Document(s) 3 of 17

Origins and botanical features of velvetbean 

Velvetbean in the United States 

Velvetbean use in Mesoamerica 

Conclusions

In recent years, cover crops have received considerable attention from scientists and development workers concerned about the productivity and sustainability of agricultural systems in the developing world. Velvetbean is prominent among the cover crops studied and promoted (Durón et al. 1989; Bunch 1990; Camas Gómez 1991; Quiroga Madrigal et al. 1991; Derpsch and Florentín 1992; Lobo Burle et al. 1992; SAA–Global 2000, Inc. 1992; Zea 1992; Buckles and Arteaga 1993; Chávez 1993; Versteeg and Koudokpon 1993; Arteaga et al. 1997; Calegari et al. 1997; Flores 1997). It is without doubt one of the most popular cover crops currently known for the tropics and a featured example of the potential contribution of cover crops to sustainable agricultural systems. What is not so well known is that velvetbean was heralded 75 years ago as "one of the most important crops of recent introduction" (Tracy and Coe 1918, p. 3). Velvetbean was cultivated extensively in the United States during the early part of this century and was included, at that time, in numerous research programs in Africa, Asia, and Latin America, with mixed success. It has also been grown successfully for more than 40 years by indigenous farmers in Mesoamerica. This chapter traces the history of velvetbean and the knowledge of its uses and identifies some of the environmental and socioeconomic conditions under which it has been used in various parts of the world. Understanding these conditions may help us to identify old constraints and new opportunities for using this not-so-new plant.

Origins and botanical features of velvetbean

Velvetbean, a vigorous annual climbing legume, originally came from southern China and eastern India, where it was at one time widely cultivated as a green vegetable crop (CSIR 1962; Burkill 1966; Duke 1981; Wilmot-Dear 1984). The genus Mucuna (Adans), belonging to the Fabaceae family, covers perhaps 100 species of annual and perennial legumes, including the annual velvetbean. The genus Stizolobium was used by Bort (1909) to distinguish velvetbean from perennial Mucuna spp., but this distinction was not maintained by Burkill (1966) or Bailey (1947).

Mucuna is self-pollinating; hence, natural out-crossing is rare (Duke 1981). The dozen or so cultivated Mucuna spp. found in the tropics probably represent a fragmentation from the Asian cultigen, and there are numerous crosses and hybrids (Piper and Tracy 1910; Bailey 1947; Burkill 1966; Bailey and Bailey 1976). The most commonly cited species include M. deeringiana Merrill, M. utilis Wallich (Bengal velvetbean), M. pruriens (L.) DC., M. nivea, M. Hassjoo (Yokohama velvetbean), M. aterrima Holland (Mauritius and Bourbon velvetbean), M. capitata, and M. diabolica (IIA 1936; Burkill 1966; Tanaka 1976; Duke 1981). However, the taxonomy of these species is confused, and some designations may be synonymous. For example, Burkill (1966) recorded M. nivea as being synonymous with M. cochichinensis and M. lyonii (Lyon velvetbean) (Awang et al. 1997).

The main differences among cultivated species are in the character of the pubescence on the pod, the seed colour, and the number of days to harvest of the pod. "Cowitch" and "cowhage" are the common English names of Mucuna types with abundant, long stinging hairs on the pod. Human contact results in an intensely itchy dermatitis, caused by mucunain (Infante et al. 1990). The nonstinging types, known by the common English name "velvetbean," have appressed, silky hairs. Cowitch may be the original type of the genus (Bailey 1947). Seed colours include shiny black, creamy white, gray, beige, and mottled. Life cycles range from 100 to 300 d to harvest of the pod (Tracy and Coe 1918; Bailey 1947). A nonvining variety, with low forage yields, is also reported under the name "bunch velvetbean" (Watson 1922; Duke 1981).

The velvetbean grown in northern Honduras is probably M. pruriens, which is the most widespread of the cultivated species. The mottled-seed type is the most common in northern Honduras, although shiny-black and creamy-white seeds are also present. Farmers note that the black-seeded velvetbean is slightly more precocious than the others, but all velvetbean types are harvested in bulk, irrespective of their type, and replanted together. All velvetbean fields observed in northern Honduras begin flowering in early to mid-October, regardless of the planting date. This suggests that the life cycle of the crop responds to shorter day lengths (photoperiodic). Flowering may also be stimulated by cooler night temperatures (21^oC) (Duke 1981). Velvetbean dies naturally after producing seed, about 45–60 d after flowering.

