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Scientific evidence that nitrogen (N) fertilizer is polluting the northern Gulf of Mexico is not conclusive. Hypoxia in the gulf has been recognized since 1935, long before commercial fertilizer use [...]

Fertiliser nitrogen (N) has been, and will continue to be, essential in nourishing, clothing and providing bioenergy for the human family. Yet, emissions of ammonia (NH3) and nitrous oxide (N2O), and losses of nitrate-N (NO3-N) to surface and groundwater resources are risks associated with fertiliser N use that must be better managed to help meet expanding societal expectations. Nitrogen fertilisers with polymer coatings, or with the addition of urease and/or nitrification inhibitors, or those possessing other characteristics that afford them either improved agronomic response and/or lessened loss of N to the environment (compared with a reference water-soluble fertiliser) may be considered enhanced-efficiency N fertilisers (EEFs). Agronomic and horticultural research with these technologies has been performed for many decades, but it has been primarily in the past decade that research has increasingly also measured their efficacy in reducing N losses via volatilisation, leaching, drainage, run-off and denitrification. Expanded use of EEFs, within the ‘4R’ concept (right source, right rate, right time, right place) of N management may help increase crop yields while minimising environmental N losses. Coupling these 4R N management tools with precision technologies, information systems, crop growth and N utilisation and transformation models, especially weather models, may improve opportunities for refined N management in the future.

Enhanced‐efficiency N fertilizers (EENFs) have potential for mitigating N2O emissions from N‐fertilized cropping systems. Stabilized EENFs contain nitrification and/or urease inhibitors. Slow‐release EENFs contain N components that are slowly released with variable release rates. Controlled‐release EENFs release N at more predictable rates. The effectiveness of several EENFs in reducing soil N2O emissions from a clay loam soil under irrigated, corn (Zea maysL.)‐based production systems in Colorado (2002–2012) was investigated. A controlled‐release, polymer‐coated urea, ESN, reduced N2O emissions by 42% compared with urea and 14% compared with urea–NH4NO3solution (UAN) in no‐till and strip‐till environments, but had no effect in a conventional tillage environment. A stabilized urea source, SuperU, reduced N2O emissions by 46% compared with urea and 21% compared with UAN. A stabilized UAN source, UAN + AgrotainPlus, reduced N2O emissions by 61% compared with urea and 41% compared with UAN alone. A slow‐release UAN source, UAN + Nfusion, reduced N2O emissions by 57% compared with urea and 28% compared with UAN. Urea–NH4NO3reduced N2O emissions by 35% compared with urea. A linear increase in N2O emissions with increasing N rate was observed for untreated urea and UAN. Developers of management protocols to reduce N2O emissions from irrigated cropping systems in semiarid areas can use this information to estimate reductions in N2O emissions when EENFs are used. Policymakers can use this information to help determine financial credits needed to encourage producers to use these technologies in their crop production systems.

Global fertilizer production and farmer use has made it possible to provide 40% to 60% of the global crop and food production necessary to sustain the human family (Erisman et al. 2008; Stewart et al. 2005). Because the world's population is growing, it has been projected that we may need to produce 50% more food by 2050 to meet the needs of nine billion people (Tomlinson 2011; Whitacre et al. 2010). Nitrogen (N) fertilizers have had a tremendously beneficial impact on society, and at least half of humanity currently depends on the food production made possible by the Haber–Bosch ammonia (NH3) synthesis process (Erisman et al. 2008). The agricultural community and nonagrarian society have a heightened awareness and are recognizing that it is becoming more important to provide balance in the use of N and other nutrient inputs for the production of food, feed, fiber, and biofuel to help achieve sustainability goals (IFA 2007). The environmental risks and consequences of increased reactive N inputs to the earth's ecosystems are also being considered and have been the subject of many environmental reports (Davidson et al. 2012; Galloway et al. 2003, 2004; Follett and Delgado 2002; Howarth 2010; Matson 1998; Schlesinger et…