The Human Creation and Use of Reactive Nitrogen: A Global and Regional Perspective

Abstract

More food and energy allow for more people who then require more food and energy, and so it has gone for centuries. At the same time, economic progress leads to a different lifestyle with an increasing demand for energy and food, also accelerating food waste. Fueling this food-energy-population dynamic is an ever-increasing conversion of unreactive dinitrogen (N2) to reactive N (Nr), which then results in a cascade of positive (food and energy for people) and negative (damage to people, climate, biodiversity, and environment) impacts as Nr is distributed throughout Earth systems. The most important step in reducing the environmental impacts of Nr is limiting its human-based creation. In this article, therefore, we focus on this most important first step: the conversion of N2 to Nr by human activities. Specifically, we examine Nr creation and use (they are different!) on a global and regional basis and Nr use on a global and regional per capita basis. In addition, we introduce the metric Nr Use Index (NUI), which can be used to track and project Nr use relative to a fixed point in time. We then assess the progress in Nr management over the past 20 years. Our article presents a case study of the Netherlands to show what one country, beset by Nr-related problems that have led to an N crisis, did to address those problems and what worked and what didn't work. The article concludes with an assessment of what the future might hold with respect to Nr creation and use, including a review of other projections. We expect that NUI will increase especially in Asia, Latin America, and Africa. The other parts of the world are consolidating or even decreasing NUI. In Latin America and Asia, there is limited agricultural land, and by increasing NUI for food the risk of Nr pollution is very high. The Netherlands has shown not only what effects can be expected with increasing NUI but also what successful policies can be introduced to limit environmental losses. Our assessment shows that Nr creation needs to be limited to prevent local to global environmental impacts. Expected final online publication date for the Annual Review of Environment and Resources, Volume 46 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Explanations for nitrogen decline

“…productivity worldwide over the past century, and that this is best explained by human-driven elevated temperatures and CO2. This is in conflict with previous studies showing strong increases in N availability compared to pre-industrial levels (2)(3)(4). They present two observational trends to support this: i) a decline in Europe and the USA since 1990 in various N availability indices; and, ii) a worldwide decline of 𝛅𝛅 15 N in plant leaves, tree rings, and lake sediments since 1920.…”

History of anthropogenic Nitrogen inputs (HaNi) to the terrestrial biosphere: a 5 arcmin resolution annual dataset from 1860 to 2019

“…Nitrogen (N) is an essential element for the survival of all living organisms as is required by various biological molecules, for instance nucleic acids, proteins, and chlorophyll (Galloway et al, 2021;Schlesinger and Bernhardt, 2013). Most N on the Earth is not readily available for organisms, as it either exists in the form of inert N 2 gas or is stored in crust and sediments (Ward, 2012).…”

Integrating Ecological Principles for Addressing Plant Production Security and Move beyond the Dichotomy ‘Good or Bad’ for Nitrogen Inputs Choice

“…Cultivation-induced biological nitrogen fixation (C-BNF) has also increased in several agricultural systems, with crop, pasture, and fodder legumes being the most important. The C-BNF estimate for 1970 was 11.5 Tg N and, because of the increase in soybean and meat production over the past five decades, increased to more than 40 Tg N in 2020 [28]. The large fertilizer consumption enlarged cereal and meat production by 20% and 26%, respectively, but increased reactive nitrogen (Nr) creation by 120% [29].…”

“…This makes Nr creation a good indicator of global human reactive N production. The loss of Nr in the environment increased from approximately 15 Tg N in 1860 to 226 Tg N in 2020 [28]. In this century, the increase in consumption of fertilizer N by the Haber-Bosch process was due to two drivers: East and South Asia development [27].…”

“…Although, there is a substantial variation by region, process, and time, the Haber-Bosch process is the most important source of new Nr creation in all regions. The exception is Latin America, where the majority of Nr creation is C-BNF, mainly due to the large-scale soy production [28].…”