For Review Only4º22’45’’W), located on the Duero Valley cereal belt in the Spanish province of Burgos. The soil, classified as Typic Calcixerolls, is characterized by a loamy-clay

For Review OnlyThe effects of soil tillage techniques on weed flora in high

input barley systems in northern Spain

Journal: Canadian Journal of Plant Science

Manuscript ID CJPS-2019-0178.R3

Manuscript Type: Article

Date Submitted by the Author: 14-Nov-2019

Complete List of Authors: Santín-Montanyá, M.I.; National Institute for Agricultural Research (INIA), Plant ProtectionSombrero Sacristán, A.; Agrarian and Technological Institute of Castile - Leon (ITACyL)

Keywords: weed community, conservation tillage, Agro-ecosystems, Germination, Light dependence

Is the invited manuscript for consideration in a Special

Issue?:Not applicable (regular submission)

https://mc.manuscriptcentral.com/cjps-pubs

Canadian Journal of Plant Science

For Review Only

The effects of soil tillage techniques on weed flora in high input barley

systems in northern Spain

M. I. Santín-Montanyá1 & A. Sombrero Sacristán2

1 Environment-Agronomy Department. Instituto Nacional de Investigación y Tecnología

Agraria y Alimentaria (INIA).Madrid, Spain

2 Agrarian and Technological Institute of Castile - Leon (ITACyL). Valladolid, Spain

*To whom all correspondence should be addressed:

Dr. M. I. Santín-Montanyá

Environment-Agronomy Department, Instituto Nacional de Investigación y Tecnología

Agraria y Alimentaria (INIA)

Ctra. de la Coruña Km. 7.5, 28040, Madrid, Spain.

Telephone and fax: +34 91 347 87 08; +38 91 347 14 79

E-mail address: [email protected]

Short running title: Weed response to soil tillage in barley systems

Abstract

In barley cropping systems of northern Spain, agronomic practices and weather

conditions are key components of weed control efficacy. We compared the short-term

effects of conventional tillage (CT) with minimum tillage (MT) and zero-tillage (ZT), in

barley monoculture and barley rotation systems. Weed density and weed species

number were measured at tillering and flowering barley stages. We found that tillage

system can influence weed density and weed species establishment due to, in part, the

available light for weed seeds.

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mailto:[email protected]

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The results obtained indicate that MT system facilitate the prevalence of the grass weed

Bromus diandrus Roth (50.37%) and the annual dicots Galium aparine (L.) and

Lithospermun arvense (L.) abundant were high in MT system too, 43.71% and 43.97%

respectively. The germination of these species showed high dependence on light

availability. We saw that barley-monoculture plots had a great infestation of Bromus

(71.29%) and barley-rotated plots presented more infestation of Galium and

Lithospermun (74.36% and 84.4%). After herbicide application, weed infestation in

conservation systems was reduced in barley-rotated plots compared to barley-

monoculture. If conservation systems avoided the presence of dominant weeds, the

weight of each weed species was balanced within competitive relationships of the

cropping systems. Our results confirmed that MT and ZT systems favour different weed

species emergences in barley-rotated plots. The combination of MT and barley rotated

cropping system resulted in terms of greater weed diversity and lower total weed

density.

Keywords: Agro-ecosystems; germination; light dependence; weed community;

conservation tillage

Introduction

Changes in weed density and weed community composition are dependent on variations

in agronomic practices and as result of selection pressure. Studies indicate that

minimum tillage, diversifying rotations, some fertilizers strategies, and combinations of

these techniques, can be effective methods of reducing weed density (Schutte et al.,

2014; Sullivan et al., 2013; Harker and Clayton, 2003). Information regarding

interaction of agronomic practices with weed species biology and environmental

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conditions (data collected from field experiments) can provide a broad basis for

understanding weed response to agronomic and environmental factors.

In agricultural environments, weed seeds fall from the mature plants in different

maturity stages. Light has an influence on the germination of the seeds of a high number

of species. Although there seems to be no single scheme of the action of light on

germination, this process has an impact on the state of dormancy or the maturity level of

the seeds. Therefore, weed germination varies greatly by species, for some weeds all

seeds complete germination within a few weeks while other can take months.

