Farmers have the Earth in their hands by Paul Luu

Foreword by Stéphane LE FOLL Ibrahim Assane MAYAKI Gabrielle BASTIEN

with Marie-Christine Bidault

Farmers have the Earth in Their Hands

Other titles available from Éditions La Butineuse:

Land and Climate. Insights from the IPCC Special report, Patrick Love

Energy chronicles. Keys to understanding the importance of energy , Greg de Temmerman

Feeding the Earth. A Manifesto for Regenerative Agriculture, Daniel Baertschi

Hydrate the Earth. The forgotten role of water in the climate crisis, Ananda Fitzsimmons

Cover and interior design: © Agence Coam

All rights of reproduction, translation and adaptation, reserved for all countries.

ISBN : 978-2-493291-09-7

© 2022 Éditions La Butineuse

Atelier des Entreprises

Place de l’Europe – Porte Océane 3

56400 Auray – France www.editions-labutineuse.com

Paul Luu

With Marie-Christine Bidault

Farmers have the Earth in Their Hands

Illustrated by Léa Cros

Chapter

Foreword

When considering the options for the future development of our agricultural production methods, it is tempting to pit organic agriculture against conventional agriculture.

However, there is no absolute truth and one of the major challenges of the current debate lie in the realisation that the context is not always as simple as it seems.

Other principles of agriculture exist, are developing, and coexist. They respond to production needs and adapt to constantly changing natural conditions, particularly under the impetus of climate change.

The intention of the book you are holding in your hands is to provide a simple and objective overview of agriculture, its scientific foundations, the history of its (r)evolutions and the situation today. It is also to open the way to the agro-ecological transition which is necessary for the future of humanity on planet Earth.

It is a question of giving everyone the means to understand what is at stake without evading the questions that are sometimes disturbing, but which are important in today’s world. Alongside the challenges, we do have realistic options to address them. This discussion is often presented in a simplistic way, whereas the reality of life is by nature complex.

This book does not pretend to explain everything exhaustively but to provide keys to understanding. The objective is to allow each person to form his or her own opinion and to engage in his or her own reflections on the

choices to be made with regard to food and therefore agriculture, and on the behavior of stakeholders with frequently divergent interests.

One thing is certain: every human being on Earth needs to feed themselves daily to enable them to survive. Tomorrow, there will be nearly 10 billion of us on a planet that, every day, shows us its limits and the consequences of our thoughtless actions.

If we wish to leave our children agricultural land capable not only of feeding us today, but also of bearing tomorrow’s crops, there is one capital that is more important than any other, that of the soil, a living soil.

The most important challenge ahead of us is to lead the agro-ecological transition to improve the world’s food security and actively contribute to the fight against climate change.

Through agriculture and forestry, soil restoration and regeneration, let us pass on this precious capital to future generations without compromising their future productive capacities!

Since the birth of the International Initiative “4 per 1000: Soils for Food Security and Climate” launched during the COP 21 in Paris in December 2015, things have started to move in the right direction.

But the main actors of this new “(r)evolution” are, first and foremost, farmers as well as citizens aware of the current global challenges.

Stéphane LE FOLL

Ibrahim Assane MAYAKI Gabrielle BASTIEN President, Vice-President and Vice-President of

the International “4 per 1000” Initiative

The International “4 per 1000” Initiative aims to show that agricultural soils can play a crucial role in food security and climate change. It consists of federating all voluntary actors from the public and private sectors and has 700 partners whom it invites to raise awareness and implement concrete actions for soil carbon storage.

Stéphane LE FOLL has been Mayor of the city of Le Mans since 2018 and was Minister of Agriculture and Food of the French Republic from 2012 to 2017. He is the author of La première graine published by Calmann Levy – 2017.

Ibrahim Assane MAYAKI is Executive Secretary of the New Partnership for Africa’s Development (NEPAD) since 2009. He was Prime Minister of Niger from 1997 to 2000.

Gabrielle BASTIEN is founder and Executive Director of the NGO Regeneration Canada since 2017. She has been distinguished as an Emerging Leader in Canada in 2021.

Chapter One

Why do we need a change in agriculture?

