Do GMOs decrease crop yield?

Expert response from Graham Brookes

Agricultural Economist, PG Economics Ltd, UK

Monday, 31/07/2017 13:58

In order the answer this question, it is important to first be clear about what a GMO is and secondly to discuss a number of issues relating to yields.

What is a GMO?

It is assumed that this question refers to genetically modified crops. GM crop technology has been widely used since the mid-1990s and in 2015 were planted on about 175 million hectares worldwide.   The main GMO traits convey:

•          Tolerance to specific herbicides (notably to glyphosate) in maize, cotton, canola (spring oilseed rape), soybean, sugar beet and alfalfa. This GM herbicide tolerant (GM HT) technology allows for the ‘over the top’ spraying of GM HT crops with these herbicides, that target weeds but do not harm the crop itself – the aim of the technology is to provide farmers with better (and usually cheaper) weed control than is possible with conventional crops;
•          Resistance to specific insect pests of maize, cotton, soybeans and brinjal. This GM insect resistance (GM IR), or ‘Bt’ technology offers farmers resistance in the plants to major pests of these crops – the aim of the technology is to control these pests more effectively than is possible in conventional crops, where the most common form of control used is insecticides. 

What factors affect yield?

Man has been cross breeding different varieties of crop species for thousands of years in order to obtain characteristics that are desirable such as higher yield, ability to better withstand diseases or improved taste. This means that there are typically a large number of crop varieties offering farmers a mix of different characteristics. High yield is one of most common desirable characteristics for farmers, although for some markets, yield may be a secondary desirable characteristic compared to other quality-related characteristics (eg, a specific oil profile in an oilseed). 

The underlying yield potential of a crop variety is the yield a variety can achieve in an environment most suited to it, with the most suitable temperature for growing, adequate access to sunshine, nutrients and water, and with pests and diseases effectively controlled. Actual crop yield will rarely, if at all (except perhaps in perfectly controlled laboratory environment) match yield potential because of variations in sunshine, temperature, soil quality, access to water, access to nutrients and the presence of pests, diseases and weeds. Factors such as temperature change, soil quality and water content, pest, disease and weed pressure vary by year and location. They are also influenced by the husbandry skills of farmers and their access to, and use of, inputs such as fertilizer and ways of protecting crops from pests, diseases and weed competition.   

Can the adoption of a specific type of farming or new seed variety result in lower yields?

The answer to this question is yes – in certain circumstances. These include:

•          Where a farmer chooses to grow for a specific market and in order to meet the requirements of this market, yield is a ‘secondary’ consideration.   A good example is the market for organic produce where farmers are required to not use GMOs, artificial fertiliser or most pesticides.  As a result, yields are typically significantly lower than yields obtained with non-organic forms of agriculture and farmers are ‘compensated’ for this lower yield through higher prices (for organically certified produce);
•          Where a farmer tries a new variety that offers improved levels of control of a common pest compared to the highest yielding existing varieties and then finds that for that particular year, the levels of pest pressure are low, meaning all varieties suffer little yield loss from the pest – in effect the benefits of the new variety are not seen in that particular year.

How has the use of GMOs impacted on yields?

There is a consistent body of evidence from 20 years of observing the impact of GM crop use showing that:

•          Insect resistant (GM IR) crop technology used in cotton and corn has consistently improved yields by reducing the damage caused by pests. From 1996 to 2015, across all users of this technology, yields have increased by an average of +13.1 per cent for IR corn and +15 per cent for IR cotton relative to conventional production systems. Farmers who grow IR soybeans commercially in South America have seen an average +9.6 per cent increase in yields since 2013 because of better control of pests;
•          In some countries, herbicide tolerant (GM HT) technology has improved yields through better weed control.  For example, in Bolivia, GM HT soybeans increased yields by +15 per cent. 

It is also of note that farmers who have used GM crops in developing countries, many of whom are resource-poor and farm small plots of land, continue to see the highest yield gains from using the technology.

References

Brookes G and Barfoot P (2016) Global income and production impacts of using GM crop technology 1996-2014. GM Crops and Food, vol 7, issue 1. http://dx.doi.org/10.1080/21645698.2016.1176817G

Klumper W and Qaim M (2014) A meta-analysis of the impacts of genetically modified crops. PLoS ONE 9: e111629

Graham Brookes is an agricultural economist with the UK-based analysts’ PG Economics (www.pgeconomics.co.uk). He has been studying the impact of crop biotechnology for nearly 20 years and is author of 24 peer reviewed papers on the economic and environmental impact of crop biotechnology