Malheur Experiment Station
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Information for Sustainable Agriculture
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MICRO-IRRIGATION ALTERNATIVES FOR HYBRID POPLAR PRODUCTION 2003 TRIAL
Clinton C. Shock, Erik B. G. Feibert, and Lamont D. Saunders
Malheur Experiment Station
Oregon State University
Ontario, OR, 2003
Summary
Hybrid poplar
(cultivar OP-367), planted for sawlog production in April 1997 at the
Malheur Experiment Station, received five irrigation treatments in
2000-2003. Irrigation treatments consisted of three water application
rates using microsprinklers and two water application rates using drip
tape. Irrigation scheduling was by soil water potential at 8-inch depth
with a threshold for initiating irrigations at -50 kPa in 2000-2002,
and at -25 kPa in 2003. Reducing the water application rate reduced the
annual growth in diameter at breast height (DBH) and stem volume for
the microsprinkler-irrigated treatments. There was no significant
difference between the microsprinkler-irrigated treatment irrigated at
the highest rate and the drip-irrigated treatments in terms of height,
DBH, or stem volume growth in 2000 and 2001. In 2002 and 2003, drip irrigation with two tapes per tree row resulted in higher tree growth than microsprinkler irrigation.
Introduction
With
timber supplies from Pacific Northwest public lands becoming less
available, sawmills and timber products companies are searching for
alternatives. Hybrid poplar wood has proven to have desirable
characteristics for many nonstructural timber products. Growers in
Malheur County have made experimental plantings of hybrid poplars for
saw logs and peeler logs. Clone trials in Malheur County have
demonstrated that the clone OP-367 (hybrid of Populus deltoides x P. nigra)
performs well on alkaline soils for at least 7 years. Other clones have
higher productivity on soils with nearly neutral pH.
Hybrid poplars are
known to have high growth rates (Larcher 1969) and transpiration rates
(Zelawski 1973), suggesting that irrigation management is a critical
cultural practice. Research at the Malheur Experiment Station during
1997-1999 determined optimum microsprinkler irrigation criteria and
water application rates for the first 3 years (Shock et al. 2002). The
results showed that tree growth was not reduced by scheduling
irrigations when the soil water potential reached -50 kPa. Irrigating
at -25 kPa necessitated 38 irrigations for 3-year-old trees, compared
to 26 irrigations when trees were irrigated at -50 kPa. Based on these
results it was decided to use an irrigation criterion of -50 kPa for
the wettest treatments starting in 1998. In 2000 we noticed that the
rate of increase in annual tree growth started to decline in the
wettest treatment. It was decided that one of the causes probably was
the use of an irrigation criterion of -50 kPa. Starting in 2003 the
irrigation criterion was changed to -25 kPa for the wettest treatment.
The objectives of this study were to evaluate poplar water requirements
in the seventh year and to compare microsprinkler irrigation to drip
irrigation.
Materials and Methods
Establishment
The
trial was conducted on a Nyssa-Malheur silt loam (bench soil) with 6
percent slope at the Malheur Experiment Station. The soil had a pH of
8.1 and 0.8 percent organic matter. The field had been planted to wheat
for the 2 years prior to 1997 and to alfalfa before 1995. The field was
marked using a tractor, and a solid-set sprinkler system was installed
prior to planting. Hybrid poplar sticks, cultivar OP-367, were planted
on April 25, 1997 on a 14-ft by 14-ft spacing. The sprinkler system
applied 1.4 inches on the first irrigation immediately after planting.
Thereafter the field was irrigated twice weekly at 0.6 inches per
irrigation until May 26. A total of 6.3 inches of water was applied in
nine irrigations from April 25 to May 26, 1997.
In late May, 1997, a
microsprinkler system (R-5, Nelson Irrigation, Walla Walla, WA) was
installed with the risers placed between trees along the tree row at
14-ft spacing. The sprinklers delivered water at the rate of 0.14
inches/hour at 25 psi and a radius of 14 ft. The poplar field was used
for irrigation management research (Shock et al. 2002) and groundcover
research (Feibert et al. 2000) from 1997 through 1999.
