IRRIGATED AGRICULTURE AND THE NONSUSTAINABLE MANAGEMENT … · IRRIGATED AGRICULTURE AND THE...
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MEDIT N° 1/2000
IRRIGATED AGRICULTURE AND THE NONSUSTAINABLE MANAGEMENT OF GROUNDWATER RESOURCES:
THE CASE OF CAMPO DE DALlAS, SPAIN
The problem of saline intrusion is specific of coastal aquifers.
Near the coast an interface exist between the overlying fresh groundwater and the underlying salt groundwater. The saline-fresh water interface in a coastal aquifer is governed by a hydrodynamic balance, which results in the natural flow of freshwater to the sea. However, if the natural flow of freshwater to the sea is interrupted or Significantly reduced by continuous pumping, overpumping or the inappropriate location and design of wells, causing an excessive lowering of the water table, then the former hydrostatic eqUilibrium is changed, saline intrusion being almost certain to oc-
SIMON PEDRO IZCARA PALACIOS (*)
ABSTRACf
In the short span of two decades, the Campo de Dalias, one of the less-endowed agricultural regions of Spain, became one of the most intensive, productive and profitable areas. However, during the last decades, the mushroOming of irrigated agriculture, the inappropriate location and design of wells, overpumping and the steady increase of groundwater withdrawals have damaged farming's productive base, causing an excessive lowering of the water table and starting a process of saline intrusion. This paper examines the problem of groundwater depletion in the Campo de Dalias and farmers view of this problem, analysing the factors impeding to implement a sustainable management of groundwater resources.
RESUME
Au cours de deux decennies, Campo de Dallas, l'une des regions agricotes les plus marginales d'Espagne, est devenue I'une des aires les plus intensives, productives et rentables. Toutefois, dans la derniere decennie, la proliferation de l'agriculture irriguee, la mauvaise localisation et conception des sondages, le soutirage excessif etl'augmentation constante des prelevements de l'eu de nappe ont pone aUeint a la base productive agricole en provoquant un rabauement de la nappe et I'intrusion de I'eau de mer. Ce travail examine le probleme du tarissement de la nappe a Campo de Dalias et exprime la vision des agriculteurs vis-a-vis de ce probleme, en analysant les jacteurs qui empechentla realisation d'une gestion durable des ressources en eau souterraines.
and profitable agricultural systems, situated principally along the Mediterranean coastline, are suffering from a tremendous problem of groundwater depletion and saline intrusion. Accordingly, only 42 per cent of Spanish coastal aquifers are not affected by the problem of salt water encroachment, and 51 hydrogeologic systems are being overexploited (MOPTMA, 1995; MMA, 1998). Among the hydrogeologic systems affected by saline intrusion and groundwater depletion stands out the "Campo de Dallas" if we consider both the volume of water resources being pumped and the importance of the farming system being fed by the aquifer.
cur (Hamill & Bell, 1986). This is the case of the acuifers situated along the Mediterranean border in Spain.
This situation has been the result of a lack of integrated planning and management of the resource and its use. This paper analyses the problem of overexploitation of groundwater resources in the "Campo de Dalias", the most intensive agricultural area in Spain.
In a country arid and dry, like Spain, the transformation of dry land into irrigated agricultural land traditionally has been seen as an important progress. As a consequence, Spanish water policy, especially during the Franco's period, focused on the expansion of irrigated farming systems in areas with very low annual rainfall. This policy directed its attention to enlarge the supply of water without a good irrigation water management. From mid-century Government subsidies and financial help contributed significantly to the rapid growth of irrigated agriculture in regions with a severe dry climate. The new farming systems created were based on the exploitation of groundwater resources at a far greater rate than they were being replenished, resulting in lower piezometric levels. As a consequence, currently, Spanish most intensive
(-) Department of Social Work and Sciences for Human Development, Tamaulipas University, Mexico.
