Received: 16 September 2019 Accepted: 6 February 2020
ORIGINAL RESEARCH ARTICLE
Variety and weed management effects on organic chickpea stand
establishment and seed yield
Yesuf Assen Mohammed1Zachariah Miller2Kyrstan Hubbel2Chengci Chen1
1Eastern Agricultural Research Center,
Montana State University, 1501 N Central
Ave., Sidney, MT 59270, USA
2Western Agricultural Research Center,
Montana State University, 580 Quast Lane,
Corvallis, MT 59828, USA
Chengci Chen, Eastern Agricultural Research
Center, Montana State University, 1501 N
Central Ave.,Sidney, MT 59270, USA.
Montana Specialty Crop Block Grant,
The need for organic produce is increasing worldwide but weed control remains a crit-
ical problem for organic crop production. Three types of weed control practices were
evaluated for two organic chickpea (Cicer arietinum L.) varieties at the Western (Cor-
vallis) and Eastern (Sidney) Agricultural Research Centers of Montana State Univer-
sity. Treatments included two chickpea varieties (Black and CDC Orion chickpeas),
two seeding rates (standard seeding rate or 1×at 43 seeds m−2and 50% increase over
the standard rate or 1.5×), and two pre-emergent weed control practices (flame weed-
ing and shallow tillage). Results revealed that Black chickpea was associated with
greater stand densities and grain yield with lower weed biomass than CDC Orion.
Increasing seeding rate for Black chickpea improved crop density and increased grain
yield to the extent of 26% compared with the standard seed rate. Flaming increased
chickpea grain yield only at Corvallis in 2016. The combined effects of shallow tillage
and increased seeding rates resulted in reduced weed biomass. Shallow tillage can be
successfully integrated to improve yields and reduce weed pressure in organic chick-
pea. However, precaution must be taken for the tillage timing to avoid damage to
emerging chickpea seedlings. More research is needed to select chickpea varieties
that have improved vigor and are more competitive to weed pressure commonly seen
in organically managed fields.
Organic agriculture is increasing in popularity worldwide
(Bruinsma, 2003). World organic food market sales reached
US$91 billion in 2015 and is projected to reach $320.5 bil-
lion by 2025 (Grand View Research, 2017). In the United
States alone, organic sales have increased from $3.6 billion in
1997 to $49.4 billion in 2017 (Delate, Cambardella, Chase,
Johanns, & Turnbull, 2013). More than two-thirds of U.S.
Abbreviations: IWM, integrated weed management; PC, previous crop;
SR, seed rate; VA, variety; WC, weed control method; YR, year.
This is an open access article under the terms of the Creative Commons Attribution- NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided
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© 2020 The Authors. Agrosystems, Geosciences & Environment published by Wiley Periodicals, Inc. on behalf of Crop Science Society of America and American Society of Agronomy
consumers buy organic products on an occasional basis and
28% buy organic products weekly (Organic Trade Associa-
tion, 2018). One crop of interest for organic farmers in the
northwestern United States is chickpea (Cicer arietinum L.).
In 2017, Montana, Washington, Idaho, and North Dakota pro-
duced 93% of chickpea grown in the United States (USDA-
NAS, 2018). Chickpea grown in Montana alone accounted for
28.1% of U.S. production. Chickpea production in Montana
increased 59.5% from 2016 to 2017 and reached 158,000 ha
in 2018 (USDA-NAS, 2018). Exact land areas for organic
chickpea in Montana and surrounding states are not currently
available. However, with an increasing demand in domestic
Agrosyst Geosci Environ. 2020;3:e20035. wileyonlinelibrary.com/journal/agg2 1of11
2of11 MOHAMMED ET AL.
consumption, and growth in exported volume, coupled with
relatively high prices in the pulse market ($0.28–$0.48 kg−1),
farmers will likely continue to increase organic chickpea hec-
tarage in the future.
Weed management is one of the main challengers in organic
agriculture and is particularly an issue in chickpea (DeDecker,
Masiunas, Davis, & Flint, 2014; Rodriguez et al., 2009).
Chickpea tends to grow slowly in the early stage, with an
open canopy and short height, which limits competitive ability
with weeds (Whish, Sindel, Jessop, & Felton, 2002). Several
studies have found that weed competition in chickpea produc-
tion significantly reduces overall yields (AL-Thahabi, Yasin,
ABU-Irmaileh, Haddad, & Saxena, 1994; Rao & Nagamani,
2010), with up to a 97% yield loss (Paolini, Faustini, Sac-
cardo, & Crino, 2006). However, little information has been
published regarding weed management in organic chickpea,
especially in the northern Great Plains.
