Benefits and Costs of Nitrogen Fertiliser for Global Cereal Production and Optimal Nitrogen Rates for Farm and Society, Present and Future Scenarios

Cereals are the most important staple crop on a global scale. Their cultivation requires over half of the global synthetic nitrogen fertiliser and more than half of the arable land. On one hand, several authors claim that synthetic fertiliser from the Haber-Bosch process could be feeding half of the population, or more precisely, supports the current food choices. On the other hand, this new nitrogen, combined with the reactive N generation by nitrogen-fixing crops and atmospheric nitrogen deposition has doubled the global natural input of reactive N.

It is widely accepted that this increase in nitrogen inputs has significant impacts on aquatic and terrestrial ecosystems. The use of synthetic fertilisers and manure in agricultural practices represents a major global source of contamination by ammonia, nitrates, and nitrous oxide, with relevant effects on ecosystems, human health and life expectancy, and climate change. These adverse impacts are an increasing offset of the obvious benefits for food security and the economy of farms and the agro-food industry. Therefore, it is increasingly challenging to manage fertiliser application, not only in terms of input levels and application (‘4R’) but also to minimise environmental impacts. With the aim of achieving the best possible synergy between food security, agricultural economy and environmental protection, the NBCalCer model (Nitrogen Benefit Cost calculator for Cereals) was developed. This model allows us to quantify, in the long-term, the effects of nitrogen inputs on grain yields, nitrogen budgets and major environmental impacts worldwide, at country- to state- resolution. NBCalCer also quantifies market and non-market (externalities) benefits and costs. For this, environmental damages are monetised. In this study, NBCalCer was used to analyse the benefit-cost consequences for both the farmer and society as a whole, and to quantify the economic optimum N rates for farmers (EONR) and for society (SONR). This is performed for the present time and for 2050 using three contrasting Shared Socioeconomic Pathway scenarios, regarding N inputs and potential yields for cereal systems in global regions.

The results show that, in general, the benefit-cost ratio for the use of N for cereal production decreases in the future, with the extent of the decrease depending on the region and the scenario. Some regions show a ratio lower than one. Globally, SONR represents 70% of the EONR value, and the actual synthetic input N rates represents 80% of SONR, implying that current inputs of synthetic N fertilisers are not providing maximum societal benefits, acknowledging that these rates are often suboptimal in many parts of the world for farm income and regional grain sufficiency.