Changes in soil carbon stocks in Brazil due to land use: paired site comparisons and a regional pasture soil survey

Abstract

In this paper we calculated soil carbon stocks in Brazil using 17 paired sites where soil stocks were determined in native vegetation, pastures and crop-livestock systems (CPS), and in other regional samplings encompassing more than 100 pasture soils, from 6.58° S to 31.53° S, involving three major Brazilian biomes: Cerrado, Atlantic Forest, and the Pampa. The average native vegetation soil carbon stocks at 10 and 30 cm soil depth were equal to approximately 33 and 65 Mg ha⁻¹, respectively. In the paired sites, carbon losses of 7.5 Mg ha⁻¹ and 11.9 Mg ha⁻¹ in CPS systems were observed at 10 cm and 30 cm soil depth averages, respectively. In pasture soils, carbon losses were similar and equal to 8.3 Mg ha⁻¹ and 12.2 Mg ha⁻¹ at 10 cm and 30 cm soil depths, respectively. The average soil δ¹³C under native vegetation at 10 and 30 cm depth were equal to −25.4‰ and −24.0‰, increasing to −19.6 ‰ and −17.7‰ in CPS, and to −18.9‰, and −18.3‰ in pasture soils, respectively; indicating an increasing contribution of C₄ carbon in these agrosystems. In the regional survey of pasture soils, the soil carbon stock at 30 cm was equal to approximately 51 Mg ha⁻¹, with an average δ¹³C value of −19.6‰. Key controllers of soil carbon stock at pasture sites were sand content and mean annual temperature. Collectively, both could explain approximately half of the variance of soil carbon stocks. When pasture soil carbon stocks were compared with the average soil carbon stocks of native vegetation estimated for Brazilian biomes and soil types by Bernoux et al. (2002) there was a carbon gain of 6.7 Mg ha⁻¹, which is equivalent to a carbon gain of 15% compared to the carbon soil stock of the native vegetation. The findings of this study are consistent with differences found between regional comparisons like our pasture sites and local paired study sites in estimating soil carbon stocks changes due to land use changes

Soil Organic Matter Responses to Anthropogenic Forest Disturbance and Land Use Change in the Eastern Brazilian Amazon

“…Moreover, the conversion from forest to pasture increased C stocks within deeper soil layers (0-100 cm) in the Brazilian Amazon region near the BR163 road, in the Mato Grosso state [25]. A regional survey of pastures that included other Brazilian biomes, such as Cerrado, Atlantic Forest, and Pampas, [35] found that the absolute change in the SOC stocks during the conversion of native vegetation to pastures, indicated an average gain of C of 6.7 Mg·ha −1 compared to native vegetation, or relative gains of 15%. However, it is worth mentioning that those authors also reported losses of SOC following the conversion to pasture in 17 paired sites, highlighting the uncertainties (e.g., soil type and management) associated with soil sample data.…”

How accurate are pedotransfer functions for bulk density for Brazilian soils?

“…Bulk density was obtained for each layer using the core method, by means of cylinders with volumetric rings 0.053 m high and 0.05 m in diameter. Detailed information can be found in Assad et al (2013).…”

Past and present land use influences on tropical riparian zones: an isotopic assessment with implications for riparian forest width determination

“…We assumed that organic matter derived from C 3 plants has d 13 C value equal to -27.9% which is the lowest d 13 C measured in our five study areas, and plant organic matter derived from C 4 plants has a d 13 C 4 as -11.3% based on an broad isotopic analysis carried out in Brazil available elsewhere (see Assad et al 2013). The percentage contribution from C 4 -derived carbon is given by the following isotope dilution equation:…”