Slash/Mulch Systems: Neglected
Sustainable Tropical Agroecosystems

H. David Thurston
Department of Plant Pathology
Cornell University
Ithaca, NY 14853

There is an extensive literature on the various slash and burn systems used throughout the tropics. For example, Conklin (1961) lists over 1,200 references to slash and burn systems in his comprehensive review of shifting cultivation systems, but lists only two references to the slash/mulch system. Peters and Neuenschwander (1988) recently wrote a comprehensive book on slash and burn systems, but made no mention of slash/mulch systems. In comparison to slash and burn systems, few references can be found regarding slash/mulch systems, although such systems are probably far more important in the hot, humid tropics than most authorities realize. The slash/mulch system is often overlooked or mistaken for a slash and burn system.

As originally practiced in the Americas slash/mulch agriculture consisted of clearing (slashing) plots from the forest, planting crops in the resulting mulch before or after the slashing, and, rather than burning, using the decomposing mulch as a source of nutrients. The principles guiding traditional slash/mulch systems around the world incorporate valuable lessons for those interested in a truly sustainable agriculture that is environmentally sound. Land degradation and the destruction of the fragile ecosystems of the tropics are major concerns today. Young (1991) noted that steep slopes and highlands make up 48% of the total area of the Andes; 78% of the total area of Central America; and 67% of the total area of selected Caribbean countries (Dominican Republic, Haiti, Jamaica, and Puerto Rico). The principles used in slash/mulch systems can make their greatest contribution in these fragile areas.

It is generally accepted that slash and burn farmers burn in order to obtain nutrients for their crops from the ash produced by burning. Jordan (1988) agreed that this is true; however, from studies made near San Carlos, Venezuela in an Amazon rain forest, he concluded: "but it is the decomposing unburned slash on top of the soil that appears to sustain the fertility of the soil over the three-year cultivation cycle, after the ash has dissolved." This finding suggests the potential of nutrients provided by decomposing slash in tropical agroecosystems.

Indians inhabiting humid tropical forests were using the slash/mulch systems when the Spanish arrived in the Americas. In his book Historia de la Actividad Agropecuaria en America Equinoccial Patiño (1965) cites a number of early Spanish chroniclers who described the use of the slash/mulch system. In the 16th Century Pedro Cieza de Leon in his Cronica General de Peru (cited by Patiño 1965) described an Indian practice in the Chocó Province of Colombia: "on hillsides they cut the vegetation and plant their roots and other food crops into it." In 1577 Miguel Cabello de Balboa (1945) reported a practice in the province of Esmeraldas on the Pacific coast of Ecuador: "they do no more than broadcast maize seed in the hillsides and cut the vegetation over it and collect the harvest: one hundred to one." These quotes are certainly early descriptions of the slash/mulch system. In 1722 Francisco Coreal (cited by Patiño 1965) noted that the Indians near Buenaventura used a slash/mulch system. In 1780 Captain Juan Jimínez Donozo gave the following description of the slash/mulch system of the Indians near the Atrato River in Colombia:

They do no more than broadcast (the maize seed) in the brush or forest, which, because of the high moisture, is impenetrable, and later they cut the brush, in such a way that the leaves begin to rot and the branches dry and thus this material serves as a mulch through which the maize germinates.

Several other early descriptions of the slash/mulch system (called tapado in Spanish) were given by Patiño, not only from Colombia, but also from Panama and Costa Rica.

The following description was written in 1801 by Francisco José de Caldas (Patiño 1965):

In those places where it rains continuously such as in the Province of Chocó, and the entire west coast of the country, they don't burn; but the excessive humidity combined with great heat makes the land there very fertile. They plant in these areas without another operation except to cut the small bushes and trees, broadcasting at the same time the grain, after which they cut the vegetation covering the already germinating maize. The nutrients which should be utilized by the forest are instead utilized in the maize planting.

