Weed Science Conference 2006

Journal of Plant Diseases and Protection
Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz
Sonderheft XX, 257-265 (2006), ISSN 1861-4051
© Eugen Ulmer KG, Stuttgart
Effects of tillage systems on the seed bank persistence and seedling
emergence of ten arable weeds
A. ROLLER, H. ALBRECHT*
Lehrstuhl für Vegetationsökologie, Technische Universität München-Weihenstephan, D-85350 Freising,
e-mail: [email protected]
* Corresponding author
Summary
To test the effects of different tillage implements on soil seed bank decline and on seedling emergence,
5000 seeds m-2 of the arable weed species Avena fatua, Echinochloa crus-galli, Stellaria media, Spergula
arvensis, Sinapis arvensis, Capsella bursa-pastoris, Raphanus raphanistrum, Thlaspi arvense, Solanum
nigrum and Tripleurospermum perforatum were broadcast in experimental plots. The implements were the
curry comb, the cultivator and the plough. After 25 months, the percentage of weed seeds recovered ranged
from 0-12 %, depending on the species. The highest number of re-detected seeds was for Thlaspi arvense in
soils under plough tillage. In contrast, no seeds were recovered from Spergula arvensis and Avena fatua. As
there were no significant differences among the three treatments concerning the decline of the soil seed bank,
seedling emergence in the curry comb and the cultivator plots significantly exceeded the values of the plots
under plough tillage.
Keywords:
Weeds, seeds, seed bank, soil, persistence, tillage, plough, cultivator, curry comb
Zusammenfassung
Einfluss der Bodenbearbeitung auf die Persistenz und den Auflauf von zehn Wildpflanzenarten
Auf Parzellenversuchsflächen wurden von den Arten Avena fatua, Echinochloa crus-galli, Stellaria
media, Spergula arvensis, Sinapis arvensis, Capsella bursa-pastoris, Raphanus raphanistrum, Thlaspi
arvense, Tripleurospermum perforatum und Solanum nigrum je 5000 Samen m-2 ausgesät. In den
folgenden 25 Monaten wurden der Rückgang der Diasporendichte und der Feldaufgang in Abhängigkeit
von der Bodenbearbeitung untersucht. Als Varianten wurden der Striegel, der Grubber und der Pflug in je
sechs Parzellen verglichen. Je nach Pflanzenart waren am Ende der Untersuchung noch 0-12 % der
ausgebrachten Diasporen vorhanden. Die meisten Samen überlebten bei Thlaspi arvense mit Pflugbodenbearbeitung, für Spergula arvensis und Avena fatua konnten in keiner der drei Varianten noch Samen
nachgewiesen werden. Im Rückgang des Bodensamenvorrates zeichneten sich zwischen den drei Bodenbearbeitungsvarianten keine signifikanten Unterschiede ab, die Zahl der aufgelaufenen Diasporen war
dagegen in der Striegel- und Grubbervariante signifikant höher als bei Pflugbearbeitung.
Stichwörter: Wildpflanzen, Samen, Diasporen, Boden, Persistenz, Bodenbearbeitung, Pflug, Grubber,
Striegel
Introduction
Seeds of arable weeds can survive for many years in the soil seedbank. Thus, the Beal experiment, which
has run for more than 100 years (KIVILAAN and BANDURSKI 1981), proved that seeds of arable weeds can
persist such a time span in a dormant state without germinating. In this experiment, seeds were mixed
with sterilised soil and poured into glass bottles. Further information on weed seed longevity comes from
258
ROLLER, ALBRECHT
sites where arable farming had been abandoned for a long time or from undisturbed field plots where
seeds had been buried in mesh bags (e.g. BRENCHLEY 1918, ROBERTS and FEAST 1973). These
experiments confirmed the high potential of arable weeds to survive in the soil seed bank. However, all
these studies do not give a reliable estimation of the longevity of seeds under practical farming conditions
where they are exposed to tillage, weed control and crop rotation. Under these conditions, most seeds of
arable weeds lose their viability within a few years (SCHWEIZER and ZIMDAHL 1994). Unfortunately,
these investigations are time consuming and labour intensive because they demand repeated seed bank
analyses and the prevention of any new seed input. Consequently, only a few authors such as BARRALIS
et al. (1988), WILSON and LAWSON (1992), LAWSON et al. (1993), LUTMAN et al. (2002) and LUTMAN
et al. (2003) provided corresponding studies. On the other hand, such information on weed seed
persistence is essential to develop and to improve management systems that are suitable for both weed
control and species conservation purposes. Hence, the present study was designed to provide insight into
the effects of different tillage treatments on the persistence and the seedling emergence of arable weed
seeds under field conditions. As seed persistence significantly varies among species, 10 different taxa
were included.
