|Keywords:||Sustainable agriculture, Agricultural inputs, Agrochemicals, Genetic engineering, Other disciplines the biotechnology, Regulations, Large-scale farming.|
|Correct citation:||Harbinson, R. (2001), "Conservation tillage and climate change." Biotechnology and Development Monitor, No. 46, p. 12-17.|
Conservation tillage farming systems have gained attention for their potential to store carbon in soils, thereby reducing the amount of carbon dioxide (CO2) in the atmosphere responsible for climate change. The model being promoted by business relies on external agrochemical inputs and genetically modified (GM) crop varieties. The negative effects of these on soil carbon storage have yet to be properly accounted for and may cancel out positive gains.
Conservation tillage practices involve a variety of methods to minimize disturbance of the soil in comparison to conventional ploughing, from low-till techniques that employ limited ploughing to no-till where drills are used for seeding and ploughing is eliminated altogether.
In recent years the concept has drawn increasing interest from governments, corporations and scientists engaged in reaching an agreement under the 1997 Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC). Carbon loss from soil is a contributory factor in global warming. Conservation tillage practices claim to reverse historical carbon loss from soils, thereby reducing CO2 in the atmosphere through storage in soil sinks - a process known as sequestration . The various models of conservation tillage are employed in widely differing farming systems from traditional and organic agriculture to intensive chemical agriculture and have more recently been combined with herbicide resistant GM crops.
Agrochemical companies have successfully promoted the intensive external input model known as conservation tillage at the climate change negotiations. Important questions need yet to be answered about the economic, social and environmental impacts of this conservation tillage model and the implications of widespread changes in agricultural practices, particularly where these may impact on traditional farming methods.
The scientific body of the UNFCCC, the Intergovernmental Panel on Climate Change (IPCC), has identified the major sources of greenhouse gases as fossil fuel-based emissions and terrestrial-based factors such as forest loss and a variety of agricultural practices. Under the protocol, industrialized countries have committed themselves to emission reduction targets, whilst developing countries do not at this stage have such commitments because of their substantially lower per capita carbon dioxide emissions. The acrimonious breakdown in negotiations at the Sixth Conference of the Parties (COP6) in the Netherlands in November 2000 centred on the question of which mechanisms and what carbon sources could be counted by a country to reach its targets. Disagreement between the Umbrella group, mainly comprising of the USA, Canada, New Zealand, Australia and Japan, and the European Union (EU) backed by many developing countries, focused on carbon sinks. The question of how much industrialized countries can offset their domestic fossil fuel emissions with terrestrial factors such forests or agricultural practices such as conservation tillage still remains open. Large countries such as Canada and Australia would also like to include the potential of their large landmass in the equation and thereby reduce the need to cut domestic fossil fuel emissions.
The Umbrella group also favoured the financing of projects in less developed countries, which sequester or reduce emissions of carbon. In contrast, the EU insists that countries have signed up to reducing the primary cause of climate change - fossil fuel emissions - and therefore other projects for offsetting emissions should be limited.
The Umbrella group is the leading proponent of the flexible mechanisms, which provide a framework that could allow industrialized countries to finance implementation of sinks projects in the developing world. In return, the financing country would gain carbon credits that could be traded on a global exchange market yet to be fully set up. At COP6, the Umbrella group pushed for a wide definition of the kinds of projects allowed under the scheme. The Clean Development Mechanism (CDM) is the section in the flexible mechanisms, that would allow implementation of projects in developing countries, but opposition to sinks projects through the CDM was stiff, with the EU taking the lead. However the break-up of negotiations and the change to a hard-line Republican administration in the USA has now changed the situation.
In a March 2001 statement, the US president George W. Bush announced that the USA was withdrawing from the Kyoto Protocol. However, the US delegation still intends to attend future negotiations. With 3 per cent of the world's population emitting 23 per cent of global carbon emissions, the USA is aware that reaching its emissions targets at home would have required costly political decisions, especially if it only included fossil fuels. The main question now taxing all concerned is how far parties are prepared to compromise in an attempt to draw the USA back to the negotiating table. Many observers contend that without USA participation, the Protocol will become unworkable because the USA is the largest national emitter of greenhouse gasses.
According to the IPCC, agriculture is responsible for 20 per cent of global emissions of greenhouse gases. This includes historical loss of carbon from cultivated land. Some estimates indicate that over the next hundred years, soils could store about 7 to 12 per cent of global fossil fuel emissions at 1990 levels through their carbon sequestration potential.
Reduced tillage has long been recognized by traditional farmers and the permaculture movement, as a way to maintain agricultural biodiversity and soil health. Complex mulching techniques, use of green manure and legume crops, multicropping practices and understanding of nutrient fixing plants and soil organisms are used in interrelated ways to reduce soil disturbance and suppress weeds through maximized soil coverage. Nevertheless, most soil carbon loss occurs within the first ten years of ploughed cultivation and several studies project that sequestration potential is limited because after some time the soil will reach a maximum carbon content, probably close to its pre-cultivation level.
