GREENHOUSE EXPERIMENTS ANALYZING THE REGROWTH CAPACITY OF WEED PLANTS AFTER CUTTING

Get Complete Project Material File(s) Now! »

Perennial forage crops (PFCs)

PFCs may consist of various perennial legume species such as lucerne/alfalfa (Medicago sativa), different clovers (Trifolium sp.), and several other legume species (Fabaceae family), as well as different grasses such as Dactylis glomerata, Festuca sp., Lolium sp., Phleum pratens, and Poa pratensis. They are often sown as legume-grass mixtures (Freyer, 2003). Such crops are habitually used for livestock forage production in mixed farming systems (mown for hay or silage or grazed as pasture) (Summers, 1998; Sulc and Tracy, 2007). In contrast to all annual crops, such crops last on the field for more than one year, typically about 2-5 years, sometimes even longer. They may thus be seen as intermediate between annual crops and permanent grasslands or pastures. In the literature, they are referred to with various names including ‘temporary grassland’ (TG), ‘artificial grasslands’, ‘pluriannual crop’, ‘ley crop’, ‘sod crop’, ‘fodder crop’, ‘hay crop’ or even ‘cleaning crop’. Since 1700, sown PFCs substituted the fallow phase of crop rotations in ‘alternate husbandry’ systems (see A.III.8). Both phases may increase soil fertility after depletion by annual crops and disrupt the cycle of diseases, pests and weeds (Freyer, 2003).
During the last 40 years, such ‘mixed’ crop–livestock farming systems have declined, especially in intensive conventional farming systems, while PFCs remained more frequent in organic and integrated systems (Freyer, 2003). In France, the area of temporary grasslands was reduced from 1.5*106 ha in 1970 to 1.1*106 ha in 2000 (-25%), while the surface of all annual crops was strongly increased from 12.2*106 ha to 15.2*106.
i) the splitting of cereal and livestock production to different farms and different regions, ha (+25%) during the same period (Bisault, 2008). Major reasons for this decline include.
ii) the substitution of grass- or roughage-based forages by grain-based forages in intensive livestock production systems.
iii) the availability of tractors replacing draught animals that needed an on-farm forage production, and.
iv) the availability of cheap and efficient mineral fertilizers, herbicides and pesticides that substituted some of the beneficial effects of perennial crops on the following annual crops (Entz et al., 2002; Katsvairo et al., 2006b).

EXPECTED IMPACTS OF PERENNIAL CROPS ON WEEDS

Empirical studies investigating the impacts of perennial crops on arable weeds are very heterogeneous in terms of methodology and not so frequent, probably as the importance of this crop type decreased during the 20th century. In this review, studies were found mainly by using the following key words in popular search engines such as the ‘ISI web of knowledge’ (www.isiknowledge.com) and ‘Google Scholar’ (http://scholar.google.com): “crop rotation”, “temporary grassland”, “forage”, “fodder”, “ley”, “mixed farming”, “alfalfa”, “lucerne”, “clover”, “legume-grass mixture”, “weed management”, “weed community”, “crop protection” and by searching both the references cited in these studies and younger articles citing them. The review was limited to cropping systems in temperate climates and to papers published after 1992, thus not included in the review of Liebman & Dyck (1993).
There are numerous studies comparing weed infestations in different crop rotations. However, most studies include only annual crops. This may also be illustrated by the fact that 26 out of 29 comparisons between rotations and monocultures reviewed by Liebman & Dyck (1993), crop rotations included only annual crops. In the literature search, 15 more recent studies reporting impacts of PFCs on weeds (sometimes described by several successive publications) were retained. These studies will be shortly reviewed in the following (see also the summary in Table 1 of Article 1). 13 studies were based on field experiments, only one study on a weed survey covering a large number of fields of a whole region and one study on interviews of farmers.

Farmers interview

Entz et al. (1995) interviewed 253 farmers known to include forages in their crop rotations in two regions of Canada, Manitoba and Saskatchewan in 1992. 67% of them reported yield benefits and 83 % weed control benefits from including forages in their rotations. Weed control benefits lasted for one (11% of respondents), two (50% of respondents), or more (33% of respondents) years after forages. Forage crops mostly lasted between 3 and 9 years on the fields. This duration mainly depended on forage yield, only 12% of the farmers adjusted it to maximize rotational benefits (Entz et al., 1995).

