ABSTRACT
The adoption of conservation agriculture technologies, which are characterized by minimal soil disturbance (tillage) before seeding (with the ultimate aim being zero-till seeding) and by diverse strategies to increase crop residue retention on the soil surface to ensure full ground cover (leading essentially to biological tillage) over time, has dramatically increased in many countries over the past 25 years. For example, there are now over 28 million ha of zero-till seeding in Latin America with the bulk concentrated in the southern cone countries of Brazil, Argentina, and Paraguay (Derpsch, 2001). Table 1 lists the adoption of zero-till in the world up to 2001 (Derpsch, 2001). Much of this acreage is zero-till with residue retention. However, upon closer inspection, the adoption of reducedzero-till seeding combined with surface crop residue retention in the countries mentioned above as well as other large area adopters such as the United States, Canada, and Australia, and particularly for wheat production systems, has occurred mainly by large-scale farmers and nearly universally for rainfed production systems with a few exceptions where sprinkle irrigation is used. The apparent exclusion of small-scale farmers in general and for essentially all surface-irrigated
production systems (especially where irrigated wheat is a major crop in the system) has several explanations.
