Weed Science Conference 2006
Transcrição
Weed Science Conference 2006
Journal of Plant Diseases and Protection Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz Sonderheft XX, 257-265 (2006), ISSN 1861-4051 © Eugen Ulmer KG, Stuttgart Effects of tillage systems on the seed bank persistence and seedling emergence of ten arable weeds A. ROLLER, H. ALBRECHT* Lehrstuhl für Vegetationsökologie, Technische Universität München-Weihenstephan, D-85350 Freising, e-mail: [email protected] * Corresponding author Summary To test the effects of different tillage implements on soil seed bank decline and on seedling emergence, 5000 seeds m-2 of the arable weed species Avena fatua, Echinochloa crus-galli, Stellaria media, Spergula arvensis, Sinapis arvensis, Capsella bursa-pastoris, Raphanus raphanistrum, Thlaspi arvense, Solanum nigrum and Tripleurospermum perforatum were broadcast in experimental plots. The implements were the curry comb, the cultivator and the plough. After 25 months, the percentage of weed seeds recovered ranged from 0-12 %, depending on the species. The highest number of re-detected seeds was for Thlaspi arvense in soils under plough tillage. In contrast, no seeds were recovered from Spergula arvensis and Avena fatua. As there were no significant differences among the three treatments concerning the decline of the soil seed bank, seedling emergence in the curry comb and the cultivator plots significantly exceeded the values of the plots under plough tillage. Keywords: Weeds, seeds, seed bank, soil, persistence, tillage, plough, cultivator, curry comb Zusammenfassung Einfluss der Bodenbearbeitung auf die Persistenz und den Auflauf von zehn Wildpflanzenarten Auf Parzellenversuchsflächen wurden von den Arten Avena fatua, Echinochloa crus-galli, Stellaria media, Spergula arvensis, Sinapis arvensis, Capsella bursa-pastoris, Raphanus raphanistrum, Thlaspi arvense, Tripleurospermum perforatum und Solanum nigrum je 5000 Samen m-2 ausgesät. In den folgenden 25 Monaten wurden der Rückgang der Diasporendichte und der Feldaufgang in Abhängigkeit von der Bodenbearbeitung untersucht. Als Varianten wurden der Striegel, der Grubber und der Pflug in je sechs Parzellen verglichen. Je nach Pflanzenart waren am Ende der Untersuchung noch 0-12 % der ausgebrachten Diasporen vorhanden. Die meisten Samen überlebten bei Thlaspi arvense mit Pflugbodenbearbeitung, für Spergula arvensis und Avena fatua konnten in keiner der drei Varianten noch Samen nachgewiesen werden. Im Rückgang des Bodensamenvorrates zeichneten sich zwischen den drei Bodenbearbeitungsvarianten keine signifikanten Unterschiede ab, die Zahl der aufgelaufenen Diasporen war dagegen in der Striegel- und Grubbervariante signifikant höher als bei Pflugbearbeitung. Stichwörter: Wildpflanzen, Samen, Diasporen, Boden, Persistenz, Bodenbearbeitung, Pflug, Grubber, Striegel Introduction Seeds of arable weeds can survive for many years in the soil seedbank. Thus, the Beal experiment, which has run for more than 100 years (KIVILAAN and BANDURSKI 1981), proved that seeds of arable weeds can persist such a time span in a dormant state without germinating. In this experiment, seeds were mixed with sterilised soil and poured into glass bottles. Further information on weed seed longevity comes from 258 ROLLER, ALBRECHT sites where arable farming had been abandoned for a long time or from undisturbed field plots where seeds had been buried in mesh bags (e.g. BRENCHLEY 1918, ROBERTS and FEAST 1973). These experiments confirmed the high potential of arable weeds to survive in the soil seed bank. However, all these studies do not give a reliable estimation of the longevity of seeds under practical farming conditions where they are exposed to tillage, weed control and crop rotation. Under these conditions, most seeds of arable weeds lose their viability within a few years (SCHWEIZER and ZIMDAHL 1994). Unfortunately, these investigations are time consuming and labour intensive because they