Fertiliser Flaws & Pesticide Problems

fertilising a field

In the second of my posts looking into the environmental impact of modern agriculture, I am exploring the use of fertilisers and pesticides to boost crop yields and what damage they could be doing to the environment.

If you’ve read the first post in this series about monocropping, then you’ll know some of the reasons why the use of fertiliser has risen so quickly over the past few decades. These artificial fertilisers are primarily nitrogen and phosphorous based and it is these constituents that lead to many of the associated issues.

I for one would hope that when farmers use such fertilisers, it remains in the soil or is absorbed by the crop itself – after all, isn’t this the whole purpose, to make crops grow larger and faster? But this is not the case; a study by David Tilman of the University of Minnesota’s Department of Ecology, Evolution and Behaviour states that less than half of the nitrogen used in agricultural practices stays within the field or gets harvested in the crop. The rest escapes into the surrounding environment or into the atmosphere where it can cause further problems.

Damaging River & Marine Ecosystems

A major problem occurs when these nitrogen based fertilisers run off into nearby lakes and rivers. Here they can cause something known as eutrophication which is the proliferation of simple life forms such as algae and phytoplankton in the water source. This, and the subsequent shortage of available oxygen for larger creatures such as fish, can lead to the complete breakdown of delicate ecosystems.

Eutrophication can happen even when the nitrogen remains in the soil itself as bacteria can then convert it into nitrate which is extremely soluble and can leach into groundwater and then get washed away into streams and other water sources.

A similar, and arguably more visible, situation arises when fertilisers find their way into the sea. The nutrient enrichment again causes vast blooms of algae to form leading to hypoxic conditions (the lack of oxygen) in estuaries around the world.

The most alarming example of this is in the Gulf of Mexico, where the Mississippi river runs into the sea. As the river runs through the heart of farming America, it takes on huge amounts of nitrogen which can, at its peak, cause a state of hypoxia across 6,000 to 7,000 square miles. This vast “dead zone” is not only a threat to wildlife but also to the livelihoods of the people who live in the Gulf where commercial and recreational fisheries worth $2.4 billion a year operate.

It seems to me that the issues affecting rivers and oceans are very counter-productive. We use fertilisers to improve crop yields and feed more people but marine biologist Robert Diaz calculates that more than 212,000 tonnes of food is lost due to hypoxia in the Gulf of Mexico every year. I wonder what the increased yield in crops equates to in terms of amounts harvested; probably a lot more than 212,000 tonnes but are there ways to avoid this loss in sea life?

Fertiliser & Greenhouse Gas Emissions

You might not think that putting fertiliser onto crops to help them grow would contribute significantly to greenhouse gas emissions but there are two ways in which it does:

  1. Denitrification of fertiliser by bacteria in the soil can convert nitrate in nitrous oxide, a potent greenhouse gas with 300 times the global warming effect of carbon dioxide. In the UK in 2009, nitrous oxide emissions weighed in at 6% of total greenhouse gas emissions with 79% of this figure being the result of agriculture at 27.4 million tonnes of CO2e.
  2. The intense pressures and high temperatures required to turn nitrogen into ammonia (most of which is then used in fertiliser) are extremely energy intensive. Roughly one percent of the world’s energy use goes into the production of ammonia which equates to around 80 million tonnes of CO2e emissions.

Because a significant proportion of the crop grown using fertiliser goes to feed livestock, you can see how most food we eat, whether animal or vegetable, has a footprint that includes nitrous oxide.

Other Issues Arising From Fertiliser

As stated earlier, only around half of the nitrogen in fertiliser remains in the soil and even less gets absorbed by the plants themselves. In some circumstances, these figures are almost unbelievable.

Corn, which is favoured for ethanol based bio fuels, has such shallow roots that it can only take up nitrogen from the top inch or two of soil and even then it only absorbs nutrients for around 60 days each year. This makes corn a particularly inefficient crop when it comes to nitrogen use.

