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International Journal of Chemical Studies 2018; 6(6): 1035-1047
P-ISSN: 2349–8528 E-ISSN: 2321–4902
IJCS 2018; 6(6): 1035-1047
© 2018 IJCS
Received: 25-09-2018
Accepted: 30-10-2018
Vivek
Department of Agronomy Sardar
Vallabhbhai Patel University of
Agriculture & Technology,
Meerut, Uttar Pradesh, India
RK Naresh
Department of Agronomy Sardar
Vallabhbhai Patel University of
Agriculture & Technology,
Meerut, Uttar Pradesh, India
DK Sachan
KVK Ghaziabad Sardar
Vallabhbhai Patel University of
Agriculture & Technology,
Meerut, Uttar Pradesh, India
Shivangi
Department of Agronomy Sardar
Vallabhbhai Patel University of
Agriculture & Technology,
Meerut, Uttar Pradesh, India
Richa Tiwari
Department of Agronomy Sardar
Vallabhbhai Patel University of
Agriculture & Technology,
Meerut, Uttar Pradesh, India
Correspondence
Vivek
Department of Agronomy Sardar
Vallabhbhai Patel University of
Agriculture & Technology,
Meerut, Uttar Pradesh, India
Weed seed bank dynamics: soil organic carbon
dynamics and weed seed bank modulation through
residue, tillage and weed management: A Review
Vivek, RK Naresh, DK Sachan, Shivangi and Richa Tiwari
Abstract Weeds are unwanted plants playing a very important role in different eco-systems and many of them cause
enormous direct and indirect losses. The losses include interference with cultivation of crops, loss of bio-
diversity, loss of potentially productive lands, loss of grazing areas and livestock production, erosion following
fires in heavily invaded areas, choking of navigational and irrigation canals and reduction of available water in
water bodies. Weed management takes away nearly one third of total cost of production of field crops. In India,
the manual method of weed control is quite popular and effective. Of late, labour has become non-availability
and costly, due to intensification, diversification of agriculture and urbanization. The usage of herbicides in
India and elsewhere in the world is increasing due to possible benefits to farmers and continuous use of the
same group of herbicides over a period of time on a same piece of land leads to ecological imbalance in terms
of weed shift and environmental pollution. The complexity of these situations has resulted in a need to develop
a holistic sustainable eco-friendly weed management programme throughout the farming period.
Weed infestation is one of the major biotic constraints in crop production. Field crops are infested with diverse
type of weed flora, weed density and weed diversity as it is grown under diverse agro-climatic conditions,
different cropping sequence, and tillage intensities and weed management strategies. The yield losses due to
weeds vary depending on the weed species, their density and environmental factors. Knowledge about how the
type, timing, and arrangement of cultural practices influence weed species composition is important for
understanding the ecological results of control strategies and designing alternative crop management systems.
Studies of soil weed seed banks are of relatively recent origin considering their importance as sources of
diversity and continued occupation of many types of habitats, including agro-ecosystems. The management of
weed seed banks is based on knowledge and modification of the behaviour of seeds within the soil seed bank
matrix. The behaviour of seeds defines the phenotypic composition of the floral community of a field. Selection
and adaptation over time have led to the highly successful weed populations that exploit resources unused by
crops. The weed species infesting agricultural seed banks are those populations that have found successful trait
compromises within and between the five roles of seeds: dispersal and colonization, persistence, embryonic
food supply, display of genetic diversity, and as a means of species multiplication.
Tillage system was more important determinant of weed seed density than the weed management practices.
Movement pattern of weed seeds by all tillage treatments differ significantly over three weeding management
practices at 0-5 cm soil core. Zero tillage system promoted infestation of some broadleaf weeds. The lowest
weed mass was determined for the conventional tillage plots, compared to minimum tillage, and especially
zeros tillage plots. Because herbicide and cultivation efficacy is generally density independent, seedling density
following these weed control practices will be proportional to the density of germinal seeds in the seed bank.
Most farmers would therefore benefit from management practices that reduce seed inputs, increase seed losses,
and reduce the probability that remaining seeds establish. Germination, predation, and decay are the primary
sources of loss to the seed bank that may respond to management. Although seeds would seem to be an ideal
carbon source for soil microorganisms. To reduce seed bank inputs and increase losses is to reduce the size of
the effective seed bank through manipulation of residues and disturbance to reduce the probability of
establishment. Incorporation of green manures generally reduces weed establishment, whereas larger-seeded or
transplanted crops may better tolerate the residue-mediated changes in the chemical, biological, and physical
properties of the soil surface environment. Evidence from no-till systems further support the changes in soil
surface conditions may regulate the abundance of “safe sites” for weed establishment, thereby modulating the
size of the effective seed bank. Crop residues on the soil surface reduce weed seedling establishment in no-till
systems, but tillage eliminates this effect. This provides useful information to improve methods for maintaining
plant population balance.
Keywords: seed bank, tillage, weed diversity, crop residues, soil health
Introduction
Weeds are a major problem in most cropping systems, and their control is essential for
successful crop production. The goal of weed control is not only to prevent crop yield loss, but
also to minimize weed seed reserves in the soil,
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International Journal of Chemical Studies
because the soil seed bank is the primary source of new
infestations of annual weeds and represents the majority of
the weed species composition. The majority of seeds entering
the seed bank come from annual weeds growing in the fields.
The size of the seed bank reflects past and present field
management (Auffret, Cousins, 2011) [2]. Weed seed bank
analysis provides knowledge on the effect of agricultural
management practices on weed community dynamics. Such
knowledge is difficult to acquire from short-term studies
based on actual weed flora, whose composition is subjected to
considerable variation in time and space (Birthisel et al.,
2015) [7]. Weed communities are also affected by crop type
and sequence. Agricultural crops with different growth cycles
(winter or spring) affect weed spread, germination and
growth.