Materials and methods
The investigation was carried out on a sandy loam at the agricultural research station of the Technische
Universität München in Roggenstein, Germany. The experimental plots were arranged in 3 blocks each
consisting of two replicates of three tillage treatments: curry comb, cultivator and plough. The blocks
were placed at different sites of the farm. Each of the two replicates was sown with a variety of oilseed
rape: either Falcon or Liberator. As these differences did not significantly affect the weed populations, the
variable ‘crop cultivar’ was not considered in the analysis.
Nomenclature1), number of seeds in soil at the beginning of the study and seed traits of the
investigated species.
Tab. 1: Bezeichnung1), Anzahl der Samen im Boden zu Versuchsbeginn und Sameneigenschaften der
untersuchten Arten.
Tab.1:
Species / Art
Avena fatua L.
Capsella bursa-pastoris (L.) Med.
Echinochloa crus-galli (L.) P. Beauv.
Raphanus raphanistrum L.
Sinapis arvensis L.
Solanum nigrum L.
Spergula arvensis L.
Stellaria media (L.) Vill.
Thlaspi arvense L.
Tripleurospermum perforatum (Merat) Lainz
Initial number of
buried seeds /
Samenzahl im Boden
zu Versuchsbeginn
Seed
longevity
index2)
Seed mass 3)
(mg/seed) /
Samenmasse 3)
(mg/Samen)
5000
5780
5885
1230
5000
1400
5000
5000
5385
5770
0.89
0.91
1.00
0.54
0.91
0.91
0.91
0.80
0.91
0.97
22.76
0.10
1.41
18.68
2.49
0.75
0.27
0.43
1.09
0.29
1) According to/nach WISSKIRCHEN and HAEUPLER (1998)
2) According to / nach THOMPSON et al. (1997) and / und THOMPSON et al. (1998)
3) According to / nach CREMER et al. (1991)
At each plot, seeds of ten different weed species were spread at a density of 5000 seeds m-2 in August
2001 (Tab. 1). The size of the plots was 9 x 3 m; the area where the weeds were broadcast was 2.5 x 3 m.
These seeds were commercially produced in Germany by the seed grower Conrad Appel in Darmstadt.
Effects of tillage systems on seed bank persistence
259
During the course of the experiment no further seeds were spread on the plots. The investigations
focussing on the oilseed rape interactions were published by ROLLER (2005).
The depth of cultivation of the three different soil-working implements varied from approximately
4 cm for the curry comb to 12 cm for the cultivator and 20 cm for the plough. The first treatment took
place the day after broadcasting on 17. August 2001. According to BARRALIS et al. (1988), the cultivation
was repeated two times a year in March and in September. The experiment ended after 25 months in
September 2003. To minimise seed movement off the plot area, the direction of cultivation was reversed
with each treatment. To prevent seed production, established plants were removed by applying the
herbicide glyphosate (Roundup Ready®) and by hand-weeding.
Soil sampling started in February 2002 and was repeated a few days before cultivation in autumn and
spring until September 2003. Four soil cores with a diameter of 7.8 cm were taken per plot, i.e. 24
samples per treatment. To evaluate the effect of different implements on the depth of burial, soil cores
were taken from the depths of 0-10 cm and from 10-22 cm. Subsequently, the samples were washed
through a series sieves, with a mesh size of 2, 1, 0.5 and 0.25 mm. The residue remaining on the sieves
with a mesh size ≤ 0.5 mm was transferred to petri dishes with paper and put into a climate chamber for
four weeks where they were exposed to a temperature of 22 °C and permanent light. Seeds were classified
as viable when they had developed a radicle of at least 2 mm.
Some of the tested species were already present in the soil seedbank before the experiment started. A
corresponding analysis revealed initial seed numbers of 885 m-2 for Echinochloa crus-galli, 780 m-2 for
Capsella bursa-pastoris, 770 m-2 for Tripleurospermum perforatum and 385 m-2 for Thlaspi arvense. In
the analysis, these numbers were added to the 5000 seeds m-2 that were spread on the plots. To calculate
the seedling emergence rates, the numbers of weed plants emerging on 4 quadrates per plot, each having a
size of 0.25 m² were recorded. Emerging plants were counted and removed every month during the
vegetation period. To re-detect the quadrates after the tillage treatments, their coordinates were exactly
measured. Recording began 6 weeks after sowing in late September 2001 and ended in October 2003.
