Tillage Handbook Series
Chapter 3 - Residue Management Considerations, No. 20, May 1998
Thistle Skeletons Provide Residue
Wheat-Fallow Cropping Systems
William Schillinger is a dryland research agronomist, Department of Crop
and Soil Sciences, Washington State University, P.O. Box B, Lind, WA 99341,
email: (firstname.lastname@example.org); Robert.
Papendick is a soil scientist (retired), USDA-ARS, Pullman, WA; Roger
Veseth is an extension conservation tillage specialist, Washington State
University and University of Idaho, Moscow, ID; Frank Young is a research
agronomist, USDA-ARS, Pullman, WA. Harry Schafer is a WSU agricultural
research technician, Ritzville, WA; Bruce Sauer is farm manager of the
WSU Dryland Research Station, Lind, WA. Funding for this study was partially
provided by the Solutions to Economic and Environmental Problems (STEEP
II) Program and the Columbia Plateau Wind Erosion/Air Quality Project.
residue to prevent wind and water erosion is often difficult in low-precipitation
(less than 12 inch annual) winter wheat (Triticum aestivum L.)-fallow
regions of the Pacific Northwest. This is especially true for spring-sown
wheat, and for winter wheat in low-moisture conditions. In these situations,
Russian thistle (Salsola iberica) can be a major weed and often
produces more biomass than the crop it infests. In a 4-year study, we
measured the effect of three tillage management treatments: i)
traditional (tillage only); ii) minimum (herbicides and tillage),
and iii); delayed minimum (herbicides and delayed tillage), on
retention of above-ground wheat residue and dead Russian thistle plants
or "skeletons" during the fallow cycle. Russian thistle infestation
occurred two of the four years when winter wheat failed and was replaced
by spring wheat. Traditional post-harvest tillage caused most Russian
thistle skeletons to be wind blown from plots by late fall, but plants
remained anchored in the soil when herbicides were used for post-harvest
thistle control. Traditional primary spring tillage with a field cultivator
or tandem disc further reduced surface cover compared to minimum tillage
treatments. During two fallow cycles where Russian thistle infested the
previous spring wheat crop, thistle skeletons on the soil surface averaged
280 and 40 vs. 1220 and 240 lb/acre in late fall and end of fallow in
traditional tillage compared to minimum tillage treatments, respectively.
Traditional tillage also reduced surface wheat residue compared to minimum
tillage plots on all sampling dates. Russian thistle skeletons can be
retained in place using conservation tillage during fallow, where they
become an important source of surface cover to combat erosion in years
when crop residues are extremely low.
Growers in low-precipitation
dryland areas of the inland Pacific Northwest practice a wheat - fallow
rotation where only one crop is grown every two years. Maintaining adequate
surface residue for erosion control is often difficult. In low crop production
years, Russian thistle is a major weed which can produce more dry matter
by grain harvest than the wheat crop it infests. In a 4-year tillage management
study, we consistently retained the most residue during fallow using minimum
tillage practices compared to traditional tillage. In addition to wheat
residue, we retained dead Russian thistle plants as an important source
of surface cover using minimum tillage, whereas thistles were wind-blown
from the field or buried with traditional tillage. Results show the value
of conserving Russian thistle skeletons for erosion control in low crop
residue situations when thistles are likely to be present in large amounts.
Wind and water erosion
are major agronomic and environmental concerns in the low-precipitation
(less than 12 inch annual) dryland wheat production region in eastern
Washington and north-central Oregon. A biennial wheat-summer fallow rotation
has been practiced in this 3.5 million acre region since native bunch
grass and sagebrush was plowed in the 1880's. In drought years, or when
winter wheat is replaced by a spring crop, residue production is low,
and growers frequently have difficulty conserving sufficient surface cover
to retard erosion during the subsequent fallow cycle. The most effective
management practice for protecting soil from erosion during fallow is
to maintain adequate surface residue (Horning and Oveson, 1962). Detailed
descriptions of the relationship between soil cover and wind erosion loss
have been reported by Bilbro and Fryrear (1994). Maximum levels of surface
residue during the fall and winter reduces water runoff during the winter
and increases over-winter soil water storage which benefits subsequent
grain yield (Lindstrom, 1974; Ramig and Ekin, 1991; Wilkins et al., 1988).
