27–0.75 kg C m − 2 yr − − 1 , and a low level of restitutions increased by 0.51 kg C m − 2 respectively compared to native forest

to 0.27–0.75 kg C m − 2 yr − − 1 , and a low level of restitutions increased by 0.51 kg C m − 2 respectively compared to native forest

(0.12 kg C m 2 the 2nd year). Two years after establishment, this ( Carvalho et al., 2010 ). Maia et al. (2010) observed in the western

system resulted in similar soil carbon masses as for forest in both part of Brazil (Rondônia and Mato-Grosso states) that full-inversion

soil fractions. In South American savannas, deep-rooted grasses tillage tended to decrease soil carbon stocks but that the potential

such as Urochloa spp. have been reported to sequester significant for C sequestration in no-till systems of annual crops under these

masses of organic carbon deep in the soil (between 100 and 507 Mt particular climatic conditions remains unclear. These authors do

yearly) ( Fisher et al., 1994 ). The turn over rate of Urochloa is high not mention whether or not these systems were based on mulch,

(e.g. Salimon et al., 2004 ). In the soils of our experiment, the carbon or the quantities of biomass restitutions. Recently, Maia et al. (2013)

returned by roots is found in both <2 mm and >2 mm soil fractions, reported that more research is needed to understand processes

which probably offsets part of the loss of C from forest. governing soil organic carbon stock dynamics in the Amazon biome

Variations of carbon stocks were measured in forest to pas- where NT-based agricultural systems do not seem to have the same

ture conversion chronosequences at Nova-Vida farm (Rondônia, effect on soil carbon stocks compared to the Cerrado biome.

Brasil) in the top 30 cm of Ultisols ( de Moraes et al., 1996; Neill Mulch-based direct seeding cropping systems have been et al., 1996, 1997 ). In 2 chronosequences, Neill et al. (1996, 1997) described in the Cerrado biome of Brazil as a means of preser-

observed C stock increases of 0.23 and 1.23 kg C m − 2 in 3 year-old ving carbon stocks in soils (e.g. Corazza et al., 1999; Bernoux

pasture (compared to a close forested area). In the same farm et al., 2006; Corbeels et al., 2006; Marchão et al., 2009; Neto et al.,

and the same type of soil, Fernandes et al. (2002) measured an 2010 ). Recently, several meta-analyses dealing with long-term field

increase of 0.8–0.9 kg C m − 2 in a 3 year-old pasture. Using the experiments (>5 years) comparing no-till and full-inversion tillage

Century model, Cerri et al. (2004) based on Nova-Vida farm data, management ( Luo et al., 2010; Angers and Eriksen-Hamel, 2008;

simulated a decline of carbon stocks during the first years after con- Virto et al., 2012 ) have shown that no-tillage practice could not

version with slash-and-burn of forest to well-managed pastures. be directly linked to higher C storage in soils but the difference in

This decline was followed by a slow increase of carbon stocks. In inputs would explain the variability in C storage between the two

the same study, the empirical model fitted by regression did not managements types ( Virto et al., 2012 ).

simulate decline during the first years. In Amazonia (Marabá, Pará From three geographical regions of the Brazilian Amazon Basin,

state, Brazil), Desjardins et − al. (2004) measured an increase in the C Koutika et al. (1999) showed that the “C decomposition of top-

stock inferior to 0.5 kg C m 2 in the 0–20 cm soil layer after 3, 9 and soils from three geographical regions of the Brazilian Amazon Basin

15 years of grassland installed after manual clearing with burning. primarily depended on soil texture, especially the sand/clay ratio.

These soils have comparable textural properties to those at Combi, However, the influence of the local climate, i.e. mainly annual pre-

but agricultural practices differed (no liming, no fertilization and cipitation, may be also important in the topsoils of coarse texture

with Urochloa humidicola ). In Pará State (near Tailândia), increases with a sand/clay ratio more than 2, such as those located in the

of about 0.62 and 0.23 kg C m − 2 (compared to forest) were mea- western and eastern Brazilian Amazon Basin.” In the Combi exper-

sured in the 0–20 cm soil layer of medium textured Typic Hapludox iment, our objective was to establish a mulch-based direct seeding

after 8 and 13 years respectively of pasture (Brachiaria brizantha , no treatment but problems with planting of cover crops after T1.5 led

lime or fertilization), established after forest clearing with burning to much lower biomass restitutions to soils than expected. This

( de Souza Braz et al., 2013 ). In the same study, C stocks decreased unforeseen situation probably increased soil organic carbon deple-

slightly in 15 year-old pasture in reason of intensive use and/or tion rates but resulted in the interesting observation that no-tillage

A.-S. Perrin et al. / Agriculture, Ecosystems and Environment 184 (2014) 101– 114

practice could increase decomposition or mineralization rates of

led to 17% (significant) and 9% (not significant) decreases in C

organic matter in soils, at least in the first years of use after for- stocks in no-tillage and disk-tillage treatments, respectively

est conversion with chop-and-mulch. Microbial, mesofauna and

- The decreasing rates of C stocks were significantly higher for

macrofauna have been shown to be influenced by tillage prac-

cropped land under no-tillage (without mulch) than for the tices (e.g. Lienhard et al., 2013a,b; Villenave et al., 2009; Blanchart grassland system, while cropped land with disk-tillage showed

et al., 2007 ). For example Balesdent et al. (2000) and Six et al. intermediate values.