Vilken effekt har lärkrutor på ogräsfloran vid ekologisk höstveteodling?

Abstract: This study forms part of the R&D project "Improved survival of bird chicks in organic fields" managed by the Rural Economy & Agricultural society in Uppsala. The skylark (Alauda arvensis) is a species that has decreased drastically in Sweden as a consequence of more intensive cropping. Studies in England have shown that skylark reproduction can be greatly improved within conventional fields, at a low cost, by establishing patches of bare ground (skylark plots). Within conventional farming, herbicides can be used in case a weed problem arises due to implementation of these skylark plots, whereas this is not allowed in organic farming. This study examined the effects of skylark plots on the weed culture in organic autumn-sown (winter) cereals and whether weeds might cause long-term problems to farmers. The study was conducted in two parts; a field study and a review of the literature regarding the weeds observed. The field study was carried out in 2007 during three weeks in June and three weeks in July, on eleven organic fields with winter cereal in the vicinity of Uppsala. In six of these fields a number of skylark plots (4x4m2) had been laid out during autumn sowing in 2006, whereas the other five fields (control) had no skylark plots. Statistical analyses showed that eight weed species had benefited from the skylark plots. With the help of the literature, these species were reviewed in more detail regarding their potential to become a problem. Four species distinguished themselves as potential problem weeds: Large flowered hemp-nettle (Galeopsis speciosa), common hemp-nettle (Galeopsis tetrahit), common chickweed (Stellaria media) and, in particular, creeping thistle (Cirsium arvense). The weed species that express themselves in a given situation, depend on the abiotic conditions (type of soil, climate) and the biotic conditions (crop, amount and structure of the existing weed population). Good knowledge of the biology of individual weeds is required to make that evaluation and to prevent or eliminate them. Such measures are necessary if skylark plots are to be implemented in a way that is not detrimental to crop production. Of the species mentioned above, particular attention should be given to the presence of perennial weeds, in this case creeping thistle, which in the case of organic cropping merits the following caveat: No skylark plots where creeping thistle is present without possible consequences being carefully considered and remedied. Other species that could cause potential problems include: Coltsfoot (Tussilago farfara), common couch-grass (Elytrygia repens), cleavers (Galium aparine) and sow-thistle (Sonchus arvensis).