Most Mucuna spp. exhibit reasonable tolerance to a number of abiotic stresses, including drought, low soil fertility, and high soil acidity, although they are sensitive to frost and grow poorly in cold, wet soils (Duke 1981; Hairiah 1992; Lobo Burle et al. 1992). The genus thrives best under warm, moist conditions, below 1500 m above sea level (asl), and in areas with plentiful rainfall. In such environments, velvetbean vines can grow to 10 m and the canopy may stand as high as 1 m above the soil surface. Velvetbean sheds significant quantities of leaves before reaching maturity, and these decay gradually in a litter layer below the actively growing velvetbean. Only a few roots tapping deep horizons can be found per square metre sampled, but surface roots are abundant (Tracy and Coe 1918; Hairiah 1992). Levels of aboveground biomass range from 5 to more than 12 t of dry matter (DM) ha^-1; below ground, more than 1 t of dried roots ha^-1 may be produced (Duggar 1899; Ferris 1917; Camas Gómez 1991; Chávez 1993; see also Chapter 5). Pod production is variable, depending on the environmental conditions, but can easily reach more than 2 t ha^-1, especially if the velvetbean vines have the opportunity to climb trees, stalks, or other tutors. Like most legumes, velvetbean has the potential to fix atmospheric N through a symbiotic relationship with soil microorganisms. The N is converted by the rhizobia on the roots of the plant to an available form that is stored in the leaves, vines, and seeds — making the plant an efficient source of N.

Mucuna spp. have been reported to contain the toxic compounds L-Dopa and hallucinogenic tryptamines and antinutritional factors such as phenols and tannins (CSIR 1962; Ravindran and Ravindran 1988; Awang et al. 1997). Because of the high concentrations of L-Dopa (7%), velvetbean is a commercial source of this substance, used in the treatment of Parkinson's disease. However, L-Dopa can also produce a confused state of mind and intestinal disruptions in humans.

Despite its toxic properties, various species of Mucuna are grown as a minor food crop. Raw velvetbean seeds contain about 27% protein and are rich in minerals (especially K, Mg, Ca, and Fe; de la Vega et al. 1981; Duke 1981; Olaboro 1993). During the 18th and 19th centuries, Mucuna was grown widely as a green vegetable in the foothills and lower hills of the eastern Himalayas and in Mauritius (Watt 1883; Piper and Tracy 1910; CSIR 1962). Both the green pods and the mature beans were boiled and eaten. Burkill (1966) and Watt (1883) suggested that Mucuna was eventually replaced as a vegetable in Asia by more palatable legumes, although it is still used as a famine food and as specialty food in northeastern India (CSIR 1962; DB's field observations). In Guatemala and Mexico, M. pruriens has for at least several decades been roasted and ground to make a coffee substitute; the seed is widely known in the region as "Nescafé," in recognition of this use. The use of Mucuna spp. as minor food crops has also been reported in Ghana (Osei-Bonsu et al. 1995), Mozambique (Infante et al. 1990), and Nigeria (Ezueh 1977). However, an outbreak of acute psychosis in Mozambique was attributed to the inappropriate consumption of velvetbean: because of famine and drought, the water used to boil the seed was not discarded, as it normally is, and larger than normal quantities of this liquid were consumed (Infante et al. 1990).

The toxicity of unprocessed velvetbean may explain why the plant has few problems with insect pests (Scott 1910; IIA 1936; Duke 1981). Velvetbean is well known for its nematicidic effects when used in rotation with a number of commercial crops (Acosta et al. 1991; Kloepper et al. 1991; Marban-Mendoza et al. 1992), although it is not itself immune to a number of nematode species (Duke 1981). It also seems to possess a notable allelopathic activity, which may help it suppress competing plants (Gliessman et al. 1981). It can, however, harbour soil-borne pathogens, such as Macrophomina phaseolina, that are detrimental to maize and other food crops (Bell and Jeffers 1992; Berner et al. 1992).