Excessive tillage in conventional agricultural systems triggers
soil movement that leads to more soil erosion and
environmental degradation.
One of the regenerative strategies of plants involved in the
natural regeneration process and secondary ecological
succession of weeds is the formation of persistent seed banks
in the soil (Grime, 2006) [27], in which the largest contribution
is made by the species that produce the largest amounts of the
smallest seeds. Resorting to seed bank input is the last
strategy for survival of a species. On the other hand, there are
weed seeds which remain in the ground only a few months of
the year. These seeds form the transient weed seed bank.
These transient seed banks are composed of species which
germinate collectively when there are adequate environmental
conditions. The literature defines the soil as an integral
component of an agro-system, which is subject to different
management practices. Tillage, which can affect the physical
properties of the soil (Álvaro- Fuentes et al., 2008) [1], is one
of the oldest agricultural practices and its objectives range
from preparing a good “seed bed” for cultivation, to the
elimination of emerging weeds. In general, tillage acts on the
soil seed bank promoting germination in some cases and
contributing to their burial in others (Trichard et al., 2013;
Chauhan et al., 2012) [53, 12]. With stubble mulch, weeds are
controlled during fallow with a sweep plough, which consists
of V-shaped blades that sever plant roots at a tillage depth of
5 to 8 cm. Each operation buries only 10% of crop residues
because of low soil disturbance, contrasting with tillage by a
tandem-disk harrow or mould-board plough that buries 60 to
100% of crop residues. Crop residue management is further
improved with no-till systems, where herbicides replace
tillage for weed control during fallow. Conventional tillage
systems may reduce weed infestation (Gajri et al., 1999) [24]
but accelerate the degradation of soil resources. Early season
weeds are effectively controlled by conventional tillage
(Steckel et al., 2007) [50]; however, the problem of weed
infestation is aggravated during later crop growth stages in
these tillage systems. Conservation agriculture (CA) involves
minimal soil disturbance, permanent soil cover and planned
crop rotations (Thierfelder et al., 2012) [52]. Reduced tillage is
the most important component of CA as minimal soil
disturbance and permanent residue cover, the two pillars of
CA, can only be achieved through reduced tillage. CA thus
helps reducing the input expenses for land preparation, and
soil and water conservation. Therefore, soil aggregates, and
the associated growth patterns of seeds may play an important
role in the distribution of seed banks and the maintenance of
species during periods without seed production.
Unfortunately, there is a lack of research available with
reference to the dynamics of seed/aggregate associations
which may also influence weed emergence, the study of said
dynamics could provide useful information for the design of
future weed management practices to prevent weed seed
germination (Reuss et al., 2001) [45].
Nonetheless, CA alters the weed flora and infestation levels
(Primot et al., 2006) [44]. For instance, CA increases the weed
infestation during initial years of infestation. Moreover,
perennial weeds tend to dominate in CA (Mashingaidze et al.,
2012) [33]. This indicates that in CA the weed flora changes
from easy to control annual broad leaf and grasses to
obnoxious perennial weeds such as couch grass (Cynodon
dactylon L.) and mexican clover (Richardia scabra L.)
(Mashingaidze et al., 2012) [33]. Chemical weed control has
been an effective weed management option in CA. However,
indiscriminate use of herbicides has resulted in the
development of herbicide resistant weed biotypes (Farooq et
al., 2011a); and has also disturbed the ecological balance
(Owen et al., 2007) [43] and human health (Morais et al., 2012)
[38]. Considering the challenge of herbicide resistance in
weeds, Farooq et al. (2011a) proposed careful and wise use of
herbicides with more emphasis on weed seed bank
modulation options, and recognized weed seed bank
modulation as the 4th pillar of CA. The purpose of this study
was thus to assess whether and to what extent can represent a
useful parameter for weed seed bank dynamics: soil organic
carbon dynamics and weed seed bank modulation strategy
based on seed dormancy and longevity which makes it one of
the most important weeds management module.
The species composition and density of weed seed in soil vary
greatly and are closely linked to the cropping history of the
land. Seed composition is influenced by farming practices,
and varies from field to field (Buhler et al. 1996b) [1] and
among areas within fields (Mortensen et al. 1993). Reports of
seed bank size in agricultural land range from near zero to as
much as 1 million seed m-2 (Fenner 1985) [23]. Generally, seed
banks are composed of many species, with a few dominant
species comprising 70 to 90% of the total seed bank (Wilson
1988) [58]. These species are the primary pests in agronomic
systems because of resistance to control measures and
adaptation to the cropping system. A second group of species,
comprising 10 to 20% of the seed bank, are generally those
adapted to the geographic area but not to current production
practices. The final group accounts for a small percentage of
the total seed and includes recalcitrant seeds from previous
seed banks, newly introduced seeds of the previous crop
(Wilson et al. 1985) [57]. This group undergoes constant
change due to seed dispersal by humans, other animals, wind,
and water.
Montanyá et al. (2016) revealed that the germinable seed
bank density was recorded as lower in NT system and D2 (7–
15 cm); and the richness of species was significantly affected
in the same manner as density [Fig.1b]. In systems that do not
require different long term management, as is the case of NT
plots, the weed control was carried out by means of consistent
use of pre and post emergence herbicides. Therefore these NT
systems in the D2 soil layer contributed to the reduction of
weed seed community and its richness of species. When
considering the richness of species present in both crop
systems, the lowest richness values were recorded in cereal
rotation system and D2 (7–15 cm). Ryan et al. (2010) [46] also
found, in the short term, that continuous use of tillage
management determined the trajectory of weed community
change. Additionally, the results of the work reported here
confirmed that the proportion of weed seedling density
obtained in the germinal study mirrored the weed abundance
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International Journal of Chemical Studies
emergence occurred in the field, and it was not affected by
seed soil layer depth.