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Firstly, it examines the process of intensification of the Campo de Dalias' agricultural system and the concomitant process of water depletion. Secondly, the paper goes on to analyse the causes of the regulatory law failure to cut down an excessive lowering of the water table. Finally, it analyses the nonsustainable management of groundwater resources as a result of farmer's production maximizing values. At a methodological level, the investigation (carried out between 1996 and 1997) is based on in-depth interviews. On the one hand, relevant actors at the regional and central Government level, along with those responsible for scientific research in the area of hydrogeology, were interviewed. On the other hand, in-depth interviews with fifty farmers were conducted in the "Campo de Dalias". Respondents were selected in five municipali-
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ties according to agrarian structure and the age structure of farmers.
THE INTENSIFICATION OF AGRICULTURE IN mE CAMPO DE
DALlAs The Campo de Dalias, situated in the south-eastern corner of Spain, in the province of Almeria, occupies an area of 33,000 hectares, and is probably the most productive and profitable agricultural zone of Spain. This is the area of Spain with the highest concentration of plastic greenhouses, mainly devoted to the production of horticultural crops during the winter season. On the one hand, the Campo de Dalias is one of the warmest areas of Spain. Average annual rains here are around 225 mm (ITGE, 1989). Hydrologically, this area lacks of surface water, and edafologycally, the land is characterized by severe soil erosion and salinity. Consequently, up to about the middle of this century this region remained uncultivated. This area was for centuries an uncultivated land that served only as a grazing place for the flocks of sheep and goats coming down from the nearby mountains every year during the winter season. On the other hand, this is one of the warmest areas of Spain. Temperatures in winter are warm enough to allow the production of horticultural crops and groundwater sources are relatively abundant. Therefore, in 1928 the first wells were constructed and exploited by using electric pumps; and, in 1934 the San Fernando's channel, from the Adra's river to El Ejido, was finished, putting into cultivation almost 1,000 hectares (IARA, 1993). Moreover, the particular climatic conditions of this area prompted Central Government intervention. In 1941 the Campo de Dalias was declared "zone of national interest" by the National Institute of Colonization (INC)(I). Between 1953 and 1977 seven plans for the transformation of uncultivated land into irrigated land were approved (IARA, 1993). Then, Government intervention contributed substantially to Campo de Dalias' agricultural transformation, although public intervention soon was outstripped by private initiative. From the 1950s onwards, new technologies, precisely adapted to the specific climatic conditions of this area, were introduced. Technological innovations, in the vanguard of technological advance, were aimed to mitigate the limiting factors (the poor quality of soil and the lack of water), obtaining the maximum advantage from sunshine (Losada and L6pez-Galvez, 1997). In 1957, the INC decided to experiment in this area a technique used from the Nineteenth century in Granada's coastline, the "enarenado". This technique helped to solve one of the limiting factors of this zone, soil salinity, spreading rapidly onto the area. From the early-1960s the use of plastic greenhouses contributed substantially in obtaining the maximum advantage from sunshine, the area covered by plastic greenhouses rising from
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1,000 hectares to almost 20,000 hectares between the early-1970s and the late-1990s. In the 1970s new technical innovations (drip irrigation and fertirrigation) were introduced, the use of water per hectare being halved in the last two decades (IARA, 1993). These innovations were generalized during the 1980s and early 1990s. In the short span of two decades, the Campo de Dalias, one of the less-endowed agricultural regions of Spain, became one of the most intensive, productive and profitable farming systems. The concentration of plastic greenhouses rapidly mushroomed from the mid-1960s. Horticultural production more than trebled between 1975 and 1996, and horticultural exports increased twelvefolds between 1980 and 1996. Likewise, the population of this area, which had remained stagnant until mid-century, nearly trebled between 1950 and 1991 (Izcara Palacios, 1997 & 1998). However, the economic miracle of the Campo de Dalias has been based upon the unsustainable exploitation of its natural resources. Between 1980 and 1995 the level of groundwater abstraction increased from 87 Hm3 to 132 Hm3, more than doubling the level of groundwater replacement by rainfall (see figure 1). During the last decades, the sudden growth of agriculture, the inappropriate location and design of wells, overpumping and the steady increase of groundwater withdrawals, both for irrigation and human consump-
140
120
100
('I) 80 E :J:
60
40
20
0 ,-
se. 0 co ~
1--Groundwater abstraction ----Renewable resources
Figure 1 - Exploitation of non-renewable resources from the Campo de Dalias' aqUifers 0980-1995). Source: elaboratedfrom rrGE, 1997.
