1. Introduction: desertification
<P>affected lands are occupied by people that live essentially by agriculture and sheep farming.
Taught in africa:
Forestry management is certainly one of the main activities to combat desertification (Berthe, 1997). Plant cover is important for soil protection
In the seventies, forest plantations were implemented in Niger and Mali using some drought resistant and fast growing species such as Eucaliptus spp., Tamarix spp., Ficusspp., Acacia spp., Euphorbia balsamiphera, Prosopis juliflora. However, these and other similar efforts were not always successful, as a consequence of the specific ecological requirements of the used species and the often not respected need to avoid grazing for a certain period in reforestation areas
large trials were implemented in many arid areas of the world such as those found in the Mediterranean basin, South Africa, Australia, Chile, Brazil, and USA
2. Actions and experiences on the use of Atriplexand Opuntiato combat desertification in the world
2.1.1. West Asia and North Africa (WANA)
West Asia and North Africa (WANA) region, which extends from Morocco to Afghanistan and from Turkey to the Arabic peninsula, is the largest continuous arid area of the world.
Since 1991, about 35% of the cultivated lands have been irrigated.
Atriplex halimus subsp. halimus and subsp. schweinfurthii, A. leucoclada, and A. mollis; while the most important introduced ones are A. nummularia, A. canescens. A. lentiformis, and A. semibaccata(Le Houérou, 1992a).
cattle can successively graze barley stubbles and Atriplex shrubs during summer and autumn
A. halimus and A. nummularia, have given the best results (Arif et al., 1994). For instance, the association of barley with forage shrubs of the genus Atriplex (strip crop or alley crop) has increased crop yield by 25% (Brandle, 1987).
Atriplex halimus L. originated from North Africa. It is well adapted to saline-clay soils under less than 150 mm/year of rainfall (Le Houérou, 1980a). In absence of grazing, this species can grow up to 4 m in height (Négre, 1961). A. halimusis one of the most palatable Atriplexspecies for cattle in the dry lands of the WANA region (Tiedeman and Chouki, 1989).
Atriplex nummularia Lindl. is a perennial upright shrub, originated from the arid and semi-arid areas of Australia. It grows where rainfall is at least 180 mm/year (Thornburg, 1982). Its root system may develop over 3 m in depth and up to 10 m in width (Jones, 1970).
In Saudi Arabia, have showed that, among various Atriplex species, A. nummularia produced the highest biomass yieldand had a high crude protein content (16%) (Hyder, 1981).
In Egypt, crude protein levels of 12.7%, 9.1%, and 11.8%, respectively, for fresh biomass, hay, and silage of A. nummularia were found. Moreover, A. nummularia had positive effects on the growth rate of wool and body weight of sheep fed under controlled conditions (Abou El Nasr et al., 1996).
biomass production varies depending on the species and plant density. For instance, in Morocco, a three-year-old plantation of A. nummularia at a density of 1,000 plants/ha showed a yield of 1,250 kg of dry matter/ha, which corresponds to a surplus of 625 forage units and 200 kg of crude protein/ha with respect to the yield of the associated herbaceous crop (El Mourid et al., 2001).
Atriplex shrub can be used as a forage reserve during summer and autumn, due to its high content of protein and minerals
allows cattle to resist prolonged periods of scarce feed caused by drought (Le Houérou, 1980b).
A. glauca, found in clayey soils (Le Houérou, 1969), and A. mollis, with upright shape and found in sandy soils (Le Houérou, 2000).
A. amnicola (A. rhagodioides), A. undulata, A. lampa, A. lentiformis, A. breweri, A. barclayana, A. canescens, A. isatidea, A. paludosa, A. cinerea, A. polycarpa, A. repanda, A. nummularia(cv. Grootfontein from South Africa), A. inflata, and A. halimoides.
In spite of its low productivity, A. canescens is another species of interest, because of its high chilling resistance (Forti, 1986). This species originated from North America and has some cultivars ('Wytana', 'Rincon', 'Marana' and 'Santa Rita') adapted to different ecological conditions.
