Soils also contain huge amounts of carbon, mostly in the form of organic matter. Much of the organic matter that is lost ends up in the atmosphere, in the form of carbon dioxide - the most important greenhouse gas.
We know more about the movement of celestial bodies than about the ground we step on - Leonardo da Vinci
Take care of the soil and all the rest will take care of itself - Peasant Proverb
Things have not changed much since the days of Leonardo da Vinci. For many people, soil is a mixture of minerals and dust. In reality, soils are one of the most amazing living ecosystems on Earth, where millions of plants, fungi, bacteria, insects and other living organisms - most invisible to the human eye - are in an ever-changing process of constant creation, composition and decomposition of organic matter and life. They are also the inevitable starting point for anyone who wants to grow food.
Soils also contain huge amounts of carbon, mostly in the form of organic matter. Much of the organic matter that is lost ends up in the atmosphere, in the form of carbon dioxide - the most important greenhouse gas.
The way that industrial agriculture has treated soils is a crucial factor that has caused the current climate crisis. However, floors can be part of the solution. By our calculations, if we could return organic matter lost from industrial agriculture back to the world's agricultural soils, we could capture at least one-third of the excess carbon dioxide currently in the atmosphere. If we continue to add organic matter to the soil over the next 50 years, two-thirds of all the current excess carbon dioxide could be captured by the world's soils. In the process we could form healthier and more productive soils and we would be able to abandon the use of chemical fertilizers that are now another powerful producer of climate change gases.
Via Campesina has argued that agriculture based on small-scale farming methods, using agro-ecological methods of production and targeting local markets, can cool the planet and feed the population. This statement is correct and the reasons are found, to a large extent, on the ground.
The growing problem of industrial fertilizers
An important factor in the destruction of soil fertility has been the tremendous worldwide increase in chemical fertilizers in agriculture, with current consumption more than five times that of 1961 (1). Graph 1 shows the increase in world nitrogen consumption per hectare, seven times higher than in the 1960s (2). However, much of all this extra nitrogen is not used by plants and ends up in groundwater or the air. The more nitrogen farmers apply as fertilizer, the less efficient it is. Graph 2 shows the relationship between yield and nitrogen fertilizer consumption in corn, wheat, soybeans and rice, the four crops that cover almost a third of all cultivated land. For all of them, the yield per kilogram of nitrogen applied is a third of what it was in 1961, when the use of chemical fertilizers began to expand worldwide.
The increasing ineffectiveness of industrial fertilizers should come as no surprise. Many soil experts and growing numbers of farmers have long known that chemical fertilizers destroy soil fertility by destroying organic matter. When chemical fertilizers are applied, soluble nutrients are immediately available in large quantities and cause a surge of microbial activity and multiplication. The increased microbial activity, meanwhile, accelerates the decomposition of organic matter and releases CO2 into the atmosphere. When the nutrients in fertilizers become scarce, most microorganisms die and the soil now has less organic matter. As this process occurs over years and decades, and is accelerated by tillage, the organic matter in the soil is eventually depleted. The problem is aggravated because the same technological approach that promotes chemical fertilizers indicates that crop residues must be removed or burned and must not be integrated into the soil-
As soils lose organic matter, they become more compact, absorb less water, and have a lower capacity to retain nutrients. Roots grow less, soil nutrients are more easily lost, and less water is available for plants. The result is that the use of nutrients in fertilizers will become increasingly inefficient, and the only way to counteract inefficiency is by increasing fertilizer doses, as global trends show. But higher doses will only aggravate problems, increasing inefficiency and destroying soils. It is not uncommon to hear of organic farmers who became such once their yields collapsed after years of heavy use of chemical fertilizers.
The problems with industrial fertilizers don't end there. The forms of nitrogen present in chemical fertilizers change rapidly in the soil, emitting nitrous oxides into the air. Nitrous oxides have a greenhouse effect that is more than two hundred times more powerful than the effect of CO23, and they are responsible for more than 40% of the greenhouse effect currently caused by agriculture. Nitrous oxides also destroy the ozone layer.
