Environmental Impacts of Agriculture

General Information
  1. Introduction

    Agriculture is facing the challenge of feeding an increasing global population while natural resources are shrinking due to a combination of factors. Many feel that biotech crops can contribute to meeting global food needs by improving agricultural productivity. Yet, the potential risks associated with the cultivation of biotech crops should be accurately evaluated and managed. The base line in evaluating those risks should be a good knowledge of the impacts and foot prints of the current agricultural systems. Current practices such as tillage, water use, intercropping, crop rotation, grazing and extensive usage of pesticides affect the biodiversity of agricultural fields as well as the environment outside of fields (Tilman, 1999, 2002; Robinson and Sutherland, 2002; Butler et al. 2007, Quemada, 2009).
    This subsection gives a brief overview on these impacts and discusses the potential benefits expected from the utilization of the new biotech crops.
  2. Land use

    By occupying 40% of the land surface, agriculture is currently a major land-use and is the main factor contributing to losses in biodiversity (FAO, 2007). Approximately 13 million hectares of biodiversity-rich forests are lost in developing countries annually (James, 2009). This situation will likely worsen in the near future as the global population must be fed and biofuel feedstocks additionally produced. The pressure to increase the area of land under cultivation will grow more and more important. Climate change also is “expected to accelerate many pressures on the wild environment, as long-established production systems become destabilized and abiotic stress (such as water shortages, salinity, aridity and heat) are increased” (FAO, 2007).

    Therefore, it is critical to increase agricultural productivity per unit of land in order to reduce land conversion and biodiversity erosion. Genetic engineering technology has a great potential to contribute increasing that productivity and help reduce deforestation and loss of biodiversity in forests. James (2009) estimates that during the period 1996 to 2007 biotech crops have already precluded the need for an additional area of 43 million hectares of crop land.
    Many studies across the world have reported on yield increases after the deployment of biotech crops. For example, from 1996 to 2006, average yield increases in the areas planted to biotech insect resistant traits was +5.7% for corn and +11.1% for cotton (PG Limited Economics, 2008). James (2009) reported that in 2008 Bt cotton yield increased by 31% in India and by 9.6%, in China; Bt maize resulted in an 11% higher yield in South Africa in 2005. Other data indicate a 31% average yield increases with herbicide tolerant soybeans in Romania, 15% increase with herbicide tolerant corn in the Philippines and more than 50% with insect resistant cotton in India (http://www.pgeconomics.co.uk/).

  3. Insecticide use

    Pests cause a loss of 40% of agricultural production worldwide, despite strategies and measures carried out to control them (Pimentel, 1998). Insects alone destroy annually about 25% of food crops worldwide. For instance, the European corn borer (the larvae of Ostrinia nubilalis) can destroy up to 20% of a maize crop (www.gmo-compass.org). In Africa, losses in agricultural production due to pests can reach 100% depending upon the agro-ecological zones (Abate et al., 2000).
    Thus, huge amounts of synthetic pesticides are used every year to control agricultural insects around the world. Those chemicals not only have serious impacts on the environment but also can cause harm to human health. Every year, thousands people are poisoned by agricultural pesticides worldwide, mostly in developing countries (Brodesser et al., 2006, CGIAR, 2008).
    Biotech crop cultivation has been shown to help reduce insecticide use in agriculture. Bt cotton cultivation, for instance, reduced insecticide use in India by 39% in 2008 and by 60% in China (James, 2009). A cost reduction of about 60% in insecticide use has been observed in South Africa due to Bt maize. In the West African country Burkina Faso, Bt cotton has reduced number of pesticide treatments from six or eight a year to one or two, while boosting production by 30% (Manson, 2009).

    Why are Bt crops resistant to insects?
    Bt crops have been transformed by adding a bacterial gene from Bacillus thuringiensis that produces Bt toxins. Those toxins affect specific groups of insects including lepidopterans and coleopterans. Bacillus thuringiensis is a bacteria naturally living in the soil. The engineered plants can produce Bt toxin on their own, and this allows them to defend themselves against specific types of insects. Consequently, farmers can use less chemical insecticides to control certain insects.
  4. Herbicide use

