The effects of some cover crops on weedspecies seed bank

Transcription

1 Technical Journal of Engineering and Applied Sciences Available online at TJEAS Journal / ISSN TJEAS The effects of some cover crops on weedspecies seed bank Ahmad Reza Mobli 1, Sirous Hassannejad 2* Department of Plant Eco-Physiology, University of Tabriz Corresponding author: Sirous Hassannejad ABSTRACT: In order to evaluate the effects of some cover crops on weed species density and their seed bank in sunflower field, an experiment was done in 2012 at the Research Field of Tabriz University, Iran. The experimental design was a randomized complete block with nine treatments in three replications. Treatments included triticale, hairy vetch, rapeseed, triticale + hairy vetch, triticale + rapeseed, hairy vetch + rapeseed, application of trifluralin herbicide, and controls (weed infested and weed free without planting cover crop). To evaluate the soil seed bank two time sampling took place (before planting and after harvesting sunflowers). Evaluation of seed bank was done by Cardina and Sparrow (1996) method, so the number of seeds per Cubic meters was calculated. Common lambsquarters (Chenopodium album L.), bindweed (Convolvulus arvensis L.), pigweed (Amaranthus sp) were observed in highest density in weed infested treatment. highest reduction in weeds seed bank density was observed in hairy vetch + rapeseed cover crop (53.24%), and this treatment was better than application of trifluralin. using of cover crops as a strategy to reduce weeds seed bank and application of herbicide can be useful in weed management. Keywords: Hairy vetch, Rapeseed, Triticale, Weed Management INTRODUCTION The European Weed Research Society defined a weed as "any plant or vegetation, excluding fungi, interfering with the objectives or requirements of people" (EWRS, 1986). The special features of weeds, such as the large number of seeds produced, the high germination rate and the rapid establishment, the very fast growth and development, the long dormancy, the preservation of vitality, the adaptation to dissemination and distribution, and the vegetative propagation parts, have always made them very strong competitors of field crops. (Douglas, 1995). Seed bank dynamics and seed persistence can have long-lasting effects of weeds on crop yields (Cavers and Benoit, 1989). The weed seed bank and annual recruitment from weeds that escape management practices are the main source of weed infestation in crops. Weed seed bank characteristics can influence both weed population and the success of weed management in cropped fields (Buhler et al. 1997). High seed bank populations can lead to substantial weed densities, and several years of intensive management may be required to minimize the problem associated with such densities (Kegode et al. 199).. The weed seed bank serves as a physical history of the successes and failures of cropping systems and management in a field. Cropping systems have also been shown to affect weed seed bank composition, density, and diversity (Cardina et al., 2002; Tuesca et al., 2004; Murphy et al., 2006; Sosnoskie et al., 2006). Weed control alone is not always enough to prevent proliferation of a certain weed species. This is particularly the case in organic farming, where the efficacy of mechanical weed control often is low. Because of this, many preventive methods including tillage, crop rotation, augmentation of the competitiveness of the crop against the weed, sowing time and harvest time and so on are included in the weed control strategy, particularly in organic farming (Kropff et al. 2000; Rasmussen et al. 2000). A ware of weed seed banks dynamics is an essential step in improving weed management plans (Buhler et al., 1997). Accurate prognostication of potential weed seedling density would allow growers to implement control measures more effectively and could help avoid inappropriate and over application of pre emergence herbicides (Cardina and Sparrow, 1996). The widespread use of herbicides has also created new weed problems, in terms of a shift in the weed populations and herbicide resistant weeds (Lemerle et al., 2001). A growing list of herbicide-