Regional weed survey

Ominski et al. (1994; , 1999) compared the weed communities in i) 63 cereal fields following 3-6 year old alfalfa stands and ii) 54 cereal fields following at least 5 years of annual cereal grain crops. Cereals after alfalfa were characterized by lower densities of Avena fatua, Brassica kaber, Cirsium arvense, and Galium aparine, higher densities of Taraxacum officinale and Thlaspi arvense while Amaranthus retroflexus, Chenopodium album, Polygonum convolvulus, and Setaria viridis had no consistent or no significant differences.

Field experiments

The largest experimental study was done by Andersson & Milberg (1996; , 1998) on 3 sites in southern Sweden. They compared 4 nitrogen application rates and three 6-year rotations comprising either (i) a 2-yr grass ley, (ii) a 2-yr legume-grass ley, or (iii) spring wheat followed by a repeatedly harrowed fallow applied since 26-30 years. These 2years phases were always followed by winter turnip rape, winter wheat, oats and barley, which was undersown in the two ley rotations. The weed communities differed strongly between the sites and the crops (highest in turnip rape) but did not differ consistently between the fertilisation and rotation treatments and none of the three rotations developed any major weed problems.
Norris & Ayres (1991) observed that yellow foxtail [Setaria glauca (L.) Beauv.] invasion was lowest when alfalfa was cut with an 37-days interval, intermediate for a 31-day interval and highest for a 21-day interval. In two out of three years, delaying the irrigation (14 days instead of 7 days after cutting) further reduced S. glauca density. While yields increased with the cutting interval, economic return was best for the intermediate 31-day cutting interval due to lower forage quality with the 37-day interval.
Gill & Holmes (1997) reported that some farmers in southern Australia include a 2-3 years pasture phase into crop rotations to manage herbicide resistant ryegrass (Lolium rigidum) and Avena fatua. A review of several small field experiments in southern Australia indicated that a combination of grazing by sheep, cutting and other IWM techniques can successfully deplete the seed bank of problematic Lolium weeds. Clay & Aguilar (1998) compared the weed seed banks, weed biomass and corn yields after (i) continuous corn or (ii) corn grown after 2-year-alfalfa stands with three fertilizer and herbicide input levels in South Dakota, USA. Alfalfa had positive impacts on corn yields and weed control, especially for the low and intermediate input systems.
Schoofs & Entz (2000) compared the weed suppressive potential of five different spring seeded one-year forage crops followed by a pea (Pisium sativum L.) test crop. All forage systems were at least as effective as a sprayed wheat (Triticum aestivum L.) control in suppressing Avena fatua L. and sometimes Setaria viridis L. Beauv. grass weeds; however, effects on broadleaved weeds were variable, especially for systems that did not provide season-long competition. In general, one-year forage crops showed significant weed control benefits, but benefits of pluriannual forage crops reported by the same research team (Entz et al., 1995) were stronger. The effectiveness of the different grain and forage crops to reduce weed seed production ranked as following: fall rye (Secale cereale L.) (grain crop) > winter triticale (Triticosecale) (simulated grazing) > spring/winter triticale intercrop (silage, then simulated grazing) > sorghum-sudangrass (Sorghum bicolour [L.] Moench × Sorghum sudanese [Piper]) (hay) = alfalfa (hay) > spring triticale (silage) = weed fallow (silage) = sweet clover (Melilotus officinalis L.)/winter triticale double crop (hay, then simulated grazing) > wheat grain crops with three different herbicide regimes.
Sjursen (2001) monitored the development of weed densities in the seed bank and the emerged vegetation in organic 6-year rotations including 3-year periods of perennial grass-clover leys and a sequence of three annual crops. Seed densities of dicotyledonous weed species were highest after the 3 annual crops (about 17600 seeds m-2) and lowest after the ley periods (7200 seeds m-2 Cardina et al. (2002a) and Sosnoskie et al. (2006) compared the weed seed density, diversity, and community composition between three crop rotations: continuous corn (CCC), corn-soybean (CS), corn-oat-hay (COH) and three tillage systems (conventional, minimum, and no-tillage) that were applied in two 35-year field experiments in Ohio, USA. Crop rotation was a more important determinant of weed seed density and species composition than tillage system. ), indicating a reduced seed input during the ley periods. In the emerged vegetation, species richness decreased from 19-20 during the annual crops to 8 in the third year ley crop while it remained constant in the seed bank (18-21 species). However, correlations between seed bank and emerged weed densities were rarely significant limiting the potential for predicting the actual weed vegetation.
On average, the 3-year rotations had highest total weed seed densities and species diversities, probably due to the strongly reduced herbicide inputs and diversified crop sowing dates in this system, while the plant communities in continuous corn had lowest species diversity and evenness (high abundances prevalence of single weed species such as C. album) and grasses were more frequent in the rotations including hay crops. Moreover, several interactions between the rotation and tillage treatments were significant.
Bellinder et al. (2004) compared the weed seed banks before and after four 2-year crop rotations including alfalfa, clover (Trifolium pratense L.), rye (Secale cereale L.), and sweet corn (Zea mays L. var. rugosa Bonaf.) with a rye cover crop at three sites in New York, USA. Weed seed banks increased in all four systems. Increases were highest in rye, while seed bank densities did not differ between the two mown forage crops and corn, although pre- and post emergence herbicides and soil tillage (disking) was used only in corn.

