Prosopis juliflora (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Prosopis juliflora (Swartz) DC.

Protologue: Prodr. 2: 447 (1825).

Family: Leguminosae - Mimosoideae

Chromosome number: 2n= 26, 28, 52, 56

Synonyms

• Mimosa juliflora Swartz (1788),
• Prosopis vidaliana Naves (1877).

Vernacular names

• Mesquite (En).
• Bayahonde (Fr).
• Algarrobo, mesquite (Sp).

Origin and geographic distribution

P. juliflora probably originates from Peru and occurs naturally in dry areas of northern South America and Central America, Mexico and the southern United States. It has been introduced into many dry tropical areas, including north-eastern Brazil, Africa, Australia, South-East Asia and the Indian subcontinent. In Malesia, it is cultivated in Java, Papua New Guinea and the Philippines. In Brazil, cultivation is becoming very important.

Uses

P. juliflora is widely planted for land reclamation, being an aggressive colonizer, tolerant of very poor, degraded, saline and alkaline soils. It controls soil erosion, stabilizes sand dunes and is planted in wind-breaks and shelter-belts. However, because of its aggressive nature, it is considered a noxious weed in more humid areas, e.g. the southern United States. The generally crooked stems and branches make a good firewood and provide excellent charcoal. The wood is durable and can be used for quality furniture, doors and flooring, but the small trees rarely produce marketable logs. A reddish-amber gum, similar in properties to gum arabic produced by Acacia senegal Willd., often exudes from the stem and older branches. The protein and sugar-rich pods are valuable livestock fodder, and serve as security food for people during famine. In Argentina, Chile and Peru the pods are an important human food item used in making bread, syrup, sweets and alcoholic drinks such as cocktails. The pods must be processed, to improve the flavour. Sugars and sweeteners can be produced from the pods. Roasted seeds are used as a coffee substitute. Flour prepared from the pods can replace wheat bran in animal feed. For dairy cows, the flour may make up 40-60% of concentrate rations, while in South Africa, it is fed unmixed to sheep. The short-fibred parts are also suitable for pigs and poultry. The leaves of most selections are unpalatable to livestock. P. juliflora is also a valuable honey plant. Medicinally, the pods are used (as tea or syrup) against digestive disturbances and skin lesions.

Production and international trade

The fruits of P. juliflora are of great economic importance locally in Argentina, Brazil, Chile and Peru, but no statistics are available. Potential agro-industrial uses are being investigated and are promising. Charcoal made from P. juliflora wood is used extensively as a barbecue fuel in the United States, where about 30% of the charcoal sold for this purpose originates from P. juliflora from the Sonora desert in northern Mexico.

Properties

The wood of P. juliflora is hard and durable and burns evenly. The basic density of sawlogs is about 935 kg/m³, of fuelwood about 750 kg/m³. The energy value of fuelwood is 17 000-19 000 kJ/kg. Pods of P. juliflora contain per 100 g: crude protein 14 g, ether extract 3 g, nitrogen-free extract 50 g, crude fibre 28 g, ash 5 g; the flour has more protein and less fibre and carbohydrates. Seed contains per 100 g dry matter: crude protein 41 g, ether extract 5 g, nitrogen-free extract 43 g, sugars 8 g, starch 1 g, crude fibre 7 g, ash 4 g. Fresh leaves contain per 100 g dry matter: crude protein 19 g, ether extract 3 g, nitrogen-free extract 48 g, crude fibre 22 g, ash 9 g. Leaves are quite rich in essential amino acids, but lack the sulphur-containing ones. The leaf litter persists much longer than that of some other legumes. The litter suppresses the growth of soil bacteria and fungi and soils covered with Prosopis litter are often agriculturally poor. The weight of 1000 seeds is 35-45 g.

Description

• A flat-topped, evergreen (sometimes deciduous) shrub or small tree with twisted stem, up to 13(-20) m tall, armed with axillary, stipular spines 1-5 cm long or unarmed. Bark rough, dull-red; inner bark yellowish.
• Leaves with 1-2(-4) pairs of pinnae; petiole 1-4 cm long, rachis 3-14 mm long, ending in a spine 2-3 mm long; pinnae 3-11 cm long; leaflets in (6-)12-25(-29) pairs, sessile, elliptical-oblong, 6-16(-25) mm × 1.5-3(-6) mm, rounded to truncate at apex, mucronulate, usually glabrous, submembranous.
• Inflorescence an axillary, pendent, densely flowered, cylindrical, spiciform raceme, 5-15 cm long.
• Flowers 4-5 mm long, yellow to creamy-brown; calyx broadly campanulate, about 1.5 mm long, teeth 5, slightly ciliate; petals 5, sharply acute, about 3 mm long, greenish-yellow, pilose within; stamens 10.
• Fruit a pendent, straight or slightly falcate, compressed pod, 8-29 cm × 9-17 mm × 4-8 mm, surface irregular, light yellow to brown; stipe up to 2 cm long, beak 3-7 mm long; valves thick, indehiscent, enclosing seeds in cavities when ripe.
• Seed broadly ovoid, 6 mm × 4 mm, brownish, embedded in a whitish, slightly sweet pulp.