demand repeated seed bank analyses and the prevention of any new seed input. Consequently, only a few authors such as BARRALIS et al. (1988), WILSON and LAWSON (1992), LAWSON et al. (1993), LUTMAN et al. (2002) and LUTMAN et al. (2003) provided corresponding studies. On the other hand, such information on weed seed persistence is essential to develop and to improve management systems that are suitable for both weed control and species conservation purposes. Hence, the present study was designed to provide insight into the effects of different tillage treatments on the persistence and the seedling emergence of arable weed seeds under field conditions. As seed persistence significantly varies among species, 10 different taxa were included. Materials and methods The investigation was carried out on a sandy loam at the agricultural research station of the Technische Universität München in Roggenstein, Germany. The experimental plots were arranged in 3 blocks each consisting of two replicates of three tillage treatments: curry comb, cultivator and plough. The blocks were placed at different sites of the farm. Each of the two replicates was sown with a variety of oilseed rape: either Falcon or Liberator. As these differences did not significantly affect the weed populations, the variable ‘crop cultivar’ was not considered in the analysis. Nomenclature1), number of seeds in soil at the beginning of the study and seed traits of the investigated species. Tab. 1: Bezeichnung1), Anzahl der Samen im Boden zu Versuchsbeginn und Sameneigenschaften der untersuchten Arten. Tab.1: Species / Art Avena fatua L. Capsella bursa-pastoris (L.) Med. Echinochloa crus-galli (L.) P. Beauv. Raphanus raphanistrum L. Sinapis arvensis L. Solanum nigrum L. Spergula arvensis L. Stellaria media (L.) Vill. Thlaspi arvense L. Tripleurospermum perforatum (Merat) Lainz Initial number of buried seeds / Samenzahl im Boden zu Versuchsbeginn Seed longevity index2) Seed mass 3) (mg/seed) / Samenmasse 3) (mg/Samen) 5000 5780 5885 1230 5000 1400 5000 5000 5385 5770 0.89 0.91 1.00 0.54 0.91 0.91 0.91 0.80 0.91 0.97 22.76 0.10 1.41 18.68 2.49 0.75 0.27 0.43 1.09 0.29 1) According to/nach WISSKIRCHEN and HAEUPLER (1998) 2) According to / nach THOMPSON et al. (1997) and / und THOMPSON et al. (1998) 3) According to / nach CREMER et al. (1991) At each plot, seeds of ten different weed species were spread at a density of 5000 seeds m-2 in August 2001 (Tab. 1). The size of the plots was 9 x 3 m; the area where the weeds were broadcast was 2.5 x 3 m. These seeds were commercially produced in Germany by the seed grower Conrad Appel in Darmstadt. Effects of tillage systems on seed bank persistence 259 During the course of the experiment no further seeds were spread on the plots. The investigations focussing on the oilseed rape interactions were published by ROLLER (2005). The depth of cultivation of the three different soil-working implements varied from approximately 4 cm for the curry comb to 12 cm for the cultivator and 20 cm for the plough. The first treatment took place the day after broadcasting on 17. August 2001. According to BARRALIS et al. (1988), the cultivation was repeated two times a year in March and in September. The experiment ended after 25 months in September 2003. To minimise seed movement off the plot area, the direction of cultivation was reversed with each treatment. To prevent seed production, established plants were removed by applying the herbicide glyphosate (Roundup Ready®) and by hand-weeding. Soil sampling started in February 2002 and was repeated a few days before cultivation in autumn and spring until September 2003. Four soil cores with a diameter of 7.8 cm were taken per plot, i.e. 24 samples per treatment. To evaluate the effect of different implements on the depth of burial, soil cores were taken from the depths of 0-10 cm and from 10-22 cm. Subsequently, the samples were washed through a series sieves, with a mesh size of 2, 1, 0.5 and 0.25 