The cumulative effects of crop systems showed a significant
effect on persistent weed seed density and diversity indices
[Fig.1c]. The first 7 cm of soil (D1) with cereal rotation
system showed greatest density of seeds and richness of
species. On the other hand, the comparison of tillage systems
within crop systems showed significant effects on the weed
seed bank. MT and NT rotated plots showed the highest
values of seed density and species richness respectively in
persistent weed seed bank. Ward et al. (2012) [55], who
observed that tillage systems can play a buffering role in
environmental fluctuation, suggesting that conservation tillage
systems with high weed density can better, respond to
environmental changes.
Mei et al. (2018) [34] found that no-tillage increased the
number of weed species and weed density in most of the
crops, while stubble retention decreased weed density in
maize and tended to suppress weeds in both no-tillage
treatments (no-tillage and no-tillage + stubble retention). No-
tillage led to an increase in the number of weed species in the
weed seed bank and tended to increase seed density during the
spring growth of winter wheat, but it decreased seed density
during post-vetch fallow. Stubble retention tended to reduce
seed density during the spring growth of winter wheat and
post-vetch fallow [Fig.2a, 2b & 2c].
(a) (b) (c)
Fig 1(a): Weed seed cycle
Fig 1(b): Depth x Tillage system and Depth x Crop system interactions on Transient seed bank parameters: Seedlings m-2 density and Dmg
index (richness of species) [Source: Montanyá et al., 2016]
Fig 1(c): Depth x Crop system and Crop x Tillage systems interactions on Persistent seed bank parameters: Seeds m-2 density and Dmg index
(richness of species) [Source: Montanyá et al., 2016]
(a) (b) (c)
Fig 2(a): Number of weed species during the growth period of winter wheat (a), common vetch (b) and maize (c), and the total number of
species across the whole season (d) under conventional tillage (T), no-tillage (NT), conventional tillage + stubble retention (TS) and no-tillage +
stubble retention (NTS) treatments [Source: Mei et al., 2018] [34]
Fig 2(b): Weed density during the growth period of winter wheat (a), common vetch (b) and maize (c), and weed density averaged over the
whole season (d) under conventional tillage (T), no-tillage (NT), conventional tillage + stubble retention (TS) and no-tillage + stubble retention
(NTS) treatments [Source: Mei et al., 2018] [34]
Fig (2c): Seed density of weeds in the weed seed bank during the spring growth of winter wheat and post-vetch fallow under conventional
tillage (T), no-tillage (NT), conventional tillage + stubble retention (TS) and no-tillage + stubble retention (NTS) [Source: Mei et al., 2018] [34]
Shahzad et al. (2016) [48] reported that tillage practices and
wheat-based cropping systems had significant effect on weed
diversity during both years of the study [Fig. 3a]. Cotton-
wheat cropping system under zero tillage (ZT) had the
maximum while sorghum-wheat cropping system under deep
tillage (DT) had the minimum weed diversity during both
years of the study [Fig.3a]. Weed seeds present in the upper
soil layer (up to 10 cm) are distributed within the upper 20 cm
of soil after tillage (Buhler et al., 2001) [10]. This indicates that
tillage practices play an important role in the distribution of
the weed flora, weed seeds and propagations in soil, because
soil disturbance regimes are related to seed distribution and
viability (Lutman et al., 2002) [32], seedling emergence and
survival (Mohler and Callaway, 1992) [37].
Cromar et al. (1999) [27] revealed that the percent seed
predation in no-till averaged 43% in the fall and fell to 24% in
the spring, whereas predation levels in the chisel and
mouldboard plough treatments were not different between
seasons, averaging 22 and 43% in the fall and 24 and 31% in
the spring, respectively [Fig.3b]. Bàrberi and Lo Cascio,
(2001) [5] showed that total weed seedling density was higher
in no tillage, minimum tillage (i.e rotary harrowing at 15 cm
depth), and chisel ploughing (at 45 cm depth) in the 0-15, 15-
30, and 30-45 cm soil layers respectively [Fig.3c]. Density in
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the whole (0-45 cm) layer did not significantly differ among
tillage systems, but in no tillage more than 60 percent of total
seedlings emerged from the surface layer, compared to an
average 43 percent in the other tillage systems. Crop rotation
did not influence either weed seed bank size or seedling
distribution among soil layers, and had a small influence on
major species abundance. The weed seed bank was dominated
(> 66 percent of total density) by Conyza canadensis and
Amaranthus retroflexus, which thrived with chisel ploughing
and no tillage, respectively.
(a) (b) (c)
Fig 3(a): Impact of different cropping systems on weed diversity under conservation and conventional practices [Source: Shahzad et al., 2016] [48]
Fig 3(b): Comparison between average fall and spring seed predation in different tillage practices [Source: Cromar et al., 1999] [27]
Fig 3(c): Percent weed seedling distribution over soil layers in mouldboard ploughing at 45 cm depth (P 45), chisel ploughing at 45 cm depth
(CP 45), rotary harrowing at 15 cm depth (RH 15), and no tillage (NT) after 12 consecutive years’ application of the different tillage systems
[Source: Bàrberi and Lo Cascio, 2001] [5]
Santin-Montanya et al. (2018) [47] also found that the
significant difference between tillage systems was found in
2012, with ZT presenting highest total weed abundance (136
plants m−2). In the following years of zero-tillage we observed
the decrease of weed abundance emerged in the field [Fig.4a].
