Field boundary vegetation and the effects of agrochemical drift: botanical change caused by low levels of herbicide and fertilizer.
Field studies were conducted in the Netherlands during 1993-96 to assess the effects of herbicide drift and fertilizer misplacement on the botanical diversity of arable field boundary vegetation in (1) a low productive meadow, and (2) a high productive fallow arable-field sown with a mixture of grassland forbs treated annually with all combinations of three levels of fertilizer (NPK at 0, 25 and 50% of the standard agricultural concentration) and four levels of herbicide (fluroxypyr at 0, 5, 10 and 50%). Botanical change and biomass production of grasses and forbs were monitored for 3 years in both experiments. Additionally, the phytotoxicity of the four levels of herbicide was screened at the seedling stage for 18 species grown in pots in a greenhouse. In both vegetation types, fertilizer application resulted in a decline in species richness through a loss of species of low stature. Fertilizer application affected species richness gradually, as demonstrated by the rare occurrence of significant effects on colonization and extinction rates. Herbicide application resulted in a decline in species richness and affected biomass production of both grasses (positively) and forbs (negatively) in the high productive fallow only. However, a small number of species decreased in abundance in the herbicide-treated plots in both experiments. Significant herbicide effects were mainly limited to the 50% herbicide plots, but the 5 and 10% herbicide levels decreased the biomass production of spontaneously colonizing forbs and increased the species extinction rates in individual years. The effects of fertilizer application on species richness, biomass production and the abundance of individual species were far more severe and constant compared to the herbicide applications. Results from pot experiments did not correspond well with results from the field. Extrapolation of the results from pot experiments to normal field conditions is, therefore, difficult and inappropriate. The implications of these results for field boundary management are discussed.