Soil management under no-tillage systems in the tropics with special reference to Brazil

Because of cost reductions and soil erosion control, no-tillage is being rapidly adopted by farmers in the Americas, particularly in the humid and sub-humid tropics. Compared to conventional tillage (tillage operations resulting in <30% cover of plant residue remaining on the surface), no-tillage combined with crop rotation involving cover crops increases soil organic matter content, whilst improving soil fertility. This was mostly evident at 0-5 cm depth. Further successful adoption by farmers, including smallholder farmers from different regions, depends on improvements of various aspects, from edaphological constraints (e.g. in Brazil) to social and infrastructural limitations (e.g. in West and Central Africa). Special emphasis is given to the effects of no-tillage on soil organic matter and the consequences on some chemical (e.g. subsoil acidity, fertilizer management) and physical properties of soils (e.g. soil compaction, aggregate stability). Research imperatives for regional improvement or adaptation of such a conservation tillage are emphasized together with social and economical aspects for its adoption.