Seed persistence listed in Table 1 was calculated employing the longevity index proposed by
THOMPSON et al. (1998). Its calculation is based on the seed bank database for north-west Europe by
THOMPSON et al. (1997) in which the authors allocated each published seed bank record for every species
to one of three longevity classes; type 1 (transient, persistence < 1 year), type 2 (short-term persistent,
persistence > 1 but < 5 years) and type 3 (long-term persistent, persistence > 4 years). Using these
persistence classes, the authors defined the longevity index for individual species as: Σ (type 2 + type 3) /
Σ (type 1 + type 2 + type 3). It can take a value between 0 (all seeds transient) and 1 (all persistent). Data
on the seed masses were adapted from CREMER et al. (1991) who measured these characteristics in ripe
and air-dried seeds from different arable sites in Germany.
Results and discussion
General development of the weed populations
Comparing the effect of the three tillage treatments reveals that they all led to a rapid decline of the soil
seedbank. Hence, as early as 13 months after weed seed spreading, more than 90 % of the broadcast seeds
were lost. Another 12 months later, only 4.8 % of the sown seeds were recovered in the soil seed bank
(median value 3.9 %). These values are distinctly below the annual decline of 40 to 80 % recorded by
BARRALIS et al. (1988) and the 20 to 60 % LUTMAN et al. (2002, 2003) found for the predominant part of
the species they investigated. This severe decline in the present study may be caused by both higher
tillage intensity at two treatments per year and by a minor depth of cultivation. In addition, natural
variation in seed losses may have affected the results. Correspondingly, MITZE (1992) and CARDINA et al.
(1996) observed that the percentage of newly produced seeds, which were not recovered in the soil seed
bank, can range between 70 % and 99 %
Despite this rapid decline of the soil seed bank, seeds of all tested species survived for more than one
year in the diaspore pool of the soil (Tab. 2). This means that – even under the practical conditions of
arable farming – all species have developed a ‘persistent’ seed bank in the sense of THOMPSON et al.
(1997). Developing a persistent seed bank is an important survival strategy in arable ecosystems where
260
ROLLER, ALBRECHT
regular tillage operations, herbicide applications and rotating crops hold a high risk of extinction for the
weed populations. The rapid initial decline turning into a moderate decrease suggests that the seed input
comprises both non-dormant and dormant seeds (COUSENS and MORTIMER 1995). If the non-dormant
fraction is more abundant, the seed number rapidly declines due to losses from germination, fallowed by a
more gradual decline due to degradation and slower germination as the remaining seeds are released from
dormancy. These weed populations may be classified into ‘seedbank type III’ of THOMPSON and GRIME
(1979) which is characterised by a low percentage of persistent and a pronounced seasonal peak of
immediately geminable seeds. Corresponding results by BARRALIS et al. (1988) and LUTMAN et al. (2002,
2003) suggest that arable weeds generally follow this strategy under practical farming conditions.
The use of different tillage implements affected the persistence of seeds in soil only moderately. Thus,
> 6 % of the seeds initially broadcasted were recovered from plots with plough tillage compared to about
4 % from those with non-inversion tillage. This difference can be interpreted as diverging effects of the
tillage implements. Thus, ploughing moves the majority of the freshly shed seeds from the surface deeper
into the topsoil. In the course of repeated treatments, this leads to a more or less homogeneous distribution of the seeds over the plough layer (Fig. 1). In contrast, non-inversion tillage with the curry comb or
with the cultivator leaves the seeds near the soil surface (CLEMENTS et al. 1996, O’DONOVAN and MC
ANDREW 2000).
The precision of this seed bank analysis may have been affected by seed movement away from the
sown area by the tillage operations. This problem is particularly important when the investigated research
area is small. REW and CUSSANS (1997) found a mean seed dispersal distance of 0.43 m on tined plots and
0.87 m on ploughed plots, and MAYER et al. (2002) also observed higher distances for the plough
compared to various non-inversion tillage implements. Transferring these results to the present study
suggests that the difference between the inversion and non-inversion tillage could have been more pronounced without this seed movement.
Tab. 2: Percentages of seeds recovered in the soil seed bank 13 and 25 months after the cultivation with
different tillage implements.
Tab. 2: Prozentanteil der nach 13 bzw. 25 Monaten Bewirtschaftung mit unterschiedlichen Bodenbearbeitungsgeräten in Diasporenvorrat des Bodens wiedergefundenen Samen.