In this context, soil tillage plays a crucial role, as it affects both the productivity of the

cropping systems in terms of yield as well as its environmental impacts (Weber et al.,

2017). Tillage causes soil disturbances, which affects weed infestation (Forcella 2000;

Chachalis and Reddy 2000; Swanton et al., 2000). The effects of tillage on weed flora

vary widely due to differences in local conditions and weed management. In some

cases, weed increase in non ploughed soils because exposure to light induces the weed

emergences from the top layer (Hartmann and Nezadal 1990; Mohler and Galford 1997;

Grundy et al., 1999; Botto et al., 2000). In Mediterranean agro-ecosystems, the seeds

exposure to light, due to different soil tillage systems, is an important factor that can

increase or hinder the germination and emergence of weeds. Increasing our

understanding of species that emerge and growth under similar conditions would allow

us to improve efficiency of control and efficacy as well within species assembly.

In northern Spain, non-inversion conservation tillage techniques (minimum-tillage and

zero-tillage systems), in winter barley systems, are very dependent on herbicides, which

are expensive. They are therefore both considered high input systems. Cost being an

important factor for farmers, explains why, when they convert conventional systems to

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conservation systems, they prefer minimum tillage, because they can reduce input costs

by adapting existing machinery.

Weed control in these non-inversion tillage systems is very difficult to achieve, with

only herbicides as a resource (Rydahl, 2004) and it will depend to a high extent on the

tillage system variant put into practice (Dorado and López-Fando, 2006). Also, the

specific weeds in the area and the crop selection on the land are considered worthy

being analysed, because weeds germination can take advantage over crops due to,

among other factors, the weather variability, which complicates the choice of

agricultural practices and cause serious economic losses, and/or which require special

control measures. In winter barley crops, conservation tillage demands a particularly

effective weed control strategy; this is in terms of sufficient doses to control weeds and

a high efficacy level herbicide, as shown by Cussans et al. (1988). Other researchers

focus their efforts to reduce the dependence on herbicides (Derksen et al., 2002) by

means of the development of strategies that minimize densities of weeds as crops

establish, and keep weed communities out of equilibrium to reduce the dominant weed

species (Légère and Samson, 1999). Buhler (2002) highlighted the challenge of

integrating multiple weed management strategies into integrated weed management

systems. A common solution in the northern provinces of Spain is using a legume in the

rotation. Liebman and Davis (2000) reported that crop rotation works to diversify weed

populations, which prevents the prevalence of a single dominant weed species.

In this article, we show a field study that assesses the effects of weed control, by means

of herbicides, in conjunction with soil tillage techniques in barley monoculture and

barley within cropping sequence, determining the extent to which agronomic practices

effect the weed community . Bearing this in mind, the overall objective of this research

was to achieve a good understanding of the relationship between agronomic practices

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(tillage, crop rotation and herbicides) and environment conditions. As specific objective,

we compared the short-term effects of conventional tillage and conservation tillage. We

looked at weed density and weed species, in barley monoculture and barley rotation

systems. In this context, our hypothesis was that conservation tillage techniques

combined with crop rotation would affect weed populations in a different way (better

weed control) than conservation tillage in monoculture.

Material and methods

An experiment was established in 1998 at the Torrepadierne farm (42º13’17’’N,

4º22’45’’W), located on the Duero Valley cereal belt in the Spanish province of Burgos.

The soil, classified as Typic Calcixerolls, is characterized by a loamy-clay texture in the

upper surface horizon, gradually changing to clay with depth (SSS, 1994). Its mean pH

is 8.3, its bulk density 1.13 g/cm3 and its organic matter content 1.8%. The area has a

Mediterranean-continental climate, according to Papadakis classification (1966), with a

frost-free period running from 3 May to 22 October, with average annual rainfall of 447

mm, and average annual temperature of 9°C. These climatic conditions are suitable for

cereal grain production. The monthly rainfall in the years and months of the experiment

is showed in Figure 1.

