P for two, sharing a scarce resource: soil phosphorus acquisition in the rhizosphere of intercropped species.

Over the last 50 years, the use of nitrogen (N) and phosphorus (P) fertilizers has increased at a faster rate than global food production, resulting in substantial decreases of N and P efficiency in agriculture (Fig. 1). Thus, considerable amounts of N and P fertilizers have beenwasted in agroecosystems, and the alteration of N and P biogeochemical cycles is among the most visible impacts of human activities on ecosystem services, far exceeding thehypothesized“planetaryboundaries” for N and approaching those for P (Rockström et al., 2009). Projections for the future suggest that a substantial further increase inN and P fertilizer use will occur to cope with increasing food demand (Tilman et al., 2001; Vance et al., 2003). Tilman et al. (2001) predicted that global consumption of fertilizer P will increase from 34.3 Tg year in 2000 to amean projected value of 83.7 Tg year in 2050 (56.2–118 Tg year depending on the calculation scenario). Such increases in fertilizer consumptionwill further threaten the global N and P cycles. Bouwman et al. (2009) estimated that in 2000, the total inputof fertilizerP incroplandsamounted to 21 Tg year, of which 9 Tg was accumulated in soils and 1 Tg was lost to erosion. Their projections for 2050 for various scenarios of future agricultural development amounted to29 to46Tgyear total P fertilizer input and 10 to 23 and 3 to 5 Tg year accumulated in soil and lost to erosion, respectively. This suggests that even in the most optimistic scenario, the contribution of P fertilization of cropland to P movement by erosion will triple over the period 2000 to 2050. While further intensification of agroecosystems is clearly needed to cover the growing food demand over the next decades, we cannot afford to accept the “business as usual” scenario that relies on ever-increasing agricultural inputs and the resultingwaste of nutrients in some regions of theworld (Vitousek et al., 2009). WHAT MAKES P SO SPECIAL?