Numerous authors have described or recorded the presence of the slash/mulch system in the Chocó: Archer (1937), Anon (1982), Ceron Solarte (1986), Eder (1963), Gamble (1967), Lotero Villa (1977), Patiño (1956, 1962, 1965), Roberts et al. (1957), Torres de Arauz (1966), Valencia-C. (1983) and West (1957).

The excellent study by Robert C. West (1957) was made from 1951 through 1954 under the auspices of the office of Naval Research, Washington, D. C. The region he described is between 1deg. and 8deg. north of the equator and consists of the lowland Pacific coast from Darien in Panama through the Province of Chocó in Colombia and extending to the province of Esmeraldas in Ecuador. The region is one of the wettest regions worldwide with an average annual rainfall ranging from 3 to 10 meters. Humidity usually ranges between 80-95 percent. Most of the area is covered by tropical rainforest. Quibdó, located in the Province of Chocó, Colombia, receives over 10 meters of rain annually. During a visit to Buenaventura I made in 1954 during the dry season, the days were bright and clear, but a heavy rain fell all night. West (1957)described the slash/mulch system as follows:

Throughout most of the Pacific lowlands, however, the heavy precipitation and lack of a dry season precludes the effective use of fire. Instead a peculiar system, which might be called "slash-mulch" cultivation, of probable Indian origin, has evolved. Seeds are broadcast and rhizomes and cuttings are planted in an uncleared plot; then the bush is cut; decay of cut vegetable matter is rapid, forming a thick mulch through which the sprouts from the seed and cuttings appear within a week or ten days. Weeds are surprisingly few, and the crops grow rapidly, the decaying mulch affording sufficient fertilizer even on infertile hillside soils.

The Chocó region is only sparsely populated by Indians as, according to West, 85 percent of the population consists of the descendants of black slaves brought to the area by the Spanish in the seventeenth and eighteenth centuries to work in gold mining. The black population has lost most of its African heritage and has adopted Indian and Spanish ways of life, and many practice the slash/mulch agriculture of the indigenous Indian populations. The cutting of vegetation for a slash/mulch plot in the Chocó by the black population was a community affair or kind of "minga" with a line of ten or fifteen men and women working together to cut the brush with their machetes. The minga is a cooperative labor group and was common among Andean Indian groups, but not among the Indians of the Chocó. West (1957) wrote:

The institution as practiced by the modern Pacific lowland Negroes contains many African elements, such as chanting, which involves a lead singer and chorus, beer drinking during progress of work, and feasting at the end of the day. According to local inhabitants, the minga, one of the few African cultural survivals of the Pacific lowland Negro, is rapidly disappearing as a social institution.

The machete is the primary tool used in slash/mulch cultivation. West writes: "the steel machete, is used to cut the bush, to dig holes for planting rhizomes and cuttings, to weed, and to harvest plantain, bananas and other fruit." Not only maize, but also cassava, bananas and plantains were planted in the Chocó using the slash-mulch system (West 1957). After planting, the bush is cut down and the shoots emerge through the rotting mulch.

A primitive race of maize variously called chococito or maiz indio, especially adapted to the slash-mulch system, is commonly planted in Ecuador, Colombia, and Panama according to Patiño (1956, 1962). Patiño (1962) made observations on the slash/mulch system and chococito maize in the Pacific lowlands region from 1945 to 1955 in studies made under the auspices of the Rockefeller Foundation and the National Research Council of the U.S.A. He noted that chococito is broadcast - not planted - on the Pacific coasts of Panama, along the coast of Colombia, and in the provinces of Esmeraldas and Pinchincha in Ecuador. This race of maize grows from sea level to almost 1,700 meters elevation. However, at the highest elevations it is planted with a digging stick (espeque) and not broadcast. Patiño noted that few references were found regarding the slash/mulch system, and that many writers, even when describing agriculture in the Chocó, ignored or overlooked the system. I have had the same experience in researching the literature on the Chocó. For example, an interesting book by W. F. Sharp (1976) entitled "Slavery on the Spanish frontier: the Colombian Chocó, 1680-1810" makes no mention of the slash/mulch system, although agriculture is the major activity of most of the people in the region.