mm. The residue remaining on the sieves with a mesh size ≤ 0.5 mm was transferred to petri dishes with paper and put into a climate chamber for four weeks where they were exposed to a temperature of 22 °C and permanent light. Seeds were classified as viable when they had developed a radicle of at least 2 mm. Some of the tested species were already present in the soil seedbank before the experiment started. A corresponding analysis revealed initial seed numbers of 885 m-2 for Echinochloa crus-galli, 780 m-2 for Capsella bursa-pastoris, 770 m-2 for Tripleurospermum perforatum and 385 m-2 for Thlaspi arvense. In the analysis, these numbers were added to the 5000 seeds m-2 that were spread on the plots. To calculate the seedling emergence rates, the numbers of weed plants emerging on 4 quadrates per plot, each having a size of 0.25 m² were recorded. Emerging plants were counted and removed every month during the vegetation period. To re-detect the quadrates after the tillage treatments, their coordinates were exactly measured. Recording began 6 weeks after sowing in late September 2001 and ended in October 2003. Seed persistence listed in Table 1 was calculated employing the longevity index proposed by THOMPSON et al. (1998). Its calculation is based on the seed bank database for north-west Europe by THOMPSON et al. (1997) in which the authors allocated each published seed bank record for every species to one of three longevity classes; type 1 (transient, persistence < 1 year), type 2 (short-term persistent, persistence > 1 but < 5 years) and type 3 (long-term persistent, persistence > 4 years). Using these persistence classes, the authors defined the longevity index for individual species as: Σ (type 2 + type 3) / Σ (type 1 + type 2 + type 3). It can take a value between 0 (all seeds transient) and 1 (all persistent). Data on the seed masses were adapted from CREMER et al. (1991) who measured these characteristics in ripe and air-dried seeds from different arable sites in Germany. Results and discussion General development of the weed populations Comparing the effect of the three tillage treatments reveals that they all led to a rapid decline of the soil seedbank. Hence, as early as 13 months after weed seed spreading, more than 90 % of the broadcast seeds were lost. Another 12 months later, only 4.8 % of the sown seeds were recovered in the soil seed bank (median value 3.9 %). These values are distinctly below the annual decline of 40 to 80 % recorded by BARRALIS et al. (1988) and the 20 to 60 % LUTMAN et al. (2002, 2003) found for the predominant part of the species they investigated. This severe decline in the present study may be caused by both higher tillage intensity at two treatments per year and by a minor depth of cultivation. In addition, natural variation in seed losses may have affected the results. Correspondingly, MITZE (1992) and CARDINA et al. (1996) observed that the percentage of newly produced seeds, which were not recovered in the soil seed bank, can range between 70 % and 99 % Despite this rapid decline of the soil seed bank, seeds of all tested species survived for more than one year in the diaspore pool of the soil (Tab. 2). This means that – even under the practical conditions of arable farming – all species have developed a ‘persistent’ seed bank in the sense of THOMPSON et al. (1997). Developing a persistent seed bank is an important survival strategy in arable ecosystems where 260 ROLLER, ALBRECHT regular tillage operations, herbicide applications and rotating crops hold a high risk of extinction for the weed populations. The rapid initial decline turning into a moderate decrease suggests that the seed input comprises both non-dormant and dormant seeds (COUSENS and MORTIMER 1995). If the non-dormant fraction is more abundant, the seed number rapidly declines due to losses from germination, fallowed by a more gradual decline due to degradation and slower germination as the remaining seeds are released