following: clearing of secondary forest fallows by slash and burn; use of acid-tolerant upland rice and cowpea cultivars in rotation, with only grain removal to minimize nutrient export; no use of fertilizers, lime, or external organic inputs; establishment of legume fallows when weed competition and nutrient deficiencies make cropping unfeasible; and elimination of fallows by slash and burn after 1 year, shifting to other management options such as grass-legume pastures, agroforestry, or mechanized continuous cropping (Sanchez and Benites, 1987).

Current results indicate the initial cropping cycle lasts 2 or 3 years and there is progressive reduction in cycle length after each legume fallow. The system is considered transitional because of two major constraints: nutrient depletion and weed encroachment. Ongoing investigations seek to prolong the duration of low-input cropping by broadening the base of acid-tolerant cultivars and species; increasing knowledge about components of the nutrient depletion process; and improving weed management through crop rotations, plant density, and frequency and time of legume cover crop fallows.

Farming systems that combine animal and crop production vary across regions and agroecological zones. In Asia the animal components of small farming operations vary with cropping systems (McDowell and Hildebrand, 1980; Ruthenberg, 1971). In lowland rice farming areas, buffalo provide (1) traction for cultivating fields and (2) milk and meat that are consumed domestically or sold in markets. Cattle, fowl (mainly chickens and ducks), and swine are also commonly raised on these farms. Feeds include crop residues, weeds, peelings, tops of root crops, bagasse, hulls, and other agricultural by-products. In highland areas, swine, poultry, buffalo, and cattle are raised in combination with rice, maize, cassava, beans, and small grains. Livestock is less important on farms dominated by multistory gardens, which may occasionally include cattle, sheep, and goats. Feed is typically cut and carried from croplands. Livestock animals are also of some importance on tree crop farms where they either graze freely in pastures, are tethered to clean specific areas, or are fed with tree cuttings.

The cropping systems of tropical humid Africa are dominated by rice, yams, and plantains (McDowell and Hildebrand, 1980; Ruthenberg, 1971). Goats and poultry are the dominant animals. Sheep and swine are less abundant, but still common. Feeds include fallow land forage, crop residues, cull tubers, and vines. The small farms of Latin