Most of the slash/mulch fields are near streams or rivers as rivers are the major means of transportation in this extremely wet region. Patiño (1962) gave the most complete description of the system of slash/mulch for maize of any of the authors found. He described the system of broadcasting and slashing of the vegetation. The grains of maize were covered with a mulch 5-50 cm thick, but germinated rapidly and broke through the mulch. No further care was given to the crop until it was close to harvest and, as Patiño wrote, after planting the field was "abandoned to luck." Near maturity, the crop was protected from animals and birds, usually by children. The maize matured after 4 to 5 months. Ears with insect damage were consumed immediately as choclo (green ears harvested and consumed before maturity), and only sound ears were stored. West (1957) noted that the harvested ears of corn were hung on the rafters of farmer's houses near the cooking fires where the heat thoroughly dried the maize.

Roberts et al. (1957) and Timothy et al. (1963) called the chococito race of maize used in the slash/mulch system "chococeño", although, according to Patiño (1962), the race should probably have been called chococito. Roberts et al. considered chococito to be a product of the hybridization of maize with Tripsacum spp. They also wrote that chococito is confined almost exclusively to the humid regions of the Colombian and Ecuadorian Pacific coast. Roberts et al. suggested that chococito must have a most uncommon "rusticity", as it is grown without any cultural care except to broadcast it into bush, which is subsequently slashed over it. Timothy et al. (1963) also described "chococeño" extending from its center of distribution in Colombia into the humid forests of the northern Ecuadorian province of Esmeraldas.

The Swedish anthropologist Sven-Erik Isacsson (1985) described in considerable detail the slash/mulch culture in the Chocó. He worked in the upper Atrato river basin near Quibdo, Colombia where there is rainfall almost 300 days per year. Isacsson made most of his observations during the five months he lived with a family group of Emberá Indians, but he made other visits to the area during the period 1969-1975. The Indians used a slash/mulch agricultural system. Isacsson noted that their cultivated fields for maize ranged from 0.09 to 1.28 hectares with an average field size of 0.49 hectares. According to his informants a fallow of two years was considered sufficient for recovery after harvest, but some fields were held in fallow for up to 15 years. Two crops were often planted per year. The Indians main crop was maize of which they had six different types: maiz colorado, maiz negro, maiz amarillo, maiz capio amarillo (a variant of maiz amarillo with large grains and cobs) and maiz blanco. At the time of planting a sower (regador), carrying the seed grain in a basket over his shoulder, broadcast handfuls of grain into the bush to be cut. Three or four individuals called socoladores followed the regador cutting the bush, consisting of small trees, vines, and bushes, over the broadcast seed. The cut vegetation was left to decay over the maize seed forming a mulch. No subsequent weeding was done, but the crop was protected from rodents and parrots. After 2-3 months, some of the maize was harvested as choclo, and, after about four months, the rest of the maize was mature. Maize was stored in the husk in the attic of the Indian's homes where smoke and heat dried the grain and reduced insect damage.

Isacsson (1985) recorded 14 different types of bananas and plantains cultivated in the slash/mulch system of the Emerá Indians. The size of fields used for plantains and bananas averaged 0.44 hectares. Plantains were by far the most important of the Musa species used. Plantain corms were spaced 1.5 meters apart and were planted in holes made with a digging stick. After planting, the bush was cut over the planted corms producing a decaying mulch. The slash/mulch practice for sugar cane was different from that used for maize or plantains in that the bush was chopped up more finely into small pieces before the cane was planted in holes. At one time cassava was an important crop in the slash/mulch system, but due to crop damage, primarily by domestic pigs, little cassava was grown in the area studied by Isacsson.

