- Six of our nine planetary boundaries have now been crossed – and industrial agriculture are the main culprit.
- This notion of overstepping boundaries is clear in regard to the best-known limit of them all: that of climate change.
- Yet in the case of the planetary boundary for nitrogen, exceeding the threshold is different, as it is the industrialisation of agriculture that is largely, and more complexly, responsible for breaking the limit.
- But how can agriculture affect the nitrogen cycle?
The natural nitrogen cycle
- First, we need to understand the natural cycle of carbon and nitrogen – two of the main elements that form living matter.
- So, the boundaries of the nitrogen cycle have to remain local: any loss of nitrogen brings about a risk of soil depletion, which jeopardises continued plant growth.
- The amount of nitrogen that is lost in the atmosphere and in groundwater is therefore considerable, and this loss makes nitrogen the main limiting factor in plant growth.
- They do so through a symbiotic association with bacteria that have enzymes needed to convert molecular nitrogen into proteins.
- It is this symbiotic fixation that offsets the natural environmental loss of nitrogen and ensures that terrestrial ecosystems function perennially.
Farming and fertilisation
- Each time plants are harvested, the nitrogen contained in them is carried far away from the plot of soil where it came from.
- That is the purpose of fertilisation.
- There are many methods of fertilisation.
- Indeed, this method was the basis of traditional systems of polyculture and livestock farming.
- They quickly made traditional polyculture and livestock farming obsolete and paved the way to intensified and specialised agriculture, which was henceforth coupled with the heavy chemical industry.
Environmental nitrogen loss
- In this accelerated flow of nitrogen, what causes trouble is the environmental nitrogen loss that results from it.
- Indeed, the more nitrogenous fertilisers are used to increase crop yields, the less the added nitrogen is effective and the greater the losses through leaching and volatilisation.
- What we call the nitrogen surplus is the excess of nitrogen put into the soil in relation to the quantity actually taken away through harvesting.
Feeding the world without ruining it
- But can we reasonably scale down intensive farming without jeopardising the food security of a world that will have 10 billion mouths to feed by 2050?
- Yet we can only do so if three major structural changes are made to the entire agrifood system at the same time as intensive agriculture is toned down.
- On the contrary, this model of agriculture has now been clearly identified as a factor that disturbs the Earth’s system profoundly.
- AFP and The Conversation France have maintained their editorial independence at every stage of the project.
Gilles Billen ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.