When it comes to food, and therefore agriculture, the opinions expressed become more radical. For many of our fellow citizens, agriculture has become an aberration that pollutes our land, our water and our air, and that no longer guarantees us sufficient and healthy food. While some people are overwhelmed by the abundance of increasingly processed products, supposedly to simplify their lives, others, elsewhere in the world, are struggling to meet their basic food needs.

For some, the choice is sensitive between an organic or vegan diet so as not to make animals suffer, or soon synthetic meat from cell cultures; for others, the only daily meal will be what they can find, regardless of the origin, the production methods and the balance between plant and animal based foods.

How can we confidently envisage feeding 10 billion human beings with food production that no longer seems able to increase, other than through extensive deforestation and increased use of fertilisers and synthetic pesticides?

Other challenges also threaten humanity, such as climate change, loss of biodiversity and the increasing frequency of pandemic diseases.

Are there another, still under-explored, ways to give us hope for a greener tomorrow? Are there solutions that are more in harmony with nature, which would allow each human being to meet his or her vital needs; access to sufficient and healthy food, breathable and unpolluted air, and clear and pure water as on the first day? Perhaps...

It is impossible not to notice how dependent our conventional agriculture, and therefore our global food supply, is on chemicals and fossil fuels. In order to exist and develop, it also continues to cause deforestation in some parts of the world, which leads to a significant loss of biodiversity, especially when it concerns primary forests.

It is nevertheless necessary to recall that this agriculture has emerged and developed in a certain context, fulfilling the objectives assigned to it by society at the time: to increase food security for a growing world population; to reduce the drudgery of work for farmers; to facilitate and reduce the production costs of agricultural products to facilitate trade and exchange, and so on.

Like many other human activities, the large-scale deployment of cheap fossil fuels, allowing both the manufacture and distribution of various chemicals and powerful mechanical means, has diverted agriculture. It has also sought to gradually free itself from climatic conditions through irrigation, from diseases, pests and weeds through the use of pesticides and, above all, from the state of the soil through application of fertilisers. This to the point of considering the soil as a mere inert substrate and not as the support and source of life.

The plant and animal species that are cultivated, bred, sorted and selected according to this evolution, have become very dependent on these factors, and they must be provided with appropriate and adapted nutrition food and protection. In short, it does not matter how degraded and unhealthy the soil that supports them becomes, since external inputs compensate for the deficiencies of its natural functioning.

This system has made it possible to achieve very high levels of production at relatively low cost, at least economically, supported by abundant and cheap fossil fuels. But the negative impact on the environment is now proven and has shown its limits in terms of productivity as well as its fragility due to its very high degree of dependence.

Conventional agriculture, an assisted agriculture

So-called conventional or industrial agriculture is dependent on many external inputs.

It uses mineral fertilisers to provide crops with the elements they need to grow, and thus compensate for the decline in natural soil fertility. Soils which are often depleted by intensive practices like deep tillage and the short rotations of the same crops in the same fields.

It is also dependent on pesticides and herbicides to ‘easily’ control diseases, pests and weeds, which are favoured in single-crop systems.

In many parts of the world, it is also dependent on irrigation because, regardless of the problem of climate change, the aim has been to produce the same species everywhere, for reasons of short-term efficiency, without regard to local climatic specificities. As a result, it is often necessary to water non-native crops at critical times because they are not necessarily adapted to local conditions.

Conventional agriculture is therefore a mechanically and chemically optimised agriculture, through the industrial processes of its upstream suppliers and downstream distributors. While it still depends on essential natural processes such as photosynthesis, it has become independent of those that can be replaced by ‘artificial means’.

Similarly, livestock farming, when conducted in this conventional way, is dependent on the production of protein-rich plants such as soya, often imported from the American continent, where they are produced at the expense of the forest. Animals, like plants, are selected from specialised, high-performance breeds, with the aim of achieving maximum profitability. This is often referred to as ‘intensive’ or ‘industrial’ livestock farming.

Livestock farming has intensified worldwide to meet the growing demand for meat and animal products such as milk and dairy products or leather,

and to lower production costs. This has led to the creation of off-farm livestock units, with animals that never or hardly ever go into fields, and where a large part of the feed is concentrated, rich in proteins and fats. The other consequence of this intensification is pollution, since off-farm cattle production generates large quantities of slurry which must be managed for disposal. The problem is exacerbated when there is a high density of such farms in limited area, leaking nitrates into rivers and groundwater.