Weed management in organic systems often relies on inte-
gration of multiple strategies (Liebman & Davis, 2009; Mason
& Spaner, 2006; Rao & Nagamani, 2010), commonly known
as integrated weed management (IWM). Integrated weed
management combines different agronomic methods to con-
trol weeds including pre-emergence shallow tillage, flaming,
mowing, residue management, use of clean agricultural equip-
ment, management of field margins, cultivar selection, seed-
ing rate and date, and other mechanical and cultural meth-
ods (Tautges, Goldberger, & Burke, 2016). Many of these
tactics are aimed at giving crops a competitive advantage
by allowing a dense crop stand to emerge into an environ-
ment with reduced weed competition, and many of these weed
management strategies are crop specific (Bastiaans, Paolini,
& Baumann, 2008; Macé, Morlon, Munier-Jolain, & Quéré,
2007), thus strategies proven to be effective in one crop may
have neutral or negative effects in another crop. In addition,
response to management practices could vary due to edaphic
and weather variability.
Crop variety selection can affect weed management and
subsequently yields in organic systems. However, the rel-
ative grain yield potential and quality of varieties grown
under conventional management does not predict varietal per-
formance in organic systems (Murphy, Campbell, Lyon, &
Jones, 2007). Crop traits associated with yield potential and
improved performance under organic management include
N use efficiency, resistance or tolerance to insects and dis-
eases, and competitive ability (Lammert van Bueren & Myers,
2011). Variations among crop genotypes in competitive abil-
ity and tolerance to weeds have been demonstrated for many
crops including pea (Pisum sativum L.), chickpea, barley
(Hordeum vulgare L.), wheat (Triticum aestivum L.), and saf-
flower (Carthamus tinctorius L.) (Christensen, 1995; Jacob,
Johnson, Dyck, & Willenborg, 2016; Mason & Spaner, 2006;
Paolini et al., 2006). Studies on varietal differences in com-
petitive ability for chickpea are limited to Kabuli-type chick-
• Variety selection is critical for organic chick-
• Increased seeding rate improved chickpea seedling
stands and suppressed weeds.
• Timely applied shallow tillage could provide weed
control and improved yield.
• Flame weeding has less effect in weed control due
to regrowth of weeds.
• Integrated weed management practices improved
pea grown in Mediterranean environments (Brennan, Boyd,
Smith, & Foster, 2009; Paolini et al., 2006). Little informa-
tion is available in the northern Plains or Pacific Northwest.
Crop competitive ability can be increased by manipulating
plant densities such as increase in seeding rates and decrease
in row spacing (Liebman & Davis, 2009; Place, Reberg-
Horton, Dunphy, & Smith, 2009). Planting with increased
rates or narrower row spacing are common practices for many
crops in organic systems because plant density often cor-
relates with canopy cover (Benaragama & Shirtliffe, 2013).
Increased canopy cover tends to reduce weed seed germina-
tion and growth rates. For example, a spring wheat study con-
ducted by Weiner, Griepentrog, and Kristensen (2001) dis-
closed that the highest crop density (600 plants m−2)sown
in a uniform pattern resulted in a 60% decrease in weed
biomass but a 60% increase in yield compared to the stan-
dard seeding rate and row spacing. However, the effects of
increasing crop density on crop yields and competitive abil-
ity are asymptotic, that is, increasing up to a maximum and
then leveling off (Lemerle et al., 2004). In Canada, increasing
lentil (Lens culinaris Medik) seeding rate in organic farming
increased lentil yield, and the greatest seeding rate reduced
weed biomass by 59% compared with the control (i.e., rec-
ommended seeding rate for conventional production) (Baird,
Shirtliffe, & Walley, 2009). Under favorable growing condi-
tions, crop competition provided 72 and 99% weed control in
pea, and 33 and 70% weed control in lentil when seeding rates
were increased by 50 and 150% from the recommended seed-
ing rates, respectively (Boerboom & Young, 1995). Another
study observed that increasing seeding rate alone did not
decrease weed density or biomass in pea and lentil and this
could be due to increased intraspecific competition (Camp-
bell, 2016). The optimal plant density for chickpea in conven-
tionally managed, weed-free systems in the northern Great
Plains is 45 plants m−2(Gan et al., 2003), but the optimal
seeding rate has not been investigated for organic production.