(I) In the areas declared as "zone of national interest" was established a financial system very favourable for fanners. Accordingly, works of general interest (principal channels, etc.) were completely financed by the Government; works of common interest (secondary irrigation networks, etc.) were financed in a 60 per cent; and fmally, works of private interest were financed in a 30 per cent. Moreover, fanners in these areas also had very favourable loans.
MEDIT N° 1/2000
tion, have damaged farming's productive base, resulting in lower piezometric levels and seawater intrusions OTGE, 1989). The introduction of modern ways of resource utilization, in the vanguard of technological advance, has contributed to increase the efficiency in the use of water. However, at the same time, has encouraged an intensive and extensive expansion of farming activities, and, as a result, a growing use of groundwater resources. The total annual renewable fresh water available in the area is estimated at a fixed rate of less than 60 cubic hectometers per year, being annually pumped more than 130 cubic hectometers. Therefore, resource exploitation is reaching levels far exceeding aquifers rates of renewal.
THE CAMPO DE DALlAs' HYDROGEOLOGIC SYSTEM
The Campo de Dallas is hydrogeologically a complex dominion. According to the GeoMinero Institute OTGE, 1989) in this area could be differentiated several hydrogeological units. In the nor-east sector are situated the Superior Central Aquifer (ASC) and the accidental Inferior Aquifer (Ala). In the nor-west sector are situated the Nor-east Inferior Aquifer (AIN) , the Intermediate Nor-east Aquifer (A.lt.N) and the Nor-east Superior Aquifer (ASN). The remainder aquifers are much smaller. These aquifers are superimposed one on top of the another, existing recharges and discharges among them. The first aquifers being exploited were the shallowest ones (ASC and ASN), because they were much easier to be exploited. But, excessive overpumping led to an acute process of sea water intrusion. As a result, the deepest aquifers (Ala and AIN) started being exploited. Nowadays, in the superficial aquifers (ASC and ASN) the level of groundwater abstraction is lower than the level of groundwater replacement by rainfall, because water quality is lower than required by crop production or human consumption. By contrast, the deepest aquifers (Ala and AIN), which are currently overpumped, are being affected by a worrying lowering of the water table. Consequently, these aquifers are starting being affected by salt water encroachment in specific areas OTGE, 1989; MMA, 1998). As can be seen from the table 1 in the early 1980s water pumping from the shallowest aquifers (ASC, ASN and AltN) was higher than water withdrawals realized from the deepest ones (Ala and AIN). However, soon water pumping from the former aquifers was substantially reduced at the expense of the latter. From the early 1980s until the mid-1990s water pumping from the shallowest aquifers has been reduced to one third whereas water withdrawals from the Ala and AIN has been more than doubled and trebled, respectively.
