Why are artificial fertilisers environmentally unfriendly? 

Fertilisers contain three elements essential to plant growth: nitrogen (N), phosphorus (P) and potassium (K). These are all present in organic material, so compost and other organic fertilisers naturally contain them. 

Artificial, or synthetic, fertilisers are produced in factories: 
• the nitrogen comes from the atmosphere, captured by the 'Haber-Bosch' process, which uses huge amounts of energy, derived from fossil fuels. The nitrogen is combined with hydrogen, which is derived from natural gas – and the two elements form ammonia (NH3), from which the final product is made.  
• the phosphorus comes from rocks, mined intensively and unsustainably. A world phosphorus shortage is looming. 
• the potassium is also mined, from rocks that were once ancient seabeds. The recovery of potassium salts in this way is energy-intensive.  

Artificial fertilisers harm the environment: 
• intensive agriculture produces high yields, but excess fertiliser runoff finds its way into rivers and ultimately lakes and oceans. Here, algae proliferate, causing 'algal blooms' – and when they die, bacteria breaking them down starve the water of oxygen, creating vast 'dead zones'. 
• intensive agriculture is a major contributor to climate change, because of the energy intensive production of artificial fertilisers. 

Jack Challoner, 2016.