This dataset consists of a range of ecological measurements collected from a set of arable fields, each sown with a combination of genetically modified and conventional spring-sown oilseed rape crops. Measurements include species counts in the following areas: weed seedbank, vegetation in the crop, field edge vegetation, invertebrates. The data were collected as part of the Farm Scale Evaluations (FSEs), a four-year programme of research by independent researchers aimed at studying the effect that the management practices associated with Genetically Modified Herbicide Tolerant (GMHT) crops might have on farmland wildlife, when compared with weed control used with non-GM crops. Data were collected by a consortium of: the Institute of Terrestrial Ecology (now the Centre for Ecology & Hydrology), the Institute of Arable Crops Research (now Rothamsted Research) and the Scottish Crop Research Institute (now the James Hutton Institute). Data were collected for four crops overall (Beet, Maize, Spring-sown Oilseed Rape and Winter-sown oilseed Rape).