A. amnicola, palatable, but sensitive to chilling and overgrazing; A. undulata, productive, palatable and chilling tolerant; A. lentiform is, tolerant to salinity by sodium carbonate and showing good self-sowing ability
Syria, Atriplex leucoclada, A. canescens, A. nummularia, and A. polycarpa. The best results were recorded with the most chilling resistant species, such as A. canescens(El Fikiki et al., 2000; Murad, 2000; Rae et al., 2000).
Jordan, Atriplex halimus and A. nummularia, included in many projects developed by national and international institutions (Mohamed, 2000; Nesheiwat, 2000; Tadros, 2000).
(over 40,000 ha) of Morocco., A. vesicaria, A. semibaccata, A. paludosa, and A. halimus, planting costs, which are too high for animal breeders.
Pakistan, the chilling tolerant Atriplex canescensand A. lentiformisare the most widespread species
Iran, more than 20 species of Atriplexgrow spontaneously. Most of them are herbaceous (Koocheki, 2000), while only Atriplex griffthi, A. leucoclada, and A. verruciferaare shrubs, Plantations are composed by exogenous Atriplexspecies, such as A. lentiformis, A. halimus, A. nummularia, and, especially, A. canescens(Rashed, 2000). The latter species is the best adapted to the environmental conditions of Iran, because of its cold tolerance (Nejad and Koocheki, 2000).
Turkey, Atriplex nitens and A. laevis are two important autochthonous shrubby species (Tahtacioglou, 2000).
A. halimusand A. nummularia, have been used in public and non-governmental projects in Tunisia (Nefzaoui et al., 2000a).
When Atriplexshrubs are associated with other crops (alley crop), such as barley, oats or Lucerne, they play an important role in wind breaking, soil protection and creation of a favourable microclimate to other forage species, which then increase their growth and yield (El Mzouri et al., 2000).
Feed integration with forage shrubs and cactus pear cladodes provide good results. In fact, Atriplex hasa good protein and a low energy content, while Opuntia cladodes have good energy and water contents
2.1.2. South America
Atriplex nummularia, A. repanda, A. semibaccata, Kochia brevifolia, Acacia saligna, and Galenia secunda
role of forage shrubs is not to increase milk, meat or wool production during the good season, like the herbaceous forages, but to provide green forage, rich in protein, during the dry season, in order to reduce animal weight loss.
Southern Coquimbo, with rainfall ranging from 100 to 220 mm/year, yields of A. nummularia plantations have varied from 50 to 900 kg of dry matter/ha per year, depending on age, field management and plant density.
A. nummularia planting densities increase from 625 to 10,000 plants/ha, yields increase. However, leaf production decreases at planting densities over 2,500 plants/ha (Soto, 1996).
Coquimbo region, under average climatic conditions, yields of A. nummularia can reach 1,000-1,500 kg of dry matter/ha per year, using 1,600 plants/ha. In order to obtain these yields, it is necessary to avoid overgrazing and to use forage shrubs from summer (November-January) until the start of winter rains, to allow a successive vegetation resprouting. The period of shoot growth during the rest period of A. nummularia varies from 4 to 7 months
first grazing of Atriplex is recommended not before 18 months from plantation. It is advisable to prune the plants every 4-5 years, by cutting-down woody branches at 25 cm above the soil level, in order to regenerate the canopy and to avoid an excessive growth in height, especially in the case of A. nummularia.
Plant growth in height increases the proportion of woody tissues, causing a decrease in leaf production and leading to plant senescence (Rivera,1996). Appropriate management of forage shrubs requires a rest period from grazing and pruning at 25-50 cm above the soil, when senescence starts and leaves tend to grow at the higher parts of the plants (Pagliaricci et al., 1984; Olivares et al., 1986; 1989). The responses of A. nummularia to these management practices are a lot better than those of A. repanda (Garcia, 1993; Soto, 1995).
Atriplex nummulariais to associate this forage with Opuntia ficus-indicacladodes. The inclusion of young cladodes of cactus pear in the diet, increases milk production of goats. (Azocar and Rojo, 1992).
