Introduction
Weeds are one of the major crops pests and cause serious
losses in grain yield of field crops (Li et
al. 2018). Therefore, effective weed management is integral component of
crop husbandry packages (Gnanavel and Natarajan 2014; Take–tsaba et al. 2018). Inclusion of some crops, which usually have different
weed floras, can avoid vigorous propagation of some aggressive weeds which are
well adapted and competitive in specific crop types (Andreasen and Skovgaard
2009; Satrapová et al. 2013; Kumawat et al. 2017). Suitable crop
rotation and use of cover crops influenced the number of weed species and their
density including Elytrigia repens (Błażewicz–Woźniak et al. 2016; Harasim et al.
2017). The rhizomatous growth of E.
repens L. (couch grass) causes serious problems for farmers in many crops.
In Slovakia, E. repens belongs to the
most troublesome weeds in winter wheat and spring barley (Týr and Vereš 2011).
Similarly, in Finland E. repens was
found to be the most frequent perennial weed species in organic spring cereals
(Salonen et al. 2013). Repeated
mowing, during autumn, can help reduce couch grass rhizome infestation. A
low-yielding cover crop (30–60 g m-2 in October) may only reduce the
shoot biomass produced during autumn with no effect on the rhizome biomass. The
rhizome biomass reflects the accumulated biomass during the whole season and
during the previous seasons as well. However, the shoot biomass adjusts quickly
to the prevailing conditions (Ringselle et al. 2015). Physical weed control methods are less effective than
the use of chemical herbicides. Therefore, weed control often requires a
support from cultural and preventive measures for satisfactory weed management
(Melander et al. 2012; Rasmussen et al. 2014). To control the competitive
and troublesome perennial weeds, like E.
repens, there is often a choice between physical weed control option and intensive use of non-selective
herbicides. In the conventional agriculture, application of glyphosate is the
most common method to control couch grass (Soukup et al. 2008; Aronsson et al.
2015). Information on influence of cultivation practices, weed management
options and crops sequences on the dynamics of E. repens in cereal-based intensive cropping systems in agroclimatic conditions of Central European countries
is lacking. Therefore, this study was conducted to evaluate the common effect
of main cultivation practices, weed management measures and crops sequences on E. repens population changes under
intensive cropping system with high share of cereals growing in large scale
fields.
Materials and Methods
Experimental site
Field investigations was conducted during 2007–2014 at the
Experimental farm of the Slovak
Agricultural University in Nitra (48°22' 0" N, 18°12' 0" E) in South-Western Slovakia. Altitude of fields varied from 180 to
260 m above sea level. The weather condition of decisive period of crop
management is given in the Table 1.
Experimental details
The six large scale arable fields located on an
experimental farm on sand loamy Haplic Luvisol were selected according the
share of cereals. The average area of surveyed field was 55.7 ha with field
size ranging from 24 ha to 131 ha. For direct control of E. repens, the total herbicides Cosmic, Glyphogan 480 SL and Kaput
with 36% content of glyphosate as the
isopropylamine salt were applied between two crops periods in dose of
1080 g ha-1, and propoxycarbazone sodium (PKS) herbicide Attribut SG
70 in dose of 60 g ha-1 was also applied. Herbicide control of E. repens was used if the actual E. repens density began to reach a 5–6
shoots m-2, with one exception on the field 1 in 2009, where the PKS
was applied to regulate Avena fatua L. The spring application of glyphosate and PKS (field
4 – 2011 and field 5 – 2008) was applied in second decade of April. The summer
application of glyphosate was made between two crops periods in August–September.
The second glyphosate application was made on 7 November in fields 3 and 5.
Application of herbicides is indicated according timing by arrow in Fig. 1.
Nutrients were added according to projected yield and soil nutrient status25.
The average yield of cereals was 4.61 t ha–1, oilseed rape 2.55 t ha–1,
grain maize 6.90 t ha–1 and silage maize 14.9 t ha–1 dry
matter of biomass in 2010–2014. Catch crops were not included in the crop
rotation. No direct mechanical weed control in canopy of row crops was used. Immediately after harvest of
cereals (winter wheat, winter rye, spring barley) and winter oilseed rape, one
summer stubble disc cultivation made by disc cultivator was followed by medium
deep mouldboard ploughing (0.2 m) in autumn. After harvest of sunflower and
grain maize, disc harrow with rollers was followed with deep autumn mouldboard
ploughing (0.26–0.28 m), except field 3 in 2009 when shallow mouldboard
ploughing was used (0.15–0.18 m). When harvesting maize for silage, the disc
harrowing was omitted. In spring barley – winter rape sequences, only stubble
disc cultivation was applied.