This picture may seem bleak, but it is nonetheless realistic. It would, however, be unfair to speak only of the negatives without also mentioning the positives: the development of this intensive agriculture has made it possible to feed a large part of growing population. According to the FAO (United Nations Food and Agriculture Organisation), between 2000 and 2020, the number of people suffering from malnutrition fell by 17.2%, from 930 million to 770 million. This decrease is even more significant if one considers that over the same period, the world’s population has increased by 29.5%, or 1.7 billion.

As it is often the case, the global analysis of the situation conceals great disparities. Excessive daily calorie intake is leading to obesity in a growing proportion of the population in developed and emerging economies. At the same time, the proportion of the world’s population with insufficient daily calorie intake continues and increases in some regions, even in developed countries.

However, global food production, particularly from conventional agriculture, would be more than enough to provide the 2,600 calories needed daily for the 7.9 billion women and men who will inhabit the Earth in 2022. For some, the problem is a lack of distribution of the resource, a problem of access to this food. For others, we must question our diets because a large part of plant production is used for livestock and animal production: a more plant-based diet would allow better use of agricultural resources to meet the food needs of the entire world population.

There are elements of a solution in each of these proposals, but at the heart of the matter, it is essential to change production methods in the short and medium term.

Conventional agriculture is certainly moving towards so-called reasoned or precision agriculture. This type of farming still employs ploughing, mineral and synthetic inputs, but better justifies their use in time and space, thanks to developing advanced technologies. The use of sensors, drones or GPS guidance, for example, make it possible to fine-tune practices according to the needs of the plants, soil and weather conditions and the pressure of pests, diseases and weeds. They aim to be more precise in the introduction of inputs to limit costs, losses and waste in the environment, and consequently pollution. Reasoned or precision farming therefore offers certain improvements in terms of environmental impact, but its philosophy remains fundamentally the same as conventional farming.

Intuitively, even if we understand the efforts made by conventional agriculture to feed a growing world population, the ever-increasing use of mineral fertilisers and synthetic pesticides does not create a sustainable perspective. In fact, this type of agriculture is finding it increasingly difficult to fulfil the role it has been assigned. Conventional agriculture is extremely dependent on fossil fuels. It also has a negative impact on soil health and on the environment in general, in terms of climate, biodiversity, soil, water or air quality.

Impacts of conventional agriculture

Soil degradation

Soil, the main and basic resource for agricultural production, is increasingly threatened by multiple degradations caused by agricultural practices.

The first major form of degradation is erosion caused by rain and wind. This natural erosion is aggravated by ploughing and overgrazing.

Water erosion is the process by which rainwater loosens and carries away soil particles by runoff. Wind erosion blows away loose, unstructured soil in the form of dust. In both cases, it is the surface particles that are carried away into rivers, lakes and oceans.

The soil can also be damaged by compaction caused by heavy mechanical equipment, by overgrazing by animals that stay in the same plot for too long, and by excessive irrigation, which causes water compaction in addition to mechanical compaction. This compaction causes fine surface particles to sink into the soil when they are not aggregated by organic matter. This reduces soil porosity. Pores, filled with water and air are key to soil structure and fertility.

Irrigation of crops in semi-arid regions, where the irrigation water is often loaded with mineral elements and salts, causes salination of the soil. This leads to a loss of fertility and a degradation of structure.

The systematic use of mineral fertilisers disrupts the natural biological activity of the soil. However, it is this biological activity that enables the recycling of organic matter into mineral elements that are available and usable by plants. Poor selection and application of fertilisers and crop protection products lead to soil pollution and an accumulation of mineral elements and potentially toxic substances.

Finally, it should be remembered that soil pollution can also have an urban and industrial origin, via the atmosphere.

Today, according to the FAO, 75% of the planet’s soils are degraded to very degraded and could become impossible to cultivate with climate change. This figure could reach 90% by 2050, according to the same source. More than 10 million hectares of arable land are lost or severely degraded each year due to water and wind erosion. Most of these soils are tired or exhausted and have lost some of their physical, chemical and biological properties. In many cases, fertilisers are no longer sufficient to compensate for this loss of fertility in economically viable amounts.

