Winter Pea: Promising New Crop for Washington's Dryland Wheat-Fallow Region

Abstract

A 2-year tillage-based winter wheat (Triticum aestivum L.)-summer fallow (WW-SF) rotation has been practiced by the vast majority of farmers in the low-precipitation (<300 mm annual) rainfed cropping region of east-central Washington and north-central Oregon for 140 years. Until recently, alternative crops (i.e., those other than WW) so far tested have not been as economically viable or stable as WW-SF. A 6-year field study was conducted near Ritzville, WA (292 mm avg. annual precipitation) to determine the yield and rotation benefits of winter pea (Pisum sativum L.) (WP). Two 3-year rotations were evaluated: WP-spring wheat (SW)-SF vs. WW-SW-SF. Winter pea yields averaged 2,443 vs. 4,878 kg/ha for WW. No fertilizer was applied to WP whereas 56 kg N and 11 kg S/ha were applied to WW. Winter pea used significantly less soil water than WW. Over the winter months, a lesser percentage of precipitation was stored in the soil following WP compared to WW because: (i) very little WP residue remained on the soil surface after harvest compared to WW, and (ii) the drier the soil, the more precipitation is stored in the soil over winter. However, soil water content in the spring was still greater following WP vs. WW. Soil residual N in the spring (7 months after the harvest of WP and WW) was greater in WP plots despite not applying fertilizer to produce WP. Spring wheat grown after both WP and WW received the identical quantity of N, P, and S fertilizer each year. Average yield of SW was 2,298 and 2,011 kg/ha following WP and WW, respectively (P < 0.01). Adjusted gross economic returns for these two rotation systems were similar. Based partially on the results of this study, numerous farmers in the dry WW-SF region have shown keen interest in WP and acreage planted WP in east-central Washington has grown exponentially since 2013. This paper provides the first report of the potential for WP in the typical WW-SF region of the inland Pacific Northwest (PNW).

Full text

ORIGINAL RESEARCH
published: 10 May 2017
doi: 10.3389/fevo.2017.00043
Frontiers in Ecology and Evolution | www.frontiersin.org 1May 2017 | Volume 5 | Article 43
Edited by:
Klaus Birkhofer,
Lund University, Sweden
Reviewed by:
José Manuel Mirás-Avalos,
Centro de Edafología y Biología
Aplicada del Segura (CSIC), Spain
Fernando José Cebola Lidon,
Faculdade de Ciências e Tecnologia
da Universidade Nova de Lisboa,
Portugal
*Correspondence:
William F. Schillinger
william.schillinger@wsu.edu
Specialty section:
This article was submitted to
Agroecology and Land Use Systems,
a section of the journal
Frontiers in Ecology and Evolution
Received: 18 February 2017
Accepted: 21 April 2017
Published: 10 May 2017
Citation:
Schillinger WF (2017) Winter Pea:
Promising New Crop for Washington’s
Dryland Wheat-Fallow Region.
Front. Ecol. Evol. 5:43.
doi: 10.3389/fevo.2017.00043
Winter Pea: Promising New Crop for
Washington’s Dryland Wheat-Fallow
Region
William F. Schillinger *
Department of Crop and Soil Sciences, Washington State University, Dryland Research Station, Lind, WA, USA
A 2-year tillage-based winter wheat (Triticum aestivum L.)-summer fallow (WW-SF)
rotation has been practiced by the vast majority of farmers in the low-precipitation (<300
mm annual) rainfed cropping region of east-central Washington and north-central Oregon
for 140 years. Until recently, alternative crops (i.e., those other than WW) so far tested
have not been as economically viable or stable as WW-SF. A 6-year field study was
conducted near Ritzville, WA (292 mm avg. annual precipitation) to determine the yield
and rotation benefits of winter pea (Pisum sativum L.) (WP). Two 3-year rotations were
evaluated: WP-spring wheat (SW)-SF vs. WW-SW-SF. Winter pea yields averaged 2,443
vs. 4,878 kg/ha for WW. No fertilizer was applied to WP whereas 56 kg N and 11 kg
S/ha were applied to WW. Winter pea used significantly less soil water than WW. Over
the winter months, a lesser percentage of precipitation was stored in the soil following
WP compared to WW because: (i) very little WP residue remained on the soil surface
after harvest compared to WW, and (ii) the drier the soil, the more precipitation is stored
in the soil over winter. However, soil water content in the spring was still greater following
WP vs. WW. Soil residual N in the spring (7 months after the harvest of WP and WW) was
greater in WP plots despite not applying fertilizer to produce WP. Spring wheat grown
after both WP and WW received the identical quantity of N, P, and S fertilizer each year.
