Abstract
A spatially explicit, two-pool soil phosphorus (P) model was used to analyze cropland P dynamics and fertilizer demand based on future crop production as projected in the shared socioeconomic pathways (SSPs). The model was initialized with historical data on P inputs and uptake, which governed the soil P accumulation up to present day. In contrast to existing scenario studies, the model accounts for both soil characteristics relevant to P retention and changing land use. At the global scale, crop uptake and the fraction of the applied P fertilizer that is directly taken up by plant roots govern the P quantities present in the soil. Despite the differences in the storylines among the SSPs, the quantitative implementation results in estimates for crop production and P inputs that are quite similar, which contrasts with the stark divergence in terms of population and incomes. In addition to global fertilizer P inputs in croplands increasing from 14.5 Tg P yr−1 in 2005 to 22–27 Tg P yr−1 in 2050, this study also estimates that 4–12 Tg P yr−1 would be needed in 2050 in global intensively managed grasslands to maintain fertility. Our new model approach can pinpoint the contribution of area expansion and crop yield improvement toward the total production, whereby the latter is shown to contribute 100% to 69%, depending on the scenario.
Highlights
Phosphorus (P) is an essential nutrient for living organisms and has played an important role in agriculture since the start of the 20th century (Koning et al, 2008; Sattari et al, 2012)
(pre-20th century) P applications in agriculture depended on manure and guano, bone meal, and urban waste (Beaton, 2006)
In the 1970s and 1980s, disproportionate fertilizer and manure P use in industrialized countries led to low P use efficiency, and large amounts of surplus P were retained as residual P in soils (Syers et al, 2008)
Summary
Phosphorus (P) is an essential nutrient for living organisms and has played an important role in agriculture since the start of the 20th century (Koning et al, 2008; Sattari et al, 2012). In the 1970s and 1980s, disproportionate fertilizer and manure P use in industrialized countries led to low P use efficiency, and large amounts of surplus P were retained as residual P in soils (Syers et al, 2008). After this accumulation phase, farmers in many industrialized countries have been able to increase their P use efficiency as a result of reduced input, mining of the accumulated residual soil P reserves, improved agricultural management, and enhanced crop uptake (Sattari et al, 2012); in many cases even increasing crop yields (Bouwman et al, 2017). Many developing countries are in the early phases of agricultural development with minimal P application rates, which often coincide with low crop yields (Bouwman et al, 2017)
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