Tillage channels or slots are effective for increasing water infiltration
when rain or snow melt occur on frozen soils (Zuzel and Pikul, 1987).
Russian thistle is
a summer-annual weed, first reported in the United States in South Dakota
in 1877 (Dewey, 1893). By the 1890's, the weed had spread to the Pacific
Northwest (Young, 1991) where it quickly became the dominant broadleaf
weed in low-precipitation dryland wheat areas.
Russian thistle grows
during both the crop and fallow cycles. A uniform and well-established
stand of winter wheat will suppress Russian thistle. On the other hand,
spring wheat or drought stressed winter wheat are much less competitive
and more subject to thistle infestation. Growers plant spring wheat to
replace winter wheat because of: i) inadequate fall stand establishment;
ii) winter kill, and; iii) the need to control winter-annual
grassy weeds (Cook and Veseth, 1991). Russian thistle infestation is frequently
acute in spring wheat due to less early growth and less canopy closure
compared to winter wheat (Young, 1986). Spring wheat yield depression
due to Russian thistle is most severe during drought years (Young, 1988).
Russian thistle has an efficient C4 photosynthetic pathway
with high water use efficiency (Fowler and Hageman, 1978).
Russian thistle rapidly
produces dry matter and sets seed after wheat harvest (Young et al., 1995),
by extracting soil moisture below the available limit for wheat. The optimum
time for post-harvest control of Russian thistle is 10-to 14-days after
harvest. Growers generally either till the soil with V-shaped sweeps or
use herbicides after grain harvest to control Russian thistle. After primary
tillage in the spring, rodweeders are used as secondary tillage to control
thistles and other weeds. Rodweeders operated at depths greater than 3
inches retain surface residue and roughness more effectively for erosion
control compared to shallow depths (Schillinger and Papendick, 1997).
thistle often has negative agronomic effects, it has some beneficial attributes.
During the dust bowl years in the 1930's, Russian thistle was used as
emergency forage for cattle (Cave et al., 1936). Protein in Russian thistle
hay can be as high as 23% (Boerboom, 1993), and the plant has potential
as an energy source as processed pellets and compressed fireplace logs
(Foster et al., 1980).
Because Russian thistle
often produces substantial dry matter both before and after wheat harvest,
it is possible that the weed could be an important source of surface cover
for erosion control during the fallow cycle. No previous research has
been reported on possible benefits of Russian thistle in conservation
systems. The objective of this study was to: (i) document the
extent of Russian thistle infestation in marginal wheat production years
and; (ii) determine if dead thistles can be conserved during
fallow as a significant source of surface cover in low crop residue situations.
A 4-year tillage
management study was conducted between August 1993 and September 1997
at the Washington State University Dryland Research Station at Lind, WA.
Long-term (82-year) average annual precipitation at the station is 9.5
inches. The soil is Shano silt loam with less than 1% organic matter in
the surface 4 inches. Soil depth is greater than 6 feet. Wind tunnel tests
have shown that this soil, when left unprotected (i.e., bare, tilled,
dry, non-crusted), is one of the most susceptible to wind erosion and
suspended dust emissions within the Columbia Plateau of eastern Washington
(Saxton et al., 1996).
design was a randomized complete block of three tillage management treatments
replicated four times. Each plot was 150 by 60 feet, which allowed use
of commercial-size farm equipment. Paired adjacent parcels of land were
used so that data could be collected from both crop and fallow phases
of the study each year.
The three tillage
management systems compared in this study were: (i) Traditional
tillage - conventional frequency and timing of tillage operations
using implements commonly used by growers; ii) Minimum tillage
- conventional frequency and timing of tillage operations, but herbicides
were substituted for tillage when feasible and a non-inversion V-sweep
implement was used for primary spring tillage, and; iii) Delayed
Minimum tillage - similar to minimum tillage except primary spring
tillage with a non-inversion V-sweep was delayed until at least late May.
A list of field operations and timing for the study are shown in Table
In traditional tillage,
post-harvest tillage was conducted in August of 1993, 1994, and 1995 with
overlapping 14-inch-wide V-sweeps to kill Russian thistle by severing
the tap root. Russian thistle was not present in August 1996 and post-harvest
sweeping was not required. Plots were chiseled in October after fall rains
to a depth of 10 inches with straight-point shanks spaced 2 feet apart
to create channels for controlling frozen soil runoff during the winter.