Nitrogen fertilization: from a world average of 8.6 kg / ha in 1961 to 62.5 kg / ha in 2006. (4)
Inefence of nitrogen fertilizers
For every kilo of nitrogen applied, 226 kg of corn were obtained in 1961, but only 76 kg in 2006. The figures are respectively 217 and 66 kg for rice and 131 and 36 kg for soybeans, and 126 and 45 kg for soy. wheat. (5)
2. Figures obtained by GRAIN based on statistics from the International Fertilizer Industry Association ( http://www.fertilizer.org/ifa/Home-Page/STATISTICS ) and by FAO ( http://faostat.fao.org/default.aspx )
3. Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland, 2007: "Changes in Atmospheric Constituents and in Radiative Forcing" in: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, p. 212
5. Figures obtained by GRAIN based on statistics from the International Fertilizer Industry Association ( http://www.fertilizer.org/ifa/Home-Page/STATISTICS ) and by FAO ( http://faostat.fao.org/default.aspx
Soils as living ecosystems.
Soils are a thin layer that covers more than 90% of the land surface of planet Earth. Contrary to what many people believe, soils are not just dust and minerals. They are living and dynamic ecosystems. A healthy soil teems with millions of visible, microscopic living things that perform many vital functions. What makes this living system different from dust is that it is able to slowly retain and provide the nutrients necessary for plants to grow. They can store water and release it gradually into rivers and lakes or into the microscopic environments around plant roots, so that rivers flow and plants can absorb water long after it has rained. If soils didn't allow for this process, life on Earth, as we know it, simply wouldn't exist.
A key component that allows the function of soils is the so-called organic matter of the soil, which is a mixture of substances that originate from the decomposition of animal and plant materials. It includes substances excreted by fungi, bacteria, insects, and other organisms. As manure, crop residues, and other dead organisms decompose, they release nutrients that can be taken up by plants and used in their growth and development. When all these substances mix in the soil, they form new molecules that give the soil totally new characteristics. Organic matter molecules absorb 100 times more water than dust and can retain and then release a similar proportion of nutrients to plants1. Organic matter also contains molecules that hold soil particles together, protecting it against erosion and making it more porous and less compact. It is these characteristics that allow the soil to absorb rain and slowly release it to rivers, lakes and plants. This also allows the roots of the plants to grow. As plants grow, more plant debris reaches or remains in the soil and more organic matter is formed, thus creating a continuous cycle of accumulation of organic matter in the soil. This process has taken place for millions of years and the accumulation of organic matter in soils was one of the key factors in the decrease of CO2 in the atmosphere millions of years ago, thus making possible the emergence of life on earth such as we know it.
Organic matter is found mostly in the top layer of the soil, which is the most fertile. For this reason it is prone to erosion and needs to be protected by a vegetation cover that is, in turn, a permanent source of additional organic matter. Plant life and soil fertility are thus mutually conducive processes, and organic matter is the bridge between the two. But organic matter is also food for bacteria, fungi, small insects and other organisms that live in the soil. They are the ones that convert manure and dead tissues into nutrients and the incredible substances described above, but they also need to feed themselves and thus break down organic matter in the soil. So organic matter must be constantly replenished otherwise it slowly disappears from the soil. When microorganisms and other living organisms in the soil break down organic matter, they produce energy for themselves and release minerals and CO2 in the process. For every kilogram of organic matter that is decomposed, 1.5 kilograms of CO2 is released into the atmosphere.