Average yield of SW was 2,298 and 2,011 kg/ha following WP and WW, respectively
(P<0.01). Adjusted gross economic returns for these two rotation systems were similar.
Based partially on the results of this study, numerous farmers in the dry WW-SF region
have shown keen interest in WP and acreage planted WP in east-central Washington
has grown exponentially since 2013. This paper provides the first report of the potential
for WP in the typical WW-SF region of the inland Pacific Northwest (PNW).
Keywords: winter pea, Inland Pacific Northwest USA, dryland cropping systems, winter wheat-summer fallow,
crop diversification
INTRODUCTION
A monoculture WW-SF rotation is the dominant cropping system practiced by farmers on 1.5
million cropland hectares in east-central Washington and north-central Oregon. Researchers and
farmers have experimented with numerous crops and rotations over many decades, but none have
been found to be as stable, reliable, and profitable as WW-SF (Juergens et al., 2004). Grassy weeds,
mostly downy brome (Bromus tectorum L.) and jointed goatgrass (Aegilops cylindrica Host.), are a
huge problem with monoculture WW-SF. Many farmers have resorted to the “Clearfield”TM system

Schillinger Winter Pea in the Pacific Northwest Drylands
for WW production that depends on use of the long soil-residual
imazamax herbicide to control grassy weeds. A viable, stable, and
profitable broadleaf crop is much needed for crop diversity and
grassy weed control without the use of soil-residual herbicides.
Pulse crops are cool-season annual grain legumes mostly
grown in the northern tier states of North Dakota and Montana,
the high-precipitation (>450 mm average annual) Palouse region
of Washington and Idaho (NASS, 2017), and the Canadian
provinces of Alberta, Saskatchewan, and Manitoba (Statistics
Canada, 2017). During the past 20 years, pulse crops have become
an integral component of diversified and profitable dryland
cropping systems in the Canadian and US northern Great Plains
(Miller et al., 2003, 2015; Chen et al., 2006; Long et al., 2014).
In the PNW Palouse region, dry edible spring pea is
commonly grown in rotation with wheat, with 48,000 ha of
this crop harvested in 2016 (NASS, 2017). However, very little
spring pea is produced in PNW areas that receive <450 mm
annual precipitation. Experience in east-central Washington has
demonstrated that water and heat stresses during flowering and
pod fill limits yield potential of spring pea whereas WP better
avoids such abiotic stresses by reaching physiological maturity
before the onset of high air temperatures (Nelson, 2017).
Chen et al. (2006) reported that fall-planted WP in the high-
precipitation Palouse of the PNW yielded as much as 1,830
kg/ha more than spring-planted pea cultivars. This (Chen et al.,
2006) is the only published paper of such nature on WP in
the PNW. Such observations of higher yield potential with WP
compared to spring pea are not in general agreement with
the much more comprehensive data sets from the Canadian
and US northern Great Plains where winter temperatures are
considerably colder than in the PNW. Chen et al. (2006) found
that WP cultivars did not have a yield advantage over spring
pea in central and south-central Montana. Similarly Strydhorst
et al. (2015) recommended that farmers consider WP over spring
pea only in the southernmost locations in Alberta. Although
edible dry pea was harvested on 206,000 ha in Montana in 2016
(NASS, 2017) only about one percent of this was WP (P.R. Miller,
personal communication).
Essentially no edible WP was produced anywhere in the PNW,
(including the typical WW-SF region that receives <300 mm
average annual precipitation, prior to 2012. Field research (this
study) conducted since 2010 near Ritzville, WA (292 mm annual
average precipitation) has demonstrated that WP is well-suited
for the low-precipitation drylands. Winter pea plantings in the
WW-SF region have gone from basically zero to 2,730 hectares
from 2013 to 2017 (Howard Nelson, personal communication).
Although the land area planted to WP currently is still small, the
annual increase in planted hectares has been exponential during
this 5-year period. The objective of the 6-year study reported here
was to determine the yield potential and yield stability of WP
and associated rotation benefits to the subsequent crop compared
to WW in the low-precipitation WW-SF region of east-central
Washington.
Abbreviations: PNW, inland Pacific Northwest; SF, summer fallow; SW, spring
wheat; WP, winter pea; WW, winter wheat.
MATERIALS AND METHODS
A long-term WP cropping systems experiment was initiated
at the Ronald Jirava farm near Ritzville, WA (47.16394,-
118.473225) in August 2010. The WP cultivar “Windham”
(McPhee et al., 2007) was selected for inclusion in the
experiment based on the experience and recommendation
of Howard Nelson of Central Washington Grain Growers.