from dormancy. These weed populations may be classified into ‘seedbank type III’ of THOMPSON and GRIME (1979) which is characterised by a low percentage of persistent and a pronounced seasonal peak of immediately geminable seeds. Corresponding results by BARRALIS et al. (1988) and LUTMAN et al. (2002, 2003) suggest that arable weeds generally follow this strategy under practical farming conditions. The use of different tillage implements affected the persistence of seeds in soil only moderately. Thus, > 6 % of the seeds initially broadcasted were recovered from plots with plough tillage compared to about 4 % from those with non-inversion tillage. This difference can be interpreted as diverging effects of the tillage implements. Thus, ploughing moves the majority of the freshly shed seeds from the surface deeper into the topsoil. In the course of repeated treatments, this leads to a more or less homogeneous distribution of the seeds over the plough layer (Fig. 1). In contrast, non-inversion tillage with the curry comb or with the cultivator leaves the seeds near the soil surface (CLEMENTS et al. 1996, O’DONOVAN and MC ANDREW 2000). The precision of this seed bank analysis may have been affected by seed movement away from the sown area by the tillage operations. This problem is particularly important when the investigated research area is small. REW and CUSSANS (1997) found a mean seed dispersal distance of 0.43 m on tined plots and 0.87 m on ploughed plots, and MAYER et al. (2002) also observed higher distances for the plough compared to various non-inversion tillage implements. Transferring these results to the present study suggests that the difference between the inversion and non-inversion tillage could have been more pronounced without this seed movement. Tab. 2: Percentages of seeds recovered in the soil seed bank 13 and 25 months after the cultivation with different tillage implements. Tab. 2: Prozentanteil der nach 13 bzw. 25 Monaten Bewirtschaftung mit unterschiedlichen Bodenbearbeitungsgeräten in Diasporenvorrat des Bodens wiedergefundenen Samen. Curry comb (Striegel) Months after seed-broadcast (Monate nach Aussaat der Samen) Avena fatua Capsella bursa-pastoris Echinochloa crus-galli Raphanus raphanistrum Sinapis arvensis Solanum nigrum Spergula arvensis Stellaria media Thlaspi arvense Tripleurospermum perforatum Mean value (Mittelwert) Median value (Median) Cultivator (Grubber) Plough (Pflug) 13 25 13 25 13 25 1.9 3.6 3.9 2.1 0.2 29.3 0.3 15.0 13.1 24.1 3.9 0.9 1.3 11.2 3.3 16.1 3.1 10.7 3.0 4.3 0.4 20.6 0.2 8.6 5.1 13.0 2.8 0.4 2.1 0.4 8.8 3.7 12.6 9.7 0.7 5.2 5.6 5.4 1.0 25.0 9.1 17.4 11.7 5.7 5.6 1.4 0.6 12.5 4.2 28.1 4.4 9.3 3.8 4.0 2.0 6.6 4.7 4.1 2.5 8.1 5.5 6.3 4.3 Effects of tillage systems on seed bank persistence 261 At the soil surface, factors that stimulate seed germination (good oxygen supply and light conditions, varying temperatures and an inconsistent availability of water) are expressed to a greater extent than in deeper soil layers. In addition, seeds deposited near the surface do not need to penetrate thick soil layers to establish seedlings. Accordingly, a Mann-Whitney test revealed significantly higher seedling emergence rates in the plots with non-inversion tillage than in those with the plough treatment. No significant difference occurred between the two variants of non-inversion tillage. The seedling emergence rates recorded in the present study are clearly above the values observed by BARRALIS et al. (1988). Although their investigation went on for five years, there were only a few species that exceeded the 10 % seedling emergence rate. As the soil had been ploughed to a depth of 25-30 cm in their experiments, the authors suggested that deep burial was an important reason for this low emergence (and the high number of seeds in soil described above). In the present study, depth of ploughing was 20 cm and most of the seeds in the non-inversion tillage plots were allocated close to the