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I have seen estimates of the reductions in greenhouse gas emissions associated with GMO usage due to reduced tillage. How are these estimates calculated? Are the reductions in greenhouse emissions expected to increase with further GMO usage and new modifications?

Submitted by: arex


Expert response from Graham Brookes

Agricultural Economist, PG Economics Ltd, UK

Thursday, 11/06/2014 14:54

The most current estimates of reductions in the level of greenhouse gas (GHG) emissions from GM crops have been made by G. Brookes and P. Barfoot (2014), and the information below is taken from this work.

GM crops contribute to reducing GHG emissions via two principal sources:

GM crops contribute to a reduction in fuel use from less frequent herbicide or insecticide applications and a reduction in the energy use in soil cultivation. For example, Lazarus (2012) estimated that one pesticide spray application uses 0.84 liters of fuel, which is equivalent to 2.24 kg/ha of carbon dioxide emissions. In the Brookes and Barfoot (2014) analysis, the conservative assumption that only GM insect-resistant crops (GM IR) reduced (insecticide) spray applications is used with the use of GM herbicide-tolerant crops (GM HT) assumed to result in no change in the number/frequency of (herbicide) spray runs. In addition to the reduction in the number of insecticide applications, there has been a shift from conventional tillage to no/reduced tillage facilitated by GM HT technology. This has had a marked effect on tractor fuel consumption because energy-intensive cultivation methods have been replaced with no/reduced tillage and herbicide-based weed control systems. The GM HT crop where this is most evident is GM HT soybean and where the GM HT soybean and maize rotation is widely practiced — for example, in the United States. Here, adoption of the GM HT technology has made an important contribution to facilitating the adoption of reduced/no-tillage (NT) farming (CTIC 2002). Before the introduction of GM HT soybean technology, NT systems were practiced by some farmers using a number of herbicides and with varying degrees of success. The opportunity for growers to control weeds with a herbicide as a “burndown” preceeding treatment, followed by a herbicide treatment when the soybean/maize crop became established, has made the NT system more reliable, technically viable and commercially attractive.

These technical advantages, combined with the cost advantages, have contributed to the rapid adoption of soybeans and maize containing GM HT technology and the near doubling of the NT soybean area in the United States (and also a seven-fold increase in Argentina). In both countries, GM HT soybean crops are estimated to account for 95 percent of the NT soybean crop area. Substantial growth in NT production systems has also occurred in Canada, where the NT canola area increased from 0.8 to eight million ha (equal to about 90 percent of the total canola area) between 1996 and 2012 (95 percent of the NT canola area is planted with GM HT cultivars). The fuel savings associated with the tillage changes facilitated by GM HT technology used by Brookes and Barfoot (2014) are drawn from a review of literature, including Jasa (2002), CTIC (2002),, University of Illinois (2006), USDA Energy Estimator (2013), Reeder (2010) and the USDA Comet-VR model (2013). The Brookes and Barfoot (2014) analysis assumes that the adoption of NT farming systems in soybean production reduces cultivation and seedbed preparation fuel usage by 27.12 liters/ha, compared with traditional conventional tillage and, in the case of RT (mulch till) cultivation, by 10.39 liters/ha. In the case of maize, NT results in a saving of 24.41 liters/ha and 7.52 liters/ha in the case of RT compared with conventional intensive tillage. These are conservative estimates and are in line with the USDA Energy Estimator for soybeans and maize.

The adoption of NT and RT systems with respect to fuel use therefore results in reductions of carbon dioxide emissions of 72.41 kg/ha and 27.74 kg/ha, respectively, for soybeans and 65.17 kg/ha and 20.08 kg/ha for maize.