Growth and development

In tests in Petrolina, Brazil, P. juliflora reached a height of 4 m, a diameter at breast height of 4.5 cm and a crown diameter of 5.4 m in 2 years. It normally grows to a height of about 10 m, while under very favourable conditions it may reach 20 m. In Brazil, it flowers profusely in December-February and pods are mature in February-May. In India, flowering and fruiting is from August-October. P. juliflora coppices readily.

P. juliflora moderately enriches the soil with atmospheric nitrogen obtained through symbiosis with cowpea-type Rhizobium. The roots also form mycorrhizal associations with Glomus fungi. Plants with both mycorrhizal and Rhizobium associations show significantly higher nitrogen fixation rates than those lacking the mycorrhiza.

Other botanical information

The taxonomy of Prosopis L. is confused and in great need of a worldwide revision. P. juliflora is a highly polymorphic species and many varieties have been described. Several varieties such as var. glandulosa (Torrey) Cockerell and var. velutina (Wooton) Sargent are often considered separate species, denoted P. glandulosa Torrey (honey mesquite, in the southern United States) and P. velutina Wooton (velvet mesquite, in Mexico and Arizona, United States), respectively. Var. torreyana L. Benson is also classified as P. glandulosa Torrey var. torreyana (L. Benson) M.C. Johnston. These varieties are difficult to distinguish, having only larger leaflets and flower spikes than var. juliflora.

Ecology

The value of P. juliflora lies in its exceptional tolerance of drought and marginal soils. In its natural habitat in Peru, average annual rainfall ranges from 250-500 mm, but plants bearing leaves and fruits can be found in locations receiving as little as 50 mm. An annual rainfall of about 800 mm is required for optimal growth. It is grown successfully on sandy soils in Brazil, in locations with 1000 mm annual rainfall, where most vegetation remains green all year. P. juliflora tolerates a dry season of 8 months or even longer. In Peru, it is found up to 100 m altitude, while elsewhere its range extends to 1500 m altitude. The mean maximum temperature of the hottest month is 22-34°, the mean minimum temperature of the coldest month 14-22°. Some selections tolerate light frost. P. juliflora is tolerant of highly saline and alkaline soils. When grown experimentally on a 20 g/l NaCl nutrient solution, it not only survived and continued to grow, but also continued to fix atmospheric nitrogen. The roots are able to exclude NaCl; the NaCl content of the ash increasing much slower than that of the nutrient solution or soil. P. juliflora survives and even flourishes in soils more saline than 2 S/m (13 g/l NaCl) if it can obtain water from a portion of the rootzone with lower salinity and its roots continue to extract water from soils with salinities greater than 2.8 S/m (18 g/l NaCl). Fair growth is also obtained on poor sandy and rocky soils.

P. juliflora is sometimes said to dry out the soil and compete with grasses, particularly in dry years, hence in some areas (e.g. the United States) it is considered a weed. The tree naturalizes easily in many regions, such as India and Australia and may become a weed in humid areas.

Propagation and planting

Propagation is possible by seed, root cuttings and grafting. Establishment by seed is feasible, although seed is difficult to extract from the pods. For small amounts, pods are cut open with a knife and seeds are removed manually. For larger amounts, pods are kept in a damp place and allowed to degrade by fermentation, releasing the seeds. Alternatively, pods are fed to goats and the manure containing the undamaged seeds is used for sowing. Treatment of seed with concentrated sulphuric acid for 30 minutes is reported to improve germination, in other cases mechanical scarification was better. Aerial seeding is applied successfully to quickly cover remote, extensive and poorly accessible areas. In the United States, aerial seeding of a mixture of P. juliflora, Nicotiana glauca Graham and several Eucalyptus species is used to revegetate abandoned copper mines. It is common practice to grow plants in plastic bags in nurseries. Inoculation with Rhizobium and mycorrhizal fungi is advantageous.

Seedlings withstand watering with saline water up to EC 0.8-1.0 S/m, and at 18 months brackish water of EC 0.4-0.6 S/m and pH 7.0-7.85 still suffices.

Spacing depends on the use of the trees. When grown for fuelwood, a spacing of 2 m × 2 m or wider is used in South America. In rangeland in association with grasses and other crops, spacing may be up to 10 m × 10-15 m. When the emphasis is on pod production, the spacing used ranges from 5 m × 5-10 m.