soil surface. In addition to this minor depth of burial, continuous removal of crop and weed plants from the soil surface may have facilitated the access of light and the stimulation of seed germination. As all these factors that favour germination simultaneously reduce the soil seed bank (ZWERGER and HURLE 1986), they may have additionally contributed to the low number of seeds in the soil seedbanks found in the present study. Depth distribution/ Tiefenverteilung 25 20 15 0 – 10 cm 10 5 5 10 – 22 cm 10 15 20 Curry comb Striegel Cultivator Grubber Plough Pflug Fig. 1: Depth distribution of all seeds found during the study period of 25 months depending on the tillage treatment. Abb. 1: Tiefenverteilung aller über den Untersuchungszeitraum von 25 Monaten gefundenen Diasporen (%) in Abhängigkeit von der Bodenbearbeitung. Development of individual species The individual species distinctly differed in their seed bank development (Tab. 2). According to their decline, species can be classified into the following three groups: 1. None of the seeds were recovered 25 months after seeding: Avena fatua, Spergula arvensis. 2. 0.1-10 % of the buried seeds survived in the soil seedbank: Capsella bursa-pastoris, Echinochloa crus-galli, Raphanus raphanistrum, Sinapis arvensis, Stellaria media, Tripleurospermum perforatum. 3. More than 10 % of the seeds were re-detected in the soil samples: Solanum nigrum, Thlaspi arvense. A rapid decline for Avena fatua was also reported by LUTMAN et al. (2003) and WILSON (1988). However, a longevity index of 0.89 (Tab. 1) shows that many other authors found persistent populations. This inconsistency may be caused by unstable seed dormancy. In relation to that, PETERS (1982) found that dormancy in Avena fatua is strongly depending on climatic conditions, and that it is particularly low under high temperatures. A moderate seed bank decline was observed for Stellaria media by Lutman et al. (2003), and an above-average seed persistence was reported for Capsella bursa-pastoris, Sinapis arvensis and Thlaspi arvense by BARRALIS et al. (1988), ZWERGER and HURLE (1986) and LUTMAN et al. (2002). 262 ROLLER, ALBRECHT Great differences among species also occurred for the seedling emergence rates. Adding up all plants which germinated in plots with curry comb and cultivator treatment (Fig. 2), the highest values were recorded for Raphanus raphanistrum, Avena fatua, Solanum nigrum and Echinochloa crus-galli. In these plots, more than 25 % of the broadcasted seeds produced seedlings. The maximum value was 68 % for Raphanus raphanistrum in the cultivator treatment plots. Percentages of emerging seedlings between 10 % and 25 % were observed for Spergula arvensis and Sinapis arvensis, and values < 10 % were recorded for Stellaria media, Capsella bursa-pastoris, Tripleurospermum perforatum and Thlaspi arvense. In the plough treatment plots, the emergence rate was 8 % for Solanum nigrum and below 3 % for all the other species. These results correspond well with the annual seedling emergence rates of < 1 % to 4 % WILSON and LAWSON (1992) observed for seven dicotyledoneous weeds in regularly ploughed plots. For some of the species, the highest numbers of seedlings were not recorded in the autumn of sowing but in the following years (Fig. 2). In the ploughed plots this phenomenon can be explained easily: plough tillage buries the seeds, which do not return to the soil surface until the next treatment (TØRRESEN 1998). For Capsella bursa-pastoris, Solanum nigrum, Thlaspi arvense and Tripleurospermum perforatum, however, delayed germination was also observed in plots with non-inversion tillage. This behaviour may have been caused by high stratification requirements or dormancy that is only broken under very specific environmental conditions. Relating the weed seedbank decline and the seedling emergence rates to the seed traits listed in Tab. 1 suggests a strong relationship of the weed population dynamics to the seed attributes