Soil biodiversity

Beyond their simple physical or chemical properties, soils are one of the most complex and diverse ecosystems on Earth. They are home to thousands of different organisms, which interact and contribute to global cycles and make life possible. Nowhere in nature is there a higher density of species than in soil communities.

The FAO likes to remind us graphically that “a teaspoon of soil contains more micro-organisms than there are people on the planet”, and biologists have indeed found that a teaspoon of soil, or about a gram, is home to an average of 100 arthropods (insects, arachnids and myriapods), 1-2,000 nematodes (microscopic worms), 200 million fungal mycelia, and hundreds of millions to many billions of single-celled organisms (protozoa, bacteria, viruses, et cetera) from more than one million species.

These organisms perform vital functions for the functioning of the soil ecosystem: maintenance of structure, regulation of hydrological processes, gas exchange and carbon sequestration, detoxification, nutrient cycling, decomposition of organic matter. They also play a role in the fight against plant pests and diseases by establishing more or less complex relationships with plants through their roots. In this way, they contribute to increasing the efficiency of nutrient absorption by plants and play an important role in their growth and health.

The loss of soil biodiversity is linked almost exclusively to agricultural practices. Deforestation and the loss of grasslands for cultivation significantly reduces the number of species and mass of living organisms. The simplification of crop management limits the variety of cultivated plants and their contribution to the ecosystem through their root systems and metabolisms. This simplification results in a loss of quantity and quality of plant residues and organic matter, which leads to a decrease in habitat and food diversity for soil organisms.

Animal and plant biodiversity

The most visible biodiversity, that the one of the plants and animals around us, is also impacted by agricultural activity. Dozens of animal and plant species disappear every day and agriculture is a major contributor to this loss. Agricultural production accounts for 80% of global deforestation and 70% of the loss of terrestrial biodiversity, according to the WWF Living Planet 2020 report.

Among the most damaging phenomena for global biodiversity, is change in land use, mainly linked to the expansion of agricultural areas through deforestation. This leads to the destruction, degradation and fragmentation of habitats and the disturbance of species. The simplification of the landscape in order to increase the size of plots of land and gain productivity – also known as re-parcelling – has led to the massive uprooting of hedges and woodland and the disappearance of field margins which has an impact on local biodiversity: there are fewer refuges for pollinators and predators of pests. Plant protection products have unintended or indirect effects on other species like birds, insects and other animals and plants. Water, soil and air pollution resulting from agricultural and human activity destroys or modifies the balance of natural ecosystems.

The simplification of crop rotations has reduced the number of plant species cultivated. At the same time, successive selection processes to obtain highpotential plant varieties and animal breeds have also reduced agricultural biodiversity.

Crop varieties grown today are derived from selections from wild plants. Some of their characteristics are considered unnecessary today but may prove indispensable in the future; hence the importance of conserving this genetic heritage. Similarly, with farmed animals, the characteristics of breeds that have disappeared could be of interest for their adaptation to changing climatic conditions. Efforts are being made to find and select animals with similar genetic heritage.

Water and air quality

Agriculture is responsible for 70% of the world’s total freshwater consumption to irrigate 20% of cultivated land (275 million hectares). This represents 40% of global food production. According to UNESCO’s World Water Assessment Programme, freshwater withdrawals for agricultural use have tripled over the past 50 years to meet growing food needs. Although freshwater is an abundant resource, it remains very poorly distributed around the world. Today, many countries are water scarce and one in five people do not have access to safe drinking water.

Some of the water used in agriculture is lost due to defective irrigation networks or poor practice and some is returned to the environment loaded with pollutants. It is estimated that about 40% of the nitrogen applied to agricultural land is lost due to over application compared to the uptake capacity of the plants. The surplus is then washed into rivers and groundwater. All over the world, plant protection products applied to crops seep into the soil and cause direct pollution of rivers and oceans.

Caring for fresh water resources means caring for life, and agriculture cannot ignore this important issue.

