16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008 Archived at http://orgprints.org/view/projects/conference.html Weed species diversity and cover-abundance in organic and conventional winter cereal fields and 15 years ago Kaar, B. 1, Freyer, B.2 Key words: conventional / organic farming, diversity, weeds, winter cereals Abstract In this research, we compared the weed species development in conventional and organic winter cereals in Upper Austria. The investigations were done in 2003 in 15 paired conventional and organic farms. Following Braun-Blanquet procedure, a total of 105 weed species were found. 57 of them were found only in organic, four only in conventional fields and 48 in both. Therefore, there were 105 weed species in organic fields and 52 in conventional fields. More of the endangered species (Red List species) were found in organic fields. Low species diversity observed in 2003 compared to that in 1988 in the same field was attributed to higher temperature and low rainfall in the recent years. The question arises if under increasing temperature and dryness the diversity of species is regressing and endangered the biodiversity of weeds and linked with that also insects and other species as well as offers space for weeds with strong competition to cultivated crops. Background and objectives Several investigations have shown, that the diversity of flora and fauna is higher under organic in contrary to conventional farming (e.g. Rasmussen et al. 2006; Frieben 1998, 1988; Plakolm 1989, Callauch 1981). The abandonment of herbicides and pesticides as well as the diversified crop rotations are well known as most important factors influencing this development. Supporting conditions for a high species diversity are not only limited to the arable fields but reach also the environment of the cultivated land e.g. hedges or balks. Plakolm (1989) compared the weed populations in arable fields in organic and conventional fields in the years 1983, 1984, 1985 and 1988 in Upper Austria. In organic farms the weed diversity was higher (steadiness) as well as their dominance. The aim of this research was to study the long term development of weed species on these fields after 15 years. Material and methods We analysed the weeds in the field border area (behind the first grain row) as well as in the centre of a field (minimum of 20m away from field border). Measurements were done by identification and estimation of abundance following Braun-Blanquet (1964) procedure. In addition to the field observations, we collected relevant data on arable techniques for the interpretation of weed data (effects not analysed). 1 2 E-Mail Bernhard.Kaar@gmx.at Division of Organic Farming; University of Natural Resources and Applied Life Sciences (BOKU), Gregor-Mendelstr. 33, A-1180 Vienna, E-Mail Bernhard.Freyer@boku.ac.at, Internet www.nas.boku.ac.at/oekoland.html 16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008 Archived at http://orgprints.org/view/projects/conference.html In 2003, 15 organic and 15 conventional farms, with mainly two fields (total of 59) of winter cereals (triticale, winter rye or winter wheat) were analysed in four arable regions of Austria in the same fields, which were already analysed by Plakolm (1989) 15 years earlier. Whereas the natural conditions of the neighbouring fields were similar, there were differences in the cereals, the varieties, the sowing intensities, as well as pre-crops. The size of analysed area was 50m x 2m along the field border and in the centre of the field following the methodology of Van Elsen (2000). The inventory method combined species abundance (number of individuals of one species) and the dominance (cover of one species in percentage) of the whole test field (coverabundance) (see Dierschke 1994; Braun-Blanquet 1964). The analysis followed the methodology of Fischer (1994). For statistical analysis, we used SPSS. Furthermore we identified Red List (endangered) species of Austria (see Niklfeld 1999). Results and discussion In total, we found 109 weed species, where 57 were only in organic and four only in conventional fields and 48 in both. Therefore, 105 species were found in organic fields and 52 in conventional fields, which translated to 100% more different species in organic than in conventional farms. This high species diversity in organic winter cereals compared to their conventional counterparts was significant at P < 0.05. In most cases the median of species frequency in organic fields was 21-25, whereas in conventional we found only 6-10 weed species. In three of four regions, the weed species in organic farms was considerably higher, while in one region the differences between organic and conventional farms were not clear. In the later case two organic farms has unusually low weed diversity, which we could not explain. Twenty-six species in the Austrian Red List were counted (Niklfeld 1999), where 18 were found in the organic, seven in the conventional fields and one only in one of the conventional fields. 