Discussion and limits of the reviewed studies

Most of the reviewed studies indicated that PFCs have negative effects on some weed species and positive effects on others (see also the species listed in Table 1 of Article 1). This indicates that PFCs basically tend to change the weed community composition.
The generality of these findings may however be limited as most of the reviewed studies (i) were based on field experiments conducted on one or few experimental sites, (ii) involved rather short duration of forage crops (1-2 years) inserted in rather short experimental rotations (2-4 years) and (iii) often focused on one or few locally important weed species. The only two exceptions are the farmer interviews (Entz et al., 1995) and the weed surveys (Ominski et al., 1999) which were both done in the same region in Canada (see above). These studies might be closer to reality, where forage crops last often for more than 2 years on the fields and farmers often do not apply fixed rotations as in the experiments but adjust their crop sequences and forage crop duration depending on various economic and agronomic factors.
One mean for increasing the generality of experimental results is to understand the underlying mechanisms. Unfortunately, most reviewed studies did not give many details on the mechanisms causing the impacts on weeds. Authors observing reduced weed abundances after forage crops sometimes cited the increased competition or the mowing or grazing activities as possible causes (e.g., Norris and Ayres, 1991; Schoofs and Entz, 2000), while increased abundances were sometimes linked to reduced herbicide use or reduced soil tillage (e.g., Cardina et al., 2002a; Bellinder et al., 2004). Few details were given for identifying which phases of the weed life cycle were mostly affected by PFCs. Only Heggenstaller and Liebman (2006) showed that alfalfa reduced the seedling survival and fecundity of Abutilon theophrasti, the most important weed species in their system.

READ  Effect of N fertilization on the mineral contents in the tissues of the plants

Hypothetical mechanisms causing the impacts

Annual and perennial crops differ in several important aspects concerning both the characteristics of the crop plants and the crop management, including weed control actions (see also Table 4). The impacts of PFCs on arable weeds might therefore be caused by various mechanisms.
1) PFCs are characterized by the absence of soil tillage during the whole duration of the crop (about 2-6 years), thus often much longer than with annual crops, where soil tillage and sowing operations are mostly effectuated once or even several times per year. This may have various impacts on weeds such as a reduced germination of weed species needing light or oxygen stimulus for germination (Huarte and Arnold, 2003) and an increased survivorship of established weed plants.
2) In contrast to these reduced soil disturbances, mowing or grazing may lead to frequent mechanical disturbances of the aboveground vegetation. While most annual crops are harvested only once per year, forage crop cutting is effectuated about 2-5 times per year, thus often both at earlier and later times of the year compared to the single harvesting date of annual crops. This may reduce the survivorship, biomass and seed production of weeds (Gill and Holmes, 1997), although species may strongly differ in their sensitivity to cutting.
3) PFCs are often characterized by strong canopy closures and deep and dense rooting systems. This may cause intense competition against weeds. Compared to annual crops, competition may not only be stronger, but also more extended in time. While annual crops are often characterized by periods of weak competition (i) during crop establishment, (ii) crop ripening/senescence and (iii) after harvest, perennial crops have only one establishment phase in the first year and regrowth after cutting may be faster than initial growth of any (crop or weed) plant leading to temporarily extended vegetation cover and competition against weeds. However, older perennial crop stands may show higher spatial heterogeneities and ‘gaps’ that may be occupied by weeds. The vigour of the perennial crops may decrease with time due to plant senescence and mortality, which is often the reason to terminate the perennial crop stand (Entz et al., 1995).
4) Herbicide use is often lower in PFCs as compared to annual crops, or even completely absent as in organic systems. In most cases, herbicides are only occasionally used during the establishment phase and sometimes for stand termination. Herbicide use reductions may be possible as the weeds are suppressed due to the other mechanisms listed here or by alternative non-chemical weed control techniques adapted to perennial crops (Summers, 1998). Several weed species may also be tolerated in forage crops, as they may have good forage values, while other weed species such as Rumex crispus L., and Conyza canadensis (L.) Cronc. may be rejected by livestock or may even be toxic such as Senecio vulgaris L. (Summers, 1998). Reduced herbicide use in the perennial crops may especially benefit all plant species with high herbicide sensitivities.
5) Fertilization and irrigation schemes in PFCs may also differ from annual crops. Nitrogen fertilization is often reduced or absent thanks to nitrogen-fixing legume crop species. Irrigation may be less necessary than for annual crops due to the deep roots of many perennial crops. Both modifications may reduce weed growth and seed production.