The abundance of Portulaca oleracea in 2012 showed lower
relative abundance in CT compared to ZT. Over the next two
years, in the ZT system, this weed abundance decreased (from
106 plants m−2 to 6 plants m−2, the lowest value, in 2013 and
17 plants m−2, in 2014). The abundance of Amaranthus
blitoides did not change significantly in the ZT systems,
although this species showed a tendency to diminish in terms
of relative density when the soil was not tilled. However, in
the CT system the abundance of Amaranthus blitoides
increased (from 7 plants m−2, in 2012, to 46 and 54 plants
m−2, in 2013 and 2014 respectively) [Fig.4a].
Colbach et al. (2014) [16] observed that approximately 33% of
the beads were retrieved and used to establish bead
distributions from which model parameters were estimated.
Cross-validation showed that prediction quality was
satisfactorily (modelling efficiency = 0.85, minimum rMSEP
= 0.11) with most of the error associated with using a harrow
in compacted soil. Subsequently, the new model was
integrated into the existing weed dynamics model FLORSYS,
and simulations were run to predict weed emergence and
dynamics for different tillage practices [Fig.4b].
(a) (b)
Fig. 4(a): Year × Tillage system’ interactions (a, b, and c) and ‘Weed seed bank test × Tillage systems’ interactions (d, e, and f) on Total weed
abundance and abundance of Portulaca oleracea and Amaranthus blitoides emerged in the field, and in the weed seed bank [Source: Santin-
Montanya et al., 2018] [47].
Fig. 4(b): Proposed conceptual model for weed seed movements during tillage [Source: Colbach et al., 2014] [16]
Colbach et al. (2014) [16] also found that the soil structure,
tillage with a tine or a harrow resulted in the same seed
distribution: seeds initially located on soil surface were buried
between 2 and 10 cm (for a tillage depth of 10 cm) whereas
initially buried seeds were placed slightly deeper, between 3
and 10 cm [Fig. 5a]. When using discs, the final seed
distribution did not change for seeds initially on surface but
initially buried seeds were displaced closer to soil surface,
between 3 and 8 cm. Tillage depth had the greatest effect.
When tine depth was decreased from 10 to 5 cm, seeds
remained closer to soil surface, e.g. seeds initially on soil
surface were buried between 0 and 5 cm, compared to 2 and
10 for the deeper operation [Fig.5a]. The soil content in fine
earth also influenced seed profile: in case of compacted soil
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structure, the top layer (0–1 cm) was devoid of seeds after
tillage, and generally seeds were buried 1 cm deeper than in
fine-earth soil [Fig.5a]. Moreover, surface seed bank, total
emergence was highest for shallow operations (harrow, discs)
and lowest for deep operations (chisel, mould-board plough).
For the latter, the spring emergence flush was particularly
reduced whereas the difference in autumn emergence was
smaller. Emergence was also lower in compact soil than fine-
earth structure, with similar differences for autumn and spring
flushes [Fig.5b].
(a) (b)
Fig.5 (a): Effect of tillage tool (A), tillage depth (B) and final soil structure (B) on seed distribution after tillage for seeds initially on soil surface
or initially close to future tillage depth [Source: Colbach et al., 2014] [16].
Fig. 5(b): Effect of tillage strategy on total weed emergence after a single tillage operation [Source: Colbach et al., 2014] [16].
Chen et al. (2017) reported that the weed seeds, 82.5% in
MTR, 75.3% in WDSR, and 81.7% in DDSR, were
distributed in soil 0- to 10-cm deep [Fig.6a]. As soil depth
increased, the seed banks of total weeds, broadleaf weeds,
grasses, and sedges all significantly decreased under the
different rice planting systems, except for sedges under
WDSR. The DDSR tended to maintain larger seed banks of
sedges and grasses, as well as some upland weeds, such as
Digitaria sanguinalis (L) and Eleusine indica. The WDSR
system contained the smallest weed seed bank overall but
tended to have larger seed banks of several weeds, such as
Ammannia arenaria and Lindernia procumbens. Weedy rice
and Cyperus difformis L. tended to maintain larger seed banks
in DSR fields. The MTR fields tended to have larger seed
banks of broadleaf weeds and some traditional rice weeds,
with significantly lower richness of weed species in the seed
bank [Fig.6b &6c].
(a) (b) (c)
Fig. 6(a): Number of rice’s companion weed species observed in soil samples with different soil depths of different fields with different rice planting
systems. DDSR: dry direct-seeded rice, WDSR: Water direct-seeded rice and MTR: machine-transplanted rice [Source: Chen et al., 2017].
Fig. 6(b): Number of seeds per m2 soil for different weed groups within different soil depths (1 = 0–5 cm, 2 = 5–10 cm, 3 = 10–15 cm, and 4 = 15–20
cm) of fields under dry direct-seeded rice (DDSR), water direct seeded rice (WDSR), and machine-transplanted rice (MTR) planting system [Source:
Chen et al., 2017].
Fig. 6(c): Canonical correspondence analysis (CCA) showing different rice planting systems [Source: Chen et al., 2017].
Brar and Walia (2007) [4] reported that CT favoured the
germination of grassy weeds in wheat compared with ZT in a
rice-wheat system across different geographical locations of
Punjab, while the reverse was true in respect to broad-leaved
weeds [Fig.7a]. Some weed seeds require scarification and
disturbance for germination and emergence, which may be
enhanced by the types of implements used in soil tillage
systems than by conservation tillage. The timing of weed
emergence also seems to be species dependent. Chauhan and
Johnson, (2009) [13] revealed that the different tillage practices
disturb the vertical distribution of weed seeds in the soil, in
various ways. Its depend largely on a good understanding of
the dynamics of the weed seed bank in the soil. Moreover,
ZT, there is little opportunity for the freshly-rained weed
seeds to move downwards in the soil and hence remains
mostly on the surface, with the highest concentration in the 0–
2 cm soil layer, and no fresh weed seed is observed below 5
cm soil depth [Fig.7b].