The experimental design was a four-replicated split-plot randomized complete block, in

which tillage was the main factor (plot) and crop system the secondary factor (sub-

plot).Three tillage systems were: mouldboard ploughing [conventional tillage (CT), at

30-45 cm], chisel [minimum tillage (MT), at 10cm], and zero-tillage (ZT). The cropping

system was based on winter barley monoculture (Hordeum vulgare L.) and winter

barley rotated with winter wheat (Triticum aestivum L.), and vetch (Vicia sativa L.).

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The three tillage systems were randomly assigned to the experimental plots in 1998 and

were maintained until 2001, and the rotational schemes were also randomly assigned

into each main plot. In this study, we compared barley monoculture vs barley rotation

plots for each tillage system. Every year, the study covered twenty-four elementary

plots of 450 m2 (15 × 30 m). Table 1 shows the list of treatments.

The crops were sown at the end of autumn, according to soil moisture conditions, with a

Sola Super 395-sd (SOLA, M.A. Santidrián, Burgos, Spain) driller on the same day in

November in all tillage systems, which were managed in accordance with local practice.

Preparatory works was conducted in early November, 15-20 days approximately before

the seeding. In CT, the crop residue was packed into bales and, in MT and NT, crop

residue was not removed. Plots were sown with 180 kg ha-1 of winter barley (cv.

Tipper), 200 kg ha-1 of winter wheat (cv.Marius) and 160 kg ha-1 of vetch (cv. Buza).

CT and MT plots were fertilised yearly with the mineral fertilizer 8-24-8 (N, P, K) at

400 kg ha-1, which was applied at seedbed preparation. In ZT plots, this fertilizer was

applied at planting time. In addition, in the subsequent tillering-stem elongation phase,

300 kg ha-1 of ammonium sulphate (27-0-0) was applied. A pre-sowing herbicide

treatment of glyphosate (360 g a.i. ha-1) was applied on minimal and zero-till plots. In

all crops, post-emergence herbicides were employed over the whole field: in all cereals,

ioxinil (187.5 g a.i. ha-1) plus bromoxinil (187.5 g a.i. ha-1) plus mecoprop (937.5 g a.i.

ha-1) and tralkoxydim (400 g a.i. ha-1) were applied. Propaquizafop at 100 g a.i /ha plus

80% nonionic surfactant (0.5 l ha-1) were applied in vetch plots.

Each year, weed species were identified and counted in two randomly sampled quadrats

(0.25m2) per sub-plot, within a 5 × 10 m central area, to avoid edge effects. Sampling

took place at the start of March, before post-herbicide treatment to control weeds, and at

the end of May every year. Sampling time was based on general tillering for cereal

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(stage 24 on Zadoks scale) and cereal flowering (stage 59 on Zadoks scale) (Zimdahl,

2004). Both stages are critical competition stages for weeds.

The data were recorded on the following parameters:

Weed density m-2: a quadrat of 0. 25 m-2 was thrown two times in each sub-plot, then

were recorded the number of weeds and were calculated per unit area (1 m2).

Relative weed density m-2 (RWD): we generated, the value for relative density by using

the following formula:

RWD = (Number of weeds of a particular species / Total number of weeds counted) x

100

A linear mixed model analysis of variance was carried out to compare the tillage

systems and cropping systems as fixed effects terms and year as random effect, over a

3-year study period, on all weed data collected for tillering stage (total weed density and

relative weed species density). At flowering stage of cereal, we also analysed the total

weed density as a linear mixed model.

Means were separated by using the Tukey´s HSD Test, calculated at α = 0.05. Weed

density data were log transformed prior to analysis to meet the normality assumptions

associated with ANOVA. For presentation, the Figures 2 and 3 show the back

transformed data. The statistical analyses were performed using the software package R

Studio (R Development Core Team, 2013)

Results

The field experiment was located in an intensively managed agrarian region.