Curry comb
(Striegel)
Months after seed-broadcast
(Monate nach Aussaat der Samen)
Avena fatua
Capsella bursa-pastoris
Echinochloa crus-galli
Raphanus raphanistrum
Sinapis arvensis
Solanum nigrum
Spergula arvensis
Stellaria media
Thlaspi arvense
Tripleurospermum perforatum
Mean value (Mittelwert)
Median value (Median)
Cultivator
(Grubber)
Plough
(Pflug)
13
25
13
25
13
25
1.9
3.6
3.9
2.1
0.2
29.3
0.3
15.0
13.1
24.1
3.9
0.9
1.3
11.2
3.3
16.1
3.1
10.7
3.0
4.3
0.4
20.6
0.2
8.6
5.1
13.0
2.8
0.4
2.1
0.4
8.8
3.7
12.6
9.7
0.7
5.2
5.6
5.4
1.0
25.0
9.1
17.4
11.7
5.7
5.6
1.4
0.6
12.5
4.2
28.1
4.4
9.3
3.8
4.0
2.0
6.6
4.7
4.1
2.5
8.1
5.5
6.3
4.3
Effects of tillage systems on seed bank persistence
261
At the soil surface, factors that stimulate seed germination (good oxygen supply and light conditions,
varying temperatures and an inconsistent availability of water) are expressed to a greater extent than in
deeper soil layers. In addition, seeds deposited near the surface do not need to penetrate thick soil layers
to establish seedlings. Accordingly, a Mann-Whitney test revealed significantly higher seedling emergence rates in the plots with non-inversion tillage than in those with the plough treatment. No significant
difference occurred between the two variants of non-inversion tillage. The seedling emergence rates
recorded in the present study are clearly above the values observed by BARRALIS et al. (1988). Although
their investigation went on for five years, there were only a few species that exceeded the 10 % seedling
emergence rate. As the soil had been ploughed to a depth of 25-30 cm in their experiments, the authors
suggested that deep burial was an important reason for this low emergence (and the high number of seeds
in soil described above). In the present study, depth of ploughing was 20 cm and most of the seeds in the
non-inversion tillage plots were allocated close to the soil surface. In addition to this minor depth of
burial, continuous removal of crop and weed plants from the soil surface may have facilitated the access
of light and the stimulation of seed germination. As all these factors that favour germination
simultaneously reduce the soil seed bank (ZWERGER and HURLE 1986), they may have additionally
contributed to the low number of seeds in the soil seedbanks found in the present study.
Depth distribution/
Tiefenverteilung
25
20
15
0 – 10 cm
10
5
5
10 – 22 cm
10
15
20
Curry comb
Striegel
Cultivator
Grubber
Plough
Pflug
Fig. 1:
Depth distribution of all seeds found during the study period of 25 months depending on the
tillage treatment.
Abb. 1: Tiefenverteilung aller über den Untersuchungszeitraum von 25 Monaten gefundenen Diasporen
(%) in Abhängigkeit von der Bodenbearbeitung.
Development of individual species
The individual species distinctly differed in their seed bank development (Tab. 2). According to their
decline, species can be classified into the following three groups:
1. None of the seeds were recovered 25 months after seeding: Avena fatua, Spergula arvensis.
2. 0.1-10 % of the buried seeds survived in the soil seedbank: Capsella bursa-pastoris, Echinochloa
crus-galli, Raphanus raphanistrum, Sinapis arvensis, Stellaria media, Tripleurospermum perforatum.
3. More than 10 % of the seeds were re-detected in the soil samples: Solanum nigrum, Thlaspi arvense.
A rapid decline for Avena fatua was also reported by LUTMAN et al. (2003) and WILSON (1988).
However, a longevity index of 0.89 (Tab. 1) shows that many other authors found persistent populations.
This inconsistency may be caused by unstable seed dormancy. In relation to that, PETERS (1982) found
that dormancy in Avena fatua is strongly depending on climatic conditions, and that it is particularly low
under high temperatures. A moderate seed bank decline was observed for Stellaria media by Lutman
et al. (2003), and an above-average seed persistence was reported for Capsella bursa-pastoris, Sinapis
arvensis and Thlaspi arvense by BARRALIS et al. (1988), ZWERGER and HURLE (1986) and LUTMAN et al.
(2002).
262
ROLLER, ALBRECHT
Great differences among species also occurred for the seedling emergence rates. Adding up all plants
which germinated in plots with curry comb and cultivator treatment (Fig. 2), the highest values were
recorded for Raphanus raphanistrum, Avena fatua, Solanum nigrum and Echinochloa crus-galli. In these
plots, more than 25 % of the broadcasted seeds produced seedlings. The maximum value was 68 % for
Raphanus raphanistrum in the cultivator treatment plots. Percentages of emerging seedlings between
10 % and 25 % were observed for Spergula arvensis and Sinapis arvensis, and values < 10 % were recorded for Stellaria media, Capsella bursa-pastoris, Tripleurospermum perforatum and Thlaspi arvense. In
the plough treatment plots, the emergence rate was 8 % for Solanum nigrum and below 3 % for all the
other species. These results correspond well with the annual seedling emergence rates of < 1 % to 4 %
WILSON and LAWSON (1992) observed for seven dicotyledoneous weeds in regularly ploughed plots.
