Figure 4. P surplus rate (kg P ha-1yr-1) by region. (a) P surplus rate (kg P
ha-1 yr-1) estimated in 2010
(average of 2005-2014). (b) P surplus rate (kg P ha-1yr-1) projected in the 2050 BAU scenario. (c) P
surplus rate (kg P ha-1 yr-1)
projected in the 2050 MPA scenario. (d) P surplus rate (kg P
ha-1 yr-1) projected in the 2050 HPA
scenario. Grey area: missing data. Orange area: P surplus rate higher
than the upper planetary boundary (6.9 kg P ha-1yr-1, rounded to 7 kg P ha-1yr-1). Blue and white areas: P surplus rate lower than
the upper planetary boundary. Rates larger than 20 kg P
ha-1 yr-1 are shown in red. Rates
lower than -2 kg P ha-1 yr-1 are
shown in blue.
Based on our estimation, the global planetary boundary of P surplus is
at 4.5-9 Tg P yr-1. To keep the global P surplus under
the boundary in 2050, we need to improve the global PUE from the current
60% to somewhere between 69% and 82%. Dividing the global P surplus
planetary boundary (4.5-9 Tg P yr-1) by global total
harvest area in 2010 (average of 2005-2014, \(1.3\times 10^{9}\) ha),
we estimated the regional planetary boundary of P surplus rate at
3.5-6.9 kg P ha-1 yr-1. With this
threshold, only in the HPA scenario or even more ambitious scenarios
could the P surplus in major countries fall into this “safe” range
(Fig. 4). In the BAU and MPA scenarios, 62 and 30 countries would still
transgress the upper planetary boundary of the regional surplus rate
(6.9 kg P ha-1 yr-1) in 2050. These
countries occupied 46% and 19% of the harvested area in 2010 (average
of 2005-2014), respectively.