This research finds that globally farmers apply around 115 million tonnes of nitrogen to our crops every year. Only around 35% of this is used by them
This research finds that globally farmers apply around 115 million tonnes of nitrogen to our crops every year. Only around 35% of this is used by them, meaning 75 million tonnes of nitrogen runs off into our rivers, lakes and natural environments. This is our “excess nitrogen”. It is quite staggering that almost two-thirds of our applied nitrogen becomes an environmental pollutant.
Which countries create the most nitrogen pollution? The maps below show this from two perspectives.
First, as the excess nitrogen per hectare of cropland. Here we see large differences across the world.
Some countries actually produce ‘negative’ nitrogen pollution, they are shown in blue. This is known as nitrogen mining. This happens when countries undersupply nitrogen fertilizers, but continue to try to grow more and more crops. Crops then have to take nitrogen from the soil. Over time this depletes soils of their nutrients which will be bad for the productivity of these soils and crop production in the long-run.
Other countries massively oversupply nitrogen. These are the countries shown in the darker shades of red here. Countries such as Kuwait, Singapore, South Korea, Egypt, New Zealand, China, and Taiwan create more than 100 kilograms of excess nitrogen per hectare. For every hectare of cropland, they produce hundreds of kilograms of pollution.
The other map shows total nitrogen pollution – the sum of pollution generated in each country, rather than per hectare. This is given as each country’s share of the global total.
China generates the most nitrogen pollution, accounting for one-third of the global total. India produces almost one-fifth (18%); the USA produces 11%; followed by Pakistan and Brazil.
It’s not that surprising that the countries with the largest populations (and some of the largest land masses) create the most pollution. But as I will explore in an upcoming article, there are lots of opportunities to reduce fertilizer use (and pollution) without sacrificing crop yields.
Both of these metrics – the amount of excess nitrogen per hectare, and the total excess are important. Excess per hectare informs us of where nutrients are being used inefficiently; if this number is high then farmers are overapplying fertilizers and organic nutrients. But total excess is also important because it informs us of where we’re likely to have hotspots of water and ecosystem pollution. We need to be aware of regions with lots of farmland and excess nutrients because surrounding rivers and lakes are at high risk of becoming polluted.