No abstract

In southern Hodna, an arid region of Algeria, the extension of irrigated agriculture and overexploitation of groundwaters have led to a rupture with traditional land use by pastoralism. Due to the arid conditions, groundwaters are the only water resources for man and irrigation. This study focuses on nitrate contamination of groundwaters and its increase since the last 40 years, on the basis of two archives and recent analyses. The chemical facies of waters is sulphate-chloride, the risk of salinity is moderate to large. The sodicity risk, as estimated by the SAR, is low due to the large salinity and the sandy soil texture. Nitrate contamination of deep groundwater is a clear evidence when recent data are compared to the historical data. From 1996 to 2008, the proportion of samples with NO 3 -concentrations larger than 50 mg/L increases from 24 to 61 %, the proportion of samples with NO 3 -concentrations larger than 100 mg/L increases from 12 to 27 %. The study points at a general contamination of aquifers from anthropic origin: phreatic water was already contaminated when pastoralism was dominant (1967); as population increased and irrigation agriculture developed with large use of N-fertilizers and organic amendments, contamination extended spatially and vertically to deep aquifer. To remediate this contamination, fertilizers should be fractionated and limited to plant requirements on the basis of soil and plant analyses. Excess of irrigation should be avoided. Soil surface should be continuously covered to prevent nitrate leaching. Secondly, more efficient irrigation techniques, such as localized irrigation, should be implemented, with adaptation of crop systems and fertilizer inputs to arid conditions. Farmers should then be trained; simultaneously, local agronomic references that are presently lacking should be acquired.

F 78000 Versailles RÉSUMÉ L'examen de l'organisation des argiles en relation avec le potentiel de l'eau ainsi que des mesures de conductivité hydraulique ont été réalisés sur des échantillons de montmorillonite préparés avec les cations Ca, Mg et Na, en présence de solutions diluées (10-3 M) et concentrées (1 M). Les résultats obtenus montrent que la teneur en eau varie linéairement avec l'E.S.P. (pourcentage de sodium échangeable). Ce n'est en revanche pas le cas de la conductivité hydraulique qui subit une chute brutale dès que E.S.P. < 10 p. 100. Les observations et mesures amènent alors les auteurs à conclure que les voies de circulation de la solution et les pores de rétention de l'eau présentent des tailles très différentes et ne correspondent pas aux mêmes sites du matériau. D'un autre côté, l'organisation et les propriétés hydriques des argiles Ca et Mg apparaissent peu modifiées par la concentration saline. C'est l'inverse qui se produit pour les smectites Na. On note alors que l'augmentation du gonflement se traduit par un abaissement de la conductivité hydraulique. Ces deux propriétés sont donc influencées de façon inverse par les potentiels osmotique et matriciel. Mots clés additionnels : Contrainte hydrique, rayon hydraulique moyen, microorganisation, quasi-cristal, feuillet, E.S.P., sols sodiques, argile biionique-argile Na, microscope électronique à balayage.

No abstract

A field study on a saline condition was carried out at agricultural farm of Deglet Nour date palm during the 2012 growing season. It focuses on the irrigation water management problem as affected by salinity in Oued Righ region (North Eastern Sahara, Algeria). To determine irrigation requirements a computer model based on the computation of reference evapotranspiration, crop coefficient, water holding capacity, leaching requirements and daily water use by date palm was used. The average annual amount of irrigation for a palm tree was varied from 145-218 m . This model was employed to improve water management practices by the farmers. The result shows that localized irrigation will, therefore, be more efficient than non-localized one (e.g., border irrigation) and it can reduce irrigation water up to 50%.