40 Mw Bio MW Konv 35 Anzahl der Arten number of species 30 25 20 15 10 5 0 Region 1 Region 2 Region 3 Region 4 Figure 1: Average number of weed species in organic and conventional fields in four regions in Upper Austria. (Anzahl der Arten means number of weed species; bars represent standard deviations) 16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008 Archived at http://orgprints.org/view/projects/conference.html Highest species diversity was found in the border section of the field, regardless of whether it was conventional or organic. The ratio between species diversity in the border and in the centre of a field was 4:1, whereas in the organic farms the species diversity was twofold more in comparison to the conventional farms. The comparison between investigations done 15 years earlier (see Plakolm 1989) and the current one (2003) showed a distinctively lower species diversity in the later. The tremendous dryness in 2003 and considerable higher temperatures can explain this decline. Temperatures in 2003 were 2.40C higher in the first seven month in contrary to the period of 1960-1990. Further, the current rainfall was 395mm lower compared to the 1960-1990 period, amounting to only 125mm in seven months (ZAMG 2003). Even under these climatic conditions, the median of species diversity was two times higher in organic as in conventional winter cereals. Another reason for the lower species diversity in comparison to Plakolm (1989) was the applied methodology. Whereas Plakolm (ibid) collected weed data from an area ranging from 0.3 to 1.5 ha, we made our observations from an area of 2x100m -2 per field. Furthermore, he integrated the species outside the field along the field border. The analysis of cover-abundance led to the following results: 56 of the 109 species were only found with a cover-abundance of “r” (1-5 individuals /m2). Most dominant endangered species in conventional plots was Anthemis arvensis (“2”; cover 16-25%), all other endangered species were in the rare category (“r”). Most dominant weeds in organic fields were Anthemis arvensis (“3”; cover 26-49%), Centaurea cyanus (“3”), Galium aparine (“+”; cover < 1%), Myosotis arvensis and Sherardia arvensis were mainly rare (“r”). Apera spica-venti, Convolvulus arvensis and Veronica arvensis were dominant in conventional fields (highest values “4”; cover 50-74%). Fallopia convolvulus, Viola arvensis were found in both organic and conventional fields with high dominance (-“1; 1-4% cover /2”). Gnaphalium uliginosum, Kickxia spuria, Stachys annua, Valerianella dentata identified by Plakolm (ibid), were not found in the present study. Instead of that, we found Geranium molle („r“), Holosteum umbellatum (“r”), Rumex stenophyllus (“r”), Trifolium campestre (“r”) and Veronica opaca (“r”) in several organic fields. Trifolium campestre was only found in one conventional field (“r”). Conclusions In organic winter cereal fields, weed species diversity is higher than in conventional fields. The high weed diversity in the field borders is expected in any investigation on weed species. Higher survival rates of endangered species under organic farming conditions are not surprisingly, however in some cases we cannot explain, why some of these species were only found under conventional farming conditions. The lower weed species diversity in comparison with previous analysis seems to be an effect of dryness and higher temperature in 2003. Some species get lost, new ones emerged, but we cannot explain this development with this survey. Today it is of interest to know if further climatic differentiation lead to new weed societies with new competition to and interactions with the cultivated crops. Therefore, investigations over several years can only explain these developments. Acknowledgments Our gratitude is for all farmers who supported us in our field studies as well as Dr. Gerhard Plakolm, for his methodological advice and the support with reference data. 16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008 Archived at http://orgprints.org/view/projects/conference.html References Braun-Blanquet, J., (1964): Pflanzensoziologie. Grundzüge der Vegetationskunde. Springer, Wien. Callauch, R., (1981): Vergleich der Segetalvegetation auf „konventionell“ und „biologisch“ bewirtschafteten Äckern in SO-Niedersachsen. Z. PflKrankh. Pflschutz, Sonderheft IX, 85-95. Dierschke, H., (1994): Pflanzensoziologie. Verlag Eugen Ulmer, Stuttgart. Fischer, R., (1994): Exkursionsflora von Österreich. Verlag Eugen Ulmer Verlag, Stuttgart. 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