THE ENACfMENT OF MEASURES TO REDUCE OVERPUMPING
In 1982 a report made by the GeoMinero Institute had alerted about the overexploitation of groundwater re-
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sources in the Campo de Dallas, launching the hypothesis of saline intrusion, that later was confirmed. Consequently, in the mid-1980s, in order to tackle down the problem of groundwater depletion and saline intrusion, the Spanish Government issued specific measures for this area. According to Spanish water laws of 1866 and 1879, only surface waters were under State control; on the contrary, groundwater was a private property. Only when the 1879 Water Law was overhauled by the passing of the 1985 Water Law groundwater was declared "public dominion". However, under the 1985 Water Law preexistent property rights over groundwater were guaranteed (Perez, 1993). In the case of the Campo de Dallas farmer's property rights over groundwater were previous to the passing of the 1985 Water Law. Because of this, the Spanish Government does not have the legal right to limit water abstraction from the mentioned aquifers. Therefore, the only way to cut down excessive overpumping was restricting land use. In May 1984 were passed two laws, the Royal Decree 117/1984 and the Law 15/1984. According to these laws farmers were not allowed to increase farm land under irrigation. Two years later was passed the Royal Decree 2618/1986 declaring the aqUifer provisionally overexploited. However, farmers' opposition to any kind of external interference in their activity has led to the failure of this policy. In the Campo de Dallas, unlike other well-endowed agricultural regions in Europe, half of the working population is engaged in agriculture. Farming is the mainstay of local economy and employment opportunities in off-farm activities are very scarce. The marked demographic growth of this area during the last four decades has been built upon a flourishing agriculture. Consequently, production maximizing values have strong currency amongst Campo de Dallas farmers, being overwhelmingly concerned with agricultural productivity. When both, central and regional Governments, issued specific measures to control land use in this area, farmers' opposition was very strong. Farmers adduced that in the past all this area was irrigated sometimes during the year. Therefore, there was not any reason to restrict the area that could be irrigated. Moreover, the enactment of restrictive laws, far from limiting the area under irrigation, has not even resulted in a reduction in the pace of transformation of new areas into irrigated land (L6pez Galvez and Losada, 1997). On the contrary, from the mid-1980s the area covered by greenhouses has soared. In 1984, when the laws prohibiting to increase irrigated farming were issued, there was 10,357 hectares of greenhouses in the Campo de Dallas. In 1991 the area covered by greenhouses had increased until 14,682 hectares (IARA, 1993). During the 1990s the concentration of greenhouses has continued raising at the same pace.
]\II:]) IT ~o J :WOO
The absolute incapacity of regional and centra l Governments to ho ld down the growth o f greenhouses, and the legal imposs ib ility to limit groundwater pumping have led to a continued worsening o f the problems of groundwater depletion and saline intrusion. In 1991, as a result of the 1986 declaration o f overexplo itation o f these aquifers, was created the "Central Committee o f Almeria's West Aquifer Users", w hich involved users' parti cipation in the management of water. Central Committee's objectives are to promote and study solutions aimed at preventing the definiti ve deterioration o f the aquifers. However, the Central Committee, representing overw helmingly farmers' interests, has not attacked the roots o f the prob lem. The Central Committee, emphasizing water savings resu lting from technica l innova tions, denies that irrigated agriculture is the main single factor contributing to groundwater depletion, when tIle farming sector is using more than 70 per cent o f ground water resources (lARA, 1993). Therefore, from the Central Committee is nor contemplated any change in farming practices as a solution to this problem. It is thought that the only possible solution to the problem will arri ve from the solidarity between water abundance and water scarcity regions (i. e. by means of water transfer from regions where water is relatively abundant). However, this solution is not only ve ly expensive and environmentally disruptive, also counts on the frontal oppositio n of the so ca lled water-rich regions.
FARMERS' PRODUCtW tST RATIONAI.E AND GROUNDWATEll
DEPLETION
In this area groundwater is administered by the "communities of irrigants", w hich are fonned by farmers owning one o r several wells. The most part o f fa rmers in the Campo de Da lias have property rights over groundwater and are members of one or more l'coml11unities of irrigants". Farnlers' property rights are materiali zed in the possession of a number o f hours o f water per day, being usually higher than the needs o f their crops. Land property is in the most part of cases associated to the property o f land. As a consequence, an adequate adnlinistration of wa ter resources in this area is not possible if fanners, grouped in "communities o f irrigants", w hich have a majority position at the Central Committee of Alm eria 's West Aqu ifer Users, are not deep ly concerned about the problem o f groundwater depletion , and do nor impose on themselves severe restrictions in the use of water.