Plots were sprayed
with glyphosate (Roundup) herbicide in late winter to control weeds. Primary
tillage was conducted in March with two passes of a duck foot cultivator
with an attached harrow, or one pass with a tandem disc (Table
1). Plots were fertilized with anhydrous ammonia nitrogen in late
spring and rodweeded three times to control weeds during the summer. Winter
wheat was planted in 16 inch rows in early September all years with a
John Deere HZ deep furrow drill.
Minimum tillage treatments
were sprayed with a nonselective herbicide for post harvest control of
Russian thistle in lieu of tillage with sweeps in August (Table
1). In October, the plots were chiseled or subsoiled to depths ranging
from 10-to 16-inches with straight-point shanks spaced 4 feet apart (i.e.,
twice the shank spacing as for traditional tillage). Chiseling was not
conducted in 1996. Glyphosate was applied in late winter, and primary
tillage was with a non-inversion sweep implement equipped with 32-inch-wide
overlapping V-blades. A rotary harrow was attached behind the wide-blade
sweep to break up large clods and fill air voids. The plots were rodweeded
three times during late spring and summer and fertilized with aqua ammonia
nitrogen injected between the rows of the deep furrow grain drill when
planting winter wheat in early September.
The delayed minimum
tillage treatment was identical to the minimum tillage treatment except
that: (i) primary spring tillage was delayed until late May or
early June, and; (ii) only two rodweedings were conducted during
late spring and summer.
All treatments were
planted at the same time. Due to inadequate fall stands of winter wheat,
all plots were replanted to hard red spring wheat in March of 1993 and
1995 (Table 1). Cultivar 'Butte
86' was sown @60 lb/acre in 6 inch rows with a disc drill.
Surface residue remaining
from the previous crop cycle was measured several times throughout the
fallow period by gathering all aboveground dry matter within a 3-ft diameter
hoop. Three samples were obtained from each plot. Wheat straw and Russian
thistle skeletons were separated, placed in paper bags, and allowed to
air dry in a low-humidity greenhouse before weighing. An analysis of variance
was conducted for both wheat straw and Russian thistle skeletons on each
sampling date. Treatment means were considered significantly different
if the P-value was <0.05, using Fisher's protected least significant
Russian thistle produced
significant biomass during two crop cycles when spring wheat replaced
winter wheat due to inadequate seed zone moisture for stand establishment.
Spring wheat residue at the beginning of both the 1993-1994 and 1995-1996
fallow cycles was less than 1300 lb/acre, whereas Russian thistle dry
matter was greater than 1550 lb/acre (Figs. 1 and 2). These data agree
with other studies showing Russian thistle capable of producing more total
dry matter than the spring wheat crop it infests (Young, 1988).
Fig. 1. Above-ground
hard red spring wheat residue and Russian thistle skeletons during the
1993-1994 fallow cycle as affected by traditional, minimum, and delayed
minimum tillage. Different letters within sampling dates indicates significant
treatment differences (P < 0.05).
plots, post-harvest tillage reduced surface wheat residue and Russian
thistle skeletons compared to minimum tillage where Russian thistle was
killed by post harvest application of herbicides (Table 1, Figs. 1 and
2). During the fall and winter, the majority of Russian thistle skeletons
were wind-blown from the field in traditionally-tilled plots because the
tap root had been severed by the post-harvest sweep operation. Conversely,
when herbicide was used for post harvest control in the minimum-tilled
treatments, most Russian thistle plants remained anchored in the soil
or trapped by standing wheat stubble. (Figs. 1 and 2).
Fig. 2. Above-ground
hard red spring wheat residue and Russian thistle skeletons during the
1995-1996 fallow cycle as affected by traditional, minimum, and delayed
Surface wheat residue
and Russian thistle skeletons were always lower in the traditional tillage
than in minimum tillage throughout the spring and summer in both the 1993-1994
and 1995-1996 fallow cycles (Figs. 1 and 2). Highest retention of surface
residue in the spring was achieved with delayed minimum tillage. Differences
in residue levels between minimum and delayed-minimum treatments did not
persist until the end of the fallow cycle (Figs. 1 and 2). A benefit of
delayed minimum tillage compared to minimum tillage was the need for one
less rodweeding operation during the summer (Table 1), which conserves
energy and labor.
