. A similar trend was observed with respect to NDVI (Fig. 8). Zoysiagrass root
biomass was similar for both mowing heights under sufficient soil moisture conditions, but more
root mass was observed in response to the 2-inch mowing height when zoysiagrass was subjected
to drought (levels 7 through 9) compared to the 1-inch mowing height (Fig. 9). Turfgrass canopy
temperature increased as soil moisture levels decreased (Fig. 10). However, mowing height had
no effect on canopy temperature. Canopy temperature of zoysiagrass was 72 to 75 °F for levels 1
and 2, 78 to 80 °F for levels 3 through 6, and 83 to 86 °F for levels 7 through 9.
Bermudagrass did not exhibit turfgrass quality above acceptable levels for any soil
moisture level, regardless of mowing height (Fig. 7). However, bermudagrass turfgrass quality
was less affected by drought (levels 7 through 9) than zoysiagrass, regardless of mowing height.
A similar trend was observed with respect to NDVI (Fig. 8). Bermudagrass root biomass was
greater when plants were mowed at 2 inches compared to 1 inch (Fig. 9). However, when
subjected to drought (levels 7 through 9), root biomass in response to both mowing heights was
similar. This trend was opposite of what was observed in gradient tanks containing zoysiagrass.
Bermudagrass was also able to maintain lower canopy temperatures (80 to 82 °F) than
zoysiagrass (83 to 86 °F) at low soil moisture (levels 7 through 9) (Fig. 10).
In our research ‘Tifway 419’ bermudagrass was more tolerant to low soil moisture and
acute drought than ‘Zeon’ zoysiagrass. However, raising the mowing height from 1 to 2 inches
did increase the tolerance of ‘Zeon’ zoysiagrass to low soil moisture. This may be due to
increases in root biomass when zoysiagrass was maintained at the higher height of cut. Mowing
height had less of an effect on ‘Tifway 419’ bermudagrass tolerance to low soil moisture, which
may be explained by similar rooting characteristics observed at both mowing heights. ‘Tifway
419’ bermudagrass was also able to maintain lower canopy temperatures than ‘Zeon’ zoysiagrass
when subjected to low soil moisture. However, canopy temperature did increase for both species
as soil moisture became more limiting. Therefore, sufficient irrigation/natural rainfall is pertinent
not only to maintain transpirational cooling, but to help mediate the surrounding temperatures.
This research is currently being replicated again in 2014.
Figure 5: Soil moisture (%VWC) recorded in the upper 6 inches of the soil profile 90 DAT.
64
9
8
52
7
Reference Levels
6
40
5
4
Capillary fringe
3
28
2
16
1
0
gravel
10.6
16.7
22.8
28.9
35
41.1
47.2
53.3
59.4
Depth to Water Table (inches)
Figure 6: Cross section of a gradient tank showing capillary rise from the water table.
Figure 7: ‘Tifway 419’ bermudagrass and ‘Zeon’ zoysiagrass turfgrass quality ratings 90 DAT
when mowed at 1 and 2 inches.
Figure 8: ‘Tifway 419’ bermudagrass and ‘Zeon’ zoysiagrass normalized difference vegetative
index (NDVI) ratings 90 DAT when mowed at 1 and 2 inches.
Figure 9: ‘Tifway 419’ bermudagrass and ‘Zeon’ zoysiagrass root biomass weights (g) 90 DAT
when mowed at 1 and 2 inches.
Figure 10: ‘Tifway 419’ bermudagrass and ‘Zeon’ zoysiagrass canopy temperatures (°F) 90
DAT when mowed at 1 and 2 inches.
Acknowledgements:
The authors wish to thank the Georgia Golf Course Superintendents Association and the
Georgia Golf Environmental Foundation for financial support of this research. We would also
like to extend appreciation to Chase Straw, Rebecca Grubbs, Kevin Tucker, Josh Andrews, Jeff
Clegg, and Kurk Lance for their technical support on this project. A special thanks to NG Turf
for providing the bermudagrass and zoysiagrass sod.