Physical weed control techniques, such as shallow tillage
(3–5 cm depth) and flame weeding, can provide a weed-free
MOHAMMED ET AL.3of11
environment during the crop establishment phase. These prac-
tices can be used after seeding but prior to crop emergence
to reduce weed pressure when crops emerge, giving crops
time to increase in size and outcompete weeds. Shallow tillage
works by disturbing the soil surface to create a loose, dry layer
of soil that is too dry for weed growth, and the tillage will
also uproot and kill existing weed seedlings. However, shal-
low tillage could also stimulate a new flush of weed seedlings
(Roberts, 1984) and damage emerging chickpea seedlings.
Flaming, a thermal weed control technique, does not disrupt
the soil surface or bring buried weed seeds to the soil surface,
and it is less expensive than hand weeding (Knežević & Ulloa,
2007; Nemming, 1994; Wszelaki, Doohan, & Alexandrou,
2007). However, it can be cost prohibitive on larger scales
and lower value crops due to higher input costs. Flaming has a
risk to fire escape and cause unwanted fire unless proper care
is taken to minimize the risk. From our observation, flam-
ing may also reduce soil carbon sequestration through stub-
ble burning. Flame weeding is likely to be cost effective in
high value organic pulse crops. Based on recent estimates,
flaming cost was $43.17 ha−1compared to the hand weeding
and organic herbicides costs ranged from $300 to $800 ha−1
(Datta & Knezevic, 2013).
Our understanding of organic weed management in chick-
pea production is limited. A single study conducted in Italy
showed that inter-row cultivation when combined with wide
row spacing produced various levels of weed control and
yields in chickpea that were equal to or greater than those
observed with pre-emergent herbicides (Avola, Tuttobene,
Gresta, & Abbate, 2008). Weed management in organic chick-
pea production poses a substantial challenge, and in the
absence of herbicides, is dominated by cultural and physical
controls. The use of IWM practices could result in improved
weed control with increased grain yield for organic crop pro-
duction than using a single practice. Therefore, in this study,
a suite of IWM strategies were evaluated to better understand
the usefulness of each strategy and their potential for inte-
gration in organic chickpea production in the northern Great
Plains of the United States. These IWM strategies include cul-
tural (variety selection and seeding rate) and physical (shal-
low tillage, flaming) weed controls. The objective of this
study was to determine the effects of these IWM strategies on
chickpea stand density, weed biomass, and grain yield under
organic production at two very distinct environments.
2MATERIALS AND METHODS
2.1 Site description
This experiment was conducted in Montana, at the Western
Agricultural Research Center in Corvallis and at the Eastern
Agricultural Research Center in Sidney. The study was con-
ducted at Corvallis in 2016 and 2017, both following flaxseed
(Linum usitatissimum L.). Two trials were also conducted in
2017 at Sidney; one trial was planted into a field following a
2016 spring wheat crop and the second trial was planted into
a field that was fallowed in 2016. The Corvallis (46◦18’ N,
–114◦6’ W) site is located at 1096 m above sea level, and
the Sidney (47◦46’ N, –104◦14’ W) site is located at 670 m
above sea level. The soil at Corvallis is a Burnt Fork loam
over coarse alluvial (coarse-loamy, mixed, superactive, frigid
Typic Haplustolls). The soil at Sidney is a deep, well drained,
nearly level in a Williams loam (fine-loamy, mixed, superac-
tive, frigid, Typic Argiustolls). Growing season monthly aver-
age air temperature and total rainfall are presented in Table 1.
Average air temperatures follow the long-term trends at both
sites. The precipitation for Corvallis was similar between 2 yr
but slightly below the long-term mean. The 2017 in-season
(April–September) total precipitation at Sidney was 45% less
than the long-term average. As shown in Table 1, year-to-year
seasonal variation in precipitation was substantial not only
between locations but also within a location. Generally, the
mean temperature and precipitation during the growing sea-
son at Corvallis was slightly cooler and drier than Sidney.
However, the experiment at Corvallis was conducted under
supplemental irrigation and received 380 and 360 mm of irri-
gation in 2016 and in 2017, respectively, while the experiment
at the Sidney site was under rainfed conditions and 2017 pre-
cipitation was well below the long-term average.
2.2 Experimental design, treatments, and
The experiment was conducted in a split-plot design with
four replicates. The main plot was pre-emergent weed control
methods (non-weeded control, shallow tillage, and flaming).
