Drivers of spatial variation in actual and potential nitrogen use efficiency at global scale

Background

Nitrogen (N) is a vital nutrient for global crop production. However, about half of the N applied to croplands globally is lost to the environment, contributing to multiple environmental threats.

Safe levels for impacts caused by excess nitrogen from agriculture have been widely exceeded, to an extent that scientists have argued that humanity has crossed the planetary boundary for nitrogen. Returning to a safe operating space thus requires reducing agricultural N losses. However, to safeguard food security this should be achieved as much as possible without yield reductions. Maintaining or even increasing yields while reducing N losses requires an increase in nitrogen use efficiency (NUE), defined as the ratio of N uptake by crops to N inputs. Average NUE of global cropping systems is around 50%, with large variations between countries and  regions. These variations are affected by N inputs, management and site characteristics, including crop cultivars, water availability (climate) and the availability of other (non-nitrogen) nutrients (soil fertility).

Aim of this thesis

The aim of this thesis to improve insights in the impacts of nitrogen inputs, nitrogen management and site characteristics on current NUEs and further develop the concept of “NUE potentials”. In analogy to the well-established concept of yield potentials, “NUE potentials” are defined as the highest NUE that can be achieved under local conditions. Activities include:

• Literature search on factors determining current NUEs  and the most important factors determining NUE potentials;
• Statistical evaluation of global datasets to assess factors explaining spatial variation in NUE and highest NUEs currently achieved under different climate and soil conditions;
• Modelling (if time allows): model to what extent environmental thresholds for N losses and targets for crop production can be reconciled by increasing NUE.