Precipitation levels were different every year, in terms of total and monthly rainfall

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(Figure 1). 1998-99 was extremely dry (329.7 mm), in 1999-00 precipitation levels

(451.4 mm) were similar to historical mean. The highest rainfall level (602.2 mm) was

recorded in 2000-01, although cumulative precipitation from April to June 2001 was

only 50.6 mm

The results showed that total weed density, at both tillering and flowering stages of

cereal, was significantly affected by tillage techniques, and the cropping systems (Table

2). Throughout the experiment, significantly higher levels of weed infestation with MT

and ZT compared to CT were observed (Figure 2A and 2B). In general, post-emergence

herbicides controlled the total weed density. The last year of study, characterized by

highest total rainfall and high total weed density at tillering stage, we saw the best

performance of post-emergence herbicides.

The effects of tillage technique in combination with crop system significantly affected

the total weed density at tillering and flowering stages (Table 2). At tillering stage, in

all tillage systems, we observed higher weed density values in barley-rotated compared

to barley-monoculture (Figure 2A). At flowering stage, after application of post-

emergence herbicides, weed infestation was reduced in all plots. The reduction in weed

density was greater in barley-rotated plots compared to barley-monoculture, in

conservation systems even though the initial density values were much higher (Figure

2B). This higher herbicide efficacy in barley-rotated plots in conservation systems was

probably due to a greater weed species variety. Herbicides were less effective when the

grass weed species Bromus diandrus Roth dominated in monoculture plots. Therefore,

by avoiding the appearance of a singular dominant weed species in rotated plots, weed

density was reduced dramatically.

Significant differences in weed species composition were found when comparing tillage

or crop systems, during the 3-year study period, at tillering and flowering stages of

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barley (Table 2). In both cereal stages, the number of species varied between the three

soil tillage systems, with highest values generally found in MT plots (Figure 3A and

3C). In both barley tillering and flowering periods, the weed number of species was

significantly higher in barley-rotated than barley monoculture plots (Figure 3B and 3D).

Table 3 shows the relative weed density (RWD) data of the most common persistent

weed species after the application of post-emergence herbicides. Regarding the relative

abundance of grass weeds, Avena sterilis (L.), during the experiment, this species

showed less density in conventional tillage systems (24.35%) than in conservation

systems, minimum tillage and zero-tillage (39.21 and 36.43% respectively). Although

its relative density did not show great differences between barley-monoculture (52.07%)

and barley-rotated (47.92%) plots, The other grass weed of this study, Bromus diandrus

Roth, is of particular concern in minimum-tillage and zero-tillage plots (50.37% and

42.19%) in contrast with CT plots (7.42%). and was especially abundant in barley-

monoculture (71.29%) compared to barley-rotated (28.70%) plots. This suggests that

both grass weeds were affected by different agronomic practices.

The dicotyledonous Galium aparine (L.) took advantage of minimum tillage fields

(43.71%), where it showed a significant prevalence. We also observed high values of

this species in ZT (34.34%) compared to CT plots (21.94%). We found this species

consistently present in barley-rotated plots (74.36%), despite the use of post-emergence

herbicides, compared to monoculture plots (25.63%). Lithospermun arvense (L.) was

more abundant in MT (43.97%) than CT (25.93%) and ZT (30.09%), and the density of

this species was particularly abundant in barley- rotated (84.74%) compared to barley-

monoculture plots (15.25%). Papaver rhoeas (L.) density was highest under ZT

(40.65%) and was higher in barley-monoculture (74.52%) than rotated (25.47%) plots.

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In contrast, Polygonum aviculare (L.) showed more density in conventional tillage

(51.37%) than conservation tillage, minimum tillage and zero-tillage (33.48% and

15.20% respectively).This dicot weed was particularly abundant in barley- rotated

(61.96%) compared to barley-monoculture plots (38.08%) during the experiment.

Sinapis arvensis (L.) was not affected by tillage systems but it showed more density in

barley-rotated (71.18%) than barley-monoculture plots (28.81%).

Discussion

In general, our short-term monitoring of this site indicated that there were significant

differences between conventional and conservation soil tillage techniques in total weed

density. These differences between the tillage techniques were consistent particularly

with the annual grass Bromus diandrus Roth and the annual dicot Galium aparine (L.).

