The combined effect of nitrogen and glyphosate on the competitive growth, survival and establishment of Festuca ovina and Agrostis capillaris

In order to study the combined effect of nitrogen and glyphosate on biodiversity in agricultural areas, a replicated long-time field experiment with glyphosate and nitrogen treated plots was set-up. The experiment allowed a quantitative estimation of the effect of glyphosate and nitrogen on competitive growth, survival and establishment of the dominating species during and between growing seasons. It was found that the observed ecological success of Festuca ovina relative to Agrostis capillaris in glyphosate treated plots was primarily due to altered competitive plant growth during the growing season rather than an immediate die back following spraying. Overall, interaction of herbicide and fertilizer on plant competitive growth, survival and establishment were demonstrated, and it was suggested that positive interactions between glyphosate and nitrogen may be important for the ecological success of A. capillaris in field margins. The used method of combining pin-point data and Bayesian state-space competition models may be applied in other ecological studies. For example, the method may be used in predicting the effects of altered weed control strategies on the botanical composition of the agro-ecosystem.