Field Boundary Vegetation and the Effects of Agrochemical Drift: Botanical Change Caused by Low Levels of Herbicide and Fertilizer

Abstract

To assess the effects of herbicide drift and fertilizer misplacement on the botanical diversity of arable field boundary vegetation, plots in (i) a low productive meadow, and (ii) a high productive fallow arable field sown with a mixture of grassland forbs were treated annually with all combinations of three levels of fertilizer (NPK; 0, 25 and 50% of the standard agricultural dose) and four levels of herbicide (fluroxypyr; 0, 5, 10 and 50%). Botanical change and biomass production of grasses and forbs were monitored for 3 years in both experiments. Additionally, phytotoxicity of the four levels of herbicide was screened at the seedling stage for 18 species grown in pots in a glasshouse. 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 the fertilizer applications on species-richness, biomass production and the abundance of individual species were far more severe and constant compared to the herbicide applications. The results of the pot experiment did not correspond well with the results of the field experiments. Extrapolation of the results of pot experiments to normal field conditions is therefore difficult and inappropriate. The implications of these results for field boundary management are discussed.