What are the farm-level economic impacts of the global cultivation of GM crops? (systematic review)

Background and objective

Globally there continues to be a steady increase in the area commercially cultivated with genetically modified (GM) crops. Alongside this, many publications have reported the economic impacts of GM crop cultivation, finding large variability in farm-level economic impacts between and within countries, across years, and between different crop/trait combinations. Variability may be due to different pest pressures, social, cultural and economic contexts, and seasonal variation in conditions. Policy makers need impartial and robust appraisal of the information. This systematic review therefore aims to answer the question: “What have been the farm-level economic impacts of the global cultivation of GM crops?”.


The question for this review contains the following components:

(1) A Population: economic indicators recorded at the farm level (2) An Intervention: the cultivation of any commercial GM modification (3) The Comparator: comparison with a conventional (non-GM) cropping system (4) Outcome: economic impacts. Change in economic indicators at the farm level

A systematic search for relevant articles was conducted using five databases and one search engine using search statements designed to identify any study in any country measuring economic parameters at the farm level, where there was cropping of a commercial GM trait. All retrieved articles were scanned at title, then abstract and finally full text level using the criteria set out below in order to select those relevant. Following the systematic search and subsequent screening, articles were critically appraised to assess study quality using 10 questions and a three point quality scale. Next, data were extracted from the articles and entered into an Excel spreadsheet. Once cleaned, the data were exported to SPSS to facilitate meta-analysis using ANOVA to conduct comparison of means. Additional narrative synthesis of qualitative data was also conducted.

Main Results

The systematic search generated 3522 extracted titles plus 56 items from grey literature sources. From these, 22 relevant articles were identified. The information within these 22 articles was first assessed using narrative synthesis. Extracted monetary values were assigned to different categories, for example, gross profit, revenue, chemical costs, and others. The categories were examined to establish the average percentage change recorded by each.

• Gross profits were 81% and net profits 66% higher for GM crops • Seed costs were 97% and total variable costs 23% higher for GM crops To facilitate further analysis, two additive categories of values were derived, namely profits and costs.

• The additive category of farm level profiti suggests there is an average increase in profit of 75% when growing GM crops as opposed to the non-GM equivalent. • The additive category of farm level costsii suggests there is an average increase in costs of 40% when growing GM crops as opposed to the non-GM equivalent.

Conducting meta-analysis revealed that crop/trait combination, level of development of a country (as measured by the Human Development Index), and date of publication were statistically significantly related to the percentage change recorded in farm level profits and costs.


Implications for policy – One of the key findings from the review is that in every case when planting GM crops as opposed to a non-GM equivalent, there was a farmlevel economic impact. This was particularly notable for certain economic variables, namely gross profit and seed costs, but less significant for other economic variables such as trading price and energy costs. The change in farm level profit was least positive in the most developed countries. Implications for research – Overall, it is important that research continues into conducting and reviewing farm level studies, particularly as there is some suggestion that changes in farm level profit and costs that arise as a result of growing GM crops as opposed to the non-GM equivalent, change through time.


Genetically modified crops, Economic Impact, Farm, Global cultivation


The commercial application of genetically modified (GM) technology in agriculture began in the 1990s in the USA. The introduction of GM crops started with a small number of crop types, notably soya engineered to be resistant to certain types of herbicide, and oilseed rape (OSR) with similar modifications (known as HT crops, after ‘herbicide tolerant’). This has since developed into widespread adoption, in a number of countries, of additional GM crops, including maize and cotton engineered to contain soil bacterium proteins that are toxic to certain pests (known as Bt crops, after the soil bacterium ‘Bacillus thuringiensis’) (Hall, 2010).

There have been many studies, reports and publications that have made claims about the economic impacts of the cultivation of GM crops globally. The diversity of the studies and the often apparently contradictory claims make it difficult to obtain an overview of the impacts. For example, impact has been addressed at the global level, national level, regional and farm level. After discussion with the funders this study will focus on the farm level impacts.

At the farm-level, numerous claims are made about the impacts of GM crop technology. In terms of economic impacts, the cultivation of GM crops involves potential revenue and cost impacts when compared with conventional crops. Notably, the farm-level profitability of GM crops is influenced by variables such as differences in yield, reductions in insecticide costs or weed management costs (depending on the modification present), differences in seed prices, and differences in price received by the farmer between the GM crop and its conventional counterpart (Gomez-Barbero & Rodriguez-Cerezo, 2006).

In detail, one farm-level impact of herbicide tolerant (HT) crops is the simplification of weed control. Farmers growing HT crops can use the application of one, broad- spectrum herbicide that kills most weeds but leaves the crop unharmed, as opposed to multiple applications of different herbicides at different times of the growing season (Hall, 2010). Farmers have therefore identified positive impacts of HT crops as being simplified management, greater flexibility because of there being a wider window available for spray applications, and less spraying, all of which have impacts in terms of costs, the environment and labour time (Oreszczyn, 2005).

These are only some of the claims that are found in the literature relating to the potential impacts of cultivating GM crops. However, the breadth and diversity of studies, and the vast body of literature, points to the need to synthesise and assess similar studies to provide a clear understanding of the body of evidence that exists. This is where the use of systematic review has value. Systematic reviews are different to so-called traditional literature reviews in that the process of review should be transparent, rigorous and replicable. It is considered a preferable option, particularly when there is a large body of evidence, and seeks to avoid the subjective selection of certain research findings that are considered by reviewers to be of most relevance or interest.

Thus this review aims to provide robust and accurate information about the farm-level economic impacts of global GM crop cultivation. A systematic review starts with a specific question or questions that is/are answerable in scientific terms. The questions

are central to the process because they generate the search terms used in the subsequent literature review and determine relevance criteria. In this case, the main question is:

What are the farm-level economic impacts of the global cultivation of GM crops?1

In the sections that follow, a detailed protocol is provided that describes how this question will be answered.