Transitions to sustainable management of phosphorus in Brazilian agriculture

Abstract

Brazil's large land base is important for global food security but its high dependency on inorganic phosphorus (P) fertilizer for crop production (2.2 Tg rising up to 4.6 Tg in 2050) is not a sustainable use of a critical and price-volatile resource. A new strategic analysis of current and future P demand/supply concluded that the nation's secondary P resources which are produced annually (e.g. livestock manures, sugarcane processing residues) could potentially provide up to 20% of crop P demand by 2050 with further investment in P recovery technologies. However, the much larger legacy stores of secondary P in the soil (30 Tg in 2016 worth over $40 billion and rising to 105 Tg by 2050) could provide a more important buffer against future P scarcity or sudden P price fluctuations, and enable a transition to more sustainable P input strategies that could reduce current annual P surpluses by 65%. In the longer-term, farming systems in Brazil should be redesigned to operate profitably but more sustainably under lower soil P fertility thresholds.

Figure 1

Brazil’s cropland area from 1975 to 2050, and effects of future cropland intensification (scenarios 1 and 2) and P input reduction strategies (scenarios 3 and 4) on annual P fertilizer demand (B), annual crop P offtake (C) and annual P surplus (D). Scenario 1 - intensify existing cropland area; Scenario 2 - intensify existing cropland area + expand cropland into native Cerrado and degraded pasture areas; Scenario 3 – ratio of P inputs:outputs in cropland areas is 1:1; Scenario 4 – ratio of P inputs:outputs in cropland areas is 0.5:1. Coloured bands give the uncertainty surrounding each scenario prediction.

Figure 2

Brazil’s animal numbers (A) and manure P production from pigs and poultry (B) from 1975 to 2050, and the contribution of manures to total annual P inputs (C) and P efficiency index (D) up to 2050 and for each scenario. Scenarios are as for Fig. 1 and coloured bands give the uncertainty surrounding predictions.

Figure 3

Total legacy P present in Brazilian soils from 1960 to 2050 for each scenario. A P input strategy of applying 50% of plant P offtake (scenario 4) is needed to limit further accumulation of P surpluses in the soil at current cropland expansion rates in Brazil. Scenarios 1–4 are as described in Fig. 1.

Figure 4

Legacy soil P in six different Brazilian long-term field sites; (A) P inputs, outputs and balance since conversion from native Cerrado vegetation; (B) Change in soil total P as a function of the total P surplus balance with the 1:1 line drawn; (C) Increase in soil P for each tillage/P input treatment as a function of P lability according to the Hedley sequential fractionation method; (D) P lability as a percentage of total soil P in native vegetation and cropped areas for each tillage/P input treatment. NT – no tillage; CT – conventional tillage; NV – native vegetation, LP – low P; HP – high P.