Procedures Common to all Treatments
In
March 2000 the field was divided into 20 plots, each of which was 6
tree rows wide and 7 trees long. The plots each were assigned one of
five treatments arranged in a randomized complete block design and
replicated four times (Table 1). The microsprinkler irrigation
treatments used the existing irrigation system. For the drip-irrigation
treatments, either one or two drip tapes (Nelson Pathfinder, Nelson
Irrigation Corp., Walla Walla, WA) were laid along the tree row in
early May 2000. The plots with two drip tapes per tree row had the drip
tapes spread 2 ft apart, centered on the tree row. The drip tape had
emitters spaced 12 inches apart and a flow rate of 0.22 gal/min/100 ft
at 8 psi. Each plot had a pressure regulator (set to 25 psi for the
microsprinkler plots and 8 psi for the drip plots) and ball valve
allowing independent irrigation. Water application amounts were
monitored daily by water meters in each plot.
Soil water potential (SWP)
was measured in each plot by six granular matrix sensors (GMS,
Watermark Soil Moisture Sensors model 200SS, Irrometer Co., Riverside,
CA); two at 8-inch depth, two at 20-inch depth, and two at 32-inch
depth. The GMS were installed along the middle row in each plot and
between the riser and the third tree. The GMS were previously
calibrated (Shock et al. 1998) and were read at 8:00 a.m. daily
starting on May 2 with a 30 KTCD-NL meter (Irrometer Co.). The daily
GMS readings were averaged separately at each depth within each plot
and over all plots in a treatment. Irrigation treatments were started
on May 2.
The five irrigation treatments consisted of three water
application rates for the microsprinkler-irrigated plots and two water
application rates for the drip-irrigated plots (Table 2). From 2000
through 2002, all plots in the three microsprinkler-irrigated
treatments were irrigated whenever the SWP at 8-inch depth for
treatment one reached -50 kPa. The plots in each drip-irrigated
treatment were irrigated whenever the SWP at 8-inch depth for the
respective treatment reached -50 kPa. Irrigation treatments were
terminated on September 30 each year.
Soil water content was measured
with a neutron probe. Two access tubes were installed in each plot
along the middle tree row on each side of the fourth tree between the
sprinklers and the tree. Soil water content readings were made twice
weekly at the same depths as the GMS. The neutron probe was calibrated
by taking soil samples and probe readings at 8-, 20-, and 32-inch depth
during installation of the access tubes. The soil water content was
determined gravimetrically from the soil samples and regressed against
the neutron probe readings, separately for each soil depth. The
regression equations were then used to transform the neutron probe
readings during the season into volumetric soil water content.
Coefficients of determination (r2) for the regression equations were 0.89, 0.88, and 0.81 at P = 0.001 for the 8-, 20-, and 32-inch depths, respectively.
2000
Procedures
The side branches on the bottom 6 ft of the tree trunk were
pruned from all trees in February, 1999. In March of 2000, another 3 ft
of trunk were pruned, resulting in 9 ft of pruned trunk. The pruned
branches were flailed on the ground and the ground between the tree
rows was lightly disked on April 12. On April 24, Prowl at 3.3 lb
ai/acre was broadcast for weed control. The microsprinkler-irrigated
plots received 0.7 inch of water to incorporate the Prowl. To control
the alfalfa and weeds remaining from the previous years' groundcover
trial in the top half of the field, Stinger at 0.19 lb ai/acre was
broadcast between the tree rows on May 19, and Poast at 0.23 lb ai/acre
was broadcast between the tree rows on June 1. On June 14, Stinger at
0.19 lb ai/acre and Roundup at 3 lb ai/acre were broadcast between the
tree rows on the whole field.
On May 19 the trees received 50 lb N/acre
as urea-ammonium nitrate solution injected through the microsprinkler
system. Due to deficient levels of leaf nutrients in early July, the
field had the following nutrients in pounds per acre injected in the
irrigation systems: 0.4 lb boron, 0.6 lb copper, 0.4 lb iron, 5 lb
magnesium, 0.25 lb zinc, and 3 lb phosphorus. The field was sprayed
aerially for leafhopper control with Diazinon AG500 at 1 lb ai/ac on
May 27 and with Warrior at 0.03 lb ai/acre on July 10.
