The fate of phosphorus fertilizer in Amazon soya bean fields

Abstract

Fertilizer-intensive soya bean agriculture has recently expanded in southeastern Amazonia, and whereas intensive fertilizer use in the temperate zone has led to widespread eutrophication of freshwater ecosystems, the effects in tropical systems are less well understood. We examined the fate of fertilizer phosphorus (P) by comparing P forms and budgets across a chronosequence of soya bean fields (converted to soya beans between 2003 and 2008) and forests on an 800 km 2 soya bean farm in Mato Grosso, Brazil. Soya bean fields were fertilized with 50 kg P ha −1 yr −1 (30 kg P ha −1 yr −1 above what is removed in crops). We used modified Hedley fractionation to quantify soil P pools and found increases in less-plant-available inorganic pools and decreases in organic pools in agricultural soils compared with forest. Fertilizer P did not move below 20 cm. Measurements of P sorption capacity suggest that while fertilizer inputs quench close to half of the sorption capacity of fast-reacting pools, most added P is bound in more slowly reacting pools. Our data suggest that this agricultural system currently has a low risk of P losses to waterways and that long time-scales are required to reach critical soil thresholds that would allow continued high yields with reduced fertilizer inputs.

Structure and composition of altered riparian forests in an agricultural Amazonian landscape

“…Original forest clearing at Fazenda Tanguro occurred in the early 1980s and land was used for cattle pasture for ;20 years until conversion to soybean cultivation from 2003 to 2008 (Riskin et al 2013). It is possible that changes to forest structure took place closer to the time of initial land clearing, but that over time these effects have lessened as altered riparian forest edges fill in, as has occurred in some forest fragments Lawton 1999, Laurance et al 2002; but see Laurance et al 1998).…”

“…Impoundments were also constructed on headwater streams throughout the region to provide water for cattle (Macedo et al 2013). To initiate soybean cultivation beginning in 2003, remaining woody vegetation was piled into rows and burned and the soil was tilled, after which soybeans were planted and maintained using no-till practices (Riskin et al 2013). …”

Aerosol Deposition Impacts on Land and Ocean Carbon Cycles

“…Similarly, Hawaiian forests have been shown to be dependent on atmospheric inputs of base cations [154], and alpine forests in Europe derive substantial portions of their base-cation subsidies for growth from dust [155]. Recent studies have shown substantial perturbations to atmospheric phosphorus in the Amazon due to deforestationrelated biomass burning [19] and land use [156] suggesting that anthropogenic phosphorus deposition in the Amazon may be enhancing productivity (i.e., net primary production) in the remaining forests, by between 0 and 0.5 PgC/year [10]. Modeling studies of the influence of phosphorus deposition onto carbon uptake are in the beginning stages [157,158]; based on ecosystem budgets, they suggest a smaller role for phosphorus deposition than for nitrogen deposition [157,158].…”

Ecology, economy and management of an agroindustrial frontier landscape in the southeast Amazon

“…Durigan et al [23] Macedo et al [24] Neill et al [27] Gardner et al [42] Le Tourneau et al [41] VanWey et al [29] Schwartzman et al [34] Riskin et al [28] Stickler et al [18] Nepstad et al [47] Galford et al [30] Schiesari et al [31] Morton et al [32] Silvério et al [36] Stickler et al [18] DeFries et al [49] Schwartzman et al [34] infrastructure Nepstad et al [47] Macedo et al [24] Neill et al [27] [35] Figure 1. Schematic diagram showing the interconnections among the processes that affect land cover and land-use change (LCLUC) and the social and biophysical outcomes of LCLUC in the Brazilian Amazon.…”