Windham is a yellow pea with mottled seed coat; with an
average 100-seed weight of 13.8 g. Windham can withstand
ambient air temperatures as low as −18◦C without undue
damage to plant stands (Nelson, 2017). This cultivar has an
average mature plant height of 44 cm with upright growth
habit that allows for direct combining at harvest with a
conventional header (i.e., swathing and/or a pick-up header not
required).
Precipitation was measured on site during all years of the
study by the Washington State University (WSU) AgWeatherNet
(http://weather.wsu.edu/) with a Campbell Scientific CR-1000
logger and associated hardware. The soil at the site is a Ritzville
silt loam (coarse-silty, mixed, superactive, mesic, Calcidic
Haploxerolls; Soil Survey Staff, 2010). The soil is more than 2
meters deep to underlying basalt bedrock with uniform texture
throughout the profile and with no rocks or restrictive layers.
Slope is <1%. Long-term (100-year) annual precipitation at/near
the site averages 292 mm. Annual crop-year (Sept. 1–Aug. 31)
precipitation during the study period ranged from 207 to 370 mm
and averaged 277 mm.
Treatments and Field Operations
Throughout the 6-year experiment, glyphosate herbicide was
applied at a rate of 0.48 kg acid equivalent (ae)/ha in March
to control weeds in the undisturbed residue of the WP, WW,
and SW plots that had been harvested the previous July or
August. The two 3-year crop rotations in the experiment were
(i) WP-SW-SF vs. (ii) WW-SW-SF. Experimental design was a
randomized complete block with four replicates. All phases of
both rotations were present every year for a total of 24 individual
plots. Size of individual plots was 5 ×30 m.
During the fallow year, conservation primary spring tillage
was conducted with a HaybusterTM undercutter implement in
mid-to-late May at a depth of 10 cm. For the WW-SW-
SF treatment, 56 kg/ha aqua NH3-N +11 kg/ha thiosol S
fertilizer was injected with the undercutter implement during
primary spring tillage. No fertilizer was applied to the WP-SW-
SF treatment with the undercutter during primary spring tillage.
Summer fallow in both treatments was rodweeded once in July at
a depth of 8 cm to control broadleaf weeds.
Winter pea (cv. Windham) and WW (cv. Xerpha) were
planted at the same time and depth each year in either the last
week of August or first week of September with a deep-furrow
drill with 43 cm spacing between rows. Seed was inoculated with
powdered rhizobium bacteria at time of planting to facilitate root
nodulation and fixation of atmospheric nitrogen. Seeding rate
for WP was 100 kg/ha (70 seeds/m2) and for WW 56 kg/ha
(160 seeds/m2). An average of 10 cm of soil covered the seeds.
Excellent stands of both WP and WW were achieved every year.
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Schillinger Winter Pea in the Pacific Northwest Drylands
Spring wheat (cv. Louise) was planted and fertilized in late
March in one-pass directly into the undisturbed soil and residue
left from the previous WP or WW crop. A no-till hoe-opener drill
was used to place seed in paired rows 10-cm apart with 30 cm
spacing between openers. Fertilizer was placed in a band between
and 3 cm below the paired rows. Seeding rate for SW was 78
kg/ha (225 seeds/m2) and soil covering the seed averaged 2 cm.
Prior to SW planting and fertilization, soil samples were obtained
from 2,014 to 2,106 in 30-cm increments from the middle of each
plot to a depth of 120 cm in all four replicates, then combined
to make one sample for each treatment per depth increment,
where the previous crop was WP or WW. Soil samples were then
analyzed for N, P, K, S, and other nutrients at a commercial soil-
testing laboratory (Soil Test Farm Consultants, Inc., Moses Lake,
WA). Fertilizer rate for SW was based on soil test residual soil
fertility, available soil water, and perceived grain yield potential.
Potassium fertilizer was not required as soils contain naturally
adequate quantities of this nutrient. Although soil fertility values
following WP vs. WW differed somewhat (Table 1), SW after
either WP or WW always received the same fertilizer application
rate each year. Solution 32 (NH4NO3+urea) provided the
liquid fertilizer base to supply an average of 38 kg N, 7 kg P
(aqueous solution of NH4H2PO4), and 10 kg S [aqueous solution
of (NH4)2S2O3]/ha. Excellent stands of SW were achieved every
year.
Crop yields were determined in early-to-mid July (WP) and
early August (WW and SW) by harvesting a 1.5-m swath
through the center of each 30-m-long plot with a HegeTM 140
plot combine. After grain harvest with the plot combine, the
remaining standing crops in the experiment were harvested with
a commercial-size combine.