Paganini (1970) describes the use of the slash/mulch system in parts of the Darien province of Panama.

In certain parts of the Darien, however, particularly those areas settled by Colombiano refugees and Nonameño Indians, a "slash-mulch" cultivation is practiced. Slash-mulch was first reported by West as being the predominant system in the Pacific Lowlands of Colombia. Paganini added: The practitioners of the slash-mulch system, however, do not used that term as a descriptive title to their peculiar activity. Planting in tierra cruda is their way of differentiating the slash and mulch from the slash and burn, the latter being called planting in tierra quemada.

Panamanian farmers noted that their tierra cruda plots suffered far less from insect attacks than slash and burn plots. Snedaker and Gamble (1969) also noted the use of the slash/mulch practice in the Darien province of Panama and noted that the fallow period in Panama varied from 4-6 years. They analyzed samples of slash for its concentration of mineral nutrients. Gamble et al. (1967) also noted the use of the slash/mulch practice in Panama and Colombia.

In his book Living Poor. A Peace Corps Chronicle Moritz Thomsen (1969) describes his negative reaction, as a Peace Corps volunteer, to the slash/mulch system. He worked and lived in a village in the province of Esmeraldas on the Pacific Coast of Ecuador where the common system of agriculture is the slash/mulch system. When he first encountered the slashed debris produced, he suggested that the local farmers should burn the three feet of dead weeds and branches they had cut in their slash/mulch plot, rather than planting in the mulch. Thomsen described his early reaction to the slash/mulch system as follows (pages 192-194):

The ground was three feet deep in dead weeds and branches. Wai came up with an ax and felled the timber. Our first hectare, but what a mess. It was the custom to plant corn on ground thus cleared, but is seemed obvious that the yields would be minimal, and I refused to let them do it. "We'll have to burn first," I insisted, talking to the socios out in the field, where we stood in a drizzle of rain. "It is hardly our custom to burn wet brush," they told me sarcastically. "This is not the United States," Ramon told me. "This is the way we do it; you should have a little more respect for our customs." "But that's the only reason I'm here," I told him, "to destroy your crazy customs."

Unfortunately, Thomsen was able to convince the farmers to burn, and later, under his direction, they cleared 20 hectares of land and even obtained a tractor for plowing the land. Because of drought, heavy rains, roving animals, and insects, the maize that was planted on the cleared land produced little yield. In order to control the insects he wrote: "We sprayed with DDT, Aldrin, Malathion, Dipterex, Chlordane, BHC, and Parathion." The tractor was later abandoned as impractical for the area. Although Thomsen undoubtedly had the best of intentions, his book provides a striking story of how agricultural ideas from the temperature zone are often inappropriate to traditional agriculture in the tropics.

Eder (1963) described the slash/mulch system of a Noanamá Indian group in the Río Siguirisúa Valley of the Colombian Chocó. After cutting the lighter understory of the forest they broadcast seeds or plant roots in holes prepared with a digging stick. Three to four weeks later the remaining trees are felled over the plot. He noted that women do the primary preparation and planting of the plot, but men fell the trees. The "minga" or communal work group common to the Choó black population in their slash/mulch system was not used by the Noanamá.

Finegan (1981) described a similar slash/mulch system in a study made 70 km inland from Tumaco on the hot, wet Pacific coast of Colombia on the border with Ecuador. His studies were in a lowland area populated by black subsistence farmers who used techniques modified from the original systems practiced by the vanished indigenous populations. The study area was between Barbacoas, with a rainfall of 7.6 m (300 inches) per year, and El Mira with a rainfall of 3.5 m (140 inches) per year. Because of the high rainfall, the farmers in the area commonly slashed vegetation consisting of small trees, vines, and bushes, but could not burn it. Maize, cassava, sugar cane, beans, fruit, trees for wood, taro, sweet potatoes, yams, and yautia were crops planted in their polyculture system.