Rural people around the world have a deep understanding of soils. Through experience they have learned that the soil must be cared for, cultivated, fed and allowed to rest. Many of the common practices of traditional agriculture reflect this knowledge. The application of manure, crop residues or compost nourishes the soil and renews the organic matter. The practice of fallow, especially covered fallow, is intended to rest the soil, so that the decomposition process can be carried out in good shape. Reduced tillage, terraces, mulch, and other conservation practices protect the soil against erosion so that organic matter is not washed away. Often, the forest cover is left intact, altered as little as possible, or mimicked, so that the trees protect the soil against erosion and provide additional organic matter. When throughout history, these practices have been forgotten or when they have been put aside, a high price was paid for it. This appears to have been a major cause of the demise of the Mayan kingdom in Central America and may have been behind various crises in the Chinese Empire and is certainly a major cause of dust storms in the United States and Canada.
The NPK mindset: bad soils, bad food
We know that plants absorb 70-80 different minerals from healthy soils, while chemical fertilizers supply only a few. In the mid-19th century, the German scientist Justus von Liebig conducted experiments in which he analyzed the composition of plants to understand which elements were essential for their growth. His early equipment allowed him to identify only three: nitrogen, phosphorus and potassium, known by their chemical symbols, N-P-K. Although von Liebig later recognized that there are many other elements present in plants, his experiments laid the foundation for a lucrative agrochemical industry, which sells NPK fertilizers to farmers with the promise of miraculous increases in yields. NPK fertilizers have certainly revolutionized agriculture, but at the cost of a tragic degradation of the quality of the soil and our food.
In 1992, the official report of the Rio World Earth Summit concluded: "There is great concern about the significant continuous drop in mineral content in cultivated and grassland soils throughout the world." This statement was based on data showing that in the last hundred years, average mineral levels in agricultural soils have fallen worldwide - 72% in Europe, 76% in Asia and 85% in North America. The biggest culprit is the massive use of artificial chemical fertilizers instead of more natural methods of maintaining soil fertility. In addition to the direct depletion that the NPK mentality causes, chemical fertilizers also tend to acidify the soil thereby killing many soil organisms that play an important role in converting soil minerals to chemical forms usable by plants. Pesticides and herbicides can also reduce the absorption of minerals by plants by killing certain fungi in the soil that live in symbiosis with the roots (called mycorrhizae). This symbiosis allows plants to have access to a much larger mineral extraction system than is possible only with their own roots.
The net result of all this is that most of the food we eat is also mineral deficient. In 1927, researchers at Kings College, University of London began to study the nutritional content of foods. Since then, their analyzes have been repeated regularly, giving us a unique picture of how the composition of our food has changed over the last century. The following table shows the alarming results: our food has lost between 20% and 60% of the minerals that they used to have.
A new study published in 2006 shows that mineral levels in animal products have suffered a similar decline. Comparing levels measured in 2002 with those present in 1940, the iron content in milk was 62% lower, the calcium and magnesium in Parmesan cheese each fell 70%, and the copper in dairy products has plummeted by 90%, no less.
Source: Marin Hum, "Soil mineral depletion," in: Optimum nutrition, Fall 2006, vol. 19.3. Institute for Optimum Nutrition, UK.
The industrialization of agriculture and the loss of organic matter from the soil.
Agricultural industrialization, which began in Europe and North America and was later replicated with the Green Revolution in other parts of the world, started from the assumption that soil fertility can be maintained and improved with the use of chemical fertilizers. The importance of having soil organic matter was ignored and underestimated. Decades of industrialization of agriculture and the imposition of technical industrial criteria in small agriculture, weakened the processes that ensure that the soils obtain new organic matter and that protect the organic matter stored in the soil from being carried away by water or wind. The effects of applying fertilizers and not renewing organic matter were not immediately noticed since there were significant amounts of stored organic matter in the soils. But over time, as these levels of organic matter have been depleted, such effects have become more visible — with devastating consequences in some parts of the world. Worldwide, in the pre-industrial era, the balance between air and soil was one ton of carbon in the air for about 2 tons deposited in the ground. The current ratio has dropped to approximately 1.7 tons in the ground for every ton in the atmosphere. (2. 3)
Soil organic matter is measured in percentage, One% means that for every kilogram of soil, 10 grams are organic matter. Depending on the depth of the soil, this can be equivalent to a ratio of between 20 and 80 tons per hectare. The amount of organic matter necessary to ensure soil fertility varies widely depending on its formation process, what other components it has, local climatic conditions, and so on. It can be said that, in general, 5% organic matter in the soil is, in most cases, an adequate minimum of healthy soil, although for some soils the best conditions for cultivation are achieved when the material content organic exceeds 30%.