Husbandry

After planting, P. juliflora benefits from weeding around the stem. Young plants also need protection from grazing animals. For older plants little care is needed. Thinning and pruning are needed to avoid P. juliflora becoming a weed and to keep the plantation accessible. In rangeland in South America, all but the large trees with a stem diameter of 30-50 cm are thinned out and the remaining trees are pruned to 30% of their canopy. The best species to grow in association with P. juliflora are Cenchrus ciliaris L., Panicum maximum Jacq. and Opuntia spp. Although better growth of Opuntia and grasses under P. juliflora trees is often reported, there have been reports that the total fodder yield may be lower than the yield from a well managed grass pasture.

Diseases and pests

In South America the wood sawyer insect Oncideres saga which cuts off young branches causes considerable damage. Other pests reported from South America are the Lycainid butterfly Hemiargus ramon damaging the flowers and the Lonchaeid fly Silba pendula and Bruchus beetles attacking the pods. The membracid treehopper Otinotus oneratus is reported to cause damage in India.

Harvesting

Firewood is generally cut in an 8-10-year cycle. Pods are either left for animals to browse or harvested manually. Prompt harvesting and processing of pods may alleviate Bruchus beetle attack, while delaying collection of pods fallen on the ground may result in heavy losses. Where pods are stored for later use or marketed, manual harvesting is required.

Yield

Wood and pod yields strongly depend on the selection used and on the environment. No difference in yield between planted trees and coppice growth is reported. When cut in an 8-10-year cycle, a firewood plantation may yield 50-60 t/ha; in a 15-year rotation, the expected yield is 75-100 t/ha. Pod production starts in the third year after planting and peaks between 15 and 20 years, provided trees are well managed. Average annual pod yield is about 15 kg per tree, but yields of 100 kg from individual trees are also reported. An annual production of 10 t/ha is possible; the average production in the United States is 8.7 t/ha.

Handling after harvest

Pods are often attacked by insects and need careful storage. Traditionally, they are stored in sealed rooms or in layers alternating with layers of sand. Alternatively, they are fumigated and stored in a well ventilated room.

Genetic resources and breeding

Various collections exist, e.g. in the United Kingdom at the Commonwealth Forestry Institute in Oxford. Genetic variation exists between populations, e.g. in Pariba, Brazil. Selection work in Haiti found spineless, erect growing forms with unpalatable foliage. Selection is being carried out e.g. in Banthra, Lucknow, India. Most research in Asia is reported from the Indian subcontinent.

Prospects

P. juliflora is considered very useful for afforestation of saline and alkaline wasteland and for the production of fuelwood and dry season fodder. Its role as a rangeland tree deserves further research attention. It is suitable for stabilizing peripheral bunds around mangrove creeks used for fish culture. On the other hand, warnings are issued against introduction into new locations, as it may become weedy on good soils and in moist locations.

Literature

• Burkart, A., 1976. A monograph of the genus Prosopis (Leguminosae subfam. Mimosoideae). Journal of the Arnold Arboretum 57: 219-249, 450-525.
• Dutton, R.W., 1992. Prosopis species, aspects of their value, research and development. Proceedings of the Prosopis Symposium, University of Durham, United Kingdom, 27-31 July, 1992. International Prosopis Association, Durham, United Kingdom. 230 pp.
• Felger, R.S., 1979. Ancient crops for the twenty-first century. In: Ritchie, G.A. (Editor): New agricultural crops. Westview Press, Boulder, Colorado, United States. pp. 5-20.
• Habit, M.A. & Saavedra, J.C. (Editors), 1988. The current state of knowledge on Prosopis juliflora. Second International Conference on Prosopis, 25-29 August, 1986, Recife, Brazil. Food and Agriculture Organization of the United Nations, Rome, Italy. 554 pp.
• Hughes, C.E. & Styles, B.T., 1984. Exploration and seed collection of multiple purpose dry zone trees in Central America. International Tree Crops Journal 3: 1-32.
• Jarrel, W.M. & Ross, A.V., 1984. Salt tolerance of mesquite. California Agriculture 38(10): 28.
• Joshi, S.C., 1986. Aerial seeding for environmental conservation. Indian Forester 112: 1-5.
• National Academy of Sciences, 1979. Tropical legumes, resources for the future. National Academy of Sciences, Washington D.C., United States. pp. 153-163.
• Wojtusik, T., Felker, P., Russell, E.J. & Benge, M.D., 1993. Cloning of erect, thornless, non-browsed nitrogen fixing trees of Haiti's principal fuelwood species (Prosopis juliflora). Agroforestry Systems 21: 293-300.

Authors

L.J.G. van der Maesen & L.P.A. Oyen