The
manage
ment and enhance
ment of soil organic carbon (SOC) is very i
mportant for agriculture (fertility) as well as for the environ
ment (carbon (C) sequestration). Consequently, changes in soil
manage
ment
may alter SOC content. No-tillage (NT) practices are potential ways to increase SOC. We studied the SOC fro
m agricultural soils in the Cerrados in Central Brazil. We co
mpared two different tillage syste
ms: conservation agriculture with no-tillage under cover crops (NT) and disc tillage (DT) for 5 years in a context of rainfed rice production. The soil is a dark red Oxisol with high clay content (about 40%). The objectives of the study were: (i) to evaluate the short-ter
m (5 years) i
mpact of tillage syste
ms on SOC stocks in an Oxisol and (ii) to better understand the dyna
mics of SOC in different fractions of this soil. We first studied the initial situation in 1998, and co
mpared it to the 2003 situation. NT with cover crop (
Crotalaria) was found to increase the storage of C in the topsoil layer (0–10 c
m) co
mpared to DT. The difference observed for the 0–10 c
m layer under NT in co
mparison with DT represented C enrich
ment under no-tillage a
mounting to 0.35 Mg C ha
−1 year
−1 and corresponding to less than 10%of cover crops residues returned to the soil. A particle-size fractionation of soil organic
matter (SOM) showed that differences in total SOC between NT and DT
mainly affected the 0–2 μ
m fraction and, to a s
maller extent the 2–20 μ
m fraction.
This specific enrichment of SOC in the silt and clay fraction was attributed to (i) the storage of a water soluble C in the field and (ii) the effect of soil biota and especially fauna activity. The mean residence time of carbon associated with the fine fractions being rather long, it might be assumed that the preferential storage in fine fractions resulted in a long-term carbon storage. This study suggests a positive short-term effect of a no-tillage system on C sequestration in an Oxisol.