THE MINIMIZATtON O F THE PllOBI.EM OF WAT ER
DEPI.ETtON
By contras!" w ith the institutional and technicians' d iscourse, w ho describes the problem of overexploitation of grounclwater resources as very severe and unsustainable, nor only in the long-term but also in the medium-
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term and short-term, farmers' discourse is quite optimistic. Farmers as a w hole, even considering that there are important variations of tone, deny that in the Campo de Dalias there is a problem o f wa ter sca rcity, at least in the short and medium terms. O n the one hand, there is a group o f farmers w ho consider that water is a sca rce resource, considering that probably in the futtlre the problem of water depletion could threaten Campo de Da lias ' agricultural system. How ever, this is only contemplated as a possibili ty in the long term. On the other hand, the most numerous group of farmers, openly denies the existence o f a prob lem o f groundwater dep letion or sal inization. Therefore, in farnlers' discourse there is a gradient expanding from the absolute nega tion o f the problem to a certain concern about excessive groundwa ter w ithdrawals. In this way, four discourses could be differentiated.
Walel; an abundant reSO~/.1-ce
The most rad ica l group o f farmers deny completely the ex istence of a problem o f water scarcity in this zone. They think that water resources are not only sufficient but abundant. Therefore, they consider that there is a real impossibility that water resources could be depleted in the futtlre, independently o f cl imatic conditions, greenhouses expansion, and so on. This group, around 15 per cent o f respondents, is co m-
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posed mainly of farm household heads with a successor, aged over 45 years old.
The drought menace A second group of farmers, around 2S per cent of respondents, at the moment they are very optimistic because during 1996 and 1997 precipitations were relatively high. For them, only the lenghtening of droughts during a long period in the future could lead to a situation of water scarcity. In the south-east of Spain rainfall is not only much lower that the national average, also is distributed very irregularly during the year, pouring down in a torrential way. Consequently, this group of farmers are showing a certain concern about future water shortages resulting from the lack of rainwater. This group of respondents do not associate the interconnectedness between groundwater depletion and an excessive overpumping resulting from farming expansion and intensification. For them the problem of groundwater depletion is only the result of specific climatic conditions, away from farmers' hands. In their opinion farming does not deplete groundwater resources, the water table lowers down if it does not rain sufficiently, this situation being reversed by rainfall. This opinion is shared principally by the most aged farmers.
Water shortage: a perennial problem There is a third group of farmers, near a quarter of respondents, aged under 4S years old, who think that water resources are scarce in this area. In their opinion, water resources must be used efficiently, not exceeding crop water requirements. However, they are optimistic about the future. They consider that the problem of water scarcity far from being a new phenomenon, is a structural feature of Campo de Dalias' farming system, being a problem of the past, present and future. However, it is not seen as an excessively worrying problem. They consider necessary to continue improving irrigation efficiency towards the introduction of new technologies, but at the same time they are very confident that water scarcity will never undermine Campo de Dallas' farming system.
The invisibility of groundwater resources Finally, the most concerned group about the problem of water depletion is formed by farmers owning small plots of irrigated land, principally young but also by older farmers without a successor. This group of farmers, including more than one third of respondents, do not contemplate the that the lack as a current problem. However, they think that in the future water scarcity could undermine farming's productive base. By contrast with the visibility of surface waters the invisibility of groundwater resources creates in this group
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of farmers a preoccupation about groundwater depletion and a possible lack of water for irrigation.