The subplot was the factorial combination of two chickpea
cultivars (cultivars Black and CDC Orion) and two seeding
rates [(1×=standard or recommended seeding rate of 43 live
seeds per m2, (Gan et al., 2003) and (1.5×=50% increased
seeding rate from the standard)]. CDC Orion seeds are nearly
twice the mass of Black chickpea, thus the 1×seeding rate
was 278 kg ha−1compared to 150 kg ha−1for the Black chick-
pea. Black chickpea and CDC Orion are commonly grown on
organic farms in the region. CDC Orion was released in 2010
by the University of Saskatchewan and is well suited to the
Canadian prairies that are much like the northern Great Plains
(Taran, Bandara, Warkentin, Banniza, & Vandenberg, 2011).
Black chickpea is a small kabuli-type with a black seed coat
and is likely a landrace from Central Asia.
The main plots were 1.5 by 24.4 m at Sidney and
1.2 by 24.4 m at Corvallis. The subplot sizes were 1.5 by 6.1 m
at Sidney and 1.2 by 6.1 m at Corvallis. Trials were planted
on 1 May 2016 and 26 Apr. 2017 at Corvallis, and on 28 Apr.
4of11 MOHAMMED ET AL.
TABLE 1 Monthly mean air temperature and monthly total precipitation at Corvallis and Sidney, MT, in 2016 and 2017 during the crop
growing season (April–September) and long-term means (LTM)
Average air temperature Total precipitation
Corvallis Sidney Corvallis Sidney
Months 2016 2017 LTM 2016 2017 LTM 2016 2017 LTM 2016 2017 LTM
April 7.9 6.7 6.7 7.2 6.7 8.3 17 21 28 89 10 27
May 11.0 7.9 11.7 13.9 13.9 14.4 30 31 32 40 19 52
June 16.4 15.3 16.1 19.4 18.9 18.9 10 56 50 41 23 71
July 23.1 20.8 21.7 21.6 25.0 22.2 42 1 15 58 3 64
August 17.5 19.4 20.0 21.6 20.0 21.6 16 318 20 45 29
September 18.4 18.8 14.4 15.5 14.4 15.5 24 18 25 101 50 32
Mean/total 15.7 14.8 15.1 16.5 16.5 16.8 139 130 168 349 150 275
2017 at Sidney. Chickpea was seeded at a depth of 5 cm using
a small plot drill. The space between rows was 25 cm with
six rows per plot at Sidney, and the plot contained seven rows
with 16.5 cm space between rows at Corvallis. The seeds were
inoculated with peat-based commercial Rhizobium N-Charge
(Verdesian Life Sciences).
Pre-emergent weed control treatments (flaming and shal-
low tillage) were applied between 9 and 10 d after seeding
chickpea, and before chickpea emerged from the soil surface
(chickpea emergence is expected to occur roughly 15 d after
planting at these sites). The Red Dragon Row Crop Flamer
(Flame Engineering, Inc.) consists of a propane tank and six
torches attached to a boom behind a tractor at 25 cm apart.
Propane gas was set at 50 PSI and the torches were set at
60 cm above the ground level to ensure the flame was able
to reach the ground level and cover it uniformly. Flaming was
done when the wind was relatively calm (below 8 mph) to
minimize fire risk. The tractor travel speed was set at around
−1while flaming. Shallow tillage used a 2-m wide
shank cultivator with duck feet shovels at 25-cm spacing.
The cultivator is attached to the three-points behind a trac-
tor and tillage was performed at about 3–5-cm deep in the
Chickpea plant density was counted 2–3 wk after crop
emergence. Weed biomass samples (consisted of both grasses
and broadleaf weeds) were collected from the center of each
plot during chickpea flowering from a single 1 m2quadrat in
Sidney and a 0.25 m2quadrat in Corvallis. Weed biomass was
dried at 65 ◦C until a constant weight was achieved. Chickpea
was harvested at maturity (seed moisture content <18%) with
a plot combine harvester (Wintersteiger) on 17 Aug. 2016
and 27 Aug. 2017 at Corvallis, and on 23 Aug. 2017 at
Sidney. Chickpea seeds were cleaned of weed seed and crop
residues. Grain moisture content was measured with a grain
moisture tester (GAC 2100-Agri Grain Analysis Computer,
Dickey-John) and grain yield was adjusted to 13% moisture
concentration before statistical analysis.