Under conventional system, weeds seeds are distributed
throughout the tillage layer with the highest concentration of
weed seeds in the 2–5 cm soil layer. Mould-board plough
buries most weed seeds in the tillage layer, whereas chisel
plough leaves the weed seeds closer to the soil surface.
Similarly, depending on the soil type, 60– 90% of weed seeds
are located in the top 5 cm of the soil in reduced or no-till
systems (Swanton et al., 2000) [51]. Chauhan and Abugho,
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International Journal of Chemical Studies
(2012) [12] reported that 6 t ha-1 crop residues reduced the
emergence of jungle rice, crowfoot grass and rice flat sedge
by 80–95% but only reduce the emergence of barnyard grass
by up to 35% [Fig.7c]. The effectiveness of crop residue to
reduce weed emergence also depends upon the nature of weed
species to be controlled.
(a) (b) (c)
Fig. 7(a): Effect of tillage on the relative density of grasses and broadleaved weeds [Source: Brar and Walia, 2007] [4]
Fig. 7(b): Effect of tillage systems on the vertical distribution of weed seeds [Source: Chauhan and Johnson, 2009] [13].
Fig. (7c): Effect of rice residues on weed germination [Source: Chauhan and Abugho 2012) [12]
Ngwira et al. (2012) [41] revealed that SOC and SON in ZT
fields were 44 and 41 % (4 years ZT) and 75 and 77 % (5
years ZT) higher, respectively, than CT plots. MB-C and MB-
N in ZT fields were 16 and 44 % (4 years ZT) and 20 and 38
% (5 years ZT) higher, respectively, than CT plots [Fig.8b].
However, MB-C and MB-N in ZT fields were 27 and 25 % (2
years ZT) and 17 and 9 % (3 years ZT) lower than in CT
plots. The proportion of the total organic C as microbial
biomass C was relatively higher under CT than ZT treatments.
The higher SOC and MB-C content in the ZT fields resulted
in 10, 62, 57 % higher C mineralization rate in ZT plots of 3,
4 and 5 years of loamy sand soils and 35 %higher C
mineralization rate in ZT plot of 2 years than CT of sandy
loam soils in undisturbed soils.
(a) (b)
Fig. 8(a): Organic carbon content in the soil as influenced by tillage and residue recycling practices [Source: Singh et al., 2015]
Fig. 8(b): Carbon mineralization rates of the undisturbed soils sampled from farmers’ fields under conventional tillage and zero tillage (2–5
years old) [Source: Ngwira et al., 2012] [41]
Ghimire et al. (2008) [25] also found that the benefit of crop
residue recycling is higher when used as mulch on ZT soil
than its incorporation under CT system. However, crop
residue treatment in ZT soils showed significantly higher
amount of SOC than other treatment combinations in the top
15 cm soil depths [Table 1]. Crop residue served as a source
of carbon especially in upper soil layers. Zero-tillage practice
minimizes exposure of SOC from oxidation, and thus
ensuring higher SOC content in surface soils of ZT with crop
residue application.
Table 1: Effects of tillage and residue treatments on the SOC content [Source: Ghimire et al., 2008] [25]
Mishra and Singh (2012a) [36] observed that the impact of
tillage vis-à-vis weed infestation in the crop field is
influenced by the previous cropping systems. Continuous ZT
increased the population density of awnless barnyard grass
and rice flat sedge in rice, but rotational tillage systems
significantly reduced the seed density of these weeds [Table
2]. Continuous ZT with effective weed management using
recommended herbicide + hand weeding was more
remunerative and energy efficient
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Table 2: Weed seed bank (no/ number per 500 g soil) in top 20 cm of soil as affected by tillage sequences in a DSR– wheat in a Vertisol of
central India [Source: Mishra and Singh 2012a] [36]
Riaz et al. (2018) observed that the wetting and drying
interval was maintained keeping in view the prevailing
edaphic and climatic conditions. Rewetting (irrigation) was
used to done, when the water level go beyond the treatments
depth (15 and 20 cm) in the PVC tubes from field surface
level [Fig. 9a]. Whereas, rice field was kept irrigated at
constant level of 5 cm above the soil surface throughout the
flowering stage, to avoid any water stress. However,
glyphosate (72 SL) was applied in ZT plots
20 days before sowing to eradicate already established weeds
to make it comparable with CT where weeds were eradicated
during cultivation. Under conventional tillage, weed free plots
showed maximum leaf area index, and leaf area duration [Fig.
9b & 9c]. Among the herbicides application, pendimethalin
followed by BS+B gave highest opportunity under both AWD
regimes.
(a) (b) (c)
Fig. 9(a): Illustration of alternate drying and wetting regimes management for direct seeded rice [Source: Riaz et al., 2018].
Fig. 9(b): Influence of weed management treatments on leaf area index in aerobic rice grown under varying tillage system and alternate wetting
and drying regimes [Source: Riaz et al., 2018].
Fig. 9(c): Influence of weed management treatments on leaf area duration (days) in aerobic rice grown under varying tillage system and alternate
wetting and drying regimes [Source: Riaz et al., 2018].