    In intensively managed agricultural systems, large amounts of the herbicides are annually used by farmers to control weeds. Many groups of herbicides are available including the chlorophenoxy acid herbicides which are selective for the angiosperm plants, the triazines herbicides used mostly to protect corn, apple, grapes, wheat; the thiocarbamates which are generally used as graminicides applied to soil before emergence of crops, to protect maize, rice, sorghum, sugar beets, soybean (Nagy et al., 1994); and the organic phosphorus herbicides including glyphosate, a non selective herbicide (http://science.jrank.org/).
    Broadcast spraying of herbicides can have negative consequences on the environment through different pathways. Drift of the herbicide beyond the intended spray site, for instance, can cause offsite damage to susceptible vegetation. Herbicides also result in reduced habitats and food for non-target organisms such as birds and mammals, especially when these herbicides are applied in forestry (http://science.jrank.org/). It has been reported in the USA that the residual herbicides commonly used for corn and soybean production have been detected in rivers, streams, and reservoirs at concentrations exceeding the U.S. maximum contaminant levels or health advisory levels for drinking water (Martin et al., 2008).
    Among the herbicides, glyphosate is the one most widely used both in agriculture and forestry. Its values include a low toxicity to animals, a rapid adsorption to soil particles reducing movement in the environment and a low persistence due to a rapid degradation by soil microbes (Cerdiera and Duke, 2006). It has been used commercially in the United States for over 35 years (Combs and Hartnell, 2008).
    Glyphosate is a nonselective herbicide that kills annual and perennial plants including both weed and crop species (Duke et al. 2003, Brown, 2006, Combs and Hartnell, 2008).

    Through genetic engineering, biotech crops have been developed that carry a gene which allows plants to tolerate glyphosate so that they are no longer killed. The use of glyphosate resistant biotech crops has the potential to reduce the use of the other more harmful herbicides and thereby reduce their negative effects on the environment, particularly in developed countries where agriculture greatly relies on herbicide use. Such a reduction has already reached 17 million of kg per year in the United States (Gianessi, 2005). Also, replacing the more harmful herbicides with glyphosate can help reduce the amounts of dissolved herbicide concentrations in runoff (Martin et al., 2008).
    Genetically modified herbicide resistant crops
    Transgenic glyphosate tolerant crops have been transformed with EPSPS* gene (taken from Agrobacterium strain CP4) that produces an enzyme resistant to glyphosate (Brown, 2006). Farmers growing glyphosate resistant crops can therefore more effectively control weeds during the entire growing season and have more flexibility in choosing times for spraying. Herbicide resistant crops also facilitate low or no tillage cultural practices, which many consider to be more sustainable.
    * EPSPS = Enolpyruvyl-shikimate-3-phosphate synthase.
  5. Tillage practices
    Tillage or plowing can increase soil erosion and cause soil loss all around the world. These practices also demand fuel consumption, which contributes to the increased carbon dioxide emissions which are responsible for the greenhouse effect and global warming.
    Reduced tillage has been shown to be environmentally beneficial by reducing soil erosion, increasing its moisture content and nutrient richness, and leading to favorable conditions for soil organisms and wildlife. Reduced tillage also contributes to decreases in the level of pollution by smoke and carbon dioxide release through reduced consumption of fuel (Fawcett and Towery, 2002; Dale et al., 2002).
    No-till hectarage has increased rapidly in the USA and Argentina through the cultivation of transgenic herbicide tolerant soybean and cotton since the beginning in 1996 (Trigo and Cap, 2003).
  6. Water consumption
    Agriculture consumes approximately 70% of the world’s fresh water that is withdrawn for human use (FAO, 2007). This demand for water is expected to increase dramatically as the world population is growing and will reach 9.2 billion by 2050 (James, 2009). At the same time, global climate change is predicted to result in increased risks of water shortage and desertification. Water shortages are already costing billions of dollars a year in crop shortfalls around the world, and are likely to grow more costly.
    Given that drought is the single most important constraint to increased productivity for crops worldwide, efforts are underway to develop biotech drought tolerant crops. This drought tolerance trait is viewed as the most important biotech trait that will be used in the second decade of commercialization 2006 – 2015 (James, 2009). Maize will be the first biotech drought crop to be commercialized, likely in 2012 in USA and by 2017 in Sub Saharan Africa (James, 2009). “Drought is the most important constraint of African agriculture severely affecting maize, the most important African staple food crop” (http://www.aatf-africa.org/).
References References

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  • http://www.aatf-africa.org/
  • http://www.gmo-compass.org/
  • http://science.jrank.org/
  • http://www.nih.gov/
  • http://www.oecd.org/

Moussa Savadogo,NEPAD-ABNE
06 BP 9884 Ouagadougou 06
E-mail: moussa.savadogo@nepadbiosafety.net
Website: http://www.nepadbiosafety.net/