Changes in soil carbon, nitrogen, and phosphorus due to land-use changes in Brazil

[摘要] In this paper, soil carbon, nitrogen and phosphorus concentrations and stockswere investigated in agricultural and natural areas in 17 plot-level pairedsites and in a regional survey encompassing more than 100 pasturesoils In the paired sites, elemental soil concentrations and stocks weredetermined in native vegetation (forests and savannas), pastures andcrop–livestock systems (CPSs). Nutrient stocks were calculated for the soildepth intervals 0–10, 0–30, and 0–60 cm for the paired sites and0–10, and 0–30 cm for the pasture regional survey by sum stocksobtained in each sampling intervals (0–5, 5–10, 10–20, 20–30, 30–40, 40–60 cm). Overall, there were significant differences in soil elementconcentrations and ratios between different land uses, especially in thesurface soil layers. Carbon and nitrogen contents were lower, whilephosphorus contents were higher in the pasture and CPS soils than in nativevegetation soils. Additionally, soil stoichiometry has changed with changesin land use. The soil C : N ratio was lower in the native vegetation than inthe pasture and CPS soils, and the carbon and nitrogen to availablephosphorus ratio (P_ME) decreased from the native vegetation to thepasture to the CPS soils. In the plot-level paired sites, the soil nitrogenstocks were lower in all depth intervals in pasture and in the CPS soils whencompared with the native vegetation soils. On the other hand, the soilphosphorus stocks were higher in all depth intervals in agricultural soilswhen compared with the native vegetation soils. For the regional pasturesurvey, soil nitrogen and phosphorus stocks were lower in all soil intervalsin pasture soils than in native vegetation soils. The nitrogen loss withcultivation observed here is in line with other studies and it seems to be acombination of decreasing organic matter inputs, in cases where cropsreplaced native forests, with an increase in soil organic matterdecomposition that leads to a decrease in the long run. The main cause ofthe increase in soil phosphorus stocks in the CPS and pastures of theplot-level paired site seems to be linked to phosphorus fertilizationby mineral and organics fertilizers. The findings of this paper illustratethat land-use changes that are currently common in Brazil alter soilconcentrations, stocks and elemental ratios of carbon, nitrogen andphosphorus. These changes could have an impact on the subsequent vegetation,decreasing soil carbon and increasing nitrogen limitation but alleviating soilphosphorus deficiency.

[学科分类] 地球化学与岩石