Mucuna spp. have also been grown for some time as a fallow crop to improve soil fertility, a smother crop to control weeds, and a forage plant. Burkill (1966) noted that Mucuna was cultivated in Bali, Java, and Sumatra in the 17th century to recover worn-out ground — its first reported use as a cover crop. A survey on legume use in tropical countries, conducted by the International Institute of Agriculture (IIA) in the 1930s (IIA 1936), documented the use of M. pruriens in the Punjab of India to provide a cover crop and on the island of Madagascar to provide fodder for cattle and improve the soil for sugar cane, cassava, and lemon grass. The same species was reportedly used in Zanzibar to prevent the growth of Imperata cylindrica and to provide a green manure for maize, cassava, and sorghum. Mucuna aterrima was used as a green manure for maize and tobacco in Malawi and as a cover crop in Sierra Leone. Mucuna deeringiana was used as a cover crop on the citrus and banana estates in Jamaica and Puerto Rico as early as 1906.

In the 1920s, several experiment stations in Nigeria grew Mucuna spp. as an improved fallow and as a relay crop (with maize and cassava), with a view to intensifying small-scale, shifting-agricultural systems (IIA 1936); however, adoption of the practice was never reported. The authors of the IIA study argued that there was no pressing need for green manuring in West Africa, as forest land was abundant and traditional shifting-cultivation practices required less labour for clearing land than permanent cultivation did. In West Africa, during the 1920s, fallowing and slash-and-burn techniques effectively controlled weeds and provided optimum land preparation for planting. Under these conditions, farmers seemed unwilling to invest additional labour to establish green-manure cover crops. As noted below, however, changing circumstances may be opening up new opportunities for cover crops in this region.

Velvetbean in the United States

Velvetbean came into its own in the southern United States at the turn of the century, when it was used widely as an animal fodder and green manure. It was probably taken to the Caribbean by indentured workers from South Asia (Burkill 1966) and from there reached Florida in the 1870s, where it drew the interest of farmers and researchers (Bort 1909). One farmer, Mr Newheart of Ocoee, Florida, provided to O. Clute, of the Florida Agricultural Experiment Station, the seed of "a pea" in 1895, noting that "the abundance of foliage and vine, so completely covering the ground after the frost, suggested the idea of planting them in the orange grove as a manure, instead of buying commercial fertilizer" (Clute 1896, p. 342). By 1897, some 300 Florida orange growers were planting velvetbean in orchards to improve soil fertility (Miller 1902; Bort 1909).

The long frost-free season required to produce velvetbean seed (190 d) initially limited its use outside Florida and the southern half of the Gulf states (Duggar 1899; Piper and Tracy 1910; McClelland 1919). This limitation was partially overcome, however, when another farmer, Mr Clyde Chapman of Sumner, Georgia, collected beans from early-maturing plants of the Florida velvetbean. Seed from these plants was distributed after 1914 throughout the southern United States as the "Georgia velvetbean" (Coe 1918). Seed was produced from these varieties in about 100 d.

Use of early-maturing velvetbean as a soil-improving crop quickly extended to the northern limits of the cotton belt (Figure 2). From 9293 ha in 1908 (Scott 1910), the area in velvetbean grew to more than 400000 ha by 1915 and 2 x10⁶ ha by 1917 (Coe 1918). The Georgia and another early-maturing variety, the "Alabama velvetbean," accounted for some 80% of the velvetbean area in 1917 (Tracy and Coe 1918).

Velvetbean was typically intercropped between rows of maize to improve soil fertility in maize and cotton rotations in the southern states. According to many researchers, as a soil improver it had no equal (Miller 1902; Piper and Tracy 1910; Ferris 1917; Braunton 1918; Cauthen 1921; Pieters 1928). Its most important use, however, was to feed hogs and cattle (Ferris 1917; Templeton et al. 1917; Scott 1919; Lamaster and Jones 1923). When first introduced in the southern states, velvetbean was grown in maize and grazed by animals in the fall and winter, after removal of the maize. The remaining residue was then ploughed under, and a new crop cycle was initiated. As experience with velvetbean grew, more of the beans were picked after the crop was killed by a heavy frost, and the beans were either fed to animals on the farm or put on the market as beans in the hull (Ferris 1917; Templeton et al. 1917; Tracy and Coe 1918; Scott 1919; Lamaster and Jones 1923). Velvetbean pods were taken to mills and crushed or ground with the hull to provide feed for cattle, horses, and mules, largely replacing cottonseed meal as the protein component in animal feed used in the southern states (Ferris 1917; Willet 1918).

Figure 2. Distribution of velvetbean use in the United States, 1917.
Source: Tracy and Coe (1918).