In-Crop and Post-Harvest Weed Control
with Herbicides
When WP reached the three-leaf (or four-node) stage of growth
in April, 1.1 kg active ingredient (ai)/ha sodium salt of bentazon
broadleaf-weed herbicide was tank mixed with 0.1 kg ai/ha
quizalofop P-ethyl grass-weed herbicide and applied. Bentazon
and MCPA Amine are currently the only non-soil-residual
broadleaf-weed herbicides labeled for use in WP. The major grass
weeds of concern in the region are downy brome and jointed
goatgrass. Both these grass weeds are winter annuals with growth
cycles similar to WW and are particularly problematic in the
2-year WW-SF rotation (Young and Thorne, 2004).
Herbicides used to control broadleaf weeds in WW were either
2,4-D ester at a rate of 0.84 kg acid equivalent (ae)/ha or 0.56 kg
ai/ha bromoxynil applied in April after WW had four tillers but
before the “jointing” stage of WW growth development. In-crop
broadleaf herbicides used for SW were 0.56 kg ai/ha bromoxynil
or 0.45 kg ai/ha bromoxynil +0.02 L ai/ha thifensulfuron applied
in May.
Glyphosate was applied at a rate of 0.90 kg ae/ha following the
harvest of SW in August of 2014 and 2015 (the two driest crop
years) to control Russian thistle (Salsola tragus L.). Post-harvest
herbicide application was not required for WP or WW in any
year.
TABLE 1 | Soil nitrate-N, Olsen-P, sulfate-S, and soil organic matter (SOM)
in late March during 3 years after either winter pea or winter wheat and
prior to planting spring wheat.
Nitrate Phosphorus Sulfate SOM
(mg/kg/120 cm) (mg/kg/30 cm) (mg/kg/90 cm) (30 cm, %)
2013
Winter wheat 24 53 39 1.7
Winter pea 30 52 45 1.5
2014
Winter wheat 16 35 17 1.8
Winter pea 22 38 17 1.6
2016
Winter wheat 17 45 16 1.4
Winter pea 24 43 13 1.6
Soil Water
Soil water was measured to a depth of 180 cm three times
each year: (i) in early August immediately after WP, WW, and
SW grain harvest (16 plots); (ii) at the end of fallow in late
August for the SF plots (8 plots); and (iii) in mid-March (all
24 plots). Volumetric soil water content in the 0–30-cm depth
was determined from two 15-cm core samples with gravimetric
procedures (Topp and Ferre, 2002) using known soil bulk density
values for these depths. Soil volumetric water content in the 30–
180-cm depth was measured in 15-cm increments by neutron
thermalization (Hignett and Evett, 2002).
Market Price, Gross Returns, and Adjusted
Gross Returns
Gross returns for WP and WW per hectare were calculated based
on the yield results for each year of the study. Edible WP grown
by farmers in eastern Washington was sold through a “market
pool” operated by Central Washington Grain Growers in Wilbur,
WA. Market streams for WP through the years included seed for
cover crops, US government food aid, export for food to Asia, and
for pet food. Winter pea marketing pool prices ranged from 160
to 339 US$/metric ton (MT).
Soft white wheat market price used was the price offered
during the first week of September for each year of the study at
Ritzville Warehouse, Ritzville, WA. Ritzville Warehouse accepts
WW and WP for storage and is the closest commercial elevator
delivery site for the study. Gross returns per hectare for both WP
and WW were calculated by multiplying yields obtained from the
study by the market prices for each year. Adjusted gross returns
were then calculated for both rotations by tabulating for each
year the cost of N and S used for WW (but not for WP) and any
differences in SW yields.
Statistical Analysis
Statistical analyses using a randomized complete block design
analysis of variance (ANOVA) were conducted for: (i) water use
of WP vs. WW as well as overwinter storage of precipitation in
the soil following these two crops averaged over 5 years, and;
(ii) within-year and 5-year average differences in SW grain yield
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Schillinger Winter Pea in the Pacific Northwest Drylands
following either WP or WW. A split-plot in time ANOVA was
used for the 5-year average soil water data and the 5-year average
SW yield data with treatment as the fixed effect factor and year
as the random effect factor. The least significant difference test
was used to detect statistical differences in treatment means. All
ANOVA tests were done at the 5% level of significance.
RESULTS
Soil Water
Averaged over the years, WP used an average of 30 mm less
soil water than WW (P<0.001, Table 2). The majority of this
water savings with WP occurred at soils depths below 100 cm
(Figure 1) as WP roots do not reach this depth. These data on
soil water use by WP agree closely with those reported by Miller
and Holmes (2012) in Montana and Merrill et al. (2004) in North
Dakota. However, by late March, WP plots had only 13 mm more
soil water than WW plots (Table 2) because: (i) the greater the
surface residue cover, the more water will be stored in the soil
(e.g., WP produces little residue compared to WW); and (ii) the
drier the soil, the more overwinter precipitation will be stored in
the soil (Kok et al., 2009).
