2.3 Projection of Future PUE and Phosphorus Budget
We projected future PUE and P budget for crop production in three PUE improvement scenarios (Table 2): 1) the Business-As-Usual (BAU) scenario, 2) the Moderate-Policy-Ambition (MPA) scenario, and 3) the High-Policy-Ambition (HPA) scenario. From scenario BAU to HPA, we assume that PUE by country and crop type would have no improvement, median improvement, and significant improvement, respectively. To decide the improvement level, we first calculated the PUE by crop type of 12 regions (Table S17) in 2010 (the average of 2005-2014). Then for each crop type, we set the median and 75th percentile value of the 12 regions’ PUE as the minimum PUE level to achieve in MPA and HPA scenarios, respectively.
Table 2 The settings of three PUE improvement scenarios and three cases of P fertilizer to total inputs ratio from 2014 to 2050.