Pruned woody branches are an important energy resource. For instance, the energy content of A. nummularia wood is of about 4,538.3 kcal/kg (Garcia, 1993).
2.2.1. West Asia and North Africa (WANA)
winter rainfall is of 200-350 mm, the main economic activity consists of meat, milk, leather and wool production by small ruminants (sheep and goats)
barley has become the most important livestock feed. However, this increase has been associated with the cultivation of marginal lands, not used previously, and the introduction of monocultivation.
"The Development of Integrated Crop/Livestock in the Low Rainfall Areas of West Asia and North Africa". The following eight countries have been involved in the project: Algeria, Libya, Morocco, and Tunisia, in the Maghreb, and Iraq, Jordan, Lebanon, and Syria, in the Mashreq. The realisation of this Maghreb/Mashreq project have demonstrated thestrong desire of these countries to overcome this critical situation (El Mourid et al., 2001).
Opuntia cultivation has been combined with the application of water storage techniques and soil surface modification in waves (Griffiths, 1933; Le Houérou, 2000). Soil waves roughly follow the contours and contain, in their internal sides, two rows of Opuntiaplants (Nefzaoui and Ben Salem, 2000).
Species of the genus Opuntiaare characterised by a deep and wide root system, which is able to stabilise soil surfaces in hilly areas
Opuntia planting is often accompanied by soil surface cover with palm leaves (IFAD, 2000a; 2000b)
Currently, the total area cultivated with Opuntiain the WANA region is of about 900,000 ha (Nefzaoui and Ben Salem, 1998).
Since ancient times, Opuntiaplants have been commonly used as a forage in Maghreb countries (Tunisia, Algeria, Morocco and Lybia) (Monjauze and Le Houerou, 1965; Boulanouar et al., 2000; Nefzaoui et al., 2000a; Redjel and Boukheloua, 2000)
150 to 400 mm/year, without fertilisation, Opuntia ficus-indicavar. inermiscan produce from 20 to 100 t of cladodes/ha per year, respectively (Monjauze and Le Houerou, 1965).
In many trials, the use of nitrogen and phosphorus fertilisers has increased the crude protein content of Opuntia cladodes from 4.5% to 10.5% of dry matter (Gonzales, 1989).
Nutritive value of cladodes varies with cladode age. Crude protein content decreased (from 5 to 3% of dry matter), while fibre content increased (from 9 to 20%of dry matter) when cladodes grew from 1 to 5 years old (Nefzaoui and Ben Salem, 2000)
Sheep fed Opuntia cladodes could swallow up to 9 kg/day of this forage (Monjauze and Le Houerou, 1965). Moreover, theuse of Opuntiaforage caused an increase in straw intake by sheep.
Sheep fed a diet containing about 300 g of Opuntia dry matter can basically eliminate direct water consumption (Nefzaoui and Ben Salem, 1998).
2.2.2. American Continent
Cactaceae has about 130 genus and 1,500 species. Three hundred of them belong to the genus Opuntia
Opuntia ficus-indica(L.) Mill. is the most commercially important species in Argentina, Chile, Mexico, and Brazil, Italy, Greece, Algeria, and South West of USA (Russel and Felker, 1987)
agamically propagated plants, fruit production starts from the second or third year after planting and reaches the maximum yield at the seventh year.
Normally, a planting density of 2,000 plants/ha can assure yields of 30 t of good fruit/ha after four years from planting (Yasseen et al., 1996). Yields are lower in Mexico, as a consequence of high soil pH (Barbera, 1987a).
Some Opuntia species produce inedible fruits, called xoconoxteles, while other species produce sweet and edible fruits commonly named tuna (Tab. 6) (Pimienta-Barrios, 1990).
traditionally used by Mexicans and Indians of New Mexico, Arizona, California and Utah (Bailey, 1976). Opuntia fruit can be consumed fresh or boiled in water, or can be dried for storage and winter consumption
from pulp, in Mexico, the following by -products are traditionally obtained: "queso de tuna" (mustard), "colonche" (fermented juice), "melococha" (marmalade), "miel de tuna" (syrup), and "tunas passas" (dried fruits) (Pimenta-Barrios, 1990; Barbera, 1991a; 1991b).