Table of contents :

A GENERAL INTRODUCTION
A.I THE CHALLENGES OF SUSTAINABLE AGRICULTURE
A.II THE ‘WEEDS TRADE-OFF’
A.II.1 Weeds & crop production
A.II.2 Weed control & environment
A.II.3 Weeds & biodiversity
A.II.4 Summary
A.III APPROACHES TO ALLEVIATE THE ‘WEED TRADE-OFFS’
A.III.1 Overview of the approaches
A.III.2 Integrated Weed Management
A.III.3 Combining high weed diversity with low weed abundance? .
A.III.4 ‘Good’ vs. ‘bad’ weeds?
A.III.5 Favouring weed seed predation
A.III.6 Integration or spatial separation of farming and biodiversity?
A.III.7 Temporal separation of farming and biodiversity?
A.III.8 Crop rotation
A.III.9 Perennial forage crops (PFCs)
A.IV EXPECTED IMPACTS OF PERENNIAL CROPS ON WEEDS
A.IV.1 Literature review
A.IV.1.1 Farmers interview
A.IV.1.2 Regional weed survey
A.IV.1.3 Field experiments
A.IV.1.4 Discussion and limits of the reviewed studies
A.IV.2 Hypothetical mechanisms causing the impacts
A.V DIVERSIFIED CROPPING SYSTEM CONCEPT
A.V.1 Expected impacts on weeds
A.V.2 Expected impacts on biodiversity
A.V.3 Expected impacts on the environment
A.V.4 Expected impacts on crop production
A.VI THE RESEARCH PROJECT
A.VI.1 Objectives and questions
A.VI.2 Structure of the thesis
B OVERWIEW OF THE MATERIALS & METHODS
B.I ANALYZING THE IMPACTS OF TEMPORARY GRASSLANDS ON WEED COMMUNITIES: LARGE-SCALE FIELD SURVEYS
B.I.1 Rationale
B.I.2 Methods in analyzing weed composition and crop rotation histories
B.I.3 Statistical analysis
B.II FIELD EXPERIMENTS ANALYZING THE IMPACTS OF TEMPORARY GRASSLANDS ON WEED POPULATIONS (EPOISSES)
B.II.1 Rationale
B.II.2 Design of the field experiment
B.II.3 Data collection
B.II.4 Statistical analysis
B.III GREENHOUSE EXPERIMENTS ANALYZING THE REGROWTH CAPACITY OF WEED PLANTS AFTER CUTTING
B.III.1 Rationale
B.III.2 Design of the greenhouse experiments
B.III.2.1 Differences between species
B.III.2.2 Plant biomass
B.III.2.3 Plant age
B.III.2.4 Cutting height
B.III.2.5 Interactions between cutting and competition
B.III.3 Cutting treatment and data collection
B.IV FIELD EXPERIMENTS ANALYZING WEED SEED PREDATION
B.IV.1 Rationale
B.IV.2 Measuring weed seed predation
B.IV.3 Design of the seed predation experiments
B.IV.3.1 Weed species
B.IV.3.2 Vegetation cover
C RESULTS (ARTICLES & MANUSCRIPTS)
C.I IMPACTS OF TEMPORARY GRASSLANDS ON WEED COMMUNITIES (CHIZÉ)
C.I.1 Article 1: Meiss, H., Médiène, S., Waldhardt, R., Caneill, J. & Munier-Jolain, N. (2010a) Contrasting weed species composition in perennial alfalfas and six annual crops: implications for integrated weed management. Agron. Sustain. Dev. 30, 657-666. 47
C.I.2 Article 2: Meiss, H., Médiène, S., Waldhardt, R., Caneill, J., Bretagnolle, V., Reboud, X. & Munier-Jolain, N. (2010b) Perennial alfalfa affects weed community trajectories in grain crop rotations. Weed Research 50, 331-340.
C.II EXPERIMENTAL ANALYSES OF THE IMPACTS OF TEMPORARY GRASSLANDS ON WEED POPULATIONS
Manuscript 3: H Meiss, R Waldhardt, J Caneill, N Munier-Jolain (in preparation) Mechanisms affecting population dynamics of weeds in perennial forage crops
C.II.1 Introduction
C.II.2 Methods
C.II.2.1 Experimental design
C.II.2.1.1 Weed seed addition
C.II.2.2 Measurements
