Impact of different mechanical weed control methods on weed communities in organic soybean cultivation in Luxembourg

Knowledge gaps have been identified for legumes cultivation in Luxembourg, especially in terms of weed control, where soybean production is still at its initial stages. The study tests different mechanical weed control methods in organic soybean cultivation on-farm. The impacts of different weeding techniques are observed from an ecological point of view, in terms of species number and diversity. The cultivation trials, one-factorial exact trials with four replicates, were conducted on two organic farms in 2018 and 2019. Five different treatments were tested: harrow, interrow cultivator with duck foot shares, interrow cultivator and finger weeder, combination of harrow, interrow cultivator and finger weeder and an intercropping soybean-camelina combined with harrow. For each, the number of weed species, as well as their identification, has been assessed three times: before weed control, after weed control and at the flowering of soybean. Calculated Shannon indexes have quantified the diversity of weeds. Forty-nine weed species have been counted in total, for all sites. Calculated Shannon indexes were common values for organic fields. Weed control has a negative impact on weed diversity. Low abundant species were more likely to disappear, while few species, one to four, keep being more dominant. The use of the interrow cultivator, in combination with the harrow (as blind harrowing) and the finger weeder, tends to lower the most the number of species and the diversity of weeds. Further ecological research is necessary to better determine the interactions between weeds and soybean.