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.

52

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-

MEDIT N° 1/2000

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

53

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-

54

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-

55

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-

MEDIT N° 1/2000

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

56

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

MEOIT N° 1/2000

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-

57

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.

58

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).