Muminov et al. (2018) [40] revealed that the total weed
biomass was much higher in the no-herbicides treatments
(H0T, H0T0) than that of herbicides ones (HT, HT0) in both
rotations. The highest weed biomass appeared in H0T
treatment. However, the weed biomass in GS was much
higher than that of WM under the same treatment. For
instance, weed biomass in GS was 18.8% higher than that of
WM in H0T treatment. Herbicides application led to more
than 40% reduction in weed biomass in both rotations
[Fig.10a]. The change of weed density was very similar to
weed biomass. Weed density of GS rotation was much higher
than that of WM rotation under the same treatment. In H0T
treatment of GS rotation, the weed density reached to 130
plants m2, which was the maximum density among the four
treatments [Fig.10a]. Although herbicides could temporarily
control weeds, the weeds still germinate in the later stage and
long term application of chemical herbicides has caused
serious environmental and food pollutions worldwide (Liu et
al., 2016; Meng et al., 2016) [31, 35]. As far as germinal seeds
was related it was found that in 0–5 cm soil layer, the total
germinal weed seed densities of the four treatments varied
from 4,766 to 15,800 No. m-2, with H0T0 having the highest
seed density in the WM rotation; In the GS rotation, seed
bank varied from 3,100 to 5,966 No. m-2, with HT0 having the
highest seed density. The total seed bank in WM was 137%
larger than that of GS [Fig.10b]. However, in 5–20 cm soil
layer, the seed bank varied from 1,933 to 4,400 No. m-2 in the
WM rotation [Fig.10b]. Similarly, in 0–20 cm soil layer, the
treatments without herbicide (H0T0, H0T) had higher SOM
content in GS than that in WM. H0T had the highest SOM in
GS, while the highest SOM was noted in H0T0 in WM
[Fig.10c]. In 20–40 cm soil layer, SOM in GS was generally
higher than that in WM; SOM under herbicide-free treatments
(H0T and H0T0) was higher than that of the herbicide
treatments (HT and HT0), the highest SOM appeared in H0T
treatment, while the lowest SOM was noticed in HT0
[Fig.10c].
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International Journal of Chemical Studies
(a) (b) (c)
Fig. 10(a): The total weeds biomass (A) and weed density (B) in wheat–maize (WM) and garlic– soybean (GS) rotation systems with different
weed and tillage managements [Source: Muminov et al., 2018] [40].
Fig. 10(b): Total germinal seeds in the soil level of 0–5 cm (A) and 5–20 cm (B) in wheat–maize (WM) and garlic–soybean (GS) rotation
systems with different weed and tillage managements [Source: Muminov et al., 2018] [40].
Fig. 10 (c): Soil organic matter of the soil level of 0–20 cm (A) and 20–40 cm (B) in wheat–maize (WM) and garlic–soybean (GS) rotation
systems with different weed and tillage managements [Source: Muminov et al., 2018] [40].
Gruber and Claupein, (2009) [29] also found that the most
effective way to control C. arvense was the integration of
grass–clover which retained the number of thistle on a low
level, an effect which lasted at least for the following 2 years,
even if the number of thistle shoots increased in these crops
again. The next effective treatment to grass–clover was the
stubble tillage by a skimmer plough. A remarkably high
density of C. arvense occurred when faba bean (Vicia faba)
was grown. Both seedlings and shoots form thistle re-growth
was observed in winter wheat. The phase of biennial grass–
clover clearly reduced the number of thistle shoots, which
quickly increased however 2 years later [Fig.11a]. This crop
rotation would include spring and winter crops, and was in
this case focused on cereals with relatively high competition
ability. Secondly, a stimulation of weed seeds to germinate by
stubble tillage (stale seedbed) was not observed, as also found
by Verschwele (2009) [54], so that the efficiency of stale
seedbed techniques has to be reassessed. Finally it can be
assumed that the effect of the plough for primary tillage
overlaid a possible effect of stubble tillage as soil inversion by
a mould-board plough shifts seeds and weed seedlings into
deeper layers of the soil profile (Gruber and Claupein, 2006)
[28].
Deep plough, shallow plough or the use of a double-layer
plough for primary tillage in combination with stubble tillage
by a skimmer plough resulted in the lowest density of C.
arvense. Particularly the double-layer plough in combination
with stubble tillage resulted in a very low thistle density after
7 years (0.4 plants m-2). In contrast the highest infestation of
the thistle was observed in the chisel plough treatment with
stubble tillage and in the shallow plough treatment without
stubble tillage (23 or 20 plants m-2) [Fig.11b]. However, the
soil seed bank showed the highest number of total weed seeds
in the chisel plough treatment [about 37,000 seeds m-2,
Fig.11c]. The number of C. arvense seeds among all seeds
was also highest in the chisel plough treatment and reached
ca. 5500 seeds m-2.
(a) (b) (c)
Fig. 11(a): Thistle shoots in autumn over 7 years in a crop rotation as affected by primary tillage and stubble tillage (Pd: deep plough; DLP:
double-layer plough; Ps: shallow plough; ChP: chisel plough [Source: Gruber and Claupein, 2009] [29]
Fig. 11(b): C. arvense biomass (DM, dry matter) in oat after 5 years of different primary tillage and stubble tillage (Pd: deep plough; DLP:
double-layer plough; Ps: shallow plough; ChP: chisel plough [Source: Gruber and Claupein, 2009] [29]
Fig. 11(c): Size of the soil seed bank (number of seeds m-2) (treatments with stubble tillage) for the total amount of seeds (‘‘all seeds’’) and
Canada thistle (C. arvense) seeds [Source: Gruber and Claupein, 2009] [29]
Opena et al. (2014) [42] reported that seedling emergence in
both populations of E. glabrescens was reduced by seed burial
depth. Estimates from the three parameter sigmoid model
indicated that 50% seedling emergence (T50) was achieved at
5.7 d in the IR population and 6.0 d in the NE population
[Fig.12a]. Fifty percent of the seeds that were buried from 0.5
to 4 cm for the IR population and from 0.5 to 2 cm for the NE
population emerged at the same time as seeds that were sown
on the soil surface. On the other hand, the time needed for
50% emergence was delayed by 13 d at 4-cm depth in the IR
population, and by 9 d at 2-cm depth in the NE population,
compared with seeds sown on the surface [Fig.12a].