According to a wide range of studies, agricultural soils in Europe and the United States have lost, on average, 1 to 2% of organic matter in the upper 20 to 50 centimeters. (4) This data may be an underestimation since almost always the point of comparison is the level of organic matter at the beginning of the 20th century, when many soils were already subjected to industrialization processes and therefore could have lost important amounts of organic matter. Some soils in the agricultural Midwest of the United States, which used to be 20% carbon in the 1950s, are now just 1 or 2%. (5) Studies from Chile, Argentina (6), Brazil (7), South Africa (8) and Spain (9) report losses of up to 10%. Data provided by researchers at the University of Colorado indicate that the global average loss of organic matter from croplands is 7 percentage points. (10)
Climate solutions through organic agriculture
For more than 50 years, the Rodale Institute (Pennsylvannia, USA) has conducted research on organic agriculture. Data on soil carbon from almost 30 years show without a doubt that better ways of caring for the planet - specifically those that incorporate organic regeneration agricultural practices - may be the most effective strategy of all currently available to mitigate carbon emissions. CO2. Some of their impressive findings are summarized below.
"During the 1990s, the results of the Compost Utilization Trial at the Rodale Institute - a 10-year study comparing the use of compost, manure, and synthetic chemical fertilizers - show that the use of compost and crop rotations in organic systems can result in the sequestration of up to 2,000 pounds of carbon / acre / year. By contrast, normally tilled fields that rely on chemical fertilizers lose nearly 300 pounds of carbon / acre / year. Storing - or sequestering - up to 2,000 pounds / acre / year means that more than 7,000 pounds of carbon dioxide are removed from the air and held in that soil. "
"It is estimated that in 2006, the carbon dioxide emissions of the United States were close to 6.5 billion tons. If 7 thousand pounds of CO2 / acre / year could be captured in the 434 million cultivated acres of the United States , about 1.6 billion tons of carbon dioxide could be captured each year, mitigating nearly a quarter of the country's total fossil fuel emissions. "
"Carbon sequestration through agriculture has the potential ability to substantially mitigate the impacts of global warming. When using bio-based regenerative practices, this dramatic benefit can be achieved without a decrease in yields or profit margins. climate and soil types affect the ability to sequester carbon, various investigations prove that organic agriculture, if practiced on the 3.5 billion arable acres of the planet, could capture about 40% of current C02 emissions "
Taken from: Tim J. LaSalle and Paul Hepperly, Regenerative Organic Farming: A Solution to Global Warming, Rodale Institute, 2008
Assume, on a cautious estimate, that, on average, soils globally have lost 1 to 2% organic matter in the top 30 centimeters since the inception of industrial agriculture. This could mean a loss of between 150 thousand and 205 thousand million tons of organic matter. If we were able to recover this organic matter from the soil, it would mean being able to capture between 220 thousand and 330 thousand million tons of CO2 from the air. This represents at least a remarkable 30% of the current excess CO2 in the atmosphere! Table 1 summarizes the data.
Table 1: Carbon sequestration through the recovery of soil organic matter
CO2 in the atmosphere (11) - 2 trillion 867 500 million tons
Excess CO2 in the atmosphere (12) - 717.8 billion tons
Agricultural area in the world (13) - 5 billion hectares
World cultivated area (14) - 1.8 billion hectares
Typical loss of organic matter in cultivated soils, according to technical reports - 2 percentage points
Typical loss of organic matter in grasslands and uncultivated soils according to technical reports - 1%
Loss of organic matter from soils worldwide - 150 thousand - 205 thousand million tons
Amount of CO2 that would be captured if these losses are recovered - 220 thousand - 330 billion tons
Source: GRAIN calculations
In other words, the active recovery of organic matter from the soil could effectively cool the planet and the cooling potential could be significantly higher than the calculations presented here, to the extent that many soils could recover more than 1-2 percentage points of matter. organic and benefit from it.
