Crop management and agronomic context of the Farm Scale Evaluations of genetically modified herbicide-tolerant crops (original) (raw)
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Philosophical Transactions of the Royal Society B: Biological Sciences, 2003
Farmland biodiversity and food webs were compared in conventional and genetically modified herbicidetolerant (GMHT) crops of beet (Beta vulgaris L.), maize (Zea mays L.) and both spring and winter oilseed rape (Brassica napus L.). GMHT and conventional varieties were sown in a split-field experimental design, at 60-70 sites for each crop, spread over three starting years beginning in 2000. This paper provides a background to the study and the rationale for its design and interpretation. It shows how data on environment, field management and the biota are used to assess the current state of the ecosystem, to define the typical arable field and to devise criteria for selecting, sampling and auditing experimental sites in the Farm Scale Evaluations. The main functional and taxonomic groups in the habitat are ranked according to their likely sensitivity to GMHT cropping, and the most responsive target organisms are defined. The value of the seedbank as a baseline and as an indicator of historical trends is proposed. Evidence from experiments during the twentieth century is analysed to show that large changes in field management have affected sensitive groups in the biota by ca. 50% during a year or short run of years-a figure against which to assess any positive or negative effects of GMHT cropping. The analysis leads to a summary of factors that were, and were not, examined in the first 3 years of the study and points to where modelling can be used to extrapolate the effects to the landscape and the agricultural region.
Proceedings of the Royal Society B: Biological Sciences, 2006
Primary results from the Farm Scale Evaluations (FSEs) of spring-sown genetically modified herbicidetolerant crops were published in 2003. We provide a statistical assessment of the results for count data, addressing issues of sample size (n), efficiency, power, statistical significance, variability and model selection. Treatment effects were consistent between rare and abundant species. Coefficients of variation averaged 73% but varied widely. High variability in vegetation indicators was usually offset by large n and treatment effects, whilst invertebrate indicators often had smaller n and lower variability; overall, achieved power was broadly consistent across indicators. Inferences about treatment effects were robust to model misspecification, justifying the statistical model adopted. As expected, increases in n would improve detectability of effects whilst, for example, halving n would have resulted in a loss of significant results of about the same order. 40% of the 531 published analyses had greater than 80% power to detect a 1.5-fold effect; reducing n by one-third would most likely halve the number of analyses meeting this criterion. Overall, the data collected vindicated the initial statistical power analysis and the planned replication. The FSEs provide a valuable database of variability and estimates of power under various sample size scenarios to aid planning of more efficient future studies.
2007
The Farm Scale Evaluations (FSE) investigated the effects of growing genetically modified herbicide-tolerant (GMHT) beet, maize, spring and winter oilseed rape on farmland biodiversity in the UK between 2000 and 2005. To date, this represents the largest field ecology experiment ever conducted. Results have been published in a range of publications. Here, we synthesise these results into one paper and summarise the findings of this work. In beet and spring oilseed rape, before post emergence herbicides were applied, there were more weeds in GMHT crops than in conventional crops. Following herbicide applications to these GMHT crops, however, weed counts, seed rain and biomass were substantially reduced in this treatment. In maize, the counts, biomass and seed rain of dicot weeds were larger throughout the season in GMHT crops. In winter oilseed rape dicot weeds were in greater abundance early in the season in GMHT crops, but after herbicides had been applied to this treatment, their counts, biomass and seed rain were larger in conventional crops. Monocot weeds, however, were more abundant in GMHT winter oilseed rape crops throughout the year. Across all crops, many of these effects were found to persist for up to two years in the seedbanks and rotations of following crops. Collembola were captured in greater numbers, particularly later in the season, from the GMHT treatments of all crops. Bees, butterflies and seed-feeding carabids often followed the trends for dicot weed resources reported for the treatments. Treatment effects on biota could be explained by differences in herbicide management and were remarkably consistent across years, regions and base-line biodiversity levels of trial sites. Using the taxa recorded in the FSE, food resources for a high proportion of farmland birds would be significantly reduced under GMHT beet, spring and winter oilseed rape cropping, but increased under GMHT maize cropping. If these trends were maintained under widespread commercial GMHT cropping it is likely that GMHT beet, spring and winter oilseed rape would exacerbate long-term declines of dicot weeds and the invertebrate and wildlife species which depend on them. Conversely, GMHT maize cropping may ameliorate such biodiversity declines. However, the magnitude of the effects of GMHT cropping need to be put in the context of changes in the wider landscape. It is likely, for example, that crop type can have a greater influence on biodiversity. Also, the effect of GMHT crops on the long-term population dynamics of biota will depend on the scale of their uptake, how their herbicide regimes are managed and the crop rotations and structure of the wider landscape in which they are grown.