2.3 Statistical analysis
Due to the significant differences in weather conditions, row
spacing, and irrigation, data from Corvallis and Sidney sites
were analyzed separately using ANOVA in R (R Core Team,
2014) with the Agricolae package. Blocks within trial were
modeled as random effects. Year (YR), weed control methods
(WC), varieties (VA), seeding rates (SR), precursor crop (PC),
and interactions of these factors with each other were consid-
ered as fixed effects. Prior to analysis, yield data and weed
biomass data from Sidney were log transformed and crop den-
sity data were square root transformed to meet assumptions
of normality of data distribution and homogeneity of vari-
ance. No data transform was needed for Corvallis site. When
ANOVA showed significant effects (P≤.05), least signif-
icant differences (LSD) were calculated to differentiate the
means of the treatment effects using the Agricolae package
3RESULTS AND DISCUSSION
3.1 Chickpea crop densities
At Corvallis, chickpea crop density was affected by year,
variety, and seeding rate (Table 2). Increasing seeding rate
increased crop density, but the magnitude of increase varied
between years. In 2016, increasing the seeding rate by 50%
increased stand density from 32 to 45 plants m−2. But in 2017,
increasing the seeding rate increased the crop density from
only 20–25 plants m−2and mean crop density was generally
lower in 2017 than in 2016. The lower stands in 2017 could be
due to an earlier seeding date and cooler soil temperatures that
possibly resulted in a greater seedling mortality than in 2016.
There were moderate (.05 <P<.1) interactive effects of VA ×
SR on chickpea density at this site (Table 2); a 50% seeding
rate increase from the normal rate resulted in increased Black
MOHAMMED ET AL.5of11
TABLE 2 Analysis of variance table showing the effects of treatments on chickpea grain yield, stand density, and weed biomass in
Stand density Weed biomass Grain yield
Source of variation FPvalue FPvalue FPvalue
Weed control (WC) 1.3 ns 23.3 ** 3.5 msa
Year (YR) 36.2 ** 2.8 *1.9 ns
WC ×YR 1.6 ns 0.5 ns 8.3 *
Var i e t y (VA) 17.1 ** 5.3 *18.9 **
Seeding rate (SR) 24.2 ** 0.5 ns 8 **
WC ×VA 0.8 ns 0.4 ns 0.6 ns
WC ×SR 2.3 ns 3.2 *2ns
VA ×SR 3.4 ms <0.1 ns <0.1 ns
VA ×YR 2.2 ns 0.7 ns 0.6 ns
SR ×YR 5.2 *0.5 ns <0.1 ns
WC ×VA ×SR 0.9 ns 0.5 ns 0.4 ns
WC ×VA ×YR 0.5 ns <0.1 ns 0.8 ns
WC ×SR ×YR 0.8 ns 4.3 *0.9 ns
VA ×SR ×YR 1.2 ns 0.1 ns 0.4 ns
WC ×VA ×SR ×YR 0.2 ns 0.4 ns 1.2 ns
Note. ns, not significant, P>.1.
aMS =0.1 >P>.05.
chickpea crop density from 28 to 41 plants m−2, but increasing
the seeding rate 50% of CDC Orion only increased stand den-
sity from 24 to 29 plants m−2(Figure 1). Therefore, increasing
seeding rate resulted in a greater stand density for the Black
chickpea than CDC Orion and Black chickpea crop density
was greater than CDC Orion, especially at the higher seeding
rate (Figure 1).
The chickpea emergence rates were low and variable at
Sidney site, but significant variety and seeding rate effects
on stand density were observed (Table 3). A 50% increase
in seeding rate generally increased the stand densities, but
the magnitude of the increase in stand densities varied in
different experiment sites (PC) and treatments. The previous
crop (experimental site) effect on stand density indicates that
seed bed condition can affect the seed and seedling mortality.
The two chickpea varieties responded differently; CDC Orion
hand a greater stand density in the site following fallow than
in the site following wheat, but the Black chickpea stand den-
sity did not differ between the two sites in Sidney (Figure 2).
This indicates that Black chickpea has a greater resilience and
wider adaptation to various sites and cropping history than
CDC Orion. Under the same seeding rate treatment, Black
chickpea showed better crop density than CDC Orion. There-
fore, it is suggested to identify the trait in the Black chickpea
variety and use it for breeding purpose to improve chickpea
production particularly for organic farming.
