An introduction to geology
An introduction to geology

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

An introduction to geology

3.3 Fertilisers

For most of you, the food you eat also relies on the oil (and gas) industry. In the developed world, our diets rely on cheap food transported significant distances. How far food has been transported depends hugely on the choices we make – whether it’s the intensively reared meat flown in from the other side of the world, or the organic farm produce driven from just a few tens of miles away, both require transport, and currently most of that transport relies on oil-based fuels.

Described image
Figure 3.3 Tractor spreading fertiliser

It isn’t just transport from farm to consumer either – since the beginning of the mechanisation of agriculture (using petroleum-powered tractors), a significant amount of oil-based fuels are used during the farming and processing of crops, meat, fish and related products.

Beyond just moving food crops around, fertilisers are (currently) produced using natural gas from the same geological reservoirs as liquid oil (more on that later). Something like 50% of all global food production relies on nitrogen-based fertilisers.

Nitrogen (N) is critical to plant growth, mainly because it is an essential component of amino acids, which go on to form proteins. Although nitrogen makes up 78% of the atmosphere, getting it into a form which can be taken up into plants is tricky. For that to happen, it has to be ‘fixed’ into a form such as anhydrous ammonium nitrate (NH4NO3) or urea (CO(NH2)2).

Described image
Figure 3.4 Photograph of Fritz Haber and Carl Bosch

Enter Fritz Haber, who, along with Carl Bosch developed the Haber–Bosch process to mass produce fixed nitrogen in the form of ammonia (NH3), from which many nitrogen-based fertilisers are made.

Described image
Figure 3.5 The two stages of Haber Bosch for CH4

The Haber–Bosch process itself takes nitrogen and hydrogen, under high pressure and temperature and in the presence of a sequence of catalysts, and converts them into ammonia. The nitrogen can be taken from the air, but the hydrogen comes from breaking down methane (CH4) into hydrogen (H2) and carbon monoxide (CO) using water in a process called steam reforming.

The methane currently comes from natural gas (predominantly, it can also be sourced from coal, but that’s less common now), which, as you’ll see later this week, comes from the same sort of geological formations as the liquid oil.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371