Agriculture also contributes to the degradation of air quality, through fires linked to deforestation and through the spraying of pesticides. The transport of agricultural raw materials, fertilisers, pesticides and animal feed from the place of production to the place of use, and the mechanisation of field work all contribute to climate change through emissions from the combustion of fossil fuels.

Agriculture and climate change

Greenhouse gases (GHGs) are the gaseous components which, when released into the atmosphere, trap the infrared radiation reflected by the Earth’s surface when exposed to the sun’s rays.

Three quarters of these emissions, on a global scale, are carbon dioxide (CO2). The other greenhouse gases are nitrous oxide (N2O, with a warming power 265x greater than CO2), methane (CH4, 30x greater than CO2), but also water vapour (H2O) and ozone (O3).

According to the Intergovernmental Panel on Climate Change (IPCC), all the GHGs emitted by agriculture – including livestock farming – account for nearly 25% of all emissions due to human activities, mainly in the form of CO2.

67% of the emissions occur on the farm through agricultural activities, 27% through deforestation, 5% through fires in tropical areas and less than 1% are indirect emissions arising from the production of fertilisers, farm machinery, et cetera.

Emissions from agriculture have several origins.

ʶ In livestock farming, enteric fermentation in the rumen of ruminants (cattle and sheep) results in methane (CH4) emissions. The decomposition of animal waste during storage and processing in intensive livestock production also emits methane in the absence of oxygen, and nitrous oxide (N2O) through nitrification and denitrification in the presence of oxygen.

ʶ Crop cultivation through the application of nitrogen fertilisers leads to nitrous oxide emissions, and irrigated rice produces large quantities of methane.

ʶ Finally, consumption of fossil fuels for farming machinery and the manufacture, transport and application of fertilisers and other inputs, and soil cultivation, particularly ploughing, generates carbon dioxide (CO2) emissions.

Agriculture remains the main cause of deforestation, particularly in South America and Africa. Globally, between 2000 and 2019, 94 million hectares of forest were lost. However, the area of agricultural land used for food production has been decreasing since 2010 due to urbanisation, desertification and the expansion of industrial and energy crops. Over the same period, 127 million hectares of agricultural land have disappeared.

Nevertheless, according to the FAO (2021), over the same period, there has been an increase in crop (+53%) and animal (+44%) agricultural production in the world. The increase in crop production is mainly due to the development of irrigation and the increased use of inputs – mineral fertilisers and plant protection products. Over the same period, total global consumption of mineral fertilisers increased by 34% and pesticides by 36%.

This increase in agricultural production has helped to improve global food security to some extent. However, the challenge for agriculture is immense because, while agriculture contributes to climate change because of its emissions, it is also the first victim and must adapt to the climate change context.

Preserving life on our planet, including humanity, depends on soils far more than we realise. Therefore, it is essential that soils return to health again as soon as possible, while ensuring food for humans in the short, medium and long term.

The environmental and climatic context requires that we put an end to deforestation, restore to original condition some of the land currently used by humans, and preserve that which is still intact or only slightly affected.

It is therefore necessary to restrict the development of land for urbanisation as well for agricultural production. On this area, agricultural practices must be managed to reduce the negative impact on the environment and even create a positive impact.

To achieve this (r)evolution of agriculture, we have considerable assets at our disposal. The biological processes involved in agricultural production are a large part of the solution to climate change. Photosynthesis transforms CO2 from the atmosphere into biomass (roots, trunks, branches, stems, leaves, flowers, seeds). This can be returned to the soil to protect it, improve function and increase fertility, once transformed into humus through natural decomposition.

The secondary effect of this process is the storage of carbon in the soil. This can be more or less important depending on the systems and techniques, but

it can reduce the concentration of CO2 in the atmosphere and thus help to combat climate change.

This can be achieved by intensifying agricultural production in a different way, particularly by drawing inspiration from natural processes, from nature, by following the path of agroecology. Changing production patterns will also need to be accompanied by appropriate changes in consumption patterns and product choice. In particular, a better dietary balance between plant and animal products, bearing in mind that some people consume too much meat while others do not have access to it. It would also make it possible to reconsider overall agricultural production and the use made of it.

Talking about and working with agriculture means talking about and working with life, it is not as simple as a mathematical equation or a controllable and mastered industrial process.