Overall, chickpea densities were often well below targeted
densities of 43 and 65 plants m−2for the normal and 50%
increased seeding rate treatments, respectively. Stand densi-
ties of CDC Orion were lower and more variable than Black
chickpea in all trials. CDC Orion stands ranged from 17 to
38% of seeded rates at Sidney and 32–67% of seeded rates at
Corvallis. This differences in stand density between the two
varieties, from our observation, was due to greater seedling
mortality in CDC Orion compared to Black chickpea. This
emphasizes the importance of selecting a suitable variety for
establishing an adequate crop stand for organic chickpea pro-
duction. Without seed treatments, chickpea varieties such as
CDC Orion are vulnerable to insects such as wire worms
(click beetle larva, Elateridae) and disease such as damping-
off caused by Pythium and Fusarium spp. (Dubey, Suresh,
& Singh, 2007; Kaiser & Hannan, 1983; Wise, Henson, &
Bradley, 2009). The increased crop density caused by an
increased seeding rate generally observed in this study showed
that recommended seeding rates may need to be increased for
organic chickpea production.
3.2 Weed biomass
At Corvallis, weed biomass was affected by variety, seeding
rate, and weed control treatments (Table 2). The three-way
6of11 MOHAMMED ET AL.
FIGURE 1Interactive effects of chickpea varieties and seeding rates on chickpea stand density (number of plants m−2) at Corvallis, MT.
Means followed by different letters at the same seeding rate were different at P=.05
TABLE 3 Analysis of variance table showing effects of treatments on chickpea grain yield, stand density, and weed biomass in Sidney, MT,
Stand density Weed biomass Grain yield
Source of variation FPvalue FPvalue FPvalue
Previous crop (PC) 1.4 ns 28.6 ** 3.8 msa
Weed control (WC) 1.1 ns 9.3 ** 0.2 ns
WC ×PC 3.1 ms 0.4 ns 1.9 ns
Var i e t y (VA) 473.5 ** 49.7 ** 1056 **
Seeding rate (SR) 27.8 ** 6.6 *9.4 **
WC ×VA 0.2 ns 1.2 ns 1.2 ns
WC ×SR 0.3 ns 3.3 *0.5 ns
VA ×SR 1.5 ns 5.9 *1ns
VA ×PC 53.8 ** 1.8 ns 43.8 **
SR ×PC 0.1 ns 0ns 2.3 ns
WC ×VA ×SR 0.4 ns 1.4 ns 2.4 ms
WC ×VA ×PC 0.9 ns 1.5 ns 5.5 *
WC ×SR ×PC 3.3 *0.2 ns 0.2 ns
VA ×SR ×PC 0.2 ns 1.8 ns 0.5 ns
WC ×VA ×SR ×PC 6.3 ** 0.1 ns 1.4 ns
Note. ns, not significant, P>.1.
ams =0.1 >P>.05.
MOHAMMED ET AL.7of11
FIGURE 2Interactive effects of previous crop (experimental site) and chickpea variety on chickpea stand density (number of plants m−2)at
Sidney, MT. Means followed by different letters under the same previous crop were different at P=.05
interactions (WC ×SR ×YR) showed that shallow tillage
decreased weed biomass in 2016 at the greater seeding
rate compared to other treatments, but in 2017 it decreased
weed biomass at both the normal and increased seeding
rates (Table 4). The combination of shallow tillage and an
increased seeding rate decreased weed biomass by 51% in
2016 and 38% in 2017 relative to the control (Table 5).
However, flame-weeding increased weed biomass in 2016 at
the greater seeding rate and no difference was observed in
2017 (Table 4). This indicated that the flame weeding is not
effective at this site and the cause of the increase in weed
biomass in flame-weeded treatment is unknown and further
research is needed to understand the reason. Weed biomass
was greater in CDC Orion (182.8 g m−2) than in Black
chickpea (155.4 g m−2). This result agreed with the greater
stand density described above in Black chickpea indicating
its increased competitive ability compared to CDC Orion.
Mean weed biomass in 2016 was greater than in 2017.
At Sidney, weed biomass was also affected by variety, seed-
ing rate, and weed control treatments (Table 3). The inter-
actions of WC ×SR showed that the shallow tillage treat-
ment was more effective in reducing weed biomass at the
higher seeding rate. Shallow tillage at the increased seeding
rate decreased weed biomass by 60%, but only reduced weed
biomass by 24% in the normal seeding rate (Table 5). The
VA ×SR interactions showed that increasing seeding rate
reduced weed biomass only in the Black chickpea variety from
30 to 19 g m−2, and increasing seeding rate had no effect on
weed biomass in CDC Orion, which is consistent with the low
emergence and less effect of seeding rate on crop densities in
this variety. Weed biomass was greater for CDC Orion than
Black chickpea (64 g m−2vs. 24 g m−2). In large part, this
can be explained by differences in stand densities between the
The results of the treatment effects on weed biomass sup-
port the idea that when stand densities are sufficiently high,
chickpea can suppress weeds. The Black chickpea that had
greater and more consistent stand densities, also had consis-
tently less weed biomass than CDC Orion.