Can this be done? Return organic matter to the soil
In developed countries, the process of industrialization of farming methods that has destroyed organic matter in the soil has continued for more than a century. However, the global industrialization process began with the Green Revolution in the 1960s. The question, then, is how long it would take to counteract the effects of, say, 50 years of soil deterioration. To recover 1% of the organic matter in the soil, it would be necessary to incorporate and retain in the soil about 30 tons of organic matter per hectare. But, on average, about two-thirds of the organic matter just added to the soil will be broken down by soil organisms, thus releasing the minerals that will nourish crops. Therefore, for 30 tons of organic matter to remain in the soil, it would take 90 tons per hectare. This cannot be done quickly. A gradual process is required.
How much organic matter could farmers around the world get into the soil? The answer varies widely depending on the location, the farming system and the local ecosystem. A production system that is based exclusively on non-diversified annual crops can deliver to the soil between 0.5 and 10 tons of organic matter per hectare per year. If the cropping system is diversified and incorporates grasslands and green manure, this figure can easily be doubled or tripled. If animals are incorporated, the amount of organic matter will not necessarily increase, but it will make the cultivation of grasslands and green manures feasible and profitable. Furthermore, if wild trees and plants are managed as part of the cropping system, not only will production increase, but more organic matter will be available. As organic matter increases in the soil, fertility will improve and there will be more matter to incorporate into the soil. Many organic farmers have started with less than 10 tons per hectare per year, but after a few years, they can produce and apply up to 30 tons of organic matter per hectare per year.
So, if agricultural policies and programs were defined that actively promoted the incorporation of organic matter into the soil, the initial goals could be quite modest but, progressively, more ambitious ones could be defined. Table 2 exemplifies the impact of progressive and feasible goals for the incorporation of organic matter into the soil.
Table 2. Impact of the progressive incorporation of soil organic matter (mos) into agricultural soils
The example is entirely possible. Today, agriculture around the world in total annually produces at least 2 tons of usable organic matter per hectare. Annual crops produce more than 1 ton per hectare (15) and if waste and urban wastewater were recycled, 0.2 tonnes per hectare could be added. (16) If the recovery of organic matter from the soil were to become a central factor in agricultural policies, an average of 1.5 tons per hectare could be a possible and reasonable starting point. The new scenario would require approaches and techniques such as diversified cropping systems, better integration between crops and animal production, greater incorporation of trees and wild vegetation, and so on. Greater diversity would increase the production potential and the incorporation of organic matter would progressively improve soil fertility creating virtuous circles of higher productivity and greater availability of organic matter over the years. The water retention capacity of soils would improve and therefore, the impact of excess rainfall would be reduced; floods and droughts would be less frequent and less intense. Soil erosion would be a less frequent problem. Acidity and alkalinity would progressively decrease, reducing or eliminating toxicity problems that have become the main problem in arid and tropical soils. Additionally, the increase of biological activity in the soil would protect the plants from pests and diseases. Each of these effects implies higher productivity and therefore more organic matter available to the soil, thus enabling higher goals for incorporation of organic matter as the years go by. In the process, more food would be produced.
But even initially modest goals would have a major impact. As shown in table 2, if the process began with the annual incorporation of 1.5 tons per year for 10 years, it would be capturing 3 750 million tons of CO2 each year. This is equivalent to 9% of all annual greenhouse gas emissions produced by humans. (17)
Two other mechanisms for reducing greenhouse gases would also occur. First, nutrients equivalent to more than everything contributed by chemical fertilizers would be captured in the world's agricultural soils (18). Eliminating the production and use of chemical fertilizers would have the potential to reduce the emission of nitrous oxides (which is equivalent to 8% of all emissions and which, after deforestation, is by far the largest cause of greenhouse gases greenhouse gases produced by agriculture), and CO2 emitted by the production and transport of fertilizers (equivalent to 1% of global emissions (19)). Second, if urban organic waste were incorporated into agricultural soils, CO2 and methane emissions from landfills and sewage, which are equivalent to 3.6% of total emissions (20), could be significantly reduced. In short, even modest initial targets would have the ability to reduce global annual emissions by about 20%.