Observations
There were six experimental fields, all with different
rotations (Fig. 1). In each field, permanently located experimental area of
3600 m2 (60 m × 60 m) subjected to common evaluated field management
practices were surveyed, positioned at least 50 m from boundaries to avoid
field edge effects following Fried et al.
(2008). Each of the experimental treatments was replicated four time. Four 1 m2
quadrants (1 m × 1 m) were placed in each replication according random
selection methods with distance of 10 m between samples square as described by
Colbach et al. (2000). Density of E. repens was recorded during spring before seed bed preparation
and spring term of herbicide application (glyphosate or PKS).
Statistical analysis
Prior to statistical analysis, the data of weed density
were checked for normal distribution by PP plots and Shapiro-Wilk test. Fields
with different crop rotation pattern associated with common effect of crop
management and year (effect of crop management and agro-climatic conditions)
were taken as experimental factors. The overall two-way analysis of variance
(ANOVA) and one-way ANOVA for main effects analysis of particular crop rotation
sequences, separately for each field, followed by Fisher post-hoc test at P = 0.05 level and Bartlett's,
Cochran's, and Hartley's tests for the equality of variances were made using
the Statistica 10 software (StatSoft Inc., Tulsa, U.S.A.). Shoot density
response was described by Microsoft Excel 2016 graphs supplemented by
statistical differences.
Results
The shoots density
response
Two–way ANOVA showed a significant effect of crop
rotation sequences and the common effect of weed and crop management practices
in year conditions (source of variation expressed as year factor) on the
population dynamics of E. repens
density (Table 2). Two–way of interaction between two sources of variation:
field (different crop rotation) and year (effect of previous crop management
and agroclimatic conditions) was also statistically significant and indicates
substantially higher influence than single effects of both evaluated factors.
Different crop sequences and crop management of growing crops significantly
influenced the temporal dynamics of couch grass population density (Table 3) in
all evaluated fields except field 1 with very low E. repens density and herbicide control of Avena fatua by PKS.
Herbicide
application
Table 1: Mean air temperature (°C) and total precipitation (mm) per month at the
experimental site during 2007–2014 and 1961–1990
Month /Year |
2007 |
2008 |
2009 |
2010 |
2011 |
2012 |
2013 |
2014 |
Long-term period 1961–1990 |
|||||||||
Temp (°C) |
Rainfall (mm) |
Temp (°C) |
Rainfall (mm) |
Temp (°C) |
Rainfall (mm) |
Temp (°C) |
Rainfall (mm) |
Temp (°C) |
Rainfall (mm) |
Temp (°C) |
Rainfall (mm) |
Temp (°C) |
Rainfall (mm) |
Temp (°C) |
Rainfall (mm) |
Temp (°C) |
Rainfall (mm) |
|
March |
7.5 |
58 |
5.5 |
63 |
5.3 |
52 |
5.2 |
21 |
6.2 |
9 |
7.6 |
5 |
2.7 |
93 |
9.3 |
15 |
5 |
30 |
April |
12.2 |
0 |
11.0 |
36 |
14.3 |
20 |
10.5 |
84 |
12 |
24 |
11.3 |
40 |
11.7 |
23 |
12.4 |
49 |
10.4 |
39 |
Aug. |
21.2 |
79 |
20.5 |
10 |
20.8 |
26 |
18.9 |
54 |
21.3 |
62 |
21.7 |
16 |
20.9 |
70 |
18.9 |
56 |
19.3 |
61 |
Sept. |
13.7 |
91 |
15.4 |
52 |
14.7 |
78 |
14 |
70 |
18.5 |
12 |
17.2 |
31 |
13.6 |
61 |
16.8 |
122 |
15.6 |
40 |
(The
Meteorological Yearbook, 2007–2014, 1961–1990)
Fig. 1: Year to year changes in Elytrigia repens infestation
Shaded arrows indicate when glyphosate was
applied between two crops, blank arrows indicate when propoxycarbazone sodium
was top-dressed in winter wheat. Different letters indicate significant
differences of E. repens density at P = 0.05 level in spring term
Field 1 without post-hoc test. M–S: silage
maize, M–G: grain maize, SU: sunflower, WW: winter wheat, WR: winter rye, W–OR:
winter oilseed rape, SB: spring barley, P: pumpkin grown on bare ground
The herbicides application varies considerably from 2–5
over the evaluated period. PKS was applied in canopy of winter wheat and
substantially reduced population density of E.