2 resistant weeds (Heap, 2005) reinforces the concept that repeated use of a single tactic for pest control may not only facilitate infestations of the most problematic species, but also may fundamentally change population genetics. Ball (1992) reported that cropping sequence was the most dominant factor influencing species composition in weed seed banks. Field management practices affect weed seedling emergence patterns (Peachey et al., 2004; Van Acker et al., 2004), weed seed bank diversity (Mayor and Dessaint, 1998), seed dormancy and viability (Davis and Liebman, 2003), and seed placement (Cardina et al., 2002; Mohler et al., 2006). All of these factors can have important impacts on seed bank management decisions Many studies have shown the beneficial effects of using cover crops and alley cropping for fertility and weed management, and other benefits (Akobundu et al. 1999; Ekeleme et al. 2000). Researches have indicated an increased weed suppression effect in conservation tillage systems by the inclusion of cover crops in the crop rotation (Teasdale and Daughtry, 1993; Galloway and Weston, 1996; Moyer et al., 2000; Shrestha et al., 2002). Cover crop use in many regions is limited and few investigations have examined efficacy of cover crops without using herbicides. For example, rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.) under no-tillage could only reduce weed density an average of 78% without supplemental herbicides (Teasdale et al. 1991). A wider range of cover crop species under various cultural practices needs to study for weed suppressive effects. Weed suppression by cover crops may involve allelopathy, the potential of which in integrated systems is essentially unknown. Kruidhof et al. (2008) showed the value of incorporating a cover crop in the rotation scheme. Two mechanisms of weed suppression were identified. In autumn, after the cover crop had been planted following the harvest of the main crop, weeds were hampered in their growth and eventually produced less seeds. In spring, after the cover crop residues were mixed through the top soil layer, weed seed germination was inhibited and early growth of the weeds was retarded (Kruidhof et al., 2008). Therefore when seeded, the cover crops can successfully suppress weeds provided they are well established before the emergence of weeds and maintain a uniform coverage of the soil. The idea of planting cover crops is to simulate plant succession aimed at replacing an unmanageable weed population with a manageable cover crop (Samarajeewa et al., 200). Despite the interest in cover crops for weed management which dates back from the early1990s, data on long term effects of cover crops and their management on the weed seed bank are lacking. Data on the weed seed bank contain useful information on past field management and it may allow forecasts of future weed problems (Barberi et al., 1998). Therefore they form an important tool for the evaluation of the effectiveness of alternative crop and weed management systems. The objective of this study was survey effects of triticale ( Triticosecale), hairy vetch (Vicia villosa Roth.) and rapeseed (Brassica napus L.) cover crops on weeds species seed banks. MATERIAL AND METHODS Field study and cover crops treatment This study was conducted in 2012 at the research field of Tabriz University, Iran ( North latitude, East longitude and an altitude of 1676 meters). The soil type was loam (42.4% sand, 38% silt, 19.6% clay, 0.17% organic matter, PH 7.4, and Ec 0.93 ds/m). The experimental design was a randomized complete block with nine treatments and three replications. Treatments included planting triticale, hairy vetch, rapeseed, triticale + hairy vetch, triticale + rapeseed, hairy vetch + rapeseed cover crops two weeks before sunflower (Helianthus annuusl) planting, application of trifluralin herbicide (2,6-Dinitro-N,N-dipropyl-4-(trifluoromethyl) aniline) two weeks before sunflower planting, and controls (weed infested and weed free without planting cover crops before sunflower planting). Triticale, hairy vetch, and rapeseed were down furrow drilled at 180, 45, and 9 kgha -1, respectively. Cover crop treatments were grown during sunflower growing seasons. Oil hybrid sunflower cv. Urofoure was direct top of the furrow drilled (seven rows per plot; 50 cm row spacing; 86,000 seeds ha -1 ) two week after cover crop planting. Taking Samples from the Seed Bankand Statistical analysis Soil samples were taken as described below by using an auger having a diameter of 7.5 cm. The first sampling was done after tillage and before planting, the second sampling was performed after harvesting sunflowers. In each plat two soil sample of 0-10 cm depth were taken. The two soil samples taken in each plat were mixed. The sampling area was one square meter. Next, 100 g of the total soil was weighed and separated. Evaluation of seed bank using Cardina and Sparrow (1996) method were done. Soil samples were passed through sieves with different mesh (0.5, 1 and 0.18 micrometer) and were washed with water and only the seeds and very small stones remained in the sieves. The seeds, together with the sand particles, were dried, counted, and identified to the level of the genus using a binocular stereomicroscope. Those seeds that resisted the pressure applied by forceps and did not yield were assumed to be healthy (Forcella, 1998). Then the number of seeds 3086

3 counted was used to calculate the number of seeds per Cubic meters. Any transformation was not necessary before ANOVA analysis, because data showed a homogeneous variances distribution. Data were analyzed using SAS (ver. 9.1) and mean comparison was conducted according to the Duncan's t-test. RESEULTS ANS DISCUTION Effects of cover crops on weeds species seed density Analysis of variances indicated that weedsspecies seed bank density except birdsfoot trefoil (Lotus corniculatusl.) was significantly affected by treatments (Table 1). Table 1. Analysis of variances of the weeds seed bank. Che.alb. = (Chenopodium album L.), Con.arv. = (Convolvulus arvensisl.), Set.vir.=(Setariaviridis L.), Ama.spp.= (Amaranthussp), Lot.cor.=(LotuscorniculatusL.) S.O.V df Che.alb. Con.arv. Set.vir. Ama.spp. Lot.cor. All weeds Replication * ns ns ns ** * Treatments ** ** ** ** ns ** Error CV (%) *=Significant at 5% level, **= Significant at 1% level, ns=non-significance Dominant weed species observed in this filed were common lambsquarters (Chenopodium album L.), bindweed (Convolvulus arvensis L.), green bristlegrass (Setaria viridis L.), pigweed (Amaranthus sp), and birdsfoot trefoil. The highest density of common lambsquarters, bindweed, and pigweed were observed in weed infested treatment, whereas lowest density of them was observed in weed free treatment. However this treatment didn t have any significant differences with other cover crops treatments. The highest density of green bristlegrass was observed in hairy vetch and weed infested treatments, but the lowest density of that was observed in triticale + hairy vetch and weed free treatments. Pigweed density was reduced in triticale and triticale + rapeseed treatments, so that the lowest density of this weed was observed in plots that triticale or triticale + rapeseed were sown as cover crops (Figure 1) Number of seed per m Che.alb. Con.arv. Set.vir. Ama.spp. Treatments other weeds Figure 1.Effects of treatments on weed species seed bank density (Tri.+Hai.= Triticale + Hairy vetch, Tri.+ Rap.= Triticale + Rapeseed, Hai.+ Rap.= Hairy vetch + Rapeseed) Inhibitory effects of cover crops on weed species seed bank In all cover crops treatments weeds seed bank was reduced. Highest reduction in total weed species seed bank was observed in hairy vetch + rapeseed (Table 2). Minimum reduction in seed bank for all weed species was 3087