Understanding the global functioning and the fundamentals of biology that govern agricultural production in the broadest sense, as well as our relationship to the living environment, is essential to understanding the solutions we might implement.

Furthermore, in order to consider where we need to go, it is vital to know where we have come from, to understand and remember the choices we have made throughout human history, the development and evolution of agriculture and the drivers of change.

The next two chapters will consider these fundamental aspects in order to address, in an enlightened way, the solutions that are available to us for a more secure future.

What about climate-smart agriculture?

Climate-smart agriculture (CSA) is not, strictly speaking, a form of agriculture, unlike those that will be presented in the rest of this book. Rather, it is a concept that was launched by the FAO, the World Bank and other

organisations after the Copenhagen climate conference in 2009, with the goal of feeding nine billion people by 2050 in the context of climate change.

It is defined as a means of helping countries and various actors to create the political, technical and financial conditions that will enable them to:

ʶ increase agricultural productivity and incomes in a sustainable way, in order to ensure food security;

ʶ increase the resilience and capacity of agricultural and food systems to adapt to climate change;

ʶ reduce or eliminate greenhouse gas emissions from agriculture to mitigate climate change.

It is conceived as a combination of agronomic practices that are implemented to maintain or increase agricultural production under adverse or worsening climatic regimes. Thus, climate-smart agriculture is not a set of practices that can be universally applied, but an approach that involves different elements in a local context. It is based on the premise that farmers are the main custodians of knowledge about their environment, their agro-ecosystem and about local weather patterns and that its adoption must be closely linked to their needs. Thus, there are no prohibited or mandatory farming practices.

Considerable resources have been mobilised to promote this concept of agriculture on a global scale, but the potential effects of its widespread adoption have not yet been studied.

Precision agriculture, by improving the use of inputs; mineral fertilisers, synthetic plant protection products, improved crop genetics, water. Compared to conventional agriculture, this is in itself a first step towards climate-smart agriculture. It reduces losses and GHG emissions and optimises use, but it does not aim to drastically reduce or eliminate them.

CSA is a step in the right direction that seeks to take into account the key variables, but it is still insufficient in its results.

Chapter Two From living principles to their substitution

If we have not studied our environment, what do we know about how nature works? Do we have any idea of how the food we eat every day is produced and manufactured and, more generally, of the major principles that govern the world in which we live?

Today, we are experiencing a global crisis due to climate change, the loss of biodiversity and the depletion of natural resources. Agriculture seems to be at the centre of it. To be able to act, it is important to understand the basics that are at the heart of the problem... but also at the heart of the solution!

This involves defining the fundamental principles at work in what we call biomass production i.e. the sum of everything that is alive and organic, on the surface of the Earth: plants, animals, from the smallest to the largest, from microbes to the blue whale and including... ourselves.

Understanding these basic principles will allow us to better understand how man has managed to optimise natural processes, to divert this production to his own benefit and to feed an ever-increasing human population, while reducing his efforts.

This is how agriculture was invented. This can be defined as “all the activities developed by man to obtain plant and animal products that are useful to him, in particular those intended for his food” (Larousse).

In order to achieve this, man has domesticated animal and plant species and developed an increasingly advanced mastery of their biological cycles, sometimes allowing us to forget that it is the fundamental natural processes that remain the basis of all agricultural production.

These fundamentals are photosynthesis, alongside the four major cycles of water, oxygen, carbon and nitrogen; and the interactions between plants, animals, their natural environment and man.

Photosynthesis

Most of us learned about photosynthesis at school, usually in secondary school, but not so much afterwards. We usually remember that plants use carbon dioxide to grow, that they need water and light, and that it is thanks to trees that we can breathe.

A very simple definition says that photosynthesis is the process by which the plant makes its own food, which is remarkable in itself. To do so, it needs four basic elements:

ʶ light energy, usually from the sun;

ʶ carbon dioxide (CO2) ;

ʶ water (H2O), transported by the plant from the soil;

ʶ chloroplasts, present in the cells of green leaves, which have the capacity to capture light energy like solar panels, and which are the site of photosynthesis.

The plant produces sugars to feed itself while releasing oxygen.