Changes in the carbon content of soil depend largely on the balance of carbon input from plant litter and carbon loss through decomposition. Practices such as stubble burning reduce the quantity of organic plant litter entering the soil. Ploughing, by aerating the soil, speeds up the rate of decomposition due to increased oxygen levels. Soil factors such as moisture and temperature also play a significant role. Overall, management practices that increase the input of organic matter to the soil and decrease the rate of decomposition are said to increase carbon sequestration.
Studies assessing practices to maximize carbon sequestration on North American farmland cite four common factors. First, reduction in tillage reduces decomposition and enhances soil health. Second, intensification of the cropping system will maximize input of crop residues (because ploughed fallow land gives space for organic matter to decompose and should therefore be kept in production). Third, practices to maximize yield such as improved crop varieties, fertilizers and nutrient supplements should be implemented to maximize crop residues. Finally , setting aside cultivated land is the most effective method of maximizing carbon storage, as the soil is left undisturbed and the perennial vegetation that emerges is left in place whereas most crops are removed from the land after harvest. Of these four points in this conservation tillage package, setting aside land is undisputedly the best option in maximizing carbon gains as long as it is left out of production.
Central aspects to be addressed with conservation tillage techniques are weed and pest control. Ploughing weeds under and leaving ploughed land fallow are long-standing practices used to deal with these problems. Another example where ploughing becomes necessary is when agricultural soil becomes fungal-dominated and the bacterial population requires increasing to restore productivity. Changing such practices through no-tillage requires careful consideration of alternative control options.
Intensive agriculture with high external inputs relies upon monocrop varieties, often derived from a single genetic origin, which need external inputs such as fertilizer, nutrients and pesticides. Choices are mainly limited to chemicals when it comes to weed and pest control, more recently coupled to genetically modified methods such as herbicide resistant crops. By contrast, other farming systems rely on the existence of a high diversity of crops and varieties to keep weeds and pests in check. They are known to become a problem if they have the space or abundance of food, in the form of a single crop variety, to spiral out of control. (See also: Zero-tilllage in the South in this issue.)
Carbon savings made by external input conservation tillage are reduced if carbon is, in turn, emitted through the production, transportation and application of increased amounts of herbicides, pesticides and fertilizers. Chemical fertilizers manufactured from fossil fuels are the most energy intensive agricultural chemicals. Nitrogen fertilizer is used the most, requires more energy in production than phosphorous and potassium and is therefore the biggest carbon dioxide emitter. Increased amounts of nitrogen fertilization result in increased emissions of nitrous oxide, one of the most potent greenhouse gases. The carbon dioxide cost of both production and use is estimated at five tons of carbon per ton of nitrogen fertilizer. There was a sixfold increase in the production and use of fertilizer between 1961 and 1990. Other chemical inputs also have a carbon cost. Monsanto (USA), the manufacturers of glyphosate herbicide Roundup , say for example that: "The main break-down product of the surfactant used in Roundup is carbon dioxide."
Increased cropping intensity and yield in external input conservation tillage are dependent on agrochemical input. The greenhouse gas emissions produced by agrochemicals at all stages from production to decay need to be accounted to evaluate the true carbon storage of the system.
Many of the gains of reducing tillage are due to enhanced soil health such as a greater abundance of soil microorganisms, and enhanced drainage through the pores created by undisturbed earthworm communities. Over one thousand species of soil organisms can be found in a single gram of soil and according to one source there are "more organisms per gram of soil than humans on earth". They are mutually interdependent and together create the necessary conditions for soil fertility. In fact a large proportion of the biomass of healthy soil is made up of microorganisms which play a role in carbon retention. For example about 40 per cent of the carbon from the breakdown of organic material in soils is retained in the biomass of bacteria, much of the rest being released into the atmosphere. Total numbers of bacteria in one gram of agricultural soil range between 1 to 100 million, but this has been recorded to drop below one million after pesticide treatment.
Further problems for soil health from the applications of herbicides, pesticides and genetically modified organisms (GMOs) have been documented. A study in New Zealand showed that glyphosate herbicide caused a reduction in growth and an increase in mortality amongst the most commonly found earthworm. The chemical has also been found to be toxic to mycorrhiza fungi, which help plants to take up nutrients from soils and protect plant roots from nematode pests.
An alarming effect of GM bacteria was highlighted by Dr Elaine Ingham of Oregon State University when Klebsiella planticola, a common soil bacterium, was genetically modified by a German research institute to make ethanol through fermentation of crop residues. The remaining sludge was to be returned as fertilizer to the fields. Ingham found that soils containing the GM bacteria killed wheat seedlings, most likely through alcohol production in the root system. Mycorrhizal fungi were also killed. Klebsiella planticola is found in the root systems of plants all over the world. Was its GM variant ever to spread, the consequences would therefore be severe.