4 observed in triticale + rapeseed cover crop treatment. Common lambsquarters and bindweed seed bank was reduced 47.42% and 88.89% in weed free treatment respectively compared to weed infested. Green bristlegrass had minimum seeds in soil seed bank after application of trifluralin, however seed density of this weed was increased in hairy vetch treatment (Table 2). Triticale and hairy vetch + rapeseed caused 51.98% reduction in pigweed seed bank density (Table 2). Miresky et al (2010) cited the five cover crop systems (1 year duration), the summer fallow and the yellow mustard buckwheat winter rape mixture consistently decreased the weed seed bank. The magnitude of decline in these high disturbance systems reached complete depletion of the Setaria spp. Germinable seed bank and an 85% and 80% reduction for C. album and A. theophrasti respectively. In contrast, treatments which involved less soil disturbance had weed escapes that set seed in one or more site years. Cover crop systems that stimulated weed seed germination and where weeds were either suppressed by the cover crop or where subsequent tillage provided control, resulted in the greatest weed seed bank declines. Averaged over a three years period, the seed bank was 55% lower in the tropical kudzu plots and 43% lower in the leucaena plots compared with natural bush (Ekeleme et al, 2003). Table 2. Inhibitory percentage of cover crops on weed species seed bank. Che.alb. = (Chenopodium album L.), Con.arv. = (Convolvulus arvensis L.), Set.vir.= (Setaria viridis L.), Ama.spp.= (Amaranthus sp), Lot.cor.=(Lotus corniculatus L.) Treatments Che.alb. Con.arv. Set.vir. Ama.spp. All weeds Triticale a b bc a ab Hairy vetch a b d ab bcd Rapeseed a b bc b cd Triticale + Hairy vetch a ab ab ab abc Triticale + Rapeseed b a c ab d Hairy vetch + Rapeseed a b a a a Application of trifluralin a ab a ab bcd Weed free a a a ab a + show additive effect and - show inhibitory effect Percent of seeds germinated Highest seed germination in total weed species was observed in hairy vetch cover crop (1.55%). Common lambsquarters, bindweed and green bristlegrass were germinated 2.27%, 2.77% and 32.38% respectively in weed infested treatment. Pigweed in triticale + hairy vetch cover crop with 0.72 % had highest germination. Lowest seed germination for all weed species, bindweed, common lambsquarters, green bristlegrass, and pigweed were observed in application of trifluralin treatment. Weed suppression by cover crops consists in the release of phytotoxic substances and a slow or delayed release of nitrogen from the residue to the soil for which nutrients become available later in the growing season, depriving the weeds of the early competitive advantage that they would have if nitrogen were more readily available (Barnes and Putnam, 1983; Lehman and Blum, 1997). It has been demonstrated that common lambsquarters seed germination in the presence of crimson clover (Trifolium incarnatum L.) residue was lower than in plots with the same nitrogen fertilization level without the residue (Dyck and Liebman, 1994). Figure 2. Effects of treatments on weed species seedgerminated (Tri.+Hai.= Triticale + Hairy vetch, Tri.+ Rap.= Triticale + Rapeseed, Hai.+ Rap.= Hairy vetch + Rapeseed) 3088

5 According to the results of Brainardet al (2008) in surveyof cover cropseffect on weed seed bank and yields in snap bean, sweet corn, and cabbage, like our survey results, cover crops can be used for reduction weed seed bank density inintegrated weed management (IWM) into sunflower production with associated weed suppression and reduce application of herbicides. REFERENCES Akobundu IO, Ekeleme F, Chikoye D Influence of fallow management systems and frequency of cropping on weed growth and crop yield. Weed Research. 39, Ball DA Weed seed bank response to tillage, herbicides, and crop rotation sequence. Weed Science. 40, Barberi P, Cozzani A, Macchia M, Bonari E Size and composition of the weed seed bank under different management systems for continuous maize cropping. Weed Research. 38, Bernes JP, Putnam AR Rye residues contribute weed suppression in no-tillage cropping systems. 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