In both populations, the cumulative seedling emergence at 24
DAS declined with increasing burial depth [Fig.12b]. The
maximum emergence (91 and 79% for the IR and NE
populations, respectively) was observed at the soil surface.
Seedling emergence in the NE population declined more
rapidly with increasing burial depth, compared with that in the
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International Journal of Chemical Studies
IR population. At 0.5-cm burial depth, seedling emergence
decreased by 63% in the NE population and 30% in the IR
population. No emergence was observed at 4-cm depth in the
NE population and at 8-cm depth in the IR population
[Fig.12b].
Greater germination on the soil surface in E. glabrescens is
consistent with stimulation of germination by light. Reduced
emergence with increase in burial depth in E. glabrescens
could be due to the absence of light to signal germination or a
limitation on soil gas diffusion, or both (Benvenuti and
Macchia, 1995) [6]. Seeds buried more than 2 mm below the
soil surface receives less than 1% of incident light (Egley,
1986) [19]. Another possible reason for reduced emergence
with increasing depth could be physical limitations of the
seedling, i.e., insufficient seed reserves to enable it to reach
the soil surface (Bolfrey et al., 2011) [8].
Seedling emergence in the NE populations decreased with
increasing rates of residues [Fig.12c].
Maximum seedling emergence in E. glabrescens was 93 and
84% in the IR and NE populations, respectively, when no
residue was applied. The NE population was more affected
than the IR population by increasing amount of residue.
Emergence in the NE population increased significantly with
the addition of 4 t ha-1 residues, although there was still no
reduction in emergence in the IR population at this level. The
addition of 5 t ha-1 of rice residue caused a 55% and 9%
reduction in maximum emergence in the NE and IR
populations, respectively, compared with when no residue was
added. Weed suppression by mulch is attributed to various
physical and chemical factors. The physical factors include
lower soil temperatures, shading, and physical obstruction
provided by the mulch itself (Crutchfield et al., 1985) [30].
(a) (b) (c)
Fig. 12(a): Seedling emergence in two populations (IR and NE) of Echinochloa glabrescens, in response to burial depth (cm) when grown in
screen house conditions for 24 d [Source: Opena et al., 2014] [42]
Fig. 12(b): Cumulative seedling emergence in two populations (IR and NE) of Echinochloa glabrescens, in response to burial depth (cm) when
grown in screen-house conditions after 24 d [Source: Opena et al., 2014] [42]
Fig. 12(c): Seedling emergence in two populations (IR and NE) of Echinochloa glabrescens, in response to residue amount (t ha-1) when grown
in screen-house conditions after 24 d [Source: Opena et al., 2014] [42]
Zhang et al. (2015) [58] revealed that all fertilizer treatments
showed improvements in harvestable above-ground biomass
production over the control [Fig.13a]. Addition of extra
mineral nutrients resulted in significantly higher plant
biomass production compared to the standard application rate.
The control treatment without any fertilizer had the lowest
maize biomass production. Moreover, total soil organic
carbon compared with the control the combination of manure
with mineral fertilizers resulted in the highest rate of soil
organic carbon accumulation [Fig.13a]. Mineral fertilizer
applications (NPK and 2NPK) had a significant positive effect
on soil organic carbon stocks compared to the control.
With mineral fertilizer application (NPK and 2NPK), maize-
derived soil organic carbon accumulated to 3.2–3.5 t C ha−1
over the first 10 years and reached 8.2 t C ha−1 in 2012; a rate
of change of 0.30 t C ha−1. After 10 years, about 11% of
original soil organic carbon had been replaced with maize-
derived carbon in the control, whereas this was 15–16% in the
NPK and 2NPK treatments [Fig.13b). After 27 years of maize
double-cropping, 26% of soil organic carbon had been
replaced by maize-derived carbon in the control, and this
value was 34–35% in the mineral fertilizer treatments. In the
NPKM treatment, manure-derived soil organic carbon
comprised about 30% of total soil organic carbon and original
soil organic carbon accounted for 43%, with the remainder
derived from maize.
Zhang et al. (2015) [58] derived the proportional contributions
of below-ground crop biomass return and external manure
amendment to the total soil organic carbon stock. The average
retention of maize-derived carbon plus manure-derived
carbon during the early period of the trial (up to 11 years) was
relatively high (10%) compared to the later period (22 to 27
years, 5.1–6.3%). About 11% of maize-derived carbon was
converted to soil organic carbon, which was double the
retention of manure-derived carbon (4.4–5.1%) [Fig.11c].
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International Journal of Chemical Studies
(a) (b) (c)
Fig. 13 (a): Annual harvestable above-ground biomass (t C ha−1) (a) and soil organic carbon (SOC) stock (t C ha−1) [Source: Zhang et al., 2015]
[58]
Fig. 13(b): Changes in stock of original, maize-derived, and manure-derived soil organic carbon (SOC) (t C ha−1) [Source: Zhang et al., 2015]
[58]
Fig. 13(c): Relationship between maize-derived soil organic carbon (SOC) and cumulative maize carbon input [Source: Zhang et al., 2015] [58]
Follett et al. (2015) [22] also found that C4–C stocks for the 0-
to 120-cm depth under NT had increased by 6.0 Mg ha−1 [Fig.