repens with a positive effect for the next crop mainly in the fields 5 and
6 (Fig. 1). The number of herbicide applications was influenced not only by the
overall effectiveness of weed management (cultural, preventive methods), but
the efficacy of the herbicides with glyphosate was related to the course of the
weather. The lack of precipitation in August 2008 (extra ordinary below normal)
and August 2009 (very below normal) associated with a smaller leaf area of E. repens has
reduced application efficiency and subsequent herbicide application in
November (field 3 and field 5) or an application for two consecutive years
(field 3 and 4) was necessary. For this reason, the frequency of herbicide
applications cannot be a decisive criterion for assessing the overall effectiveness
of weed control measures.
Crop rotation
Table 2: Analysis of
variance of Elytrigia repens density
at experimental site during 2007–2014
Source of variation |
Sum of squares |
d.f. |
Mean squares |
F – ratio |
P – value |
Field–crop rotation |
743.214 |
5 |
148.643 |
52.224 |
0.000 |
Year |
46.870 |
7 |
6.696 |
2.352 |
0.029 |
Replication |
5.724 |
3 |
1.908 |
0.670 |
0.572 |
Field × Year |
1154.911 |
35 |
32.997 |
11.593 |
0.000 |
Residual |
298.859 |
105 |
2.846 |
|
|
d.f. = Degree of
freedom
Table 3: Analysis of
variance of Elytrigia repens density
grown in different crop rotation sequences at six experimental fields during
2007–2014
Source – Year |
Sum of squares |
d.f. |
Mean squares |
F – ratio |
P – value |
Field 1 |
18.875 |
7 |
2.696 |
1.457 |
0.236 |
Field 2 |
80.500 |
7 |
11.500 |
5.111 |
0.002 |
Field 3 |
500.469 |
7 |
71.496 |
15.028 |
0.000 |
Field 4 |
126.500 |
7 |
18.071 |
11.677 |
0.000 |
Field 5 |
397.969 |
7 |
56.853 |
16.154 |
0.000 |
Field 6 |
77.4688 |
7 |
11.067 |
5.481 |
0.001 |
d.f. = Degree of
freedom; All experimental fields were conducted during all period of
investigation 2007–2014, totally 8 years;
Response of couch grass proliferation on common effect
of preceding crops and management practices is describe in Fig. 1. These fields
reflect the intensive crop management practices broadly employed in large scale
farm in Slovakia. The share of cereals ranged from 50 % (field 1, 2, 3 and 6),
over 62.5 % (field 5) up to 75 % (field 4) of which 60 % was winter wheat and
the second cereals was spring barley, except field 4 where winter rye was
growing in 2009. Winter rye with good supressing ability (Askegaard 2017) was
grown in a sequence of 3 winter cereals which finally lead to the increase of E. repens, even though glyphosate was
applied. Two crops period of spring barley and sunflower substantially change
population dynamics of E. repens.
Proliferation of E. repens
significantly increased after the successive cultivation of spring barley –
sunflower (field 5, 2007–2009) or sunflower – spring barley sequences (field 4,
2012–2014) respectively. Maize was grown mainly for silage, except for field 6
where maize was grown for grain in 2008 and 2014.
Discussion
The population dynamics of E. repens influenced by the common effect of crop rotation
sequences, weed and crop management practices in particular year conditions is
demonstrated separately for all evaluated fields (Fig. 1). According to the
Bond and Grundy (2001) classification, preventive
measures (crop rotation, primary tillage) cultural methods (crop competition)
and direct control methods (stubble cultivation and herbicides application)
were taken into consideration. The purpose of this study was to depict the
factors influencing E. repens
population changes over time especially those important for out-breaks of E. repens infestation. Effect of soil
tillage adopted, in respective crops, is an important part of weed management
strategy. For managing
the troublesome perennial weeds, like E. repens, in the northern and
southern temperate zones, the growers need to make a choice between autumn
tillage and intensive use of non-selective herbicides. The control of E.