The overwinter precipitation storage efficiency (PSE) in the
soil averaged 55 and 69% for WP and WW plots, respectively
(Table 2). Similar overwinter PSE-values were reported following
spring lentil (Lens culinaris L.) vs. following SW in a 21-year
study in Saskatchewan (Campbell et al., 2007). This increase in
overwinter PSE for WW over WP plots occurred within the first
100 cm of the soil profile whereas the relative difference in spatial
water distribution at the 100–180-cm depths remained about the
same for WP and WW plots (Figure 1). The end result, however,
was that when SW was planted in late March, average overwinter
soil water content was 290 and 277 mm following WP and WW,
respectively (Table 1).
Soil Nitrate-N
When measured in late March, soil nitrate-N-values trended
higher after a crop of WP compared to WW, despite the fact that
zero N was applied for WP and 56 kg of N/ha was applied for WW
(Table 1). This can be explained by the fact that WP is a legume
that fixes atmospheric nitrogen. Although statistical analysis was
not possible (soil samples were pooled from the four replicates),
nitrate-N-values were 25–41% greater following WP vs. WW.
Grain Yield
Yield of WP ranged from 1,696 to 3,158 kg/ha and averaged 2,443
kg/ha over 5 years (Table 3). Winter pea was killed by −21◦C air
temperatures with no snow cover in 2014 and was replaced by
spring pea (cv. Banner) which yielded 870 kg/ha. Winter wheat
grain yield ranged from 3,372 to 5,841 kg/ha for an average of
4,878 kg/ha over 6 years (Table 3).
Spring wheat grain yield was significantly greater following
WP vs. following WW in 2013 and 2015. The 5-year average
SW grain yield of 2,298 kg/ha following WP was significantly
different from 2,122 kg/ha following WW (Table 3).
TABLE 2 | (i) Soil water content to a depth of 180 cm measured after
harvest of winter pea and winter wheat and again in late March following
these two crops; (ii) overwinter gain in soil water, and; (iii) overwinter
precipitation storage efficiency in the soil (PSE).
Beginning
(late Aug.)
Spring (late
Mar.)
Overwinter
gain
PSE (%)
Soil water content (mm)
Winter pea 180 290 110 55
Winter wheat 150 277 127 69
P-value <0.001 ns 0.001
Data are averaged over 5 years. Average overwinter precipitation was 164 mm.
FIGURE 1 | Soil volumetric water content to a depth of 180 cm in early
August after harvest of winter pea and winter wheat (red lines on left)
and overwinter soil water recharge following these two crops
measured in late March (blue lines on right). Data are averaged over 5
years.
Market Price, Gross Returns, and Adjusted
Gross Returns
Gross returns for WW exceeded that for WP in most years
(Table 4). However, cost of 56 kg/ha aqua NH3-N +11 kg/ha
thiosol S fertilizer for WW (where none was used for WP) ranged
from $66 to $97/ha and averaged $86/ha over the 6 years (actual
costs paid for the fertilizer each year). Also, SW yield after WP
vs. WW from 2012 to 2016 ranged from −143 to +589 kg/ha
and averaged +176 kg/ha (Table 3). Using the commodity market
prices shown in Table 4, SW after WP generated from −$35
to +S85/ha and averaged +$39/ha more return than SW after
WW. Thus, the fertilizer savings plus the greater SW grain yield
revenue provided in the WP rotation should be considered rather
than just the gross returns shown in Table 4.
DISCUSSION
Winter wheat-summer fallow has been the dominant cropping
system practiced throughout the low-precipitation dryland
cropping region of east-central Washington and north-central
Oregon for well-over 100 years. Despite long-term and ongoing
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Schillinger Winter Pea in the Pacific Northwest Drylands
TABLE 3 | Yield of winter pea (WP) and winter wheat (WW) as well as the
subsequent yield of spring wheat (SW) following both WP and WW over a
6-year period at Ritzville, WA.
Grain yield (kg/ha)
2011 2012 2013 2014 2015 2016 Avg.
WINTER CROP
Winter pea 2,193 3,158 2,336 - - - -*1,696 2,833 2,443**
Winter wheat 5,180 5,729 5,841 3,372 4,211 4,932 4,878
SPRING CROP***
SW after WP 2,010 2,992 a 1,043 2,293 a 3,151 2,298 a
SW after WW 2,153 2,700 b 965 1,704 b 3,086 2,122 b
Crop-year precipitation (mm)
330 294 254 207 208 370 277
Values at the bottom show crop-year (Sept. 1–Aug. 31) precipitation at the site.