For some of the species, the highest numbers of seedlings were not recorded in the autumn of sowing
but in the following years (Fig. 2). In the ploughed plots this phenomenon can be explained easily: plough
tillage buries the seeds, which do not return to the soil surface until the next treatment (TØRRESEN 1998).
For Capsella bursa-pastoris, Solanum nigrum, Thlaspi arvense and Tripleurospermum perforatum,
however, delayed germination was also observed in plots with non-inversion tillage. This behaviour may
have been caused by high stratification requirements or dormancy that is only broken under very specific
environmental conditions.
Relating the weed seedbank decline and the seedling emergence rates to the seed traits listed in Tab. 1
suggests a strong relationship of the weed population dynamics to the seed attributes of individual
species. Hence, both a rapid decline of the soil seedbank as well as a high initial seedling emergence rate
were characteristic for Avena fatua, Raphanus raphanistrum and Sinapis arvensis. All these species
produce particularly large and heavy seeds (see Tab. 1). This observation agrees with THOMPSON et al.
(1998) and BEKKER et al. (1998) who found seed persistence to be clearly related to a low seed mass. The
suspected cause underlying this relationship is that small seeds would be more easily buried by rain,
animals or gravity than larger ones (PEART 1984). When seeds are buried e.g. in the course of tillage, a
large seed size enables the plants to germinate from greater depths (GRUNDY et al. 2003) and to establish
under a wide range of environmental conditions (WESTOBY et al. 1997). As these options are rather
limited for the small seeds, seed persistence seems to be advantageous, because it increases the chances to
survive the burial phase and to germinate when favourable conditions recur. This means that the practical
farmer may control the seed bank development of large-seeded species by non-inversion tillage.
However, the soil seed bank and the emergence rates of Spergula arvensis quickly decreased despite
its production of very small seeds. The 25 % seedling emergence rate in the curry comb plots and < 1 %
after ploughing shows that this species is extremely sensitive to burial. Thus, not all species follow the
regularity described above. In these taxa other factors such as their phylogenetic relationship or
adaptation to the living conditions in the former natural habitats may have determined seed size and
persistence as well.
Fig. 2:
Percentage of seeds emerging as seedlings 1, 13 and 25 months after starting cultivation with
different tillage implements. Mean values ± SE; means were compared with an ANOVA and
post hoc TUKEY-test (P < 0.05) (page 263).
Abb. 2: Prozentanteil der 1, 13 und 25 Monate nach der Aussaat aus dem Diasporenvorrat des Bodens
bei unterschiedlicher Bodenbearbeitung aufgelaufenen Samen. Mittelwerte mit Standardabweichung; Mittelwertvergleich mit ANOVA und Posthoc-Test nach Tukey (P < 0,05) (Seite 263).
Effects of tillage systems on seed bank persistence
Avena fatua
Raphanus raphanistrum
80
70
60
50
40
30
20
10
0
a
a
a
a
b
b
1
13
25
40
35
30
25
20
15
10
5
0
a
a
a
a
Total
1
Seedling emergence / Auflaufrate (%)
a
a
a
a
b
b
b
b
c
1
13
13
25
Total
35
30
25
20
15
10
5
0
a
a
a
a
a
b
a
20
a
30
15
25
20
10
25
Total
Sinapis arvensis
a
a
a
5
c
a
b
b
b
0
0
1
13
25
Total
1
a
a
10
a
a
6
4
b
b
2
0
1
13
25
a
a
a
a
b
b
b
1
Tripleurospermum perforatum
13
b
25
Total
Thlaspi arvense
a
5
a
5
a
4
a
a
Total
25
a
9
8
7
6
5
4
3
2
1
0
Total
6
4
13
Capsella bursa-pastoris
Stellaria media
8
13
10
15
12
b
a
b
5
b
c
1
Spergula arvensis
35
Total
25
Echinochloa crus-galli
Solanum nigrum
45
40
35
30
25
20
15
10
5
0
b
b
3
3
a
2
b
b
a
2
1
1
0
0
1
13
25
Total
1
13
25
Total
Months after weed seeding / Monate nach der Wildpflanzen-Aussaat
Curry-comb / Striegel
Cultivator / Grubber
Plough / Pflug
263
264
ROLLER, ALBRECHT
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