of individual species. Hence, both a rapid decline of the soil seedbank as well as a high initial seedling emergence rate were characteristic for Avena fatua, Raphanus raphanistrum and Sinapis arvensis. All these species produce particularly large and heavy seeds (see Tab. 1). This observation agrees with THOMPSON et al. (1998) and BEKKER et al. (1998) who found seed persistence to be clearly related to a low seed mass. The suspected cause underlying this relationship is that small seeds would be more easily buried by rain, animals or gravity than larger ones (PEART 1984). When seeds are buried e.g. in the course of tillage, a large seed size enables the plants to germinate from greater depths (GRUNDY et al. 2003) and to establish under a wide range of environmental conditions (WESTOBY et al. 1997). As these options are rather limited for the small seeds, seed persistence seems to be advantageous, because it increases the chances to survive the burial phase and to germinate when favourable conditions recur. This means that the practical farmer may control the seed bank development of large-seeded species by non-inversion tillage. However, the soil seed bank and the emergence rates of Spergula arvensis quickly decreased despite its production of very small seeds. The 25 % seedling emergence rate in the curry comb plots and < 1 % after ploughing shows that this species is extremely sensitive to burial. Thus, not all species follow the regularity described above. In these taxa other factors such as their phylogenetic relationship or adaptation to the living conditions in the former natural habitats may have determined seed size and persistence as well. Fig. 2: Percentage of seeds emerging as seedlings 1, 13 and 25 months after starting cultivation with different tillage implements. Mean values ± SE; means were compared with an ANOVA and post hoc TUKEY-test (P < 0.05) (page 263). Abb. 2: Prozentanteil der 1, 13 und 25 Monate nach der Aussaat aus dem Diasporenvorrat des Bodens bei unterschiedlicher Bodenbearbeitung aufgelaufenen Samen. Mittelwerte mit Standardabweichung; Mittelwertvergleich mit ANOVA und Posthoc-Test nach Tukey (P < 0,05) (Seite 263). Effects of tillage systems on seed bank persistence Avena fatua Raphanus raphanistrum 80 70 60 50 40 30 20 10 0 a a a a b b 1 13 25 40 35 30 25 20 15 10 5 0 a a a a Total 1 Seedling emergence / Auflaufrate (%) a a a a b b b b c 1 13 13 25 Total 35 30 25 20 15 10 5 0 a a a a a b a 20 a 30 15 25 20 10 25 Total Sinapis arvensis a a a 5 c a b b b 0 0 1 13 25 Total 1 a a 10 a a 6 4 b b 2 0 1 13 25 a a a a b b b 1 Tripleurospermum perforatum 13 b 25 Total Thlaspi arvense a 5 a 5 a 4 a a Total 25 a 9 8 7 6 5 4 3 2 1 0 Total 6 4 13 Capsella bursa-pastoris Stellaria media 8 13 10 15 12 b a b 5 b c 1 Spergula arvensis 35 Total 25 Echinochloa crus-galli Solanum nigrum 45 40 35 30 25 20 15 10 5 0 b b 3 3 a 2 b b a 2 1 1 0 0 1 13 25 Total 1 13 25 Total Months after weed seeding / Monate nach der Wildpflanzen-Aussaat Curry-comb / Striegel Cultivator / Grubber Plough / Pflug 263 264 ROLLER, ALBRECHT References BARRALIS, G., P. CHADOEUF, J.P. LONGCHAMP: Longevité des semences de mauvaises herbes dans un sol cultivé. Weed Research 28, 407-418, 1988. BEKKER, R.M., J.P. BAKKER, U. GRANDIN, R. KALAMEES, P. MILBERG, P. POSCHLOD, K. THOMPSON, J.H. WILLEMS: Seed size, shape and vertical distribution in the soil: indicators for seed longevity. Functional Ecology 12, 834-842, 1998. BRENCHLEY, W.E.: Buried weed seeds. Journal of Agricultural Science 9, 1-31, 1918. CARDINA, H., H. NORQUAY, B. STINNER, D. MCCARTNEY: Postdispersal predation of velvetleaf (Abutilon theophrasti) seeds. Weed Science 44, 534-539, 1996. CLEMENTS, D.R., D.L. BENOIT, S.D. MURPHY, C.J. SWANTON: Tillage effects on weed seed return and seedbank composition. Weed Science 44, 314-322, 1996. COUSENS, R., M. MORTIMER: Dynamics of weed populations. Cambridge University Press, Cambridge, 1995. CREMER, J., M. PARTZSCH, G. ZIMMERMANN, C. SCHWÄR, H. GOLTZ: