Sustainable Soil Management Is More than What and How Crops Are Grown - Principles of Sustainable Soil Management in Agroecosystems - page 364

both substantial no-till in the tropics as well as, importantly, a significant amount of
smallholder no-till farms (Ralisch et al. 2003; Wall and Ekboir 2002; Bolliger et al.
2006). The latter is perhaps of particular significance, as, contrary to no-till spread
in general, the adoption of true (permanent rather than sporadic) no-till systems by
smallholder farmers worldwide has been poor, remaining, as yet, relatively marginal
outside Brazil, Paraguay (where appropriate systems have spread from Southern
Brazil), and small parts of Central America, where similar systems were already
traditional (Buckles et al. 1998). Berton (1998) suggests that the main reasons for
smallholder farmers in Southern Brazil to adopt no-till practices include labor and
time savings, erosion control, greater income, and higher yields. Ribeiro and Milléo
(2002) concur that once plowing and mechanical weeding are discontinued, labor
savings and less drudgery are the major incentives expressed by smallholder farm-
ers. Some Brazilian farmers are now into their third decade of practicing no-till land
management.
In regions that experience high-intensity rainfall and support undulating terrain
and/or erodible soils, protecting the soil from erosive raindrop impact through suf-
ficient vegetative mulch is conceivably the best strategy against excessive runoff and
erosion (Amado 1985; Calegari 2000, 2002; Erenstein 2003; Wildner 2000). Only
not plowing, in turn, means that a protective biomass cover or mulch from previous
crops is maintained on the soil surface.
The main advantages of mulch agriculture include reducing evaporation from
bare soil (Stone and Moreira 1998), mediating soil temperature extremes (Derpsch
2001), providing a buffer against compaction under the weight of heavy equipment
(Séguy et al. 2003), smothering weeds (Darolt 1997; Kumar and Goh 2000), creat-
ing a favorable environment for beneficial soil fauna and flora (Balota et al. 1996),
and preventing soil and water contamination from pesticides and nutrient leaching
(Scopel et al. 2004). However, the practice may also make the planting process
more complicated, allow pests and pathogens to reproduce and spread longer in
close proximity to crops (Forcella et al. 1994), protract the warming up of soil after
cold periods, induce erratic crop germination, and decrease the efficiency of fertil-
izers and herbicides (Banks and Robinson 1982; Rodrigues 1993). Nevertheless,
no-till in itself, without soil cover (e.g., if residues are burnt, grazed, or otherwise
exported from the field) or under an unbalanced nutrient budget, can lead to simi-
lar soil degradation and reduced crop productivity issues as conventional tillage
system.
Rather than rely purely on crop residues from a main crop to provide adequate
and permanent soil cover, especially in regions where the climate favors fast decom-
position of residues, one of the major Brazilian adaptations of no-till has been the
strong emphasis on integrating fast-growing winter cover crops and summer crop
rotations into no-till cropping systems. Such crops can be intercropped prior or
planted immediately after the harvest of the main crop and rapidly produce abundant
mulch, consequently allowing a succession of enhanced, year-round biomass accu-
mulation. This can compensate for fast residue decomposition, as well as offsetting
any potential lack of soil cover (Séguy et al. 1996).
Due to the high amount of mulch left on the soil surface at seeding time, Brazilian
farmers hence commonly refer to no-till as “plantio direto na palha” or “planting