The Carbon Footprint of Fertilisers
List of contents
The massive use of fertilisers on extensive crops over the last decades is leaving a pollution footprint, both in the soil and in the atmosphere, that is now beginning to be looked at with concern. While it is well known from numerous studies that the overuse of fertilisers (especially mineral fertilisers) damages the substrate for future crops, often - even if it works against them - growers only have one thing in mind: maximising yields in their fields and facilities.
However, it is not just about how we use these products, but also about how the fertilisers are manufactured, processed and transported. Because, as in many other areas and sectors, each and every one of these steps causes pollution. It's a curious paradox... shouldn't we growers be the first to take care of the environment where we intend to plant?
Agriculture & greenhouse gases
The world's population is growing all the time, which means that we need more and more food to support this growth. But it is not just the demand for food that is increasing daily, because as well as more food, we are also going to need more animal feed, natural fibre and biofuels, so the forecasts are clear; as the population continues to grow, the demand for a series of products related to agricultural activity will increase proportionally.
The FAO (Food and Agriculture Organisation of the United Nations) forecasts a global population of around 9 billion people in 2050, approximately one-third more than today. Logically, this increase means a greater need for food and other agricultural products, so this sector will have to "catch up" and work to ensure that its activity is as non-polluting as possible, reducing greenhouse gas (GHG) emissions as much as possible and, in short, the carbon footprint of its activity.
What is the carbon footprint of a fertiliser?
When we talk about the carbon footprint of an agricultural product (or any type of product, in fact), we are referring to the total amount of greenhouse gases produced directly or indirectly during its life cycle, which includes everything from its production or manufacture to its transport or use. So, we're talking about raw materials and how they are obtained and transported, the manufacturing and production processes, storage and transport, marketing or waste management - a whole range of activities necessary to obtain that product and which leave their footprint in the form of pollution.
Seen in this way, buying anything doesn't seem so environmentally friendly anymore, does it? Hence the importance of this type of calculation, as we need to know both how much we pollute and what we can do to reduce our total GHG emissions. As we will see, agriculture, apart from having a number of environmental benefits, is not exactly an environmentally friendly activity, especially when a number of good practices in the field are ignored.
Carbon footprint and agriculture: how to reduce it?
Greenhouse gas emissions are mainly associated with three types of gases: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), with CO2 and N2O being the most produced by the agricultural sector. Today, it is estimated that 25% of GHG emissions come from agriculture, forestry and livestock, including related phenomena such as fertiliser management and deforestation.
If we focus on the total GHG emitted by these activities, a third of them are caused by sources such as seeds, pest control products or the fuels necessary to carry them out, while the rest, 70%, are directly associated with mineral fertilisers, either through gas emissions once applied to the soil or through their manufacture and transport.
We certainly have the capacity to make these figures change and become more environmentally benign. From local trade strategies to the use of modern fertiliser formulas that are more environmentally friendly both in their manufacturing processes and once in use, applied to the field. "Reinventing" the agricultural sector is a tremendously complex challenge, but it is really necessary considering the world population data we have seen, as well as other factors such as climate change or the appearance of new pests and diseases. Of course, organic farming techniques, biological pest control or allelopathy will have to become more important if we want to reduce GHG emissions into our atmosphere.
How do plants interact with each other? Can you achieve better yields growing other plant species simultaneously? Allelopathy is a phenomenon by which a living organism has a direct impact on other organisms in its environment. In this article, we’ll tell you more about this, and explain how growing other types of plants can help you to obtain healthier and more productive cannabis.
Nitrous Oxide or N2O: Public Enemy Number One
We know that the 3 main greenhouse gases are carbon dioxide, methane and nitrous oxide, the first and the third being those most produced by agriculture. Although the total amount of N2O produced by this sector is much lower than that of CO2, its effect on the atmosphere is much more pronounced. In fact, N2O is the gas with the greatest greenhouse effect, with a global warming power approximately 300 times greater than that of carbon dioxide. But how exactly is this gas produced?
N2O is produced from the soil, whether we are talking about agricultural or forestry land, and the use of nitrogen fertilisers is not necessary for it to be emitted. In fact, it is produced thanks to the nitrogen cycle in two biochemical processes called nitrification and denitrification. During the former, and due to the activity of a series of bacteria that obtain energy from the process, ammonium nitrogen is transformed into nitric nitrogen or nitrites, which will subsequently oxidise and give rise to nitrates, the forms of nitrogen that can be assimilated by plants.