14a]. In contrast the only significant decrease of SOC under
CT was within the 60- to 90-cm layer [Fig.14b]. The C4–C
stocks under CT increased in the 0- to 7.6, 7.6- to 15, and 90-
to 120-cm depth increments but only by a total of 1.9 Mg ha−1
for the entire 0- to 120-cm depth. Under CT, the C3–C stocks
decreased significantly at all depths except the 0- to 7.6 cm
increment and had decreased significantly within the 0- to 120
cm depth by a total of 10.9 Mg ha−1 compared with a decrease
of only 2.2 Mg ha−1 under NT. In addition, the retention of
C4–C stocks was greater under NT than under CT.
Comparisons of NT with CT show higher amounts SOC and
C3–C (0–120-cm depth) under NT than CT [Fig. 14a & 14b].
Auskalniene et al. (2018) observed that the highest number
(14700) of weed seeds m-2 was extracted from the soil
samples taken from the no tillage plots. Similar seed counts
(14233) were found in the minimum tillage plots, while the
seed counts in the conventional tillage plots were significantly
lower.
However, the differences between the tillage systems
remained – in less disturbed soil there was a significantly
higher weed seed number, compared to conventional tillage
[Fig.14c].
(a) (b) (c)
Fig. 14 (a): Comparison of the mass of soil organic C (SOC), C4–C, and C3–C for continuous corn under no-till (NT) [Source: Follett et al.,
2015] [22]
Fig. 14 (b): Comparison of the mass of soil organic C (SOC), C4–C, and C3–C for continuous corn under conventional tillage (CT) [Source:
Follett et al., 2015] [22]
Fig. 14 (c): Changes in the number of weed seeds in 0–10 cm soil layer as influenced by the different tillage systems [Source: Auskalniene et
al., 2018]
Clements et al. (1996) [15] reported that the soil disturbing
mechanisms associated with various tillage systems affects
the vertical distribution of weed seeds in the soil profile
differently [Fig.15a]. Mouldboard plough results in the burial
of most weed seed in the tillage layer, whereas chisel
ploughing leaves most weed seed closer to the soil surface.
Similarly in reduced or no-till systems, 60 to 90% (depending
on the soil type) of the weed seeds are located in the top two
inches of the soil. These seeds are thus at a relatively shallow
emergence depth and with suitable moisture and temperature
may more readily germinate and emerge than those buried
deeper with the other tillage systems. Dahal and Karki, (2014)
[18] revealed that interaction effects on weed number was
observed between tillage and weed management; residue and
weed management; fertilizer and weed management; tillage,
fertilizer and weed management; tillage, residue, fertilizer and
weed management at 30 DAS of maize. At 90 DAS of maize,
it was observed between tillage and residue; tillage, residue
and weed management; tillage, residue and fertilizer
management. Interaction effects on dry weight of weeds was
observed between residues and weed management; fertilizer
and weed management; tillage, residue and weed
management; tillage, fertilizer and weed management at 30
DAS. At 60 DAS of maize, it was observed between tillage,
fertilize and weed management; residue, fertilizer and weed
management [Fig.15c].
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International Journal of Chemical Studies
(a) (b) (c)
Fig.15 (a): The vertical distribution of weed seeds in the soil profile at depths of 0-2, 2-4, and 4-6 inches [Source: Clements et al., 1996] [15]
Fig.15 (b): Seed germination (%) and initial viability as well as post-burial viability [Source: Grace et al., 2016] [26]
Fig.15 (c): Interaction effect on number of weeds m-2 between (a) tillage and weed management (b) residue and weed management at 30 DAS
of maize [Source: Dahal and Karki, 2014] [18]
Conclusion
Although weeds are a challenge in the current cropping
systems in India, there are many opportunities to develop
sustainable and effective weed management programmes.
Weed management research is lacking under conditions of
CA. Major efforts should be made to get profound
understanding of weed, weed seed bank dynamics, soil
organic carbon dynamics and Weed seed bank modulation to
tillage intensities, reside retention and micro climatic
conditions on long term basis. The study indicates that the
potential to manage weed populations by fitting the tillage
system to the appropriate crop if continuous tillage is not
possible. Total weed density was significantly lower with a
mouldboard primary soil tillage system than with reduced
tillage systems. When compared to mouldboard ploughing,
disk ploughing and shallow loosening treatments increased
weed density. Tillage system was more important than crop
rotations in affecting the composition of the weed flora, weed
density and weed biomass.
There is limited information available on the persistence of
weed seed banks under Indian conditions, especially in CA
systems. These could be rotation of establishment methods,
tillage systems, crops or herbicides. Greater herbicide efficacy
may be achieved when crops and herbicides are rotated.
However, information on the role of different rotations in
suppressing the build-up of weed populations in different
cropping systems is very limited. Both agronomic
management and with appropriate traits are needed to achieve
maximum potential under CA system. Much research and
many adoptive evaluations carried out during the past decade
have provided management options. We are making good
progress in managing weeds using integrated approaches.
However, additional research is needed in weed management,
including (1) monitoring shifts in weed flora, (2) developing
management strategies for emerging problems of weedy, (3)
identifying new herbicides/tank mixtures with wide-spectrum
weed control ability, (4) identifying vulnerabilities in weed
life cycles through analysis of weed population dynamics
under CA technologies, and (5) developing integrated
strategies to minimize/avoid/ delay the development of
herbicide resistance in weed populations. Organic weed
control method could increase SOM, soil moisture and
earthworms which are beneficial to the soil productivity. Crop
rotation was tested to be successful and environmentally
friendly in weed control. The current study highlights the
importance of agricultural practices including crop sequences
or disturbance levels in determining the characteristics of
weed populations. This provides useful information to
improve methods for maintaining plant population balance.
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