*WP was winterkilled in 2014 and replanted to Banner edible spring pea, which yielded
870 kg/ha.
**Winter pea average yield is for 5 years (i.e., 2014 not included).
***ANOVA is for SW only. Within-column means followed by a different letter are
significantly different at P <0.05.
TABLE 4 | Ritzville soft white wheat market prices during the first week of
September and winter pea market pool price as well as gross return for
these crops based on the yield results of the experiment from 2011 to
2016.
Commodity market price (US$/MT)* Gross returns (US$/hectare)**
Soft white
wheat
Winter pea Soft white
wheat
Winter pea
2011 198 291 1,245 776
2012 242 289 1,680 1,112
2013 202 339 1,433 963
2014 172 No pool, winterkill 701 - - - -
2015 145 377 746 778
2016 123 160 731 674
*Soft white wheat price data from Ritzville Warehouse, Ritzville, WA. Winter pea market
pool price data from Howard Nelson, Central Washington Grain Growers, Wilbur, WA.
**Gross return values shown here to not account for cost of N and S used for WW (but
not used for WP) or the additional revenue from greater SW yield after WP vs. WW (see
Results section).
efforts, farmers and scientists have not yet identified any spring-
planted crop, including SW spring barley (Hordeum vulgare L.),
and numerous others, that can provide the yield stability and
economic viability of WW-SF.
A big benefit of growing WP in wheat-based cropping systems
is the opportunity for in-crop control of winter-annual grass
weeds such as downy brome and jointed goatgrass. These two
grass weeds have growth cycles similar to WW and infestations
are frequently heavy and troublesome (Appleby and Morrow,
1990), especially in the 2-year WW-SF rotation.
Another benefit of WP is its large seed size and strong
“push” by the elongating hypocotyl which enables it to emerge
from deep planting depths. For optimum grain yield potential,
farmers in east-central Washington seed WW into SF as deep
as 20 cm below the soil surface with deep-furrow drills to reach
adequate soil moisture in late August-early September, and WW
seedlings need to emerge through as much as 15 cm of dry
soil cover. Data from planting-date experiments in east-central
Washington suggest that late August-early September is also the
best planting time for optimum yield potential of WP (Rebecca
McGee, personal communication). Experience of farmers and
scientists strongly demonstrates that WP seedlings can emerge
from even deeper planting depths than WW. In addition, WP
seedlings easily emerge through surface soil that has been crusted
by rain showers whereas WW seedlings cannot do so.
A new yellow WP cultivar “Blaze” (ProGene Plant Research,
Othello, WA) is presently under seed multiplication and will
be available to farmers in 2018. Compared to Windham in
regional trials, Blaze has (i) 13% higher yield, (ii) 18 cm taller
plant height at maturity, 22% larger seed, and (iii) better cold
tolerance (Nelson, 2017). For example, during a cold event of
−18◦C with no snow cover in 2014, Windham was winterkilled
at regional locations whereas, at these same locations, Blaze
survived (Nelson, 2017). It is estimated that Blaze has similar
cold tolerance as regionally-adopted WW cultivars. Additionally,
three advanced WP numbered lines in the USDA-Agricultural
Research Service legume breeding program in Pullman, WA
show excellent potential and are expected to be released soon.
These numbered WP lines have better cold tolerance than
Windham in addition to smooth seed coat, clear hilum, and
large seed size that are deemed highly desirable for food markets
(Rebecca McGee, personal communication).
A soil management concern about growing WP is the fact
that they produce very little durable residue. Wind erosion and
dust emission from agricultural soils is a major environmental
and air quality concern in east-central Washington (Sharratt
and Vaddella, 2012). Wind tunnel studies during the fallow year
after the oilseed crops camelina (Camelina sativa L. Crantz)
and safflower (Carthamus tinctorius L.) showed up to 250%
greater blowing dust emissions even using best management
practices for tillage-based SF compared to after WW (Sharratt
and Schillinger, 2014). Personal observation suggests that WP
residue decomposes at about the same rate as residue of camelina
and safflower. In a practical sense, this means that farmers must
be especially judicious in protecting the soil after WP by either
(i) recropping to the spring crop (as done in this study), or (ii)
conducting no tillage during the 13-month SF cycle.