Fig. 3. Above-ground
hard red winter wheat residue during the 1994-1995 fallow cycle (A), and
soft white winter wheat residue during the 1996-1997 fallow cycle (B),
as affected by traditional, minimum, and delayed minimum tillage.
At the end of the
1993-1994 fallow cycle, only 230 lb/acre of wheat residue and 55 lb/acre
of Russian thistle skeletons remained on the soil surface in traditionally
tilled plots (Fig. 1). Wheat growers in the dryland areas of the Pacific
Northwest are required to maintain a minimum of 350 lb/acre surface residue
on highly erodible land in order to participate in government farm programs.
With traditional tillage, we were unable to meet this requirement in the
1993-1994 fallow cycle.
In contrast, residue
compliance was easily met with combined wheat residue and Russian thistle
skeletons exceeding 740 lb/acre in the minimum and delayed-minimum tillage
treatments. Residue compliance was marginally met (380 lb/acre) with traditional
tillage at the end of the 1995-1996 fallow cycle (Fig. 2), but residue
was likely reduced a further 20% after planting winter wheat with deep
furrow drills (McClellan, 1988). More than 750 lb/acre combined surface
cover remained with minimum and delayed-minimum tillage at the end of
the 1995-1996 fallow cycle (Fig. 2).
Russian thistle did
not infest good stands of hard red winter wheat (cv. 'Buchanan') and soft
white winter wheat (cv. 'Eltan') planted in early September of 1993 and
1995, respectively. Residue production from winter wheat exceeded 1800
lb/acre, and we maintained more than 500 lb/acre surface cover with traditional
tillage and more than 1,000 lb/acre for the minimum tillage treatments
at end of both the 1994-1995 and 1996-1997 fallow cycles (Fig. 3).
affected surface wheat residue and Russian thistle skeleton retention
throughout the fallow cycle. In low production years, Russian thistle
produced more dry matter at grain harvest than the spring wheat crop it
infested. By using herbicides rather than tillage for post harvest thistle
control and non-inversion sweeps for primary spring tillage, we consistently
retained more wheat residue and Russian thistle skeletons on the soil
surface throughout the fallow cycle than was possible with traditional
tillage. We could not retain the minimum required quantity of surface
residue for erosion control during the 1993-1994 fallow cycle using traditional
tillage, but easily met this requirement using minimum tillage.
Russian thistle did
not infest well established stands of winter wheat and maintenance of
adequate surface residue during the subsequent fallow cycle was achieved
even with traditional tillage. Conserving dead Russian thistle plants
in low crop residue situations can be beneficial for meeting residue requirements
and controlling both wind and water erosion.
Bilbro, J.D., and
D.W. Fryrear. 1994. Wind erosion losses as related to plant silhouette
and soil cover. Agron. J. 86:550-553.
Boerboom, C. Russian
thistle. 1993. Pacific Northwest Extension Publication 461. Washington
State University, University of Idaho, and Oregon State University.
Cave, H.W., W.H.
Riddell, and J.S. Hughes. 1936. The digestibility and feeding value of
Russian thistle hay. J. Dairy Sci. 19:285-290.
Cook, R.J., and R.J.
Veseth. 1991. Wheat health management. APS Press, St. Paul, MN.
Dewey, L.H. 1893.
The Russian thistle and other troublesome weeds in the wheat region of
Minnesota and North and South Dakota. USDA Farmers' Bull. 10. 16 p.
Foster, K.E., R.L.
Rawles, and M.M. Karpiscak. 1980. Biomass potential in Arizona. Desert
Fowler, J.L., and
J.H. Hageman. 1978. Nitrogen fertilization of irrigated Russian-thistle
forage. I. Yield and water use efficiency. Agron. J. 70:989-992.
Horning, T.R., and
M.M. Oveson. 1962. Stubble mulching in the Northwest. Agric. Info. Bull.
No. 253. USDA-ARS and Oregon Agric. Exp. Sta., Corvallis, OR.
Lindstrom, M.J. 1974.