Velvetbean was very popular in the cotton belt of the United States because of its extreme vigour and its pod-producing capacity (Scott 1910, 1919). According to the early literature, velvetbean's growth greatly exceeded that of cowpeas — a common alternative green-manure crop — and it was never attacked by nematodes, a parasite that could be spread on cotton plantations by cowpea. When killed by frost, velvetbean leaves and vines would go down on the ground together, forming a close-knit mat that stayed in place until the whole crop was ploughed under. Bean yields (in the pod) of 2–3 t ha^-1 were easily attained. The feed value of velvetbean produced on the farm for beef and milk production was comparable to that of purchased alternatives, such as cottonseed meal, but at less than 20% of the cost (Scott 1919; Cauthen 1921).

Although velvetbean was appreciated mainly for its role as a forage crop, its soil-improving effects were also well documented (Duggar 1899; Stubbs 1899; Miller 1902; Ferris 1917; McClelland 1919; Cauthen 1921). An estimated 155–200 kg N ha^-1 was found in the leaves, pods, and roots of well-grown, sole-crop velvetbean, without mineral fertilization. When velvetbean was intercropped with maize at 30 d after maize planting, maize yields were reduced by up to 10%, but these losses were more than compensated for by subsequent crops (Ferris 1917; Tracy and Coe 1918). Maize-yield increases of 60–80% following velvetbean use were consistently reported in the early literature, prompting one researcher of that period (Duggar 1902, p. 176) to note that "velvetbeans are a cheaper source of nitrogen than is any nitrogenous material which may be bought as commercial fertilizer." Experiments conducted at various experiment stations with maize, sorghum, wheat, cotton, and oats showed that velvetbean was superior to cowpea or soybean for improving yield (Duggar 1899; Stubbs 1899; Miller 1902; Ferris 1917; Coe 1918; McClelland 1919). Even when velvetbean was grazed by cattle, soil fertility was maintained for succeeding crops (Scott 1910).

The invasion of the boll weevil and a decline in the cotton industry of the southern states boosted expansion of the area dedicated to velvetbean (McClelland 1919). Lands left relatively idle by the cotton crisis were brought back into production with velvetbean, which rapidly became one of the most important crops in the southern United States for feed and soil improvement. One researcher (Scott 1919, p. 216) noted that "the story of the velvet bean might be called an agricultural romance." Velvetbean was hailed by scientists and farmers alike as the saviour of southern agriculture because the large quantity of feed produced by the crop and its low cost stimulated the production of livestock (Ferris 1917; Coe 1918; Scott 1919). The net cash value of velvetbean produced as an intercrop in maize in 1917 was estimated by Scott (1919) at more than 20 million United States dollars (USD).

Velvetbean use declined somewhat at the beginning of the 1920s, but the crop continued to be important in the southern states until the mid-1940s, when the number of hectares in velvetbean dropped quickly (Figure 3). By 1965, velvetbean had disappeared from US agricultural statistics.

The decline of velvetbean in the southern United States was probably due to sharp drops in mineral fertilizer prices and to the increased popularity of soybean as a commercial crop. Both velvetbean and soybean could be intercropped with maize to improve soil fertility and could be grazed by cattle and pigs, and the seed of either one could be harvested for use in animal feed. Soybean, however, was a more versatile crop, garnering a much higher price as a grain crop.

Figure 3. Velvetbean area, fertilizer use, and soybean area, United States, 1900–70 Source: USDA (1910–70); Hayami and Ruttan (1985, table c-2); Buckles (1995). Note: Current farm expenses for fertilizer divided by quantity of principal plant nutrients (N, P, and K).

According to United States Department of Agriculture (USDA) statistics, the production value of velvetbean grain in 1944 — the year the velvetbean area began to decline sharply — was 29 USD ha^-1, compared with 91 USD ha^-1 for soybean. The soybean area in the United States began to increase sharply as the velvetbean area declined, reflecting the substitution of the one crop for the other. This shift in production was accompanied by a drop in the real price of commercial fertilizers during the mid-1940s, which further contributed to the decline of velvetbean and other soil-improving crops, such as cowpea, in the United States.

