Between 1994 and 1998, various trials were established on the experimental plots of the Gumpenstein Agricultural Research Centre (BAL). Most of these were implemented as rotational fallows within the crop rotations of the respective arable crops; only at the Bischofshofen site was one plot converted into permanent fallow.
In 1994, part of the permanent fallow trial was established in Bischofshofen, comprising five different variants. The respective seed mixtures were individually formulated for each location. Due to technical reasons, the wildflower meadow could not be sown until spring 1995. The mixtures for the rotational fallows were either taken from literature or used based on personal recommendations.
Of greatest interest were the extent of weed infestation, specifically the distribution and occurrence of certain plants within the sown plots. To determine this, plant identification surveys were conducted for each trial. First, the degree of cover by green plants was recorded, followed by the percentage distribution of the plants. The sown plant species were also documented, providing a good overview of the ratio of desired to undesired plants. In each trial, the self-seeding plot served as a control, as a very specific flora develops depending on the location. For practical reasons, the rotational fallow plots were all spring sowings, mostly consisting of annual plants.
Nevertheless, some of these trials were left standing over the winter, assessed again in the spring, and the development and changes in the plant population were closely observed. The variants consisted partly of clover-grass mixtures and partly of non-legumes, with the latter group forming a dense stand. Furthermore, the fresh biomass yield of each variant was determined in almost all trials, and samples were also taken for the chemical laboratory to determine the dry matter and crude protein content.
Results:
The results clearly show that yields from the Bischofshofen site far exceed those of the other two sites, Gumpenstein and Authal. This is certainly due to the favorable microclimate at this location; furthermore, growth was not impaired by water scarcity. The non-legumes outperformed the clover-grass mixtures not only because of their rapid formation of a dense stand but also because of their high dry matter yield. However, this can pose a significant problem when incorporating the material, especially since plants such as oilseed radish, forage rape, and yellow mustard contain a high amount of crude fiber in their stems soon after flowering. Clover-grass mixtures are much better suited for incorporation as green manure. With regard to nitrate levels, legume-rich crops are considerably more problematic when plowed under. However, the value of clover-grass mixtures as a preceding crop is undeniably high. In addition to trials with various fallow mixtures, a combined trial with a thistle control project was conducted at the Bischofshofen site in 1998. Four different variants were established, consisting of alfalfa grass, spring barley, red clover grass, and a self-seeding crop. Spring barley proved to be the crop under which the creeping thistle spread least effectively, as it developed more rapidly than the other weeds. The two legume mixtures, while otherwise well-suited for weed suppression, were too slow in developing a dense stand, thus providing favorable conditions for thistle spread. Besides weed infestation and biomass production, cost is a crucial factor in selecting a specific fallow mixture. There are significant differences in seed costs, although most clover-grass mixtures are quite similar in price. Added to this are the costs of maintenance and tillage, which may require the use of herbicides if difficult-to-control weeds have become established. Considering all potential problems, incorporating a fallow area into a crop rotation can only be viewed positively from an ecological perspective if appropriate accompanying maintenance measures are also implemented.