FARMERS' LACK OF CONCERN
The lack of concern of farmers about the overexploitation of the aquifers owes to four factors: In the first place, farmers are clearly aware of the mushrooming of the area covered by plastic greenhouses in the last decades. However, farmers do not link the expansion of irrigated agriculture with the depletion of groundwater resources. They consider that the introduction of new ways of resource utilization (Le. drip irrigation and fertirrigation) has increased dramatically the efficiency in the use of water. New technologies have halved the use of water per hectare; notwithstanding, the improvement of irrigation efficiency has not offset the continuous growth of irrigated farming and the intensification of farming practices. But farmers, principally those older than 50 years old, tend to overestimate water savings. They frrmly think that as a result of the generalization of drip irrigation water consumption in the farming sector is now much lower than in the past. This belief contrast with young farmers' opinion, who consider that water consumption is at present higher than in the past. Therefore, the higher indifference of older farmers about the problem of groundwater depletion is the consequence of their over-estimation of water savings resulting from the substitution of surface irrigation by drip irrigation. In the second place, in the short span of three decades the Campo de Dalias has passed from being one of the poorest agricultural areas of Spain to constitute the richest farming system. Technological innovations have overcome edafoclimatic limitations, converting the Campo de Dalias in the backbone of the provincial economy. This area contributes to almost 70 per cent of Almeria's foreign trade, and this province, one of the poorest of Spain four decades ago, now, as a result of irrigated farming, has one of the lowest unemployment rates (Izcara Palacios, 1997). Therefore, the strong dependency of local economy in the farming sector contributes to generate in farmers an indifference towards the problem of water scarcity. They think that the lack of water resources can not curb the development of a sector of the importance of irrigated agriculture. In the worst case, farmers are confident of Government intervention to solve the problem of water depletion towards water importation from other water abundance regions. Moreover, a number of farmers think that seawater desalting could be the definitive solution. In the third place, principally young farmers are very concerned about the loss of water resources caused by the obsolescence of water distribution networks. Accordingly, in a study carried out in 1988 the loss of water in the irrigation networks was estimated in 21 per
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cent (Losada & L6pez-Gc11vez, 1997). Therefore, farmers believe that if water distribution networks were repaired water savings would be enormous. However, they are not worried as a result of their concern about groundwater depletion, but because water is expensive and they have to pay also for the amount of water lost in the distribution networks. For example in Adra, situated in the western part of the Campo de Dalias, in 1997 water distribution networks were restructured to avoid the loss of water. As a consequence, the majority of farmers of this zone considered that the betterment of irrigation infrastructures would eliminate the problem of water scarcity. Finally, the most part of farmers interviewed do not think that water scarcity is a problem of the zone where their greenhouses are situated. However, there is an inclination to consider that groundwater depletion is a worrying problem in other areas. On the one hand, farmers whose greenhouses are situated in the central and eastern part of the Campo de Dalias tend to see the problem as exclusive of the "Campo de Nijar", situated in the eastern part of Almeria. On the other hand, farmers whose farms are situated in the western part of the Campo de Dallas think that the problem of water depletion affects only to Campo de Dalias' central and eastern zones. Therefore, neither the former nor the later contemplates groundwater depletion as an environmental problem their surroundings.
CONCLUSION
In the Campo de Dallas unrestrained water demand, resulting from the rapid growth of irrigated agriculture and population explosion, has outstripped the amount that can be sustainably provided causing lower piezometric levels and seawater intrusions. Mismanagement of water resources has resulted in environmental damage very difficult to control and reverse. Present deteriorating situation cannot last unchecked any longer because the continuous mining of non-renewable groundwater resources is menacing farming's productive base. Water conservation measures such as seawater desalting to provide drinking water, restructuring of water distribution networks and urban wastewater management, have started being implemented. However, these measures are insufficient. A sustainable planing and management of the aquifers requires water demand for irrigation to be dramatically reversed. Water importation from water abundance regions is not a feasible solution, and the development of an extensive seawater desalting technology is economically unsound. Moreover, water management practices that increase irrigation efficiency contribute to palliate the problem but do not solve it. Therefore, the sustainability of irrigated agriculture will be jeopardized if in the short term the Campo de Dallas' agricultural system is not restructured. Users' participation in the manage-
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ment of water keeps the problem unchecked as the decision-making process is dominated by farmers' interests. Farmers, overwhelmingly concerned with agricultural productivity, are very reluctant to adjust farming practices taking ecological considerations into account. Farmers, whose perception of the problem is inaccurate, do not accept that environmental factors could interfere with agricultural production, and as long as their crops remain competitive they will reject regulatory controls intended to restrain farming activities. However, agricultural production can only be sustained on a long term basis if the agricultural resource base is restored, sustained and enhanced, regulatory controls becoming essential. The implementation of regulatory controls has failed not because of the lack of technical or administrative capacities but as a result of farmers frontal opposition to any external interference in their activity. However, in the future hard decisions have to be taken and these measures have to be backed up by farmers. Therefore, it is pressing to change farmers' wrong perceptions of the problem of groundwater depletion. Younger farmers' perceptions could be changed if they were accurately informed of the severity of the problem, also older farmers without a successor could show receptiveness to new information. However, it will be very tough to change the attitudes of farm household heads with a successor. •
REFERENCES
Hamill L. and Bell F.G. (1986) - Groundwater Resource Development, Butterworths, London.