2001 Procedures
In
March of 2001, another 3 ft of trunk were pruned, resulting in 12 ft of
pruned trunk. The pruned branches were flailed on the ground on April
2. On April 4, Roundup at 1 lb ai/acre was broadcast for weed control.
On April 10, 200 lb N/acre, 140 lb P/acre, 490 lb S/acre, and 14 lb
Zn/acre (urea, monoammonium phosphate, zinc sulfate and elemental
sulfur) were broadcast. The ground between the tree rows was lightly
disked on April 12. On April 13, Prowl at 3.3 lb ai/acre was broadcast
for weed control. The microsprinkler-irrigated plots received 0.8 inch
of water to incorporate the Prowl.
A leafhopper, willow sharpshooter (Graphocephala confluens,
Uhler), was monitored by three yellow sticky traps attached to the
lower trunk of selected trees. Traps were checked weekly. From
mid-April to early June only adults were observed in the traps. A
willow sharpshooter hatch was observed on June 6, as large numbers of
nymphs were noted in the traps and on the lower trunk sprouts. The
field was sprayed aerially with Warrior at 0.03 lb ai/acre on June 11
for leafhopper control.
2002 Procedures
In March of 2002,
another 3 ft of trunk were pruned, resulting in 15 ft of pruned trunk.
The pruned branches were flailed on the ground on April 12. On April
23, 80 lb N(urea)/acre, 40 lb K(potassium sulfate)/acre, 150 lb
S(elemental sulfur)/acre, 20 lb Mg(magnesium sulfate)/acre, 6 lb
Zn(zinc sulfate)/acre, 1 lb Cu(copper sulfate)/acre, and 1 lb B(boric
acid)/acre were broadcast and the field was disked. On April 24, Prowl
at 3.3 lb ai/acre was broadcast for weed control. The
microsprinkler-irrigated plots received 0.7 inch of water to
incorporate the Prowl.
The willow sharpshooter was monitored by three
yellow sticky traps attached to the lower trunk of selected trees.
Traps were checked weekly. The field was sprayed aerially with Warrior
at 0.03 lb ai/acre on June 10 for leafhopper control.
2003 Procedures
In
March of 2003, another 3 ft of trunk were pruned, resulting in 18 ft of
pruned trunk. The pruned branches were flailed on the ground on March
31. On April 23, 80 lb N/acre as urea and 167 lb S/acre as elemental
sulfur were broadcast and the field was disked. On April 16, Prowl at
3.3 lb ai/acre was broadcast for weed control. The
microsprinkler-irrigated plots received 0.4 inch of water to
incorporate the Prowl.
Starting in 2003 the irrigation criterion was
changed to -25 kPa and the water applied at each irrigation was reduced
accordingly (Table 2). All plots in the three microsprinkler-irrigated
treatments were irrigated whenever the SWP at 8-inch depth for
treatment one reached -25 kPa. The plots in each drip-irrigated
treatment were irrigated whenever the SWP at 8-inch depth for the
respective treatment reached -25 kPa. Irrigation treatments were
terminated on September 30.
The drip tape needed to be replaced because
iron sulfide plugged the emitters. The drip tape was replaced with
another brand (T-tape, T-systems International, San Diego, CA)
in mid-April because Nelson Irrigation discontinued production of drip
tape. The drip tape specifications were the same.
The willow
sharpshooter was monitored by three yellow sticky traps attached to the
lower trunk of selected trees. Traps were checked weekly. The field was
sprayed aerially with Warrior at 0.03 lb ai/acre on June 5 for
leafhopper control.
The heights and diameter at breast height (DBH, 4.5
ft from ground) of the central three trees in the two middle rows in
each plot were measured monthly from May through September. Tree
heights were measured with a clinometer (model PM-5, Suunto, Espoo,
Finland) and DBH was measured with a diameter tape. Stem volumes
(excluding bark and including stump and top) were calculated for each
of the central six trees in each plot using an equation developed for
poplars that uses tree height and DBH (Browne 1962). Growth increments
for height, DBH, and stem volume for 2003 were calculated as the
difference in the respective parameter between October 2003 and October
2002.
Results and Discussion
The microsprinkler-irrigated
treatment with 1 inch of water applied at each irrigation consumed 47
acre-inch/acre of water in 47 irrigations (Table 1). The drip treatment
with 1 inch of water applied with 2 tapes consumed 52 acre-inch/acre
applied in 35 irrigations. The drip treatment with 0.5 inch of water
applied with 1 tape consumed 29 acre-inch/acre in 35 irrigations.
