We quantified the impact of the production of energy crops on the global N cycle for the recently published OECD “Global cooperation for environmental policy” (GC) scenario. We project that large amounts of N fertilizers are needed for future production of first- and second-generation energy crops.
Nitrogen fertilizer use for energy crop production
In the OECD-GC scenario 19 Tg N fertilizer (or 14% of global N fertilizer use projected for 2050) is required to support the annual biomass production of 5.6 Pg dry matter. The associated emission sum of direct and indirect emissions of N2O is 0.7 Tg N2O-N per year (8% of total agricultural emissions), 0.2 Tg of NO-N per year (6%) and 2.2 Tg NH3-N per year (5%). We recognize that our estimates of the N use in energy crop production fields and the associated N gas emissions may be conservative, especially for the second generation energy crops.
Greenhouse gas balance
We show that GHG reduction by substitution of fossil fuels by biofuels are offset by 20% in 2030 and 15% in 2050 if N2O emission from the cultivation of energy crops is accounted for. The N2O emissions from cultivation make up a considerable share of total emissions from the cultivation, processing and transport of biofuels (30-60% for maize and sugar cane). In the discussion on sustainability of energy cultivation as a measure to meet Kyoto targets and increase energy security, N effects other than those affecting the greenhouse gas balance should thus be considered too.
Human and ecosystem health impacts
On a regional scale, increased N leaching, groundwater pollution, eutrophication of aquatic and terrestrial ecosystems, N2O and NH3 emission from energy crop production and NOx emissions from combustion of biofuels may cause relevant loss of human and ecosystem health. With respect to the availability of land, the OECD-GC scenario shows a rapid expansion of agricultural land, mainly in Africa and the former Soviet Union. This expansion will lead to a further loss of biodiversity. Because we include sustainability criteria in the scenario, direct deforestation for bioenergy production is not possible. However, second-generation energy crop cultivation expands mainly at the expense of savannah areas, which are not protected by sustainability criteria. Clearly, future sustainability criteria should focus on these types of ecosystems as well, since low productive lands are not necessarily of low biodiversity value.