Weed Research, 2007
The Farm Scale Evaluations (FSEs) of genetically modified herbicide-tolerant crops (GMHT) compared the effects of conventional and GMHT crop management regimes on weed densities. Weeds were sampled in quadrats at 5 distances along 12 transects systematically arranged within experimental half-field treatment units. Weed densities declined with increasing distance from field margins. Random variation within transects was about 80% of the total within-half-field variation, i.e. relatively large variation at a small scale. The spatial autocorrelation between counts on the same transect declined as the distance between quadrats increased. Sampling schemes with fewer distances along transects required more transects but fewer quadrats to achieve similar precision as the 5-distance scheme; on average 32 quadrats were sufficient. The frequency of detection of treatment effects (5% level) was little affected by using six or even three transects (30 and 15 quadrats respectively). However, the use of the 12 transects greatly improved the detection of treatment effects at 1% and 0.1% levels. The effectiveness of the reduced schemes for detecting differences between treatments (5% level) with as few as three transects compared with 12, reflects, in part, the relatively large treatment effects (e.g. 1.5-fold or greater), which emerged for many of the sampling occasions. The FSEs provide an unusually extensive data set. Both the data and the methodology developed for their design and analysis are valuable for the planning of future weed sampling schemes.
Journal of Applied Ecology, 2003
The effects on British farmland wildlife of the management of four genetically modified herbicide-tolerant crops are currently being studied in a 5-year trial termed the Farm-Scale Evaluations (FSE), the first 4 years of which are completed. The FSE is controversial and extensive. There has been intense scrutiny of the experimental design and proposed analysis, and of the estimated statistical power to detect effects of a given magnitude, should any exist. 2. For each crop, the FSE is a form of on-farm trial with a single composite null hypothesis and a simple randomized block experimental design. This has statistical implications for the imposition of treatments by growers and the need for proper randomization. The choice of a half-field experimental unit was based on field availability, the focus on herbicide management, the need to reduce variability and efficiency gains in sampling effort. Farms and fields were selected to represent the range of variability of geography and intensiveness across Britain for each crop. 3. Results of a power analysis suggested that the planned replication of the FSE of about 60 fields per crop over 3 years would be sufficient to provide useful information, from which valid statistical inferences could be drawn. The achieved replication for spring crops in the FSE exceeded, by more than threefold, that in any of 82 comparable terrestrial manipulative ecological experiments undertaken previously. 4. Here, we exemplify a range of analyses including covariates, interactions between various factors including years and treatments, diagnostic procedures to aid selection of the most efficient statistical model, the estimation of power from coefficients of variation, a novel and apparently robust test statistic and the calculation of overall variance from within-and between-unit variability. Preliminary results indicated that a simple log-normal model appeared adequate for most analyses. 5. Synthesis and applications. Statistical challenges created by the scope of the FSE were resolved from a sound knowledge of good experimental design. There is an urgent need for further statistical studies to develop experimental designs or modelling approaches that allow similar studies of genetically modified (GM) crops, at reduced cost. However, this power analysis has shown that this cannot be achieved at the expense of adequate replication, essential for all risk assessment studies.
An introduction to the Farm-Scale Evaluations of genetically modified herbicide-tolerant crops
Journal of Applied Ecology, 2003
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Genetically modified herbicide tolerant crops – Aims and apprehensions
Indian farming, 2010
Genetically modified (GM) crops have been and continue to be a subject of controversy despite their rapid adoption by farmers where approved. For the last two decades, an important matter of debate has been their impact on pesticide use, particularly for herbicide-tolerant (HT) crops. Some claim that these crops bring about a decrease in herbicide use, while others claim the opposite. In fact, since 1996, most cultivated GMOs have been GMHT crops, which involve the use of an associated herbicide, generally glyphosate. In their very first years of adoption, HT crops often led to some decrease in herbicide use. However, the repetition of glyphosate-tolerant crops and of glyphosate only applications in the same fields without sufficient alternation and herbicide diversity has contributed to the appearance of glyphosate-resistant weeds. These weeds have resulted in a rise in the use of glyphosate and other herbicides. This article explores this situation and the impacts of herbicide-resistant weeds, using an interdisciplinary approach and drawing on recent data. The paper analyzes the spread of GMHT crops worldwide and their consequences on herbicide use in the USA in particular. It then addresses the global development of glyphosate-resistant weeds and their impact, particularly focusing on the USA. Finally, the last section explores how industry, farmers, and weed scientists are coping with the spread of resistant weeds. The concluding comments deal more widely with trends in GM crops.