Acker und Gartenwildkräuter. Deutscher Landwirtschaftsverlag, Berlin, 1991. GRUNDY, A.C., A. MEAD, S. BURSTON: Modelling the emergence response of weed seeds to burial depth: interactions with seed density, weight and shape. Journal of Applied Ecology 40, 757-770, 2003. KIVILAAN, A., R.S. BANDURSKI: The one hundred year period for Dr. W. J. Beal’s seed viability experiment. American Journal of Botany 68, 1290-1292, 1981. LAWSON H.M., G. WRIGHT, B.J. WILSON, K.J. WRIGHT: Seedbank persistence of five arable weed species in autumn sown crops. Brighton crop Control Conference, Weeds, 305-310, 1993. LUTMAN, P.J.W., G.W. CUSSANS, K.J. WRIGHT, B.J. WILSON, G. WRIGHT, H.M. LAWSON: The persistence of 16 weed species over six years in two arable fields. Weed Research 42, 231-241, 2002 LUTMAN, P.J.W., N.C. B. PETERS, K. BERRY, R.I. HULL, N.H. PERRY, K.J. WRIGHT: The persistence of seeds of two populations of six arable weeds. Aspects of Applied Biology 69, 195-202, 2003. MAYER, F., H. ALBRECHT, J. PFADENHAUER: Secondary dispersal of seeds in the soil seed bank by cultivation. Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz, Sonderheft XVIII, 551-560, 2002. MITZE, H.: Bilanzierung wichtiger populationsdynamischer Parameter ausgewählter Unkrautarten in Winterweizen. MSc Thesis, Georg-August-Universitaet Goettingen, 1992. O’DONOVAN, J.T., D.W. MC ANDREW: Effect of tillage on weed populations in continuous barley (Hordeum vulgare). Weed Technology 14, 726-733, 2000. PEART, H.M.: The effects of morphology, orientation and position of grass diaspores on seedling survival. Journal of Ecology 72, 437-453, 1984. PETERS, N.C.B.: The dormancy of wild oat seed (Avena fatua L.) from plants grown under various temperature and soil moisture conditions. Weed Research 22, 205-212, 1982. REW, L.J., G.W. CUSSANS: Horizontal movement of seeds following tine and plough cultivation: implications for spatial dynamics of weed infestations. Weed Research 37, 247-256, 1997. ROBERTS, H.A., P.M. FEAST: Emergence and longevity of seeds of annual weeds in cultivated and undisturbed soil. Journal of Applied Ecology 10, 133-143, 1973. ROLLER, A.: Persistenz von Diasporen gentechnisch veränderter Kulturpflanzen und potentiell kreuzungskompatibler Wildpflanzen. Diss. TU München-Weihenstephan, 2005. SCHWEIZER, E.E., R.L. ZIMDAHL: Weed seed decline in irrigated soil after rotation of crops and herbicides. Weed Science 32, 84-89, 1984. THOMPSON, K., J.P. BAKKER, R.M. BEKKER: The soil seed banks of North West Europe. Cambridge University Press, Cambridge, 1997. THOMPSON, K., J.P. BAKKER, R.M. BEKKER, J.G. HODGSON: Ecological correlates of seed persistence in soil in the north-west European flora. Journal of Ecology 86, 163-169, 1998. THOPMSON, K., J.P. GRIME: Seasonal variation in the seed banks of herbaceous species in ten contrasting habitats. Journal of Ecology 67, 893-921, 1979. TØRRESEN 1998: Emergence and longevity of weed seeds in soil with different tillage treatments. Aspects of Applied Biology 51, 197-204. Effects of tillage systems on seed bank persistence 265 WESTOBY, M., M., LEISHMAN, J. LORD: Comparative ecology of seed size and dispersal. In: Silvertown, J., Franco, M., Harper, J.L. (eds.): Plant Life Histories. Ecology, phenology and evolution, 143-162. Cambridge University Press, Cambridge, 1997. WILSON, R.G.: Biology of weed seeds in the soil. In: Altieri, M.A., Liebman, M. (eds.): Weed management in agroecosystems: ecological approaches, 25-39, CRC Press, Boca Raton, 1998. WILSON, B.J., H.M. LAWSON: Seedbank persistence and seedling emergence of seven weed species in autumn-sown crops following a single year´s seeding. Annals of Applied Biology 120, 105-116, 1992. WISSKIRCHEN, R., H. HAEUPLER: Standardliste der Farn- und Blütenpflanzen Deutschlands. Ulmer Verlag, Stuttgart, 1998. ZWERGER, P., K. HURLE: Veränderung der Lebens- und Keimfähigkeit von Unkrautsamen im Boden. Med. Fac. Landbouww. Rijiksuniv. Gent, 51/2a, 325-332, 1986.