Four plant layers were identified in the subsistence plots: ground level, second level, middle level, and overstory. The ground level consisted of crops less than two meters in height, such as cassava, beans and maize. The second level consisted of taller perennials such as bananas and plantains. In the middle level fruit trees and palms dominated and reached nine meters or more. The overstory consisted of timber species and, occasionally, high growing fruit trees. After the first years of cropping, the economic importance of the lower levels was minor as weeds took over. Finegan (1981) noted that farmers also utilized various plants as "site indicators" for determining the degree of soil fertility, drainage conditions, and the amount of shade present in a potential slash/burn field. They also knew plants that indicated when land was ready for replanting.

Cerón Solarte (1986) described the slash/mulch system of the Awa-Kwaiker Indians who occupy an area of 500 to 1500 meters elevation in the foothills of the Andes near the lowland area described above by Finegan. The Awa-Kwaiker area is primarily in the province of Nariño in Colombia, but also extends into neighboring Ecuador. In their slash/mulch system (called tumba y pudre in Spanish) chococito maize is the most important crop in the system. Maize seed is broadcast after cutting the bush consisting of small trees and bushes. Larger trees were cut after the maize germinates. Other crops grown by the Indians in the system were plantains, sugar cane, cassava, and beans.

Hiraoka and Yamamoto (1980) described the extensive use of the slash/mulch practice in the eastern lowlands of the Amazon basin. They wrote:

The prevalent farming system in the eastern lowlands of Ecuador and Colombia is a variant of the more widely known and more really extensive shifting cultivation. The slash-mulch variant is distinguished by the fact that the felled vegetation is not burned.

Their studies of agricultural development in the eastern Amazonian lowlands took place from 1975 to 1977. The area was populated primarily by colonists who probably developed the slash/mulch systems based on practices of indigenous Indians. They noted that the slashed vegetation served as a mulch and, as it decomposed, nutrients became available for the plants cultivated in the system. There is no dry season in the area, thus the system was an adaptation to a wet environment that has no distinct dry season. Hiraoka and Yamamoto described four processes (socola, plantio, tumba and chapeo) that constituted the practice. Socola is the slashing or cutting of the brush consisting of small trees, vines, and bushes and could begin at any time of the year. The planting of seed or cuttings, called plantio, took place 5-10 days after socola. Tumba, the next stage, was described as follows:

When sprouts appear, the remaining vegetation, excepting economically useful types, is removed. In the tumba, as this phase is known, between 20 and 30 percent of the seedlings are crushed or covered by the felled vegetation, but enough plantings survive to provide harvests.

If weeds were a problem there might be one or two weedings (chapeo) before the harvest of annual crops. A large number of crops were planted in the fields in the Lago Agrio area, and Hiraoka and Yamamoto (1987) suggested that the farmers of the area practiced a "true polyculture." Annuals included rice, maize, and sweet potatoes while semiperennials were yams, papa mandi, plantains, bananas, and cassava. Perennials were tree or shrub crops such as coffee, cacao, chonta, achiote, and various citrus species. The canopy produced by the semiperennials and perennials eventually took over the plots after the harvest of the annual crops. Hiraoka and Yamamoto concluded that the system was sound from both a human and an ecological perspective and ideal both for the physical environment and the settlers. The mixture of annuals, semiperennials, and perennials extended the life of the plots; the canopy produced by semiperennials and perennials protected the soil from direct sunlight; the mulch reduced erosion, provided organic matter, reduced runoff of rain, and provided nutrients to the crops. This slash/mulch system appears to be sustainable and should slow rates of deforestation in the Amazon, given a stable population of low-density.