In
November 2003 (seventh year), trees in the wettest sprinkler-irrigated
treatment averaged 57 ft in height, 8.3-inch DBH, and 1,697 ft3/acre
of stem volume (Table 2).In November 2003, trees in the treatment
drip-irrigated with 2 drip tapes per tree row averaged 64 ft in height,
8.5-inch DBH, and 2,090 ft3/acre of stem volume.
Comparing
all treatments, drip irrigation with two tapes per tree row (water
application rate of 1 inch) resulted in the highest DBH growth, height
growth, and stem volume growth in 2003 (Table 2). Using one drip tape
instead of two per tree row resulted in a reduction in DBH growth,
height growth, and stem volume growth. For the microsprinkler-irrigated
treatments, the highest growth in DBH and stem volume was achieved with
a water application rate of 1 inch.
There were positive linear
relationships, with similar slopes, between total water applied and
stem volume growth for both the drip and microsprinkler systems (Fig.
1). However, the line for the drip system was above the line for the
microsprinkler system, reflecting the higher water use efficiency of
the drip system (Table 1).
The SWP at 8-inch depth was reduced, as
expected, with the reductions in water application rate in the
sprinkler treatments (Fig. 2, Table 3). There was no significant
difference in 8-inch average SWP among the two drip treatments and the
sprinkler treatment with 1 inch of water application rate. The SWP at
8-inch depth in the drip treatments oscillated with a higher amplitude
(became wetter) than in the sprinkler plots, as expected, since the
wetted area was smaller with drip irrigation. The SWP at 32-inch depth
in the wettest sprinkler treatment remained drier than in the first
foot during the season, suggesting that applied irrigation water was
not lost to deep percolation.
The rate of increase in annual stem volume growth increased (growth approximately doubled every year) up to 2000, when the stem volume growth for the microsprinkler irrigated trees started to decline (Table 4). In 2002 the stem volume growth
for the drip-irrigated trees started to decline. The decline in annual
growth would not be expected until later when the trees are approaching
harvest size. The reduction of the SWP for irrigation scheduling from
-25 to -50 kPa in 2000 might be associated with the decline in annual
stem volume growth. Tree growth was
substantially higher in 2003 and was approximately double the growth in
2002. The higher tree growth in 2003 could have been due to the change
to a wetter irrigation threshold from -50 to -25 kPa. Season-long
average soil water potential at 8-inch depth for the wettest
microsprinkler treatment and for the treatment drip irrigated with two
drip tapes was substantially higher (wetter) in 2003 than in the last 3
years (Table 4).
References
Browne, J.E. 1962. Standard
cubic-foot volume tables for the commercial tree species of British
Columbia. British Columbia Forest Service, Forest Surveys and Inventory
Division, Victoria, B.C.
Feibert, E.B.G., C.C. Shock, and L.D.
Saunders. 2000. Groundcovers for hybrid poplar establishment,
1997-1999. Oregon State University Agricultural Experiment Station
Special Report 1015:94-103.
Larcher, W. 1969. The effect of
environmental and physiological variables on the carbon dioxide
exchange of trees. Photosynthetica 3:167-198.
Shock, C.C., J.M. Barnum,
and M. Seddigh. 1998. Calibration of Watermark Soil Moisture Sensors
for irrigation management. Pages 139-146 in Proceedings of the
International Irrigation Show, Irrigation Association, San Diego,
CA.
Shock, C.C., E.B.G. Feibert, M. Seddigh, and L.D. Saunders. 2002.
Water requirements and growth of irrigated hybrid poplar in a semi-arid
environment in eastern Oregon. Western J. of Applied Forestry
17:46-53.
Zelawski, W. 1973. Gas exchange and water relations. Pages
149-165 in S. Bialobok (ed.). The poplars-Populus L. Vol. 12. U.S. Dept. of Comm., Nat. Techn. Info. Serv., Springfield, VA.