IARA (1993) - Plan de transformaci6n y estudio de posibles actuaciones en la comarca del ponieme de la provincia de Almeria, Junta de Andalucia. 5 Volumes.
ITGE (1989) - Sintesis Hidrogeol6gica del Campo de Dalias (Almeria). Propuesta de primeras actuaciones de investigaci6n y gesti6n. Ministerio de Industria y Energia, 147 p.
ITGE (1997) - Evoluci6n temporal de 105 aspectos esenciales del conocimiento que mas pueden interesar para la planificacion y gestion de los acuiferos del Campo de Dalias. (Paper presented at the symposium on water resources and farming in Almeria, C.I.F.A., La Mojonera, A1meria, 17 of April of 1997).
Izcara Palacios S.P. (1997) - Modemizacion de la agricultura espanola y contaminacion de las aguas en relaci6n con la aplicacion de la politica medioambiental de la Union Europea (PhD thesis) 435 p.
Izcar.l Palacios S.P. (1998) - Farmers and the Implementation of the EU Nitrates Directive in Spain, Sociologia Ruralis, 38 (2), 146-162.
L6pez-Galvez). and Losada A. (1997) - Uso del agua de riego en Almeria p. 143-176, in W.AA. La economia del agua en Espana. Fundacion ArgentariaVisor, Madrid. 237 p.
Losada A. and L6pez-Galvez). (1997) - Gestion del regadio en el Campo de Dalias p. 33-72. in]. L6pez-Galvez and ].M. Naredo (eds.), La gestion del agua de riego, Fundaci6n Argentaria-Visor, Madrid, 406 p.
MMA (1998) - Libro blanco del agua en Espana, Madrid. 847 p.
MOPTMA (1995) - El Iibro blanco de las aguas subterraneas, Serie Monografias, Madrid, 135 p.
Perez E. (1993) - Estudios juridicos sobre propiedad, aprovechamiento y gestion del agua, Serie Monografias, Madrid, 196 p.
MEDlT N° 1/2000
AMELIORATION DE L'EFFICACITE D'UTILISATION DE L'EAU CHEZ LE BLE PAR
Q uand le sol s'asseche, son potentiel hydrique s'abaisse
et l'extraction de l'eau par les racines devient difficile. A ce moment la plante regIe sa transpiration en fonction de ce qu'elle peut absorber au niveau racinaire. Cet ajustement se traduit par une fermeture plus ou moins complete des stomates. Les consequences de cette reaction sur le rendement sont defavorables, vue la correlation entre le rendement et la capacite d'assimilation de la plante. En regions arides et semiarides, les pertes en eau par evapotranspiration sont extremement importantes, en raison de la temperature elevee, de l'ensoleillement et du vent.
L'EMPLOI D' ANTITRANSPIRANTS
M'BAREK BEN NACEUR - MONCEF BEN SALEM (*)
ABSTRACI'
Trials under controled and field conditions were carried on wheat (Triticum durnm Desf.) to study the effect of antitranspirant (linseed oil) on water management of plant subjected to water deficit. The influences of the antitranspirant on foliar water potential, hydration of different plant parts, water use efficiency and soil moisture were discussed. The critical antitranspirant rate suitable to cereal which preserves moisture without inducing foliar damage was detennined. The gain on foliar hydration, at the treatment compared to the control, fluctuated from 12 to 16%, according to the antitranspirant rate used. Eventhough the stems were less sensitive than foliar, they got an improvement from 4 to 7.5%. The water use efficiency showed also a better improvement, by use of antitranspirants, fluctuated from 5 to 20% under controled and from 3 to 7% under field conditions.