The Urarina, an Indian people of the Amazon in northern Peru have an interesting agricultural system which can become either slash and burn or slash/mulch (Kramer 1977). They slashed the understory brush, planted plantains in the cut brush, and then felled trees on the cut brush and plantains. Sometimes they burned the slashed brush after it dried, but sometimes, if there was too much rain or if there was insufficient vegetation for a good burn, they did not burn, but simply let the slashed vegetation decompose. They also planted maize, cassava, peanuts, squash, sugar cane, taro, and sweet potatoes in their plots. Plots were generally abandoned after 2-3 harvests. Their system also effectively protected the soil from erosion. Kramer noted that the Urarina consider the system less difficult and labor intensive than the conventional slash and burn system.

Charles Staver (personal communication) described the use of both the slash and burn and the slash/mulch system in the Guanare River basin of Venezuela. Both maize and beans were grown in the system. Beckerman (1987) also mentions the use of the slash/mulch practice in the Amazon.

Reynolds (1921, 1927) described the early system which banana companies used to establish new banana plantations in Central and South America and the Caribbean. Large areas of forest land were cleared for planting bananas. Although few details were given, Wardlaw (1929, 1961) described the same system which he called the "extensive" system. The system used was essentially a slash/mulch system. In 1961 Wardlaw wrote:

The forest underbrush is cutlassed to allow of the staking out of the rows, and the planting holes, 15 in. in diameter and 15 in. deep, are dug at regular distances. Suckers or "bits" are planted and the forest is then felled. After some two or three months, the young banana plants begin to appear through the tangled mass of trunks, branches and twigs. As the growth of the young banana plants and the decay of the forest debris take place with astonishing rapidity under the prevailing warm, humid conditions, very soon, with periodic cutlassing of the secondary bush, especially round the young plants, an orderly plantation comes into being, and bunches of fruit may be obtained within the year.

Wardlaw noted that upkeep of the plantation was very simple and consisted of slashing the bush, drainage, and removal of superfluous suckers. The system was extensively used initially in Latin America, but now has been replaced with a more "modern" agriculture which includes extensive drainage, tilling, liming, and maintenance of nutrients. Reynolds (1921) noted:

The enormous amount of logs, branches, leaves and trash covers the ground like a mulch and instead of being destructive, actually establishes the most favorable conditions possible for the growth of the young banana plant. The hot humid atmosphere and the wealth of fungus and bacterial organisms cause the felled trees to undergo rapid decomposition. The twigs and smaller branches quickly rot, adding humus to the soil.

Simmonds (1966) also described the use of the slash/mulch system for establishing banana plantations. He wrote :

Thus, in Central America, land brought into commercial banana cultivation from forest is usually surveyed, underbrushed, drained, lined out and then planted with bananas; as soon as the suckers have been planted but before the shoots have appeared above the ground, the bigger forest trees are felled. Thereafter, the only treatment is a periodic lopping of branches which are interfering with banana growth.

According to Borel and Pélegrin (1951) the same system of slash/mulch plantation establishment was used in the Cameroons, Africa as was used in Central America.

Few references were found in the literature on the occurrence of slash/mulch systems in Asia. Conklin (1961) cited Maas (1902) as describing a slash/mulch practice on Mentawei, Indonesia associated with taro production. The practice has been recorded several times in Papua New Guinea according to Vasey (1992). Clarke (1966) reported that the people of the Nduimba basin and the Kompai people used both slash and burn and slash/mulch practices in New Guinea.

The people known as the Kaluli of the Orogo live in a region of Papua New Guinea known as the Great Papuan Plateau. Schiefflin (1975) described their swidden system in which, instead of slashing and burning vegetation before planting, they plant in the underbrush first and then fell trees on the top of the planting. The Kaluli live in an area covered with a dense tropical forest at elevations from 750 to 1050 meters and with an annual rainfall of almost 500 cm. Many different crops are grown in the area, however Schiefflin writes:

Bananas, breadfruit, and pandanus are grown on the slopes down the sides of a ridge and are planted in the opposite manner. The people first cut the underbrush under the canopy and then plant shoots (obtained from old gardens) with a digging stick. Then, after four or five days, when the crop has " taken " groups of men fell the canopy on top of the crop and the tangled wreckage is left to itself. The plants soon find their way up between the fallen trunks and the garden grows normally.