C.II.2.2.1 Plant densities
C.II.2.2.2 Biomass
C.II.2.2.3 Chemical soil parameters
C.II.2.3 Statistical analysis
C.II.2.3.1 Emerged weed densities
C.II.3 Results
C.II.3.1 Dynamics of emerged weeds
C.II.3.1.1 Dynamics of weed plant density and diversity
C.II.3.1.2 Dynamics of weed community composition
C.II.3.1.3 Dynamics of individual weed species
C.II.3.1.4 Effect of weed seed addition
C.II.3.1.5 Dynamics of weed and crop biomass
C.II.4 Discussion
C.II.4.1 Differences between crop treatments
C.II.4.1.1 Plant densities
C.II.4.1.2 Species composition
C.II.4.2 Grassland management practices
C.II.4.2.1 Sowing date
C.II.4.2.2 Crop species
C.II.4.2.3 Cutting frequency
C.II.4.3 Underlying mechanisms
C.II.4.3.1 Soil tillage (A)
C.II.4.3.2 Competition (B)
C.II.4.3.3 Hay cuttings (C)
C.II.4.3.4 Interactions between the three factors
C.II.4.4 Strength, limits, perspectives and preliminary recommendations
C.III REGROWTH AFTER CUTTING
C.III.1 Article 4: Meiss, H., Munier-Jolain, N., Henriot, F. & Caneill, J. (2008b) Effects of biomass, age and functional traits on regrowth of arable weeds after cutting. J. Plant Dis. Prot. XXI, 493-499.
C.III.2 Article 5: Meiss, H., Bonnot, R., Strbik, F., Waldhardt, R., Caneill, J. & Munier-Jolain, N. (2009) Cutting and competition reduce weed growth: additive or interactive effects? XIIIth International Conference on Weed Biology, Dijon, 28-37.117
C.IV WEED SEED PREDATION
C.IV.1 Article 6: Alignier, A., Meiss, H., Petit, S. & Reboud, X. (2008) Variation of post-dispersal weed seed predation according to weed species, space and time. J. Plant Dis. Prot., XXI, 221-226.
C.IV.2 Article 7: Cordeau, S.; Meiss, H.; Boursault, A. (2009) Bandes enherbées: Quelle flore, quelles prédateurs, quelle prédation? XIIIth International Conference on Weed Biology, Dijon, 50-59.
C.IV.3 Article 8: Meiss, H., Lagadec, L. L., Munier-Jolain, N., Waldhardt, R. & Petit, S. (2010c) Weed seed predation increases with vegetation cover in arable fields. Agric. Ecosyst. Environ. 138, 10-16.
D GENERAL DISCUSSION
D.I EVIDENCE OF THE IMPACTS OF PFCS ON WEEDS
D.I.1 Differences in species composition between current crops
D.I.2 Weed community trajectories during crop rotations
D.I.3 Weed population dynamics under various crop management practices in the small-scale field experiment
D.I.4 Comparison of weed species reactions between the large-scale surveys and the small-scale field experiment
D.I.5 Functional groups
D.I.5.1 Annual vs. perennial weed species
D.I.5.2 Small vs. tall or climbing species
D.I.5.3 Grasses vs. broadleaved species
D.I.6 Weed abundance and diversity
D.I.7 Conclusion: PFCs, useful tools for Integrated Weed Management .
D.II UNDERLYING MECHANISMS
D.II.1 Absence of soil tillage (A)
D.II.2 Competition (B)
D.II.3 Hay cuttings (C)
D.II.4 Interactions between cuttings and competition (B*C)
D.II.5 Seed predation (D)
D.II.6 Overview of the underlying mechanisms
D.III PERSPECTIVES: PREDICTING THE IMPACTS OF PFCS
D.III.1 Mechanistic models
D.III.2 Predicting weed regrowth after cutting
D.III.3 Factors determining weed seed predation
D.IV GENERAL CONCLUSION
E CITED REFERECES .

GET THE COMPLETE PROJECT

Related Posts