RESUME
Des essais en milieu controle et au champ ont ete conduits sur ble dur (friticum durum Desf.) pour etudier l'eJ!et d'un antitranspirant de type film (huile de lin) sur la geslion de I'eau chez les plantes soumises a un deficit hydrique. L'influence de I'antitranspirant sur le potentiel hydrique joliaire, I'hydratation des differents organes de la plante, I'efficacite d'utilisation de I'eau et I'humidite du sol, en fin de I'experience, ont ete discutees. La dose optimale d'antitranspirant qu 'il jaut utiliser sur ble, celle qui induit une preseroation de I'humidite sans pour autant provoquer des degats au niveau des jeuilles a ete determinee. Le benefice d'hydratation joliaire des traitements par rapport au temoin varle de 12 a 16%, selon la dose d'antitranspirant utilisee. Bien que moins sensibles que les jeuilles aux eJ!ets de I'antitranspirant, les tiges ont, elles aussi, montre une amelioration de leur pourcentage d'hydratation de 4 a 7.5%. L'efficience d'utilisation de I'eau est amelioree par I'emploi d'antitranspirant de 5 a 20%, en chambres de cultures et de 3 a 7% en pots de vegetation places au champ.
plante, tout le reste est perdu par les stomates (Coudret et Ferron, 1977). Plusieurs chercheurs ont essaye de reduire la transpiration et preserver l'eau au niveau des feuilles et des racines. Nous citons Neumann (1974) sur haricot, Ferron et Costes (1977) sur vigne et sur melon, Barkley (1986) sur mats doux; EIBory (1988) sur mandarinier; AI-Kay'Ali (1990) sur pecher et olivier, et Zowain et Narang (1991) sur ble. Les resultats sont parfois contradictoires du fait de la multiplicite des protocoles experimentaux utilises pour etudier l'effet des antitranspirants. Le present travail tente de caracteriser l' effet combine de la secheresse et des antitranspirants sur les parametres physiologiques du ble, soumis a un deficit hydrlque et vise l'amelioration
Pour limiter la perte en eau, on pourrait intervenir au niveau du sol et/ou au niveau de la plante. Au niveau du sol, le recours aux techniques permettant d'emmagasiner (travail et amendement organique du soO, et d'economiser l'eau (application de methodes limitant l'evaporation du sol, notamment le recouvrement des rigoles par des films plastiques et l'utllisation des canalisations en polyveny1chlorure: PVC) et le choix d'un systeme d'irrigation adequat pourraient eviter des pertes en eau considerables et proteger les plantes d'une penurie.
de l'efficacite d'utilisation de l'eau par l'emploi de ces antitranspirants.
Au niveau de la plante, bien que la reponse au deficit hydrique soit immediate et englobe plusieurs mecanismes (Levitt, 1980), si l'on veut economiser de l'eau c'est sur les stomates qu'il faut agir, car 1% seulement de l'eau absorbee par les racines, est retenu dans la
(*) Institut National de la Recherche Agronomique de Tunisie, Ariana, Tunis.
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MATERIEL ET METHODES
Materiel vegetal
Les essais ont porte sur une varlete de ble dur (Triticum durum Desf. cv. Khiar). Cette varlete est issue du croisement Chen "S" X Alter 84 realise au Mexique (C.I.M.M.Y.T.) et introduite en Tunisie en 1987. La selection de la lignee est effectuee a l'INRAT et elle est inscrlte au catalogue officiel en 1993 (Slama, 1996). La varlete Khiar a ete choisie apres testage de 13 varietes quant a leur efficience d'utilisation de l'eau. Cette variete a un cycle de developpement moyen (c'est une varlete demi-precoce), une bonne production en conditions favorables et une bonne efficacite d'utilisation de l'eau (Maamouri et al., 1988; Paul et al., 1996).