Denitrification, on the other hand, occurs when the oxygen content of the soil decreases, for example, due to a prolonged period of rainfall or irrigation. In this case, a number of microorganisms replace atmospheric O2 with molecules with a high oxygen content, such as nitrate NO3. During this process, NO, N2O and N2 are generated, of which only the latter is environmentally harmless.
Which type of fertiliser pollutes the most?
Using any type of fertiliser, however organic it may be, has its carbon footprint, but... are there fertilisers that pollute less than others? Which is the most polluting? Well, it is the mineral fertiliser, and within mineral fertilisers, we would highlight those that contain urea instead of ammonium nitrate as the most polluting. We will tell you why.
The ammonium nitrate present in many fertilisers is processed from ammonia and nitric acid, and its carbon footprint depends mainly on three aspects: The energy consumption required for its manufacture, the raw material used to make the ammonia, and, finally, the N2O emissions produced during the processing of nitric acid. In contrast, the carbon footprint during the production of urea is smaller, as the CO2 generated during the production of ammonia is absorbed by the urea itself. However, this CO2 will also be released once the fertiliser is applied to the field, and in the case of urea, the N20 emissions due to the nitrification process are higher. Thus, in the end, urea ends up polluting more than nitrates.
Of course, the pollution generated during the manufacture of fertilisers depends to a large extent on the techniques used during the process. To give you an idea, producing one kilo of Nitrogen for fertilisers emits approximately 7kg of CO2 into the atmosphere. If the practices suggested by the European Union in terms of production techniques and technology (a concept called BAT or Best Available Technologies) are followed, this figure drops to 3.6kg of CO2, halving the pollution for the same product.
Other common fertilisers on the market that are known to be highly polluting are ammonium sulphate or potassium chloride. If we want to protect our environment and future crops as much as possible, the use of nitrates will always be much more advisable. At a time of high global growth and with half the people on the planet already dependent on crops fertilised with mineral fertilisers, it is worth looking at these aspects and trying to reduce unnecessary pollution as much as possible, whether we are talking about their manufacture or their use (it is estimated that the pollution generated during production is similar to that generated by gas emissions once the fertiliser has been applied in the field).
The carbon footprint of cannabis cultivation
As with any other plant or vegetable, growing cannabis can also be highly polluting. Even more so if we take into account the amount of cannabis grown indoors today, with all that this implies: the use of lighting systems, air conditioners, large air extraction fans, CO2 generators (which represent between 11 and 25% of the facility's total CO2 emissions), irrigation systems and, of course, pesticides and fertilisers. If we add the energy expenditure involved in this activity to the carbon footprint we have seen (in fertiliser alone), we soon realise that, on an environmental level, the large grows we see today do not exactly represent an example of ecological sustainability.
To give you an idea: in 2012 (that is, before the real boom in cannabis cultivation in North America), producing one kilo of cannabis was equivalent to 4,600 kilos of CO2 emitted, with electricity costs amounting to 6 billion dollars. That's roughly 1% of the total electricity consumed in the US. The numbers are easy to work out; a single joint of weed "costs" about 2 kilos of CO2 in the atmosphere.
Another example; in 2021, in the state of Colorado, the cannabis industry was responsible for 1.3% of the total CO2 emissions in the entire state, similar to the coal mining industry or waste collection and management. One of the main problems? Because the sector has grown so rapidly, many states still do not have GHG emissions legislation on cannabis cultivation, so there are no limits or protocols on how to do it in a more eco-efficient way. Considering that the sector has an expected growth rate of 16% per year, this legislation is more crucial than ever to achieve some sustainability in this activity.
As you have seen, there is no shortage of reasons for all growers around the world, be it cannabis or any other plant, to "get our act together" and try to see how we can reduce the carbon footprint of our crops. From the use of LED grow lights instead of high discharge lamps to climate controllers or, of course, the use of 100% organic fertilisers... it will all help to achieve this!
- Fertilización y CO2. Implicaciones en la huella de carbono, Antonio Vallejo, Diego Ábalos, Ángela Téllez, Guillermo Guardia
- The carbon footprint of Indoor Cannabis production, Evan Mills
- Carbon footprint of fertilizer technologies, K. Chojnacka, Z. Kowalski, J. Kulczycka, A. Dmytryk, H. Górecki, B. Ligas, M. Gramza
- Carbon footprint analysis of mineral fertilizer production in Europe and other world regions, Frank Brentrup, Antoine Hoxha