The physical proximity of soil life to GM crops and the essential interactions they perform in nutrient uptake through root systems makes them particularly susceptible to adverse effects. Currently only a small number of these microorganisms and their interrelationships are understood, making even the most thorough risk assessment programmes unreliable. Biodiversity in soils remains an understudied field of research, but it is understood that upsetting the species equilibrium can allow opportunistic pest organisms to flourish in the absence of species competition. Also recognized is that maximizing soil biodiversity plays an essential role in increasing carbon sequestration.
With soil sinks it is extremely difficult to account for small changes in soil carbon content over a large land area that includes soils of different types. Changes in carbon content over short periods - a year, for example - are difficult and costly to calculate and require numerous soil samples from any given field. In the context of the Kyoto Protocol other issues become problematic. In order to calculate a nation's total agricultural emissions, necessary for the assessment of national targets, all types of agriculture need to be included, from those that emit carbon to those that store it. Merely subtracting carbon savings made from conservation tillage projects from overall emissions targets gives a false result. There is also the question of project sustainability. If the use of low-till practices is stopped, the accumulated carbon will quickly be released into the atmosphere. This could be exacerbated by the expected impact of climate change itself. Global warming will produce changes in local climates coupled to higher carbon dioxide levels in the atmosphere, creating radical changes in the types and varieties of crops suitable to the area, as well as changes in the composition of soil microorganism communities. In such scenarios management practices would be forced to adapt, with unknown consequences for carbon sequestration projects.
Studies assessing soil carbon sequestration potential on a global scale indicate great regional differences, largely due to climate and soil type. While there is evidence to suggest conservation tillage as a carbon sequestration option in parts of North America, the same cannot be said of other areas. For example, in the Argentinean Pampa it has been found that no-till actually increases carbon losses when compared to conventional ploughing. Other examples suggest regional differences and difficulties particularly with compaction of soils. The danger is that if the climate protocol accepts conservation tillage it could be pushed as a global cure-all panacea, neglecting local differences.
The Kyoto process has become increasingly influenced by corporations and corporate lobby organizations like The World Business Council for Sustainable Development (WBCSD). They are strong proponents of carbon sinks and the development of a global carbon trading system to allow trading of credits gained from implementation of sink projects. Since COP4 at Buenos Aires in 1998, Monsanto has promoted its model of conservation tillage, which it claims could meet up to 30 per cent of USA reduction targets. Robert B. Horsch , Monsanto's President for Sustainable Development, explained that "Monsanto and others worked hard and successfully at the meeting to persuade delegates to look into agricultural carbon 'sinks' as a way to reduce atmospheric greenhouse gases."
Monsanto's strategic influence on the climate process continued when in May 1999 its representative Peter Hill sat on the IPCC panel that wrote the influential Special report on land use, land use change, and forestry . The lobbying effort appears to have paid off, as at COP6 the issue of soil sinks became a major bargaining chip of head USA negotiator Frank Loy. Loy was looking for 25 million tons of USA farm soils to be accepted, worth an estimated US$ 1 billion to USA farmers in carbon credits. While disagreement was rife over forest sinks, the USA proposals for soil sinks remained on the table, largely uncontested.
Some conservation tillage practices deserve attention for their carbon sequestration potential and agricultural benefits. However, conservation tillage models that prescribe GM crops with high chemical inputs have yet to be proven effective over the long term. So far studies have focused on developing a workable accounting procedure for determining quantities of carbon sequestered under conservation tillage. The financial potential of the evolving carbon credit market gives a significant incentive to do so, though procedures are yet far from adequate. Studies that count the wider costs of the external input conservation tillage model are lacking. Carbon emissions from production, transport and use of agrochemicals have yet to be fully included in the balance sheet. Indicators suggest that these factors will significantly reduce carbon savings. The increase of carbon in soil depends largely on soil health, with biodiversity as the key measure. Agrochemicals and GMOs have been found to reduce soil biodiversity and hence the capacity of soil to store carbon.
Agrochemical companies have successfully promoted soil sinks at the climate change negotiations. There is a danger that the prominent political differences in the Kyoto process are overshadowing the scientific evidence, and that negotiations are being played out based on national and corporate interests, leaving a scientific deficit. If external input conservation tillage were to be accepted by the Kyoto Protocol, it would have a number of important effects. Promotion of chemical and GM agriculture would accelerate throughout the world, driven by the financial incentives of the carbon credit market. Its adoption under a significant UN agreement would lend environmental credentials to agribusiness to market its chemical and GM products. The momentum of the protocol coupled with corporate and governmental backing would lead to a tendency to promote conservation tillage as a global cure, overriding real concerns that it is site specific, and inappropriate in large areas of the world.
*Editor Biotechnology and Development Monitor.
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