3.3 Chickpea grain yield
At Corvallis, chickpea grain yields were significantly affected
by variety and seeding rate, but the effects of weed con-
trol methods varied between 2 yr (Table 2). The two-way
(WC ×YR) interactions showed that there was a significant
increase in chickpea grain yields with flamed weeding and
shallow tillage compared to the non-weeded control in 2016
but there were no differences observed in 2017 (Table 6). The
shallow tillage increased seed yield by 150% and flame weed-
ing increased seed yield by 68% compared to the non-weeded
control in 2016 (Table 6).
Black chickpea consistently had greater yield than CDC
Orion and increasing seeding rates produced greater chickpea
grain yield. Average over years and treatments, grain yield of
8of11 MOHAMMED ET AL.
TABLE 4 Interactive effects of seeding rate and weed control
methods on weed biomass (g m−2) in Corvallis, MT
Year Weed control Standard 50% more
Flame weeded 200ab 256a
Tillage 196ab 91c
Control 162ab 174a
Flame weeded 186a 177a
Tillage 113b 108b
aMeans followed by different letters in the same column were different at P=.05.
Black chickpea was 1096 kg ha−1, which was 332 kg ha−1
greater than CDC Orion. The difference in yields between
varieties was consistent across years and treatments. Increas-
ing seeding rate by 50% increased chickpea grain yields from
823 kg ha−1at the standard seed rate to 1038 kg ha−1.
At the Sidney site, chickpea grain yields were significantly
affected by variety and seeding rate but weed control meth-
ods had little effect on grain yield at this site (Table 3). There
was a severe drought in the summer of 2017 (Table 1), and
the low plant density in combination with drought resulted in
a very low chickpea yield. The VA ×PC interactions showed
that Black chickpea yielded greater than CDC Orion at both
sites (following fallow and wheat), but the magnitude of yield
increase was different at the two fields. While Black chick-
pea yielded about 530 kg ha−1at the field following fal-
low and 290 kg ha−1following wheat, CDC Orion chick-
pea was almost failed (yielded <100 kg ha−1). Increasing the
seeding rate by 50% consistently increased yields by 15%
from 380 to 439 kg ha−1, particularly for the Black chick-
pea when averaged over trials. Physical weed control prac-
tices did not have consistent effects on yields in the trials in
Sidney (Table 7).
Above results indicate that environments and soil condi-
tions can significantly affect chickpea emergence and yields.
Some practices, such as shallow tillage and flaming, could
be effective at one site or 1 yr, but a combination of practices
may provide a better solution in multiple sites and years,
such as variety selection and seeding rate increase. Given
the variations in weed seeds in the soil bank and weather
conditions at various organic chickpea production sites,
combining multiple tactics may provide better assurance.
Consistent benefits have been demonstrated in this study
when using better varieties exhibiting consistently good
emergence under organic management (e.g., Black chickpea),
together with higher seeding rates. Also, when combining
the shallow tillage with increased seeding rate consistently
reduced weed biomass across all experimental sites. Inte-
grated practices that reduce weed biomass should also reduce
TABLE 5 Interactive effects of seeding rates and weed control
methods on weed biomass (g m−2) in Sidney, MT, in 2017
Weed control Standard 50% more
Flame-weeded 41a 32ab
Tilled 44a 25b
aMeans followed by different letters in the same column were different at P=.05.
weed seed production and weed pressure in subsequent
years (Liebman & Davis, 2009) thus could provide a long-
The efficacy of physical weed control practices may be
affected by the crop stand density and row spacing. The shal-
low tillage or flaming practices are designed to create a tem-
porary window of reduced weed pressure in which crops
can rapidly grow, increasing competitive ability and form-
ing a closed canopy that creates less favorable conditions for
weed seed germination. In this study, Sidney trials were con-
ducted in rain-fed or dryland conditions (that also had greater
seedling mortality) and used a wider row spacing (25 cm) than
the Corvallis trials (16.5 cm). With wider rows and reduced
chickpea emergence rates, the chickpea in the Sidney trials
may not have been able to capitalize on the reduced weed pres-
sure created by pre-emergent weed control treatments, which
explains why shallow tillage did not improve yields in trials
conducted at Sidney but did in one trial conducted in Corval-
lis. We also noticed that there were high populations of grass
weeds at the Sidney site, which made the flaming less effec-
tive, because grasses have a growing point under the soil sur-
face, the flaming is less effective if the growing point is still
intact after flaming.