Young cladodes (nopalitos) of 10-15 cm of length are also edible, as vegetable
Opuntia lindheimeri is commonly used as forage for the livestock in critical periods, in Texas and Mexico
spines can be burned off or immersion in water, vapour application or washing in soda
3.1. The genus Atriplex
Atriple<P>x contains ~200 species, a few in polar
In general, plants ofthe genus Atriplex grow in saline or alkaline soils, and in arid, desert or semidesert environments (Rosas, 1989; Par-Smith, 1982).
widespread in Australia
Perennial herbs are the main components
shrubs and trees are less common
halophytes or salt tolerant
largely distributed in temperate and subtropical saline habitats, Mediterranean Sea, Caspian Sea and Red Sea, in the arid steppes of Central and East Asia, in the margins of the Sahara desert, in the alkaline prairies of USA, in the Karoo of Southern Africa, in Australia, andin the pampas of Argentina
deep and well-developed roots, able to absorb large amounts of underground water.
Pollination is made by wind
igh tolerance to drought and salinity. Moreover, they can provide a high quantity of leaf biomass during unfavourable periods of the year, being used as a forage rich in protein and carotene
Most species of the genus Atriplex are dioecious
Flowers are monoecious
3.1.1. Management of Atriplex plantations
South of Spain, A. halimusproduced yields of edible biomass of 450-500 g/plant per year (Papanastasis, 2000)
Atriplex halimus responded better to direct grazing than A. nummularia (Aouissat et al., 1993).
In Southern Africa, several shrub species were comparedin trials on desertification combat. The best results were obtained using Atriplex nummularia and A. halimus, followed by A. undulata and A. breweri (Van Heerden et al., 2000a; 2000b)
when irrigated and with a salinity of 15-20 mS/cm of EC, yields can be higher than 30 t of dry matter/ha per year (Le Houérou, 1994);
After complete leaf removal, the plant needs a rest period of about 8-10 months to recover. On the other hand, if the plant is never grazed, its lifespan will be not longer than 12-15 years. Every 5 years, a renovation pruning at 20-40 cm above the soil is recommended (El Mzouri et al., 2000).
2nd most used
Syria, Jordan, Egypt, Saudi Arabia, Libya and Tunisia.
main shrubby species of Atriplexcan be propagated agamically. Nevertheless, the most used propagation technique is by seed
Planting density affects mean yield per plant, which tends to decrease as densities increase from 2,500 to 10,000 plants/ha (Van Heerden et al., 2000b)
Atriplex can grow and reproduce under rainfall conditions ranging between 100 and 400 mm/year
Atriplex has a high water-use efficiency. In fact, A. nummularia, A. halimus, and A. canescens produce 10-20 kg of dry matter/ha per year per mm of rain (Forti, 1971;Correal et al., 1990b)
Western Australia, plantations of Atriplex irrigated with 500 mm/year yielded more than 5 t of dry matter/ha per year (Malcom and Pol, 1986).
In Saudi Arabia, six species of Atriplex irrigated with 420 mm/year of water provided by a centre-pivot were compared. In the first year, average yield was 3,290 kg/ha, while in the fourth year it was 6,579 kg/ha.
WUE 7.8 and 15.7 kg of dry matter/ha per year per mm of water, respectively, in the first and fourth year (Mirreh et al., 2000).
these forage shrubs showed a water-use efficiency high enough to produce a quantity of dry matter twice that of wheat and barley, and 4-5 times higher thanthat of Lucerne (Le Houérou, 1992a).