We consistently observed that both species were more abundant in MT and ZT than in

CT plots. However, Torrensen (1998) found that for most of annual weed species, in the

experiment, a more intensive tillage resulted in greater emergence in the field. In this

study was reported the highest emergence rates in ploughing, intermediate rates in

minimum-tillage and the lowest rates in zero-tillage. Contrary findings by Torrensen et

al. (2007) were observed in the long-term. They reported that weed flora increased with

less intensive tillage compared to ploughed plots, especially perennial weed species.

Soil tillage alters soil seed depth (Cousens and Moss 1990; DuCroix Sissons et al.

2000). Conservation and conventional soil tillage techniques move weed seeds within

the soil profile in different ways (Gallagher and Cardina 1998). Shaner and Beckie

(2014) propose that soil management methods can be used to control the dominance of

problematic weeds. The conditions created in the topsoil, in particular the soil moisture

and light availability, due to different soil tillage technique leads to variations of weed

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emergences (Bullied et al. 2003). Therefore, a better understanding of the ecology of

these weeds is important to improve farm management regarding weed control.

In Northern Spain, Bromus diandrus Roth is widespread (Riba and Recasens, 1997;

Arrúe et al., 2007), proliferating in wheat and barley with the introduction of

conservation tillage over the past 20 years (Young and Thorne, 2004; Kleemann and

Gill, 2006). Pre-sowing control of this species, with glyphosate treatment, leads to

extended seedling establishment and avoidance of early control measures (Kleemann

and Gill, 2006). Furthermore, chemical control of B. diandrus in post-emergence is

usually not completely effective and surviving plants are able to restore, maintain or

even increase the infestations. The use of mesosulfuron-methyl plus iodosulfuron-

methyl sodium offers an efficient control of B. diandrus (Couloume and Adrien, 2005;

Rapparini et al., 2006). However, this post-emergence herbicide is selective in wheat

but not in barley, which is the main crop in the region. Although there is little published

information about Bromus diandrus Roth, we know more information about related

species such as B. rigidus and B. hordeaceus. Germination in these species seems

dependent on light, and this means that seeds closer to the surface are more likely to

germinate, in fact, the majority of these weeds emerge from the top layer (often less

than 3cm) (Grundy et al., 1999; Mohler and Galford, 1997). Conventional tillage is

therefore a useful strategy to control B. diandrus because the ploughing movement

pushes the seeds deeper into the ground. ZT management practices reduce soil

disturbance and keep B. diandrus seeds near the soil surface, a more favourable

condition for germination and seedling establishment. Additionally, the general lack of

B. diandrus specific herbicides (Dastegheib et al., 2003), has accentuated the spread of

this species.

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Regarding the other grass weed, Avena sterilis (L.) germination also seems dependent

on light and CT system controlled this species better than MT and ZT systems.

With respect to the dicot weed species in our experiment, we found that Galium aparine

(L.) was increasingly problematic in MT systems. In this context, Reid and Van Acker

(2005) clearly showed that under field conditions, Galium genus is facilitated by tillage,

even low-intensity, minimum tillage. Chauhan et al. (2006) concluded that Galium

tricornutum seedling establishment was higher under minimum tillage (25 to 27%) than

ZT (15 to 18%) in the field. Similarly, Lithospermun arvense (L.), showed higher

density in conservation system (MT) than conventional system (CT). Other dicot weed

species of our study, Papaver rhoeas (L.) was highest under ZT, and its germination

seemed dependent on light. In contrast to Polygonum aviculare (L.) that was abundant

in CT system, and its germination was less dependent on light. And Sinapis arvensis

(L.) was not affected by tillage techniques, therefore it’s germinationis likely influenced

by other untested factors.

The cropping systems affected the weed relative density. B. diandrus Roth, as dominant

weed in our experiment, showed a better control in barley-rotated system than in barley-

monoculture plots. In contrast, the relative weed density of dicot weeds in this study

showed higher values in barley-rotated than barley-monoculture plot. These results

confirm us that, without dominant species, the weeds have a balanced weight within

competitive relationships in barley-rotated systems.

Our estimation of total weed species number in each cropping system shows us that a

crop-rotation system is an agronomic practice that favours weed species diversity

compared to monoculture systems.

