Too much of a good thing.

Like all living organisms, plants depend on nitrogen as an essential nutrient for growth. In natural ecosystems plants are supplied with nitrogen by microorganisms in the soil that decompose organic matter and break down large, complex organic nitrogen molecules into the smaller, usable forms nitrate and ammonium. Other microbes assist plants with their nitrogen need by fixing atmospheric nitrogen into mineral nitrogen, or by helping plants reach distant soil nitrogen when it is in short supply.

The nitrogen cycle reliably churns along, supporting plant life and all dependent organisms, as long as all of the elements are in place. In agricultural systems, the most important part of the equation is removed when the crops are harvested. Without that plant matter returning to the ground to decompose, soils quickly become nitrogen deficient, and agricultural yield drops. To combat this, farmers must restore the lost nitrogen, and they do so with the addition of nitrogen fertilizers. Unfortunately, fertilizers are often applied in excess as farmers try to maximize yield. Far more nitrogen is added to the system than can be utilized by crops, and the excess finds its way into the atmosphere and bodies of water where it wreaks havoc. A single molecule of nitrous oxide contributes to global climate change with 296 times the global warming potential as a molecule of carbon dioxide. When nitrogen fertilizers reach the water, they promote the growth of algae, leading to massive blooms that choke off marine and aquatic life.

An essay by Allen Good and Perrin Beatty published in this month’s PLoS Biology draws attention to the imbalance of nitrogen fertilizer usage in different regions of the world. For instance, China uses far more nitrogen than is needed for optimal yields, yet their fertilizer use continues to rise. In contrast the countries of sub-Sahara Africa don’t use enough nitrogen and as a result, they have nutrient-poor soils and low yields. When faced with poor water quality due to nitrogen surplus, the European Union established and implemented best nutrient management practices in 1987, resulting in a 56% usage decrease in twenty years.

How was this achieved? Scientists conducted long term studies to determine the optimal amount of nitrogen fertilizer for each crop species in various regions of the world. Ordinarily farmers would apply fertilizers willy nilly with little consideration for the specifics of the plant species, application method, and fertilization rate. The results of these experiments proved that even in well-balanced systems, farmers can reduce the application of nitrogen fertilizer with no loss in yield.

Good and Beatty used this idea and took it a step further by quantifying the potential economic and environmental savings to be gained if fertilizer usage is reduced. First they determined the economic cost associated with the environmental damage of excess fertilizer use. Then they used fertilizer use and price projections to calculate the cost savings if nitrogen use is reduced to match the regional recommendations. All of the countries that were analyzed, which account for 74% of global fertilizer use, required either no change in nitrogen use or a reduction from 5 to 20%. Based on their analysis, Good and Beatty found that directed nutrient management strategies could achieve a total savings of $19.8 billion a year by 2020 and $56 billion a year by 2030. These values are shocking, not only because of the amount of money that is wasted through careless use of fertilizers, but also the magnitude of environmental damage that is incurred year after year. To learn more about the study, and to see Good and Beatty’s recommendations, you can find their essay at PLoS Biology.