Other crops have deeper roots and longer absorption periods but thanks to the rise in the price of corn, more farmers are switching back to it as a key part of their livelihoods which causes more of the problems discussed.

Moreover, nitrogen and its resulting oxides, nitrates and nitrites are so harmful to the environment that replacing traditional oil based fuels for bio fuels grown with the help of modern fertilisers may actually make the global warming situation worse not better, not to mention the incredible strain it would put on available arable land.

The last problem with fertilisers that I am going to highlight comes not in the form of nitrogen but rather in phosphorous. Unlike nitrogen, phosphorous is retained by the soil and cannot be “washed away” in the same sense that nitrogen is. It can, however, get into streams and lakes by clinging to eroded soil which escapes the farm environment.

Monocropping, as I discussed in a previous post, causes a great deal of soil erosion so phosphorous is able to reach water sources all too easily. Phosphorous in drinking water can actually encourage microbial growth which reduces the hygienic quality of the water coming out of the taps.

Pesky Pesticides Get Everywhere

As I mentioned in the first post in this series, the use of pesticides has grown rapidly and more are required each year as biodiversity is reduced and natural predators continue to be wiped out.

I found a quite amazing statistic in Miller’s “Sustaining The Earth: An Integrated Approach” which states that 98% of insecticides and 95% of herbicides sprayed on crops end up somewhere other than their intended target.

Worryingly, the US Geological survey found that water samples from streams contained 2 or more pesticides 90% of the time. Around 20% of samples had 10 or more pesticides present.

Over the years some pesticides have been used that have since been found to be extremely dangerous to the health of humans and animals. DDT is one such example and while this and others have been banned for decades, they still persist in the environment today with half lives as long as 30 years. They can even accumulate in the fatty tissue of animals that have inadvertently ingested them, including humans.

In her sometimes controversial book Silent Spring, Rachel Carson claims that pesticides are responsible for the decline in many bird, animal and insect populations. The book itself prompted the banning of DDT, which has also been linked with many human conditions such as diabetes and cancer.

Another example of how pesticides can linger in ecosystems can be found on the islands of Martinique and Guadeloupe in the French Antilles. The insecticide chlordecone (also know as kepone) was sprayed on banana plantations there for several decades until it was banned in 1993. Chlordecone is a known carcinogen and these islands experience one of the highest rates of prostate cancer in the world – around 50% of men are likely to develop the disease. Studies in 2005 found that fish in the area had concentrations of this substance that are amongst the highest ever recorded even though it’s use ended several years ago.

The Bugs Fight Back

Viva la Revolution! Those darn pests are revolting, and I don’t mean the way they look. Rather, the continued use of pesticides inevitably leads to a build up of resistance in the pest population and these resistances are passed down to future generations through breeding.

This all means that greater amounts of pesticides and new and more formidable chemicals are needed to combat the pest problem. Farmers and scientists face an ongoing struggle to control pests and this will inevitably cost money.

In organic farming, pests cannot form resistances against natural predators and so we come back to square one – using pesticides indiscriminately takes away nature’s own defence and, without it, we can only rely on our own efforts to combat the problem.

Inevitable Downsides Of An Essential Practice?

It probably seems like I have been very negative about fertilisers and pesticides in this article but the truth is that they have allowed humankind to feed millions, if not billions, more people and society would not have advanced so much without them

The problem comes when we overlook the environmental costs of growing food this way instead of trying to find more sustainable alternatives. We have killed countless numbers of animals, birds and fish in many different ways and have irreversibly impacted ecosystems.

In a future post in this series, I will look at ways in which science is trying to reduce the impact of both fertilisers and pesticides on the environment. Reducing greenhouse gas emissions, preventing dead zones and eliminating dangerous pesticides from food chains and water sources all need to be tackled.

For now, I’ll leave you to ponder over the impact the food on your plate has on the environment we live in.

Steve (152 Posts)

I am chief writer and editor on Green Steve. Blogging since 2011, I like to delve into a wide number of topics to help people reduce their carbon footprint. You should follow me on Twitter here. And add me to your Google+ circles here.


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