Physico-chemical characteristics of soils are detailed in Table 1.Soils were loamy (trials B and C) to sandy (trial D) textured. Soiltexture differed between tillage type within trial C and, to a lesserextent, trial D. Soil pH values were associated with bedrocks, fromgranite in trial A (pH–H2O = 6.2) to aerial loess deposits in trialsB and C (pH–H2O = 7.0–7.6) and carbonated alluvium deposits intrial D (pH–H2O = 7.8–7.9). Similarly, CaCO3content reflected thebedrock nature of each site but no differences existed within plotsof the same site. Organic matter content was higher in soils of trial Athan in the other soils (35 and 14–21 g kg−1respectively). No differ-ences occurred between tillage types in trial A whereas soil organicmatter content was increased when conservation agriculture hadbeen adopted in the other three trials. The gain ranged from +6% to+25% in trial D (plowing vs surface tillage) and B (plowing vs directseeding) respectively.