Velvetbean use in Mesoamerica

Enthusiasm for velvetbean in the United States stimulated diffusion of seed to many countries in the tropics for experimentation during the early part of this century. Initially, velvetbean seed was sold by seed companies in the United States under the name "banana field bean" (Duggar 1899; Bort 1909, p. 26) and was later distributed as velvetbean throughout the tropics by the USDA (Piper and Tracy 1910). Velvetbean and knowledge of its uses in Mesoamerica can be linked to management practices developed by farmers in the southern United States. The plant was probably introduced as a forage crop in Mesoamerica in the 1920s by the United Fruit Company, a banana producer with extensive tracts of land along the Atlantic coast of Central America. Elderly banana-plantation workers in Morales and Puerto Barrios, Guatemala, reported that velvetbean was grown in maize by plantation workers on company land and grazed by mules used to transport bananas from the plantations to the railway depots (Buckles 1995).

The use of velvetbean as a forage crop by the banana companies faded as mules were replaced by tractors during the 1930s, but the plant retained the name "mule bean," or quenk mula, among the Ketchi natives of Guatemala. The Ketchi, originally from the densely populated highland area of Verapaz, were employed on banana plantations in Guatemala and may have become familiar with velvetbean on these estates. Carter (1969) reported that the Ketchi migrating to the lowland valley of Polochic, in the department of Izabel, Guatemala, had been planting velvetbean in rotation with maize since their arrival in the 1950s. Commercial farmers, also settling in the valley during the 1950s, used velvetbean for a dual purpose: as a soil improver for maize and as a forage crop for cattle. According to elderly residents interviewed by DB, the crop was first introduced in the valley during the 1930s by a Jamaican banana-plantation owner financed by the United Fruit Company (see also Carter 1969).

The velvetbean-management strategy used by commercial farmers and Ketchi in the Polochic Valley differed from that used by US farmers. Whereas velvetbean was intercropped in summer maize in the United States, in Guatemala a rotation strategy with second-season maize was developed. As in northern Honduras, the mature velvetbean crop was slashed with a machete in November, and then maize was stick planted into the layer of decomposing velvetbean leaves and vines. After the maize harvest, the velvetbean crop reestablished itself through natural reseeding or was replanted by the farmer, thereby continuing the rotation indefinitely. These farmers also grew maize during the main wet season on a different field, using traditional techniques of slash-and-burn cultivation (Carter 1969).

The use of velvetbean by commercial farmers in the Polochic Valley declined sharply during the 1970s, when much of the land used for maize production was diverted to pasture for cattle (Buckles 1995). The increased area of pasture in turn reduced requirements for velvetbean as a forage crop. These changes occurred before commercial fertilizers became widely available in the valley. In fact, the few remaining large-scale maize producers in the valley continue to grow second-season maize in rotation with velvetbean, reportedly with better yields and higher net returns than those gained from maize-production practices based on commercial fertilizers (Chávez 1993; Buckles 1995). This account suggests that broad changes in land-use patterns may have more of an effect on the use of velvetbean in Mesoamerica than alternative maize-production techniques — an issue that emerges again in northern Honduras.

Velvetbean is still used by the Ketchi in the Polochic Valley, the northern coastal mountains near Livingstone, the Petén, and border areas in Belize. The crop has also been used since at least the 1950s by indigenous farmers in the Mexican states of Chiapas, Oaxaca, Tabasco, and Veracruz. The Mames of southwestern Chiapas (Tsuzuki, personal communication, 1993 ¹) and the Nahua of Mecayapan in southern Veracruz (Buckles and Perales 1995) manage velvetbean on hillside land as a rotation crop, with winter maize, using practices similar to those of the Ketchi. The Popoluca of San Pedro Soteapan, also in southern Veracruz, broadcast velvetbean over maize fields they intend to fallow, giving rise to a practice they refer to as making a fallow field (hacer acaual). According to experienced farmers, maize yields on land improved using velvetbean for 2 years rival yields on land fallowed for 5 years with native trees and shrubs, a significant intensification of the traditional cropping cycle (Buckles and Perales 1995).

The Mixe and Chinantecos of southeastern Oaxaca have also used velvetbean for several decades in rotation with winter maize (Arévalo Ramírez and Jiménez Osornio 1988). However, the land type dedicated to the rotation differs from the hillside land used by the Ketchi, Nahua, and Popoluca. In southeastern Oaxaca, velvetbean is established on riverbanks subject to occasional flooding. This land is often very fertile because of the periodic deposition of new soil through floodwaters, but it is unsuitable for most wet-season crops because of the risk of flood damage. Furthermore, the riverbanks are heavily infested with weeds brought in with the sediment, and this increases the cost of cultivation. These features make riverbanks ideally suited, however, to the production of winter maize with velvetbean; the aggressive cover crop chokes out weeds, and when it is cut down, it forms a mulch that conserves the residual moisture from the wet season, which is needed to produce maize during the relatively dry period of the year (Narváez 1996.

