Agriculture; staff at work: Applying 16-10-10 compound fertiliser (arable rotation - spring-sown oats & grassland). Oronsay RSPB reserve, Argyll. Scotland

Fertilisers

Like most plants, crops need nutrients from the soil to grow properly. Over time, these nutrients become depleted so many farmers use fertilisers to top them up. Over-use of fertilisers can cause big problems for the environment.

What are fertilisers?

A simple way to think about fertilisers is that they are products which feed plants, as opposed to manures and composts, which feed the soil. There are many different sorts of fertilisers, but two of the most commonly used are nitrogen and phosphorous.

Inorganic fertilisers are made synthetically through an energy-intensive process using natural gas, which is of course, a fossil fuel and has a carbon impact. Organic fertilisers come from plants or animal by-products. While the word ‘organic’ might sound better for the environment, organic fertilisers and manures can still cause problems depending on how they’re used.

Organic farming tends to avoid the use of fertilisers and concentrate on improving the soil and other more traditional methods of growing crops. However, much modern farming is heavily reliant on inorganic fertilisers, with one estimate being that almost half of the global population are fed as a result of synthetic nitrogen fertiliser.

Tractor in distance spreading fertilizer in ploughed field

Widespread pollution

The main problem with fertilisers is the sheer quantity being used. In Europe, for example, around 11 million tonnes of nitrogen fertiliser is added to fields each year. Around half of the nitrogen from these fertilisers, and from the additional manures that are used, leaches into the surrounding environment.

On land, that can cause problems for wild plants which are adapted for poorer soils, but in water, it can lead to toxic algal blooms and have a disastrous impact on marine and freshwater wildlife. In fact, nitrate pollution is recognised as being one of the five greatest threats to global biodiversity.

Nitrogen pollution also has an impact on human health, with the fallout estimated to cost each person in Europe up to £650 every year.

In addition to nitrogen, modern farming is also dependent on phosphorous. This is made from phosphate rock, which is a non-renewable resource that will start to run out in the next few decades. Processing the rock produces carbon emissions, radioactive by-products and heavy metal pollutants. Its over-use can also cause similar problems to nitrogen in the environment.

Lake with algal bloom | The RSPB

The grass isn't always greener

Fertilisers aren’t just used on crops that people eat, they’re also used on grass that feeds livestock. Grassland on dairy farms are particularly intensively managed, receiving twice the rate of inorganic fertilisers used on an average beef cattle or sheep farm. The use of phosphate fertilisers is also much higher on farms that raise livestock.

Large numbers of animals kept in small areas can also cause problems with their dung and urine. When managed properly, these by-products can be useful fertilisers, but too much in one place can result in excess nutrients leaching into the environment.

Farmland landscape with cattle grazing

Sustainable solutions

To make farming more sustainable, we need to start reducing our reliance on fertilisers and embrace the more wide-spread use of organic practices.

On organic farms, nutrients are added to the soil using methods that have often been used for hundreds of years, such as crop rotation, the use of manure and composts, and growing so-called ‘green manures’, which are plants grown specifically for benefiting the soil. Not only do these measures reduce or even eliminate the need for fertilisers, they also play an important role in building and maintaining the soil structure. This helps plants to grow, but can also reduce erosion, and have an impact on how the soil holds water.

Crop spraying, Hope Farm RSPB Knapwell

What can we do at home?

One way to reduce our reliance on fertilisers is to reduce our demand for meat and dairy products. Livestock consume a significant proportion of the nitrogen in crops that we currently grow, which is an inefficient use of limited resources.

Choosing organic products where possible will also help to support businesses using more traditional farming methods.

If you have a garden, try to avoid the use of synthetic fertilisers and choose organic methods instead.

Close-up of shovel in an allotment | The RSPB