Optimizing nitrogen management in food and energy production and environmental protection: summary statement from the Second International Nitrogen Conference

Nitrogen flow analysis in Spain: Perspectives to increase sustainability

Nitrogen (N) is a macronutrient that, together with P and K, is vital for improving agricultural yields, but its excessive use in crop fertilisation and presence in treated wastewater and sludge are generating emissions both into the atmosphere and into natural water bodies, which leads to eutrophication events. The Haber-Bosch process is energy-intensive and it is the main chemical route to produce reactive nitrogen for the production of fertilisers. Furthermore, there is a strong dependence on imports of reactive nitrogen in Spain and Europe. For these reasons, it is necessary to propose sustainable alternatives that allow solving environmental and supply problems, in addition to proposing efficient management schemes that fit into the circular economy approach. In this context, a nitrogen flow analysis (NFA) was carried out for Spain with the year 2016 as reference. To assess some interactions and flows of N, specific sub-models were also considered for the agriculture and waste management systems. For the food and non-food flow systems, country-specific data were considered. The sectors covered were crop production (CP), animal production (AP), food processing (FP), non-food production (NF) and human consumption (HC). The results reveal a total annual import of 2142 kt N/y, of which 43 % accumulated in stocks of soils and water bodies (913 kt N/y). The largest proportion of losses was associated with emissions from agriculture (724 kt N/y to water bodies and 132 kt N/y accumulated in soils), followed by industry emissions to the atmosphere (122 kt N/y). Wastewater treatment plants (WWTPs) received around 67 kt N/y, of which 26 % was removed as biosolids and 20 % of these biosolids were recovered to be used for fertilising applications. The 49 kt N/y discharged in the final treated effluent represented 79 % of the total loss of reactive nitrogen to water bodies. In addition, an analysis of N-use efficiency and the actions required for its improvement in Spain, as well as the impact of the current diet on the N cycle, was carried out.

The Effect of Nitrogen Fertilization on Tree Growth, Soil Organic Carbon and Nitrogen Leaching—A Modeling Study in a Steep Nitrogen Deposition Gradient in Sweden

Nitrogen (N) fertilization in forests has the potential to increase tree growth and carbon (C) sequestration, but it also means a risk of N leaching. Dynamic models can, if the important processes are well described, play an important role in assessing benefits and risks of nitrogen fertilization. The aim of this study was to test if the ForSAFE model is able to simulate correctly the effects of N fertilization when considering different levels of N availability in the forest. The model was applied for three sites in Sweden, representing low, medium and high nitrogen deposition. Simulations were performed for scenarios with and without fertilization. The effect of N fertilization on tree growth was largest at the low deposition site, whereas the effect on N leaching was more pronounced at the high deposition site. For soil organic carbon (SOC) the effects were generally small, but in the second forest rotation SOC was slightly higher after fertilization, especially at the low deposition site. The ForSAFE simulations largely confirm the N saturation theory which state that N will not be retained in the forest when the ecosystem is N saturated, and we conclude that the model can be a useful tool in assessing effects of N fertilization.

Sustainable Non-Thermal Plasma-Assisted Nitrogen Fixation-Synergistic Catalysis

In this Minireview, the multiple chemical synergies present in catalytic non-thermal plasma-assisted nitrogen fixation (NTPNF) are uncovered through a critical exploration of the underlying mechanisms, during which the catalyst, plasma, and reactants play different roles. For the gas-phase NTPNF, the synergies consist of different aspects of the catalytic pathways such as electron-impact dissociation; Zeldovich mechanism in the PNO interactions; and Eley-Rideal, Langmuir-Hinshelwood, surface adsorption, and diffusion mechanisms for the plasma-catalyst interactions. The synergies within the gas-liquid NTPNF involve contributions of plasma and UV excitation to the gas-phase reactions and the UV excitation of molecules at the liquid-surface interface, which improves synthesis of aqueous nitrate, nitrite, and ammonium products. Based on the various synergistic mechanisms during NTPNF, future potential applications are proposed for how NTPNF could benefit the sustainable nitrogen fixation industry.

Plasma-Assisted Nitrogen Fixation Reactions

The preferences for localized chemicals production and changing scenarios of renewable electricity cost gives a renewed boost to plasma-assisted valuable chemicals production. Especially, plasma-assisted nitrogen fixation for fertilizer production has the potential to largely change the energy structure in bulk chemicals production. Nitrogen is the most fundamental element for sustaining life on earth and responsible for production of a wide range of synthetic products. The chemical nitrogen fixation process, i.e. the Haber–Bosch ammonia production process, is one of the most important chemical processes, which supports ∼40% of the global population by producing more than 130 million tons of ammonia per year and requires ∼1–2% of the world’s total energy consumption. Thermal plasma nitric oxide synthesis was already commercialized in 1903, however it had lower energy efficiency. It is theoretically possible to fix nitrogen with lower energy input by non-thermal plasmas. Therefore, much effort has been expended to develop and improve plasma NO, NH3 and HCN syntheses—this includes investigation of the different types of plasma reactors, the synergy between plasma and catalysts as well as improvement of the heat exchange. All these reported literature efforts have been summarized and critically analyzed in this book chapter. An outlook on further possible developments in plasma-assisted chemical synthesis processes is also given.

Diet and the environment: does what you eat matter?

Food demand influences agricultural production. Modern agricultural practices have resulted in polluted soil, air, and water; eroded soil; dependence on imported oil; and loss of biodiversity. The goal of this research was to compare the environmental effect of a vegetarian and nonvegetarian diet in California in terms of agricultural production inputs, including pesticides and fertilizers, water, and energy used to produce commodities. The working assumption was that a greater number and amount of inputs were associated with a greater environmental effect. The literature supported this notion. To accomplish this goal, dietary preferences were quantified with the Adventist Health Study, and California state agricultural data were collected and applied to state commodity production statistics. These data were used to calculate different dietary consumption patterns and indexes to compare the environmental effect associated with dietary preference. Results show that, for the combined differential production of 11 food items for which consumption differs among vegetarians and nonvegetarians, the nonvegetarian diet required 2.9 times more water, 2.5 times more primary energy, 13 times more fertilizer, and 1.4 times more pesticides than did the vegetarian diet. The greatest contribution to the differences came from the consumption of beef in the diet. We found that a nonvegetarian diet exacts a higher cost on the environment relative to a vegetarian diet. From an environmental perspective, what a person chooses to eat makes a difference.

Reduced nitrogen in ecology and the environment

Since the beginning of the 19th century humans have increasingly fixed atmospheric nitrogen as ammonia to be used as fertilizer. The fertilizers are necessary to create amino acids and carbohydrates in plants to feed animals and humans. The efficiency with which the fertilizers eventually reach humans is very small: 5-15%, with much of the remainder lost to the environment. The global industrial production of ammonia amounts to 117 Mton NH(3)-Nyear(-1) (for 2004). By comparison, we calculate that anthropogenic emissions of NH(3) to the atmosphere over the lifecycle of industrial NH(3) in agriculture are 45.3 Mton NH(3)-Nyear(-1), about half the industrial production. Once emitted ammonia has a central role in many environmental issues. We expect an increase in fertilizer use through increasing demands for food and biofuels as population increases. Therefore, management of ammonia or abatement is necessary.