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Conclusions

In arable fields, weed communities vary according to agricultural practices. Therefore,

all information must be understood in light of the interaction of agronomic practices

with weed species biology and environmental conditions. We found that soil tillage

influences germination and emergence of weed species due to, in part, the available

light conditions created by each tillage technique. Giving this kind of information

allows farm managers to adopt specific tillage practices based on detection of certain

weeds to avoid dominance of a single species.

Despite the fact that conservation tillage techniques (minimum-tillage and zero-tillage

systems) conserve soil and reduce tillage costs compared to conventional tillage, they

are still considered high input, expensive, systems because of the dependence on

herbicides to control weeds. Bearing this in mind, we conclude that minimum tillage, as

a tillage technique more available for farmers who want to change from conventional to

conservation systems, combined with a crop rotation. There is a need for further

research focussed on specifically problematic weeds. In order to maximize profits, we

need to improve integrated weed management options for farmers who would like to

have greater weed control while protecting the soil.

Acknowledgments

We are grateful to Spanish Ministry of Economy and Competitiveness, Grant/Award

Number: RTA 2017-00006-C03-01, that supports this study.

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Sullivan, L.S., Young, F.L., Smiley, R.W., and Alldredge, J.R. (2013). Weed and

disease incidence in no-till facultative wheat in the Pacific Northwest, USA. Crop

Protection 53: 132-138.

Swanton, C. J., Shrestha, A., Knezevic, S. Z., Roy, R. C., and Ball-Coelho, B. R.

(2000). Influence of tillage type on vertical weed seedbank distribution in a sandy soil.

Canadian Journal of Plant Science 80: 455-457.

Torrensen, K. S. (1998). Emergence and longevity of weed seeds in soils with different

tillage treatments. Aspects of Applied Biology 51: 197-204.

Torrensen, K. S., Skuterud, R., Tandsaether, H. J., and Hagemo, M. B. (2007). Long-

term experiments with reduced tillage in spring cereals. I. Effects on weed flora, weed

seedbank and grain yield. Crop Protection 22: 185–200.

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Weber, J. F., Kunz, C., Peteinatos, G. G., Zikeli, S., and Gerhards, R. (2017). Weed

control using conventional tillage, reduced tillage, no-tillage, and cover crops in organic

soybean. Agriculture 7 (43).

Young, F. L., and Thorne, M. E. (2004). Weed-species dynamics and management in

no-till and reduced-till fallow cropping systems for the semi-arid agricultural region of

the Pacific Norwesth, USA. Crop Protection 23: 1097-1110.

Zimdahl, R. L. (2004). Weed-crop competition: A review. 2nd Ed., 220. Ames, IA:

Blackwell.

Figure captions

Figure 1. Monthly rainfall (mm) at Torrepadiernes, Spain, in growing seasons 1998-

2001 and historic means values.

Figure 2. Effects of tillage systems by crop systems, over 3-years of study, on total

weed density, at Tillering (A) and Flowering stages (B) of barley.

Figure 3. Effects of tillage systems and cropping systems, over 3-years of study, on

number of weed species emerged in the field, at Tillering (A and B) and Flowering (C

and D) stages of barley.

Tables

Table 1. Experimental designed scheme used in the growing season.

Table 2. Analysis of variance results (F statistics and p-values in italics) for tillage

system, crop system effects over 3 years of study, on total weed density and total weed

species at barley Tillering and Flowering stages.

Table 3. Analysis of variance results (p-values in italics) for tillage system, crop system

and the interaction effects, on weed species density, found over three seasons (1999-

Page 18 of 25



For Review Only

2001). The Relative weed density (RWD) expressed as percentage, at each tillage and

crop systems, after application of post-emergence herbicides.

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For Review Only

Figure 1. Monthly rainfall (mm) at Torrepadiernes, Spain, in growing seasons 1998–2001 and historic mean values.

