Effects of management by glyphosate or tillage on the weed vegetation in a field experiment

Abstract

Glyphosate herbicides play a prominent role internationally in weed management due to their broad spectrum effectiveness. There are concerns that a high reliance on glyphosate herbicides will negatively affect biodiversity over time. In Europe, where cropping systems are carried out without glyphosate resistant crops (GMO), glyphosate herbicides are applied between cropping seasons either in combination with or in place of plowing. We explored the effects of mouldboard plowing, chisel plowing, and glyphosate herbicide application (in a dose reflecting 100% of the manufacturer’s recommendation and a dose reflecting 50%) on weed species number, density, true diversity and community composition. The field experiment was conducted for three consecutive years in a randomized plot design on a naturally occuring weed community without a crop.A total of 83 species and 4 genus were identified over the three years of surveying. By applying a Multinomial Species Classification to the dataset, it was determined that root and rhizome propagating species as well as annual agricultural weeds with no pronounced seasonality in their germination were rarer on glyphosate treated plots than on tillaged plots. Promoted by glyphosate application were in particular grassland legumes and hemicryptophytes. Partial Redundancy Analyses (pRDA) showed that the species communities evolved over the years with dependency on the type of treatment and timing of the treatments. The overall average number of species was 19.7/m2 and the true diversity was 8.3/m2. The average density was 295 plants/m2. In all of the treatments, a factorial ANOVA demonstrated that species numbers and true diversity sank in all three of the years of the experiment over the course of the vegetation period whereas the density tended to rise.The reality of weed management is that any method employed will influence the weed composition in some way. Our experiment demonstrated that some species will be favored over others depending on the weed management method, but the overall biodiversity of the weed community was not more negatively affected by one method compared to another.