The use of reduced/no-tillage farming systems that utilize less plowing increase the amount of organic carbon in the form of crop residue that is stored or sequestered in the soil. This carbon sequestration reduces carbon dioxide emissions to the environment. Rates of carbon sequestration have been calculated for cropping systems using normal tillage and reduced tillage, and these were incorporated in the Brookes and Barfoot (2014) analysis on how GM crop adoption has significantly facilitated the increase in carbon sequestration, ultimately reducing the release of CO2 into the atmosphere. Of course, the amount of carbon sequestered varies by soil type, cropping system, and eco-region. The Brookes and Barfoot (2014) analysis assumes the following:


  • United States:the soil carbon sequestered by tillage system for maize in continuous rotation with soybeans is assumed to be a net reduction of 250 kg of carbon/ha/year based on NT systems storing 251 kg of carbon/ha/year, RT systems storing 75 kg of carbon/ha/year and CT systems storing 1 kg of carbon/ha/year;
  • United States: The soil carbon sequestered by tillage system for soybeans in a continuous rotation with maize is assumed to be a net saving of 100 kg of carbon/ha/year, based on NT systems’ release of 45 kg of carbon/ha/year, RT systems’ release of 115 kg of carbon/ha/year and CT systems’ release of 145 kg of carbon/ha/year;
  • Argentina and Brazil:soil carbon retention is 275 kg carbon/ha/year for NT soybean cropping and CT systems that release 25 kg carbon/ha/year (a difference of 300 kg carbon/ha/year).


Table 1 summarizes the impact on GHG emissions associated with the planting of GM crops in 2012. In 2012, the permanent CO2 savings from reduced fuel use associated with GM crops was 2,111 million kg. This is equivalent to removing 0.9 million cars from the road for a year.

Table 1: Impact of GM Crops on Carbon Sequestration Impact in 2012; Car Equivalents


Permanent carbon dioxide savings arising from reduced fuel use (million kg of carbon dioxide)

Permanent fuel savings, as average family car equivalents removed from the road for a year (’00s)

Potential additional soil carbon sequestration savings (million kg of carbon dioxide)

Soil carbon sequestration savings, as average family car equivalents removed from the road for a year (’00s)

United States: GM HT soybeans





Argentina: GM HT soybeans





Brazil: GM HT soybeans





Bolivia, Paraguay, Uruguay: GM HT soybeans





Canada: GM HT canola





United States: GM HT corn





Global: GM IR cotton





Brazil: IR corn










Source: Brookes and Barfoot (2014)

Notes: Assumption: an average family car produces 150 grams of carbon dioxide per km. A car does an average of 15,000 km/year and therefore produces 2,250 kg of carbon dioxide/year.

The additional soil carbon sequestration gains resulting from reduced tillage with GM crops accounted for a reduction of 24,613 million kg of CO2 emissions in 2012. This is equivalent to removing nearly 10.9 million cars from the roads per year. In total, the carbon savings from reduced fuel use and soil carbon sequestration in 2012 were equal to removing 11.88 million cars from the road (equal to 41 percent of all registered cars in the UK).

With respect to the future, there is further scope for GM crop technology contributing to reducing GHG emissions if more farmers plant crops containing GM IR technology that reduces insecticide use and more farmers adopt NT production systems that use GM HT technology as a key part of weed control.

Brookes, G., and Barfoot, P. (2014), “Key global environmental impacts of GM crop use 1996-2012, GM Crops and Food,” Biotechnology in Agriculture and the Food Chain, 5:2, 1–12, Apr-May 2014.
Conservation Tillage and Plant Biotechnology (CTIC) (2002), “How New Technologies Can Improve the Environment by Reducing the Need to Plough” (
Jasa, P. (2002), “Conservation Tillage Systems,” Extension Engineer, Univ Nebraska.
Lazarus, W. F. (2012), Machinery Cost Estimates May 2012, University of Minnesota Extension Service.
Reeder, R. (2010), “No-till benefits add up with diesel fuel savings.”
University of Illinois (2006), Costs and fuel use for alternative tillage systems. 07/fefo06 07.html.
USDA (2013), An online tool for estimating carbon storage in agroforestry practices (COMET-VR).
USDA Energy Estimator: tillage (2013),

No-tillage farming means that the ground is not ploughed at all, while reduced tillage means that the ground is disturbed less than it would be with traditional tillage systems. For example, under a no-tillage farming system, soybean seeds are planted through the organic material that is left over from a previous crop such as corn, cotton, or wheat. No-tillage systems also significantly reduce soil erosion and hence deliver both additional economic benefits to farmers, enabling them to cultivate land that might otherwise be of limited value and environmental benefits from the avoidance of loss of flora, fauna, and landscape features