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For Review OnlyA) B)

0

100

200

300

400

500

CT MT ZT

nº p

lant

s.m

-2

Til lage techniques

B-mon

B-rot

0

100

200

300

400

500

CT MT ZT

nº p

lant

s.m

-2

Til lage techniques

B-mon

B-rot

Figure 2. Effects of tillage systems by crop systems, over 3-years of study, on total weed density, at Tillering (A) and Flowering stages (B) of barley.

TILLERING FLOWERING

Note: Significant level was set at P ≤ 0.05 according to Tukey´s HSD Test. Bars represent the standard deviation of the data.

CT- conventional tillage; MT- minimum tillage; ZT- zero-tillage; B-mon (Barley-monoculture) and B-rot (Barley-rotated).

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For Review Only

A) C)

B) D)

0

1

2

3

4

5

CT MT ZT

nº s

peci

es

Ti l lage techniques

0

1

2

3

4

5

B-mon B-rot

nº s

peci

es

Crop system

0

1

2

3

4

5

CT MT ZT

nº s

peci

es

Ti l lage techniques

0

1

2

3

4

5

B-mon B-rot

nº s

peci

es

Crop system

Figure 3. Effects of tillage systems and cropping systems, over 3-years of study, on number of weed species emerged in the field, at Tillering (A and B) and Flowering (C and D) stages of barley.

TILLERING FLOWERING

Note:

Significant level was set at P ≤ 0.05 according to Tukey´s HSD Test. Bars represent the standard deviation of the data.

CT- conventional tillage; MT- minimum tillage; ZT- zero-tillage; B-mon (Barley-monoculture) and B-rot (Barley-rotated).

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Table 1. Experimental designed scheme used in the growing season.

Main plot (CT/MT/ZT)Year Sub-plot 1

(Monoculture scheme)Sub-plot 2

(Rotation scheme)

1998-99 Barley-monoculture Wheat Vetch Barley-rotated

1999-00 Barley-mononulture Vetch Barley-rotated Wheat

2000-01 Barley-mononulture Barley-rotated Wheat Vetch

Note: Main plot (CT = conventional tillage, mouldboard ploughing at 35-40 cm; MT = minimum tillage, chisel ploughing, 15 cm; and ZT = zero tillage, direct drilling). Sampling was carried out in barley sub-plots: Barley-monoculture) and Barley-rotated.

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Table 2. Analysis of variance results (F statistics and P values) for tillage system, cropping system effects over 3 years of study, on total weed density and total weed species at barley Tillering and Flowering stages.

Tillering Flowering

Treatments Df Total weed densityTotal weed

speciesTotal weed

densityTotal weed

speciesTillage system

(TS) 222.410

(

For Review Only

Table 3. Analysis of variance results (P values in italics) for tillage system, crop system and the interaction effects, on weed species density, found over three seasons (1999-2001). The Relative weed density (RWD) expressed as percentage, at each tillage and crop systems, after application of post-emergence herbicides.

Treatments Avena sterilisBromus diandrus

Galium aparine

Lithospermun arvense

Papaver rhoeas

Polygonum aviculare

Sinapis arvensis

Tillage system (TS) 0.001** 0.000*** 0.000*** 0.022* 0.125 0.000*** 0.236

CT 24.35 7.43 21.95 25.93 15.44 51.32 38.09

MT 39.21 50.37 43.71 43.98 30.13 33.48 30.72

ZT 36.43 42.19 34.34 30.09 54.43 15.20 31.19

Crop system (CS) 0.428 0.000*** 0.000*** 0.000*** 0.038* 0.021* 0.000***

Barley-monoculture 52.07 71.29 25.63 15.25 74.52 38.08 28.82

Barley rotated 47.93 28.70 74.37 84.75 25.47 61.92 71.18

TS x CS 0.441 0.000*** 0.456 0.208 0.008** 0.525 0.006**

Note : CT (conventional tillage); MT (minimum tillage); ZT (zero-tillage).All weed density data were log transformed before analysis.Significant P values are indicated at the 0.05*, 0.001** and 0.0001*** significance level.

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Documents

For Review Only4º22’45’’W), located on the Duero Valley cereal belt in the Spanish province of Burgos. The soil, classified as Typic Calcixerolls, is characterized by a loamy-clay