There are currently few effective in-crop broadleaf herbicide
options for WP. Bentazon herbicide (used every year in
WP in the study) provides little control for tumble mustard
(Sisymbrium altissimum L.) or tansy mustard (Descurainia
pinnata L.). Although considered minor weeds that are easily
controlled with herbicides in WW, both were present in
minor to moderate levels in WP. The soil residual imazamox
herbicide can be used in WP and is used by many farmers
who practice the ClearfieldTM method for WW production.
However, many farmers are reluctant to use soil-residual
herbicides due to limitations imposed on rotation to other
crops or to WW cultivars that are not tolerant of this
herbicide. Russian thistle, by far the most troublesome broadleaf
weed in the region, was not a problem in WP in any year,
presumably due to the ability of WP to provide canopy
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Schillinger Winter Pea in the Pacific Northwest Drylands
closure relatively early in the spring before this weed can
establish.
The potential impact of increased pulse crop production on
greenhouse gas emissions deserves some discussion. Lemke et al.
(2007) and Cutforth et al. (2007) wrote review articles about
the impact of pulse crop production on climate change in the
Canadian and US northern Great Plains and the contribution of
pulse crops to the balance of greenhouse gases. Authors of these
papers agreed that rotations which include pulse crops will likely
have lower nitrous oxide emissions compared to rotations that do
not contain a pulse because legumes fix atmospheric N compared
to rotations that rely solely on fertilizer N. Lemke et al. (2007) and
Cutforth et al. (2007) further agreed that replacing a cereal with a
pulse crop will likely result in the same or slightly smaller carbon
dioxide emissions in direct relation to reduction in fertilizer N
usage.
CONCLUSION
This study showed that WP has excellent production potential in
the typical WW-SF region of east-central Washington. Although
gross returns for WW were greater than for WP during
most years, adjusted gross returns for the two rotations were
equivalent. Winter pea has unsurpassed seedling emergence from
deep planting depths, even when surface soils have been crusted
by rain showers before emergence. Excellent WP plant stands
were consistently achieved that effectively competed against
Russian thistle. New WP cultivars will be available to farmers
in 2018 that have cold tolerance similar to that of WW, greater
yield potential than cv. Windham, and better quality traits that
will fetch higher prices in regional, national, and international
markets.
Land area planted of WP in the PNW drylands is still minor,
but farmers and scientists are excited about this crop and planted
acreage has increased exponentially every year since 2013. This
paper provides the first report in the literature on WP production
in the typical WW-SF region of the PNW.
AUTHOR CONTRIBUTIONS
Contributions to this article were made by WS and he is
accountable for the content of the work.
ACKNOWLEDGMENTS
The author gratefully acknowledges the cooperation and
support of Ronald Jirava on whose farm the research was
conducted. Excellent field and office support was provided by
John Jacobsen, Steve Schofstoll, and Samantha Crow located at
the WSU Lind Dryland Research Station. Much appreciation
is extended to Howard Nelson and Kurt Braunwart for
sharing their knowledge about producing and marketing
WP. Funding was provided by the WSU Agricultural
Research Center through Hatch Project 0250, the USDA-
NIFA through the REACCH Project, and by ProGene Plant
Research.
REFERENCES
Appleby, A. P., and Morrow, L. A. (1990). “The Pacific Northwest,” in Systems
of Weed Control in North America. WSSA Monogr, Vol. 6. ed W. W. Donald
(Champaign, IL: WSSA), 200–232.
Campbell, C. A., Zentner, R. P., Basnyat, P., Wang, H., Selles, F., McConkey, B.
G., et al. (2007). Water use efficiency and water and nitrate distribution in soil
in the semiarid prairie: effect of crop type over 21 years. Can. J. Plant Sci. 87,
815–827. doi: 10.4141/CJPS06034
Chen, C., Miller, P., Muehlbauer, F., Neill, K., Wichman, D., and McPhee,
K. (2006). Winter pea and lentil response to seeding date and micro-
and macro-environments. Agron. J. 98, 1655–1663. doi: 10.2134/agronj200
6.0085
Cutforth, H. W., McGinn, S. M., McPhee, K. E., and Miller, P. R. (2007). Adaptation
of pulse crops in the changing climate of the northern Great Plains. Agron. J. 99,
1684–1699. doi: 10.2134/agronj2006.0310s
Hignett, C., and Evett, S. R. (2002). “Methods for measurement of soil water
content: neutron thermalization,” in Methods of Soil Analysis.Part 4—Physical
Methods, eds J. H. Dane and G. C. Topp (Madison, WI: SSSA), 501–521.
Juergens, L. A., Young, D. L., Schillinger, W. F., and Hinman, H. R. (2004).