Northern Africa and Iran, present in Israel, Jordan, Syria, South Africa, Mexico, Australia, and USA
Species of the genus Atriplex also have a high ability to absorb nitrogen from the soil and can benefit from the action of nitrogen-fixing microorganisms (Ismaili et al., 2000).
hay of lucerne and Atriplex forage seemed to be the most effective nitrogen sources for rumen microorganisms (Silva and Pereira, 1976).
high nutritional value of A. nummularia forage (i.e. leaves), characterised by a protein content similar to that of the lucerne hay (Tab. 8) (Chiriyaa and Boulanouar, 2000).
Small ruminants exclusively fed Atriplex spp. forage had a negative nitrogen balance. The main reason for that are the lack of available carbohydrates in the diet and the fast hydrolysis of crude protein in the rumen. These two events lead to the accumulation of ammonia in the rumen that cannot be used by livestock (Hassan et al., 1979; Kandil and El Shaer, 1988). When the diet is not composed exclusively by Atriplex and is integrated with forages having more carbohydrates and energy, the quantity of retained and available nitrogen increases significantly.
Many studies have showed the positive effects of using straw to integrate diets based mainly on Atriplex nummularia (Correal and Sotomayor, 2000) and A. halimus (Sotomayor and Correal, 2000).
salt content of the edible parts of Atriplex plants, such as leaves and young shoots, is high. For this reason, sheep fed Atriplex need to drink frequently and the amount of ingested water may reach 11 L/head/per day (Le Houérou, 1991; Mirreh et al., 2000).
Range Research Methods defined palatability as "quality that determines the preference for a particular forage species by livestock having the possibility to choose among many alternatives" (Marten, 1970).
3.2. The Opuntia genus
Mexico. In that country, fossil seeds of the seventh millennium b.C. were found, indicating the use of this species as food in prehistoric times (Barbera and Inglese, 1993). In pre-Columbian times, the prickly pear (Opuntia ficus-indica) and other Cactaceaehad a fundamental role for the survival of the population living in the area comprised between Southern USA and Mexico (Pimienta-Barrios, 1990).
In the first half of the XVI century, Opuntia ficus-indica, similarly to other vegetal and animal species, was introduced into Europe by Spanish colonisers (Prescott, 1843). Later on, the species spread out in all continents, especially in areas with warm and dry climate
Australia and South Africa, Opuntia ficus-indicais generally considered a weed, because of its easy propagation and of the damages it causes to sheep wool. On the contrary, in Brazil, Tunisia and Italy, the species is an important forage or fruit crop.
Opuntia ficus-indica is the most agronomically important species for the production of edible fruits and cladodes
domestication of O. ficus-indica started about 8.000 years ago (Bravo, 1991; Pimienta-Barrios and Muñoz-Urias, 1995)
height from 1 to 5 m
host nitrogen-fixing symbiotic microorganisms in the roots.
An edible oil extracted from the seeds has the following main characteristics: high unsaturation level, high percentage of linoleic acid, and low content of linolenic acid. For those and other chemical and physical characteristics, the cactus pear oil belongs to the same group of soya bean, maize, and sunflower oils (Sepúlveda and Sáenz, 1988).
Spanish colonisers were attracted by the presence of a cochineal scale insect (Dactilopius coccus) on cactuspear plants in Mexico. After drying and grinding the insect body, a powder could be extracted and used as a tissue colouring agent, as a water soluble colouring agent for the food and pharmaceutical industry, and as a lacquer to make paints. The powder could also be used for the extraction of carminic acid (10% of the raw material) which is used as a staining agent in histology and microbiology (Barbera, 1991b).