Table 1. Irrigation rates, amounts, and water use efficiency for
hybrid poplar submitted to five irrigation regimes, Malheur Experiment
Station, Oregon State University, Ontario, OR, 2003.
| Treatment |
Irrigation threshold |
Water application |
Irrigation system |
Total number of irrigations |
Total water applied† |
Water use efficiency |
|
kPa* |
inch |
|
|
acre-inch/acre |
ft3 of wood/acre-inch of water |
| 1 |
-25 |
1 |
Microsprinkler |
47 |
47.1 |
12.9 |
| 2 |
coincide with trt #1 |
0.77 |
Microsprinkler |
47 |
35.8 |
8.2 |
| 3 |
coincide with trt #1 |
0.39 |
Microsprinkler |
47 |
21.6 |
4.3 |
| 4 |
-25 |
1 |
Drip, 2 tubes |
35 |
54.8 |
17.1 |
| 5 |
-25 |
0.5 |
Drip, 1 tube |
35 |
29.8 |
14.8 |
LSD (0.05) |
|
|
1 |
0.8 |
6.4 |
*Soil water potential at eight-inch depth.
†Includes 2.39 inches of precipitation from May through September.
Table
2. Height, diameter at breast height (DBH), and stem volume in early
November 2003 and 2003 growth for hybrid poplar submitted to five
irrigation treatments, Malheur Experiment Station, Oregon State
University, Ontario, OR.
Treatment |
November 2003 measurements |
|
2003 growth increment |
Height |
DBH |
Stem volume |
|
Height |
DBH |
Stem volume |
|
ft |
inch |
ft3/acre |
|
ft |
inch |
ft3/acre |
| 1 |
56.5 |
8.27 |
1,697.0 |
|
7.7 |
1.50 |
605.9 |
| 2 |
47.0 |
6.96 |
1,020.0 |
|
5.6 |
0.98 |
293.7 |
| 3 |
32.5 |
5.00 |
351.0 |
|
2.5 |
0.71 |
91.4 |
| 4 |
63.6 |
8.45 |
2,090.0 |
|
14.0 |
1.89 |
937.9 |
| 5 |
51.7 |
7.73 |
1,370.0 |
|
7.1 |
1.27 |
438.2 |
| LSD (0.05) |
16.7 |
0.76 |
507.2 |
|
5.7 |
0.26 |
221 |
Table 3. Average soil water potential and volumetric soil water
content for hybrid poplar submitted to five irrigation treatments,
Malheur Experiment Station, Oregon State University, Ontario, OR, 2003.
Treatment |
Average soil water potential |
| 1st ft |
2nd ft |
3rd ft |
|
------------------- kPa -------------------- |
| 1 |
26.9 |
36.9 |
36.1 |
| 2 |
65.3 |
83.2 |
62.9 |
| 3 |
92.8 |
84.9 |
90.8 |
| 4 |
21.8 |
25.5 |
27.4 |
| 5 |
28.3 |
25.2 |
35.7 |
| LSD (0.05) |
20.8 |
25.8 |
26.0 |
Table 4. Annual stem volume growth and seasonal average soil water
potential at 8-inch depth for hybrid poplar under drip and
microsprinkler irrigation at highest irrigation intensities, Malheur
Experiment Station, Oregon State University, Ontario, OR.
|
Stem volume growth |
|
Seasonal average soil water potential at 8-inch depth |
| Year |
Drip |
Microsprinkler |
|
Drip |
Microsprinkler |
|
---- ft3/acre ---- |
|
---- kPa ---- |
| 1997 |
|
1.3 |
|
|
-21.4 |
| 1998 |
|
78.5 |
|
|
-20.0 |
| 1999 |
|
177.7 |
|
|
-22.2 |
| 2000 |
361.9 |
401.5 |
|
-24.2 |
-37.9 |
| 2001 |
448.7 |
354.7 |
|
-26.4 |
-33.9 |
| 2002 |
413.1 |
256.8 |
|
-31.3 |
-35.8 |
| 2003 |
937.9 |
605.9 |
|
-21.8 |
-26.9 |
Figure
1. Response of stem volume growth to water applied in 2003 for hybrid
poplar using microsprinkler and drip irrigation, Malheur Experiment
Station, Oregon State University, Ontario, OR.
Figure
2. Soil water potential at three depths using granular matrix sensors
in a poplar stand submitted to five irrigation regimes, Malheur
Experiment Station, Oregon State University, Ontario, OR, 2003.
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For
additional information about the Malheur Agricultural Experiment
Station, please send an e-mail request to:
Dr. Clinton C. Shock
Clinton.Shock@oregonstate.edu
Malheur Agricultural Experiment
Station
595 Onion Avenue
Ontario, OR 97914
(541) 889-2174
FAX (541) 889-7831
Last updated
Friday July 30, 2004 .
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