repens relies on intensive tillage, often in the form of repeated
post-harvest stubble cultivation (Rasmussen et
al. 2014). In Slovakia, E. repens
was traditionally controlled by cereals stubble cultivation by shallow
mouldboard ploughing with skim-coulter, with the best results of perennial weed
control, because the rhizomes plough into a deeper layer were not capable of further reproduction (Mikulka 2014). Unfortunately,
mainly for economic reasons, stubble cultivation by shallow mouldboard
ploughing has been replaced by disc stubble cultivation which tends to decrease
the E. repens control. Rhizomes of E. repens are mainly located within the
plough layer of 0–0.2 m soil depth (Melander et al. 2013). Disc-based stubble cultivators only partly uproot
below-ground propagules; with the fragmentation of rhizomes and insufficient
exhaustion of the fragments promoted E.
repens infestation (Legere 1999). On the other side intensive mouldboard
ploughing gives a significant control of perennial weeds and effectiveness
increases with ploughing depth (Legere 1999). Mouldboard ploughing was the most
frequent basic soil tillage methods applied in our study fields except spring
barley – winter oilseed rape sequences when stubble disc cultivation was used,
only. Stubble disc cultivation followed by mouldboard ploughing in autumn was
broadly adopted in all evaluated fields which contributed to more efficient
weed management. According to a recent study of Brandsćter et al. (2017) which compared stubble disc-harrowing
cultivation period followed by mouldboard ploughing, for E. repens control, the important factor was whether stubble
cultivation was carried out or not. When assessing the suppressing ability of cereals and winter oilseed rape,
the benefit of stubble cultivation followed by moldboard ploughing should be
considered. Herbicide application to control E. repens started from second year of experiment when the
previously applied preventive and cultural measures were insufficiently
effective. When evaluating couch grass proliferation, we must stress the
importance of preceding crops and their management (Rasmussen et al. 2014). The competitive ability of
crops has to be associated with soil cultivation and adopted weed management
practices of growing crops (Yadav et al.
2017). Diverse crop rotations,
with inclusion of allelopathic crops in rotation, are key element for weed
control in low-input organic production systems (Mandi et al. 2017). Weed infestation
level could be lowered if maize is grown with increased stand density
(Simić et al. 2012). Maize and
winter wheat are crops with weak competitive ability against perennial weeds
but catch crops prevent spread of perennial weeds (Askegaard 2017). E. repens is a cumbersome weed in Europe
and cannot be managed solely by crop diversification and nitrogen-fixating
perennial crops. It is a perennial grass weed which causes yield losses in
temperate areas. Once established in a field it spreads quickly through
underground rhizomes. It is controlled either with glyphosate, or repeated
stubble cultivations to fragment and starve the rhizomes. Tillage only helps if
it completely and deeply burrows the rhizomes and is not repeated again,
creating a danger of bringing up rhizomes to the surface before they die. Disk
tools are useless, as they cut and spread the rhizomes and do not incorporate
completely. Glyphosate works, depending on the application conditions. Another
practice, which works and avoids reinfestation, is dense soil mulch cover to
starve the plants; couch grass only starts growing again, if it gets light to
feed the rhizomes; kept in complete shade it can be controlled; important is
the permanent soil cover. This is explained later, but should be made clearer,
since a permanent soil cover can only be maintained without tillage; any
tillage, even reduced tillage, interrupts the permanent soil cover and gives
the grass a chance to regrow. In case of poorly developed cover crops they did
not affect E. repens (Melander et al. 2013). Crop sequences of surveyed fields generally do not
create a sufficiently long intercrop period often associated with inappropriate
rainfall distribution during the summer months. For these reasons, catch crops
were not grown on any single fields of observed period. The absence of catch
crops in crop rotation reduced the competitive ability of the growing
sequences. The
winter oilseed rape was included 5 times into 4 crop rotations (field 1, 2, 5
and 6) and significantly maintained the population density of couch grass for
following crop without herbicide application. The higher
proportion of winter oilseed rape and limitation of sunflower in intensive
cereal crop rotation pattern can be considered as one of the appropriate
cultural measures for E. repens
control.
Conclusion
Conservation
agriculture, (including minimum soil disturbance, permanent soil cover and
diversified crop rotation) should be promoted to reduce the weed infestation
and herbicide application for sustainability of agricultural ecosystem.
Inclusion of crops with strong allelopathic crops, like winter oilseed rape,
may further reduce the infestation of E.
repens.
Acknowledgements
Financial
support from The Ministry of
Education, Science, Research and Sport of the Slovak Republic, project VEGA
1/0544/13 and Ministry of Education, Science and Technological Development of the
Republic of Serbia through project ''Improvement of maize and sorghum production under stress conditions''
(TR 31073) is highly acknowledged.
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