As a chemical equation, photosynthesis can be summarised as follows:

6 CO2 + 12 H2O + light energy => 1 C6H12O6 (sugar) + 6 O2 + 6 H2O

Mineral carbon (a component of CO2) and water (H2O) are the two basic ingredients plus the energy of the sun, for photosynthesis and thus for life. Without them, there is no capture of CO2 from the atmosphere, no release of oxygen, no sugar production, no plant growth, no agricultural production, no animals, no humans.

In this process, green plants play a vital role. They are the only living organisms (alongside a few groups of bacteria) capable of synthesising organic compounds, which constitute the plant biomass and create life from inorganic elements.

The oceans play an essential role in photosynthesis, thanks to the phytoplankton that form an even greater biomass than the forests on land. These tiny photosynthetic organisms, cyanobacteria and microalgae, play the

largest role in renewing the oxygen in the air we breathe. Scientists estimate they are the source of 50-85% of total oxygen production.

Water, oxygen and carbon are at the heart of the photosynthetic process; each entering a cycle in which they react with each other and with their environment. However, we must not forget about the nitrogen cycle, which also plays a vital role for life on Earth.

The course of these four cycles can be disrupted by human activities, particularly by agricultural practices. It is essential to understand the basic functioning of these processes, as they are the pillars which support life on Earth.

The major cycles

Water

The fact that water is essential to life is obvious to everyone. Plants must find water within reach of their roots in sufficient quantity and at the right time to grow and develop. It is an essential requirement for all living organisms.

Water is constantly circulating between its major reservoirs: oceans, glaciers and ice caps, groundwater, rivers, lakes, soils, water vapour, clouds and living organisms. The driving force behind the water cycle is solar energy, which promotes evaporation and drives all other exchanges, particularly photosynthesis and respiration.

Solar energy causes water to evaporate, the vapour mixes with the atmospheric air mass, cools down as it rises, then condenses and forms droplets that give rise to clouds and rain. Depending on the nature of the place where it falls, this rain will infiltrate the soil and subsoil or will run off. It will, ultimately, always return to the rivers and oceans carrying sediments and nutrients with it...

Living beings, especially plants, have an influence on this cycle. The roots of plants draw water from the soil, while absorbing mineral elements essential

to their development, transporting them through the plant. 98% of this uptake evaporates from the leaves to regulate their temperature and prevent damage from scorching: this is called evapotranspiration. Thus, almost all the water drawn from the soil only passes through the plant before evaporating into the atmosphere.

When the air and soil are too dry, the plant can completely stop transpiration by closing its stomata, the small pores on the leaves that open or close depending on climatic conditions. This can lead to leaf death if the heat and lack of water continue for too long. No plant can thrive in the complete absence of water, but their needs vary greatly between varieties and species, and the amount of water available has a huge influence on plant productivity.

Oxygen and carbon

Along with water, oxygen is the other key element associated with respiration and living organisms.

During cellular respiration, which is effectively the reverse of photosynthesis, the oxygen molecule (O 2) burns sugars, converting them into carbon dioxide (CO 2) and water (H 2O), releasing energy. It can be summarised in the following formula:

C6H12O6 (sugar) + 6 O2 + 6 H2O => 6 CO2 + 12 H2O + energy

These two complementary processes are the basis of life. Photosynthesis and respiration make us all dependent on one another: plants, animals and humans.

How do the oxygen and carbon cycles work?

Oxygen is produced on land by vegetation, particularly forests, through photosynthesis. But the net balance of a mature forest in terms of oxygen production is almost zero because it can consume as much oxygen through respiration as it produces. Plants also ‘breathe’ and emit CO2, as do the living creatures that live in them. Even dead organic matter oxidises as it decomposes through the activity of micro-organisms.

In the ocean, the plant-like plankton, phytoplankton, produce oxygen through photosynthesis just like land plants. Some of this oxygen is utilised for respiration by the animal component of plankton and other, larger, marine animals. Again, the decomposition of organic matter, which

consumes oxygen, must be taken into account. Nevertheless, the balance remains positive, which makes the ocean the main source of atmospheric oxygen.

Carbon is the basis of all animal and plant tissues. All living organisms are based on carbon-based compounds. Atmospheric carbon (CO2) is captured