Mineral fertilisers should be pure nutrients, free of additives and pollution, and their environmental footprint, both at production and application shall be as low as possible.
Modern fertiliser plants produce nitrogen fertiliser from natural gas. In several transformation steps, natural gas, essentially methane, is upgraded by combination with nitrogen from the air to form nitrogen fertiliser. 80% of the gas is used as feedstock for fertiliser while 20% is used for heating the process and producing electricity.
The first step is to produce ammonia. Natural gas is combined with nitrogen from the air to produce ammonia and as a by-product carbon dioxide is also produced. This step requires very high temperature and pressure and is known as the Haber-Bosch process.
At this point, there is a choice, ammonia can be used to create either nitric acid or urea, or indeed the ammonia can be used for other industrial purposes.
The second step in manufacturing nitrate fertiliser is to react ammonia with air to produce nitric acid which is then combined with ammonia to produce ammonium nitrate fertiliser.
Alternatively, ammonia can be combined with carbon dioxide from the first step to manufacture urea fertiliser. It is worth noting that the production of urea does not produce carbon dioxide as a by-product, but consumes carbon dioxide which is later released when the fertiliser is applied to crops, contributing to the fertiliser carbon footprint.
Ammonia can also be produced by using renewable energy sources such as hydroelectric, solar power or wind turbines, this is known as Green Ammonia. Yara is currently involved in developing commercial-scale initiatives to develop this technology.
Based on the two main end products, ammonium nitrate and urea, different fertiliser types are manufactured by mixing with ingredients such as phosphorus and potassium to form NPKs, dolomite to form CAN or by mixing urea and ammonium nitrate solution to make UAN.
Phosphorus fertilisers are produced by acidulating phosphate rock. By itself, phosphate rock is not soluble and so cannot provide phosphorus in an available form for plant use.
Many of the sources of phosphorus are sedimentary deposits on old ocean floors which were later uplifted by upheavals of the earth. These deposits can also contain many other minerals and so contamination with heavy metals such as cadmium can be an issue.
The other sources of phosphate rock are from igneous rock deposits, from molten lava, having volcanic origin. This rock is in general very low in contaminants. Yara's mines in Finland produces this type of phosphate rock.
To produce a phosphorus fertiliser, the rock is treated with acid; sulphuric, phosphoric or nitric. Each method has its advantages and constraints. The sulphuric acid route produces a low phosphorus fertiliser – single superphosphate - which is half gypsum. The use of phosphoric acid produces a higher concentration of phosphorus fertiliser.
The third manufacturing process is to use nitric acid to acidulate the rock phosphate. This process is a cleaner process with no waste products and produces two fertilisers:
The limitation of this process is that the phosphate content of the fertiliser cannot exceed the nitrogen content.
Most potassium used in fertiliser production is taken from natural deposits of potassium chloride. The mined material is crushed and purified by the removal of rock particles and salt. Deposits of potassium sulphate and potassium nitrate are rarer, but when used, are treated in a similar manner.
Deposits of potassium chloride are also reclaimed from concentrated salts in places like the Dead Sea.
For the fertiliser to have the desired physical properties is important for the farmer in order to succeed in his spreading of the product in an even and controlled manner.
The most important physical properties are: free-flowing in nature, hard granules or prills, consistent in particle size, easily spread – ensuring even distribution patterns, packed with as many nutrients as possible in each particle, quickly dissolving when in contact with moist soil, free from undesirable contaminants.
Yara fertiliser plants are located all over Europe, in close vicinity to seaports and rivers to enable efficient transportation: Montoir, Ambès and Le Havre in France, Brunsbüttel and Rostock in Germany, Tertre in Belgium, Sluiskil in the Netherlands, Ravenna in Italy, Porsgrunn and Glomfjord in Norway to name only a few.
Yara’s fertiliser factories run 24 hours 7 days a week. They only stop once in a while for maintenance work and installation upgrades. Huge storage areas hold sufficient stock to ensure continuous deliveries and compensate for demand variations.
For more information on specific issues check out these related articles.
Improving nitrogen fertiliser efficiency is one way your farm can become more productive, profitable and sustainable. Try our quiz to find out how you can improve your farm's nitrogen fertiliser efficiency.