Costs and benefits of synthetic nitrogen fertilizer for global production of cereal grains in 2015 and in 2050 under contrasting scenarios

A newly developed global nitrogen benefit cost model for Cereals (NBCalCer)

Cereals are the most important global staple crop and use more than half of both the global production of synthetic nitrogen (N) fertilizer and crop area. NBCalCer quantifies the global effects of N input on crop yields, N budgets and environmental impacts at country scale (state scale for USA and China) and monetizes these effects to allow aggregation and comparison of effects, ultimately to establish the integral ratio of costs and benefits.

Scenarios

We analyzed three contrasting and modified Shared Socioeconomic Pathway scenarios (SSPs) where N policy ambitions were superimposed on the SSP climate-sustainability storylines. In order of decreasing N agri-environmental ambitions: sustainability (SSP1H), middle-of-the-road (SSP2M) and fossil-fueled development (SSP5L).

Main findings

In the base year the contribution of synthetic N fertilizer to global cereal production was 44 %. Global modelled grain yield was projected to increase under all scenarios while the use of synthetic N fertilizer decreases under all scenarios except SSP5L. The total N surplus was projected to be reduced up to 20 % under SSP1H but to increase under SSP5L. The Benefit-Cost-Ratio (BCR) was calculated as the ratio between the market benefit of increased grain production by synthetic N and the summed cost of fertilizer purchase and the external cost of the N losses. In base year the BCR was well above one in all regions, but in 2050 under SSP1H and SSP5L decreased to below one in most regions. In the  context of sustainability the paradigm for global cereal production is producing sufficient food with minimum N pollution. Our results indicate that achieving this goal would require a massive change in global volume and distribution of synthetic N.