young cladodes have a hypoglycaemic effect related to glucose absorption and a consequent non stimulation of insulin production. Similarly, due to the adsorption of bilious salts and a further use of the haematic cholesterol, young cladodes also have a hypocholesterolhaemic effect (Mulas, 1992). Moreover, it seems that cactus pear cladodes have antipyretic, antinflammatory, analgesic, and antispasmodic effects, while its dry flowers can be used to prepare diuretic infusions (Barbera, 1991b; Mulas, 1992)
sandy or intermediate textured, superficial soils having low
can colonise the sterile soils around the Etna Vulcan (Sicily , Italy), thus creating soil conditions favourable to other more profitable crop (Bonifacio, 1961; Barbera et al., 1993). A similar soil improvement was also observed in subtropical regions, where the roots and cladodes of cactus pear were transformed in o rganic matter, leading to higher availability of nutrients, increase in microorganisms, and improvement of water budget and soil structure (Monjauze and Le Houèrou, 1965)organic matter content (Barbera et al., 1993)
live in symbiosis with nitrogen-fixing bacteria is another positive ecological characteristic of the species that has also been studied (Llovera et al., 1995)
Propagation by seed has many disadvantages: germination is slow and preceded by a dormancy period; seedlings are genetically and phenotypically non uniform; plants show a very long juvenile period (Escobar et al., 1986; Pimienta Barrios, 1990)
The highest numbers of shoots and fruit per cutting were observed at spring and winter plantings, respectively
a higher number of roots per cutting was observed after the autumn plantation. [b/c of more rain]
can plant portions of cladodes, ¼ works almost as well as whole cladodes but take longer to produce sizable plants
3.2.1. Ecophysiology of the genus Opuntia
most active roots are in the superficial soil layers, up to 30-cm in depth, and in an 8-m range of lateral growth (Sudzuki Hills, 1995)
The main drought tolerance mechanisms of the family Cactaceae are the following (Sudzuki Hills, 1995):
-reduction of root surface and water permeability;
-fast absorption of small water amounts fallen as ephemeral rains, due to a fast development of roots that disappear when the soil dries up;
-creation of a more negative water potential. The latter is considered a drought-resistancemechanism.
rainfall of short duration and little amount (few millimetres) can be efficiently used by Opuntia plants.
Mycorrhizal symbiosis helps the optimisation of water absorption by the roots and water storage in reserve tissues (Pimenta-Barrios et al., 2002). Even though only few studies have focused on this aspect, it seems that symbiosis with mycorrhizal microorganisms improves the performance of the host plant, due to its greater ability to absorb water
Opuntiae photosynthetic organs may reach temperatures 15 °C above the environmental ones (Gates et al., 1968)
CAM plants generally show an optimal level of CO2 assimilation when night temperatures are around 10-15 °C.
3.2.2. Growing management ofthe genus Opuntia
along rows or strips, following the contours at variable distances depending on surface slope; cuttings are planted in 30-cm deep furrows ridges
preparation of cladodes for planting requires a clean cut made at the point of their attachment to the well developed plant. Air exposure of detached cladodes for some weeks will then allow the wounded surface to heal. After that, cladodes can be buried obliquely, leaving half or three quarters of their length under the soil, in order to offer less resistance to the wind.
best planting time should be distant from the rainy season, in order to avoid the risk of cladode rot.
If the plantation purpose is forage production, higher planting densities should be used. A high competition among plants reduces their reproductive activity, increasing their juvenile period
Another alternative is to add hay of Atriplex nummularia (about 300 g of dry matter/day) to cladode-based diets. Atriplexis a good source of protein and, furthermore, the nitrogen supplied facilitates the organic matter digestion by sheep (Nefzaoui et al., 1996).
best way to obtain good silage is to cut cladodes in small pieces and to add oats straw and a small quantity (respecting a ratio of 84:16 with cladodes) of lucerne hay and molasses (2%).
Species of the genus Opuntia, particularly O. ficus-indica, and of the genus Atriplex, such as A. nummularia, A. halimusand A. canescens, have useful characteristics to combat desertification successfully, and can assure feed production for livestock and incomes sometimes higher than those of traditional forage systems (Le Houérou, 2000).
the use of shrub species represents a clear advantage with respect to other marginal agricultural systems, such as the systems based on barley monoculture, which is responsible for the degradation, erosion and salinity problems of many lands under desertification risk.
species of the generaOpuntiaand Atriplex integrate each other, since the first are rich in water and fibre, and the second are mainly rich in protein. Opuntia cladodes water content can be useful to counterbalance the higher water requests of the livestock fed the salty Atriplex leaves