Influence Of Land Use (Savanna, Pasture,Eucalyptusplantations) On Soil Carbon And Nitrogen Stocks In Brazil

Summary

In Brazil, mostEucalyptusstands have been planted on Cerrado (shrubby savanna) or on Cerrado converted into pasture. Case studies are needed to assess the effect of such land use changes on soil fertility and C sequestration. In this study, the influence of Cerrado land development (pasture andEucalyptusplantations) on soil organic carbon (SOC) and nitrogen (SON) stocks were quantified in southern Brazil. Two contrasted silvicultural practices were also compared: 60￢ﾀﾃyears of short￢ﾀﾐrotation silviculture (EUCSR) versus 60￢ﾀﾃyears of continuous growth (EUCHF). C and N soil concentrations and bulk densities were measured and modelled for each vegetation type, and SOC and SON stocks were calculated down to a depth of 1￢ﾀﾃm by a continuous function.

Changes in SOC and SON stocks mainly occurred in the forest floor (no litter in pasture and up to 0.87￢ﾀﾃkg C￢ﾀﾃm￢ﾈﾒ2and 0.01￢ﾀﾃkg N￢ﾀﾃm￢ﾈﾒ2in EUCSR) and upper soil horizons. C and N stocks and their confidence intervals were greatly influenced by the methodology used to compute these layers. C/N ratio and13C analysis showed that down to a depth of 30￢ﾀﾃcm, the Cerrado organic matter was replaced by organic matter from newly introduced vegetation by as much as 75￢ﾀﾓ100% for pasture and about 50% for EUCHF, poorer in N forEucalyptusstands (C/N larger than 18 forEucalyptusstands). Under pasture, 0￢ﾀﾓ30￢ﾀﾃcm SON stocks (0.25￢ﾀﾃkg N￢ﾀﾃm￢ﾈﾒ2) were between 10 and 20% greater than those of the Cerrado (0.21￢ﾀﾃkg N￢ﾀﾃm￢ﾈﾒ2), partly due to soil compaction (limit bulk density at soil surface from 1.23 for the Cerrado to 1.34 for pasture). Land development on the Cerrado increased SOC stocks in the 0￢ﾀﾓ30￢ﾀﾃcm layer by between 15 and 25% (from 2.99 (Cerrado) to 3.86 (EUCSR)￢ﾀﾃkg C￢ﾀﾃm￢ﾈﾒ2). When including litter layers, total 0￢ﾀﾓ30￢ﾀﾃcm carbon stocks increased by 35% for EUCHF(4.50￢ﾀﾃkg C￢ﾀﾃm￢ﾈﾒ2) and 53% for EUCSR(5.08￢ﾀﾃkg C￢ﾀﾃm￢ﾈﾒ2), compared with the Cerrado (3.28￢ﾀﾃkg C￢ﾀﾃm￢ﾈﾒ2), independently of soil compaction.