Wheat-fallow management practices in the low rainfall areas of the United
States Pacific Northwest. In Tillage and cultural practices for
wheat under low rainfall conditions. Proc. 2nd Regional Wheat Workshop,
Ankara, Turkey. 6-11 May. Rockefeller Foundation, New York.
McClellan, R.C. 1988.
Small grain residue production in eastern Washington dry-farmed croplands.
Agronomy Tech. Note No. 10. USDA-Soil Conserv. Service, Spokane, WA.
Ramig, R.E., and
L.G. Ekin. 1991. When do we store water with fallow? pp. 56-60. Oregon
Agric. Exp. Stn. Special Report No. 680, Corvallis, OR.
Saxton, K.E., L.D.
Stetler, and L.B. Horning. 1996. Principles to predict and control wind
erosion and dust emissions from farm fields. p. 7-12. In R. Papendick
and R. Veseth (ed.) Northwest Columbia Plateau Wind Erosion Air Quality
Project: An Interim Report of Solutions in Progress. Washington State
Univ. Misc. Pub. No. MISC0184.
and R.I. Papendick. 1997. Tillage mulch depth effects during fallow on
wheat production and wind erosion control factors. Soil Sci. Soc. Am.
Wilkins, D.E., B.L.
Klepper, and P.E. Rasmussen. 1988. Management of grain stubble for conservation
tillage systems. Soil Tillage Res. 12:25-35.
Young, F.L. 1986.
Russian thistle (Salsola iberica) growth and development in wheat
(Triticum aestivum). Weed Sci. 34:901-905.
Young, F.L. 1988.
Effect of Russian thistle (Salsola iberica) interference on spring
wheat (Triticum aestivum). Weed Sci. 36:594-598.
Young, F., R. Veseth,
D. Thill, W. Schillinger, and D. Ball. 1995. Managing Russian thistle
under conservation tillage in crop-fallow rotations. Pacific Northwest
Extension Publication 492. University of Idaho, Oregon State University,
and Washington State University.
Young, J.A. 1991.
Tumbleweed. Scientific Am. 82-87.
Zuzel, J.F., and
J.L. Pikul, Jr. 1987. Infiltration into a seasonally frozen agricultural
soil. J. Soil Water Conserv. 42(6):447-450.
The Pacific Northwest
Conservation Tillage Handbook is a large three-ring binder handbook
that is updated with new and revised Handbook Series publications. It
was initiated in 1989 as a PNW Extension publication in Idaho, Oregon
and Washington. Updates to the Handbook are provided when the updating
card is returned. By 1997, 34 new PNW Conservation Tillage Handbook Series
have been added to the original 98 publications Copies are available for
$20 through county extension offices in the Northwest or ordered directly
by calling state extension publication offices: Idaho -- (208)
885-7982; Oregon -- (541)-737-2513; Washington -- (509)
335-2999 (some shipping and handling charges and sales tax may apply).
It's now accessible
on the Internet! All of the PNW Conservation Tillage Handbook
and Handbook Series are being put on the World Wide Web Home
titled Pacific Northwest STEEP III Conservation Farming Systems Information
Source. The Web site also contains recent issues of the PNW STEEP
III Extension Conservation Tillage Update, listings of other conservation
tillage information resources, coming events and much more. For more information
on the Handbook or updates to the Handbook, contact Roger Veseth, WSU/UI
Conservation Tillage Specialist, Plant Soil and Entomological Sciences
Department, University of Idaho, Moscow, ID 83844-2339, phone 208-885-6386,
FAX 208-885-7760, e-mail (email@example.com).
Conservation Tillage Handbook Series publications are jointly produced
by University of Idaho Cooperative Extension System, Oregon State University
Extension Service and Washington State University Cooperative Extension.
Similar crops, climate, and topography create a natural geographic unit
that crosses state lines in this region. Joint writing, editing, and production
prevent duplication of effort, broaden the availability of faculty, and
substantially reduce costs for the participating states.
For herbicide application
recommendations, refer to product labels and the Pacific Northwest
Weed Control Handbook, an annually revised extension publication
available from the extension offices of the University of Idaho, Oregon
State University and Washington State University. To simplify information,
chemical and equipment trade names have been used. Neither endorsement
of named products is intended, nor criticism implied of similar products
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