The varied land types and traditional farming practices of the Chontales of Tabasco have given rise to yet another variation on the management of velvetbean with winter maize. These farmers use hummocks in the marshlands of their territory to grow winter maize in a velvetbean mulch, into which they also interplant squash (Cucurbita pepo L.) — an adaptation of the maize–bean–squash triad characteristic of indigenous intercropping systems in Mesoamerica (Miranda Medrano 1985; Granado Alvarez 1989). The diversified system controls soil pests that would otherwise significantly affect maize yields (Quiroga Madrigal et al. 1991).

Figure 4. Areas in Mesoamerica with spontaneous adoption of velvetbean–maize rotations.

Velvetbean was introduced in northern Honduras during the early 1970s, possibly by two Guatemalan brothers who settled in Planes de Hicaque near Tela. A Honduran brother-in-law of theirs is credited with introducing the seed into San Francisco de Saco, also one of the earliest sites of velvetbean use in northern Honduras. It grew wild there, unnoticed, for a number of years. A few farmers in the community observed the plant's ability to control weeds and improve maize yields in fields where it dominated, thereby rediscovering the rotation practice of the Ketchi and others. In northern Honduras, a field of velvetbean became known as an abonera, or "fertilized field." The velvetbean seed became known as frijol de abono, "the fertilizer bean," in recognition of one of its main benefits.

No evidence has been found to explain how velvetbean was diffused among all these populations (Figure 4). Migration patterns and trade links among indigenous peoples in the region may have played a role. The Ketchi (early users of velvetbean) were displaced by political forces to areas throughout Guatemala and Belize and into southern Mexico, possibly taking velvetbean seed and knowledge of its uses with them. The person credited with introducing velvetbean to the Nahua of southern Veracruz migrated to the area from a Nahua enclave in Tabasco, where velvetbean is also used (Buckles and Perales 1995). Currently, velvetbean seed produced in the Guatemalan lowlands is marketed as a coffee substitute among indigenous people in the highlands who are linked culturally to the Mames of Chiapas. The use of velvetbean as a coffee substitute may also have stimulated diffusion of the seed, if not the cover-crop management practices as well.

Conclusions

The development and diffusion of velvetbean–maize associations are the result of experimentation by numerous farmers and scientists, spanning four centuries and taking place in at least eight countries. Farmers, agronomists, and transnational corporations are all linked in a fortuitous and complex chain of events that confound both conventional and farmer-first notions of technology generation and transfer. The development of velvetbean-management practices in the United States and Mesoamerica did not proceed in a linear fashion from agricultural research stations to farmers' fields. Nor did these practices simply arise from unadulterated local knowledge and innovation; rather, velvetbean seed and knowledge of its uses were diffused because numerous groups' "borrowed" and adapted foreign species and practices. This experience illustrates the dynamic and social nature of agricultural innovation: new ideas do not emerge from a vacuum, nor are they the purview of a privileged class of innovators.

The links to the past and across continents are strong. At the same time, current uses and adaptation of the crop show that farmers are sophisticated knowledge producers in their own right. Within a very short period, farmers in various places were able to assimilate, adapt, and integrate the use of velvetbean into cropping systems with distinctive land types and crop mixtures. The speed and inventiveness with which this was accomplished illustrate the close relationship between local knowledge and innovation. For the Popoluca of Veracruz, broadcasting velvetbean to make a fallow field was an extension of shifting-cultivation practices, used to restore soil fertility, eliminate weeds, and improve soil structure. The Chontales' management of maize, velvetbean, and squash arose from a traditional intercropping strategy. The use of velvetbean by the Mixe to control weeds on riverbanks derived from a well-developed understanding of local land types and plant biology. A practical understanding of the logic behind the way velvetbean works was a distinct advantage in the innovation process. Recognizing and strengthening this knowledge may provide new opportunities for building on older practices — an issue to which we return in the final chapter of this book.

Document(s) 3 of 17