This only in the first ten years. Table 2 shows that if we continue with a gradual increase in the return of organic matter to the soil, in the period of 50 years it will have been possible to increase the organic matter of the soil by 2% worldwide. In the first place, this time is similar to the time it took to destroy it. In the process we will have captured 450 billion tons of CO2, almost two-thirds of the excess currently in the atmosphere!
Recovery of organic matter: fungi in action
Researchers are unraveling the mechanisms by which carbon is captured in the soil. One of the most significant discoveries is the high correlation between high levels of carbon in the soil and a large number of fungi that form mycorrhizae. These fungi help slow down the degradation of organic matter. "A partir de nuestro sistema de ensayos de campo, realizados en colaboración con el Servicio de Investigación Agrícola del del Departmento de Agricultura de Estados Unidos, y encabezados por el doctor David Douds, es posible demostrar que el sistema de soporte biológico de las micorrizas es más prevalente y diverso en sistemas manejados orgánicamente que en suelos tratados con fertilizantes y pesticidas sintéticos. Estos hongos ayudan a conservar la materia orgánica formando agregados de materia orgánica, arcilla y minerales. En estos agregados el carbono se hace más resistente a la degradación que cuando está libre y por lo tanto hay mayores posibilidades de que se conserve. Estos descubrimientos demuestran que los hongos que forman micorrizas producen una sustancia llamada glomalina que actúa como un poderoso pegamento y que estimula una mayor agregación de las partículas del suelo. El resultado es una mayor capacidad del suelo para retener carbono.
Tomado de: Tim J. LaSalle and Paul Hepperly, Regenerative Organic Farming: A Solution to Global Warming. Rodale Institute, 2008
Se puede hacer, pero se necesitan las políticas correctas.
Al presentar estos datos, GRAIN no está presentando un plan de acción. Tampoco estamos diciendo que la recuperación de materia orgánica al suelo por sí misma resolverá la crisis climática. Si no ocurren cambios fundamentales en los patrones de producción y consumo a nivel mundial, el cambio climático continuará acelerándose. Pero los datos que presentamos muestran que la recuperación de la materia orgánica del suelo es posible, factible y beneficiosa para el enfriamiento de la Tierra. También queremos mostrar lo absurdo de considerar la materia orgánica como desperdicio o —lo que escuchamos más y más— como biomasa para hacer combustible. Cómo puede recuperarse un nivel saludable de materia orgánica en el suelo es un problema que requiere respuestas a nivel político, siendo necesarios muchos grandes cambios sociales y económicos para hacerlo posible.