Economics of alternative no-till spring crop rotations in Washington’s wheat-
fallow region. Agron. J. 96, 154–158. doi: 10.2134/agronj2004.0154
Kok, H., Papendick, R. I., and Saxton, K. E. (2009). STEEP: impact of long-term
conservation farming research and education in Pacific Northwest wheatlands.
J. Soil Water Cons. 64, 253–264. doi: 10.2489/jswc.64.4.253
Lemke, R. L., Zhong, Z., Campbell, C. A., and Zentner, R. (2007). Can pulse crops
play a role in mitigating greenhouse gases from North American agriculture?
Agron. J. 99, 1719–1725. doi: 10.2134/agronj2006.0327s
Long, J. A., Lawrence, R. L., Miller, P. R., and Marshall, L. A. (2014).
Changes in field-level cropping sequences: indicators of shifting agricultural
practices. Agric. Ecosyst. Environ. 189, 11–20. doi: 10.1016/j.agee.2014.
03.015
McPhee, K. E., Chen, C. C., Wichman, D. M., and Muehlbauer, F. J. (2007).
Registration of “Windham” winter feed pea. J. Plant Regist. 1, 117–118.
doi: 10.3198/jpr2006.12.0828crc
Merrill, S. D., Tanaka, D. L., Krupinsky, J. M., and Ries, R. E. (2004). Water use
and depletion by diverse crop species on Haplustoll soil in the northern Great
Plains. J.Soil Water Conserv. 59, 176–183.
Miller, P. R., Bekkerman, A., Jones, C. A., Burgess, M. H., Holmes, J. A.,
and Engel, R. E. (2015). Pea in rotation with wheat reduced uncertainty
of economic returns in southwest Montana. Agron. J. 107, 541–550.
doi: 10.2134/agronj14.0185
Miller, P. R., Gan, Y., McConkey, B. G., and McDonald, C. L. (2003). Pulse
crops for the Northern Great Plains: II. Cropping sequence effects on
cereal, oilseed, and pulse crops. Agron. J. 95, 980–986. doi: 10.2134/agronj20
03.0980
Miller, P. R., and Holmes, J. A. (2012). Comparative soil water use by annual
crops at a semiarid site in Montana. Can. J. Plant Sci. 92, 803–807.
doi: 10.4141/cjps2011-191
NASS (2017). Northwest Regional Field Office. National Agricultural
Statistics Service. Washington, DC: USDA. Available online at:
https://www.nass.usda.gov/Statistics_by_State/Washington/index.php
Nelson, H. (2017). Central Washington Grain Growers 2016 Test Plot Results.
Available online at: http://www.cwgg.net/images/603/2016 TestPlotResults.pdf
(Accessed Feb 17, 2017).
Sharratt, B., and Schillinger, W. F. (2014). Windblown dust potential from
oilseed cropping systems in the Pacific Northwest United States. Agron. J. 106,
1147–1152. doi: 10.2134/agronj13.0384
Sharratt, B. S., and Vaddella, V. K. (2012). Threshold friction velocity of soils within
the Columbia Plateau. Aeolian Res. 6, 13–20. doi: 10.1016/j.aeolia.2012.06.002
Frontiers in Ecology and Evolution | www.frontiersin.org 6May 2017 | Volume 5 | Article 43

Schillinger Winter Pea in the Pacific Northwest Drylands
Statistics Canada (2017). Ottawa. Available online at: http://www.statcan.gc.ca/
eng/start
Strydhorst, S., Olson, M. A., Vasanthan, T., McPhee, K. E., McKenzie, R. H.,
Henriques, B., et al. (2015). Adaptability and quality of winter pea and lentil
in Alberta. Agron. J. 107, 2431–2448. doi: 10.2134/agronj15-0092
Soil Survey Staff (2010). Keys to Soil Taxonomy, 11th Edn. Washington, DC:
USDA-Natural Resources Conservation Service.
Topp, G. C., and Ferre, P. A. (2002). “Methods for measurement of soil water
content: Thermogravimetric using convective oven-drying,” in Methods of Soil
Analysis. Part 4—Physical Methods. SSSA Book Series: 5, eds J. H. Dane and G.
C.Topp (Madison, WI: Soil Science Society of America), 422–424.
Young, F. L., and Thorne, M. E. (2004). Weed-species dynamics and management
in no-till and reduced-till fallow cropping systems for the semi-arid
agricultural region of the Pacific Northwest, USA. Crop Prot. 23, 1097–1110.
doi: 10.1016/j.cropro.2004.03.018
Conflict of Interest Statement: The author declares that the research was
conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
Copyright © 2017 Schillinger. This is an open-access article distributed under the
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reproduction in other forums is permitted, provided the original author(s) or licensor
are credited and that the original publication in this journal is cited, in accordance
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