Increasing seeding rate consistently increased chickpea
yields across trials. The advantage of this practice depends
upon the return on investment (e.g., does increased yields sur-
pass the increased seed costs). For example, increasing the
seed rate by 50% requires an additional 140 kg ha−1of seed
in the CDC Orion variety and 75 kg ha−1of seed in the Black
chickpea variety. In low-yielding environments, this invest-
ment of additional seed may not be recovered. In contrast,
in Corvallis, increasing seeding rates increased yields in both
varieties by 215 kg ha−1, indicating that both investments in
higher seed rates provided a yield increase that was greater
than the additional cost of seed at planting, but there were
greater returns (2.9×) for the Black chickpea variety compared
to CDC Orion (1.5×).
The large and consistent differences in stand density, yield,
and weed biomass between varieties demonstrates the impor-
tance of varietal choice to organic management, which should
be given attention for future investigation. The varietal differ-
ences in emergence (i.e., stand density) in this study appeared
to be due to resistance to soilborne disease and pests. On a
MOHAMMED ET AL.9of11
TABLE 6 Effects of weed control methods on chickpea grain
yields (kg ha−1) in Corvallis, MT, in 2016 and 2017
Weed control 2016 2017
Flame weeded 847b 978a
Tillage 1241a 929a
aMeans followed by different letters in the same column were different at P=.05.
TABLE 7 Interactive effects of weed control methods and
previous year crop (experimental site) on grain yield (kg ha−1)of
BLACK chickpea in Sidney, MT
Weed control Fallow Wheat
Flame 528ab 287a
Tillage 448b 306a
aMeans followed by different letters in the same column were different at P=.05.
population level, dense crop stands, which are produced by
high seed and seedling survival rates, are directly linked to
the effective suppression of weed species (Liebman & Davis,
2009). Low CDC Orion emergence was likely a driving factor
in yield reductions and higher weed biomass levels than those
found in Black chickpea plots. While we did not directly mea-
sure the causes of seed and seedling mortality, common issues
in the region are damping-off and wire worm feeding on crop
seeds. Previous research has shown that Kabuli chickpea (like
CDC Orion) have thinner seed coats and are more suscepti-
ble to damping-off than desi-type chickpea (Kaiser & Han-
nan, 1983). In conventional production, kabuli varieties are
commonly treated with both fungicide and insecticide, there-
fore, these varieties perform well under conventional produc-
tion. In addition, the genes conferring resistance to damping-
off pathogens are closely linked with the genes associated
with anthocyanin production in seed coat and the pink–purple
flower color that the Black variety exhibits (Kumar, Kaiser,
& Hannan, 1991). Seed coat tannin content of common bean
(Phaseolus vulgaris L) also has been associated with reduced
damage due to plant feeding insects as tannins act to reduced
nutritional quality and deter feeding (Islam, Rengifo, Red-
den, Basford, & Beebe, 2003). Identification of crop traits
that suite better under organic farming in terms of compe-
tition with weeds and resistance to disease should be given
research priority to address the major challenges of organic
Black chickpea had a greater stand density and produced a
greater grain yield than CDC Orion. Increasing seeding rate
generally resulted in reduced weed biomass with an increased
grain yield. However, greater seeding rates need to be con-
sidered in future studies to determine the most economical
rate. Precaution must be taken when using pre-emergent shal-
low tillage and flaming to control weeds as it requires a close
watch of seed germination status to avoid emerging chick-
pea seedling damage. Integrated use of a disease resistant
chickpea variety together with increased seeding rate and pre-
emergence weed control practices can increase organic chick-
pea grain yields. Selection of varieties revealed substantial
differences, thus further research is needed in developing vari-
eties that are suitable for organic production.
We are grateful for the Montana State University Exper-
iment Station and Montana Specialty Crop Block Grant
(no. 16SC0005003) for financing this study and the anony-
mous reviewers for their constructive inputs.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
Chengci Chen https://orcid.org/0000-0002-7758-082X
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How to cite this article: Mohammed YA, Miller Z,
Hubbel K, Chen C. Variety and weed management
effects on organic chickpea stand establishment and
seed yield. Agrosyst Geosci Environ. 2020;3:e20035.