Devolver la materia orgánica al suelo no será posible si continúan las actuales tendencias a una mayor concentración de la tierra y a la homogenización del sistema alimentario. El objetivo abrumador de devolverle al suelo más de 7 mil millones de toneladas de materia orgánica cada año, sólo será posible si lo llevan a cabo millones de campesinos y comunidades agrícolas. Se requieren reformas agrarias radicales, de forma que los pequeños agricultores —que son la gran mayoría de los agricultores del mundo— tengan acceso a la tierra necesaria para hacer posible económica y biológicamente las rotaciones de cultivos, los barbechos cubiertos y la formación de pastizales. Se necesita detener y desmantelar las actuales políticas anti-campesinas, que están reduciendo a una velocidad alarmante el número de fincas y comunidades agrícolas, que corren a la gente de sus tierras, que cuentan con leyes que fomentan la monopolización y privatización de la semillas y con regulaciones y criterios que protegen a las corporaciones pero aniquilan los sistemas alimentarios tradicionales. Los ecosistemas locales necesitan ser protegidos. Se requiere promover y apoyar las tecnologías basadas en saberes y culturas locales. Se debe liberar a las semillas de cualquier forma de monopolización y privatización, y se debe promover los sistemas locales de intercambio y mejoramiento de ellas. No deberían imponerse estándares industriales en la agricultura. La producción industrial e hiperconcentrada de animales, que literalmente crea montañas de estiércol y lagunas de orines, enviando millones de toneladas de metano y óxido nitroso al aire, necesita ser reemplazada por la crianza de animales descentralizada e integrada a la producción de cultivos. Nuestros hábitos de consumo necesitan ser re-examinados. Es necesaria una revisión total del sistema alimentario internacional que es, actualmente, una de las causas centrales tras la crisis climática. Si esto se hace, entonces la crisis climática tiene una solución posible: el suelo.
Informe de Grain – http://www.grain.org
1. C.C. Mitchell and J.W. Everest. "Soil testing and plant analysis". Dept. Agronomy & Soils, Auburn University.
2. Y.G. Puzachenko et al. "Assessment of the Reserves of Organic Matter in the World’s Soils: Methodology and Results". Eurasian Soil Science, 2006, vol. 39, núm. 12, pp. 1284–1296.
3. Rothamsted Research, uno de los principales centros de investigación de Reino Unido, calcula que en el suelo hay dos a tres veces el carbono que hay en la atmósfera.
4. R. Lal and J.M. Kimble "Soil C Sink in us Cropland",
y P.Bellamy. "UK losses of soil carbon —due to climate change?"
5. Tim LaSalle et. al, "Regenerative Organic Farming: a solution to global warming", Rodale Institute, 2008.
6. I. Gasparri, R. Grau, E. Manghi. "Carbon Pools and Emissions from Deforestation in Extra-Tropical Forests of Northern Argentina Between 1900 and 2005"
y J. Galantini. "Materia Orgánica y Nutrientes en Suelos del Sur Bonaerense. Relación con la textura y los sistemas de producción", http://www.fertilizando.com
7. Carlos C. Cerri. "Emissions due to land use changes in Brazil".
8. C. S. Dominy, R. J. Haynes, R. van Antwerpen, "Loss of soil organic matter and related soil properties under long-term sugarcane production on two contrasting soils". Biol Fertil Soils (2002) 36:350–356.
9. E. Noailles, A. de Veiga. "Pérdida de Fertilidad de un Suelo de Uso Agrícola".
10. K. Paustian, J. Six, E.T. Elliott and H.W. Hunt, "Management options for reducing CO2 emissions from agricultural soils". Biogeochemistry. volume 48, number 1, enero 2000.
11. Carbon Dioxide Information Analysis Center.
12. Cálculos en base a cambios de la concentración de CO2 en el aire
15. Cálculos de GRAIN con base en la producción mundial de cultivos anuales. De acuerdo a datos de Holm-Nielsen hay por lo menos el doble de residuos vegetales cada año. (www.dgs.de/uploads/media/18_Jens_Bo_Holm-Nielsen_AUE.pdf ) y al Oak Ridge National Laboratory del Departamento de Energía de los Estados Unidos (http://bioenergy.ornl.gov/papers/misc/energy_conv.html). Cifras similares se obtienen utilizando los datos de la Universidad de Michigan en el sitio
16. Los cálculos están basados en las cifras proporcionadas por wri.
17. Cálculos hechos con datos del Greenhouse Gas Bulletin núm. 4,
18. Cálculos basados en los siguientes contenidos de nutrientes de la materia orgánica y los siguientes niveles de eficiencia de recuperación: Nitrógeno: 1.2-1.8%, 70% eficiencia; Fósforo: 0.5-1.5%, 90% eficienca; Potasio: 1.0-2.5%, 90% eficiencia
19. Ibid, nota 16