Skip to content


Author;  Good, A.G.

Nitrogen (N) is the key limiting nutrient for most crop plants and is also the most limiting nutrient in many aquatic and terrestrial ecosystems. However, as a result of the massive increase in the amount of anthropogenic N introduced into the environment, largely through the production of nitrogen fertilizers, there have been a number of significant negative environmental consequences. The link between agriculture and nitrate pollution is now been well established with the effects including the impact on drinking-water supplies and the eutrophication of fresh water and marine ecosystems, including the proliferation of harmful algal blooms and “dead zones” in coastal marine ecosystems. In fact, in the US is has been estimated that 80% of anthrogenic N which enters the environment comes from agricultural losses. Other consequences, such as the health impacts of nitrate in drinking water are less clear. In addition to these environmental costs, agriculture plays a substantial role in the balance of the three most significant anthropogenic GHGs emitted. These gases are CO2, N2O (nitrous oxide), and CH4 (methane). The GWP (Global Warming Potential) of each of these gases can be expressed in CO2 equivalents. The GWPs of N2O and of CH4 are 296 and 23 times greater, respectively, than a unit of CO2. Among the three gases, N2O may be the most important emitted by fertilizer use, because of its large CO2 equivalent influence on GWP.

While even two decades ago, the cost and environmental damage of excessive nutrients was largely ignored, this is no longer the case. There is now a recognized need to protect terrestrial and aquatic ecosystems by reducing anthropogenic nutrient inputs, and in addition, there is also a significant economic argument to do so, as a result of the dramatic increase in nitrogen based fertilizers from $US425/Mton of N in 1987 to over $US1000/ton, in 2007. While the most recent spike in fertilizer prices in 2007 was not sustainable, with current prices being approximately $US625/ton, the cost of N fertilizers, which is determined largely by fossil fuel costs will continue to increase. Interestingly, while there has been a global increase in the consumption of N fertilizers, this trend is not universal. Instead, in certain developed countries, particularly in the EU, there has been a significant reduction in the use of N fertilizers over the past 20 years (56%), despite a worldwide increase of 18% during this time period. On the other hand, there are some countries, such as in sub-Saharan Africa, that are chronically nutrient poor, resulting in poor agricultural yields. Due to a significant political commitment, the EU has successfully developed both N and phosphate (P) reduction programs and these are beginning to result in improved water quality in ground water, rivers and many lakes.