Short term crops such as banana and sugar cane are planted higher on the slopes of the ridge, while breadfruit and pandanus (screw pines, Pandanus spp.) which take much longer to mature, are planted lower down. As each crop is harvested the area is abandoned and allowed to regenerate to forest. Government officers thought the practice of felling trees on top of the crops was destructive and estimated that 40% of the crops were destroyed because of this practice. Schiefflin and his collaborators found that less than 5% of the crops were damaged and pointed out the several advantages of the practice. The tangle of trees and the mulch produced by the slashed vegetation protect the soil from the intense rains of the region, most of which fall in a few very heavy showers. Thus, erosion is prevented and the organic matter produced helps maintain good soil structure and fertility. The Kaluli cycle of rotation was 25-30 years. Schiefflin concluded that "It would appear that Kaluli methods of cultivation, though quite different from the highlands, produce a better diet for less work while preserving the character of the forest environment." Schiefflin mentions other systems of slash/mulch agriculture used by other tribal groups in Papua New Guinea (the Etoro people and the Onabasulu people).

The Etoro people of Papua New Guinea also live on the Great Papuan Plateau in an area with a rainfall of over 600 cm. Kelly (1977) describes their slash/mulch system for taro and bananas:

In taro-banana gardens, no effort is made to create brush piles or to clear most of the garden of debris. Larger trees are felled first to form a network of trunks which will keep the bulk of the timber off the ground and prevent crop damage. The remaining trees are felled across these trunks in an irregular manner and are left untrimmed. In overall appearance, the garden resembles a section of forest recently struck by a tornado. The leaves and twigs decompose providing a gradual release of nutrients and the taro and bananas grow up through the debris.

Kelly noted that felling trees after the taro and bananas were planted minimized the time when soil was exposed to the high intensity rains common to the region.

A key element which makes slash/mulch systems productive and sustainable is their production of mulches. Mulching practices in the tropics have been reviewed by Lal (1975) and Sanchez (1976). Nair (1984) discussed their use in agroforestry systems. One of the major problems with the use of mulches is that large quantities of material are often needed and, unless crop residues produced in situ are used, material has to be brought in from sources outside of the field. A major advantages of slash/mulch systems is that materials for the mulches are produced in situ. Mulches provide numerous benefits. Wilson and Akapa (1983) wrote: "Mulches also decrease soil moisture evaporation, increase infiltration rate, smother weeds, lower soil temperature, and enrich soils." Mulches protect seedlings from the impact of rain, hail, and the wind. Mulches are especially important in tropical areas with heavy rainfall, as they improve water absorption and are important in water conservation. Mulches reduce rain splashing, an important means of dissemination for numerous bacterial and fungal pathogens. Soil temperatures are lower under mulches in warm tropical areas. Beneficial microbiological activity is enhanced under mulches.

Many systems other than those discussed above use slash/mulch principles. For example, the frijol tapado or covered bean system common in Costa Rica and other areas of Central America is an ancient slash/mulch system (Araya and Gonzalez 1987). The periodic pruning of poró (Erythrina poeppigiana), a shade tree in coffee plantings in Latin America, constitutes a slash/mulch system (Russo and Budowski 1986). Slashing velvet beans and planting maize or sorghum in the mulch produced is another slash/mulch system becoming increasingly important in Mexico and Central America (Flores 1989). There is an immense literature on the recently developed alley cropping system which also is essentially a slash/mulch system (Kang et al. 1984). Systems pollarding or coppicing trees which produce a significant mulch are slash-mulch systems. A study of the principles used in traditional and indigenous slash/mulch systems may provide important lessons for improving the sustainability and productivity of agriculture in developing countries.

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