AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: 2151-7517, ISSN Online: 2151-7525, doi:10.5251/abjna.2012.3.3.105.116 © 2012, ScienceHuβ, http://www.scihub.org/ABJNA Estimation of root-zone salinity using SaltMod in the irrigated area of Kalaât El Andalous (Tunisia) 1*Ferjani Noura, 2Dhagari Hedi and 3Morri Mabrouka 1Faculty of Sciences of Bizerte, 7021 Zarzouna Bizerte, Tunisia, University of Carthage 2Resources Management and Conservation Research Unit, National Agronomic Institute of Tunisia (INAT), 43 avenue Charles Nicolle, Cité Mahragène -Tunis 1002-Tunisia, University of Carthage 3Resources Management and Conservation Research Unit, National Agronomic Institute of Tunisia (INAT), 43 avenue Charles Nicolle, Cité Mahragène -Tunis 1002-Tunisia, University of Carthage *Corresponding author. E-mail adress: [email protected] ABSTRACT The objective of this study was to predict the root zone salinity in the irrigated area of Kalaât El Andalous using the SaltMod simulation model over 10 years. En general, the model predicts more or less similar values of electrical conductivity in the root zone. Highest electrical conductivity values equal to 7.7 dS m-1 would be reached during the irrigation season. Following the rains fall particularly during the winter season there would be a decrease of the soil salinity when the average minimum value of electrical conductivity would reach 3.1 dS m-1. This seasonal variation of root zone salinity was confirmed from the measured values. Investigations were made also to study the impact of varying drain spacing and drain depth on root zone salinity and water table depth and drain discharge. The simulation show that the decrease in the depth of the drain does not change significantly the root zone salinity which reaches 6.21 dS m-1 during the irrigation season and 3.67 dS m-1 during the non irrigated season. The depth of the drain can be reduced to 1.6 m without any damage to crops. A water table depth (Dw= 1.8 m) appears to be excessive and would increase the cost of system installation. We can see a slight reduction in drainage flow when the depth of the drain goes from 1.8 m to 1.2 m. A decrease of the drain depth decreases the water table level. Although there was no variation in root zone salinities due to change in drain spacing. The predicted drainage flows have registered an evolution related to the occurrence of irrigation and rainfall. This evolution was confirmed by observed values. In this study, calibration of SaltMod for water-salt balance parameters shows the reliable validity of the model for the local conditions. Key words: Root zone salinity; subsurface drainage; SaltMod; water table; drain discharge. INTRODUCTION mainly chloride, carbonates and sulphates of sodium, calcium and magnesium. There are various factors High soil salinity is a serious problem often that cause salinization which include natural or encountered in the arid and semi-arid regions of the inherent and human induced factors and these are world where there is insufficient rainfall to leach generally categorized into primary and secondary accumulated salts from the crop root zone, especially salinization respectively (Shrestha, 2006). Primary in irrigated areas. Other factors contributing to the salinization results from natural weathering of parent problem are high evaporative demand and shallow material (e.i rock and minerals) and is influenced by ground water which cause accumulation of salts at factors related to climatic, topographic, hydrologic, the soil surface. Since soil salinity imposes a stress and geologic and soil condition. Secondary on the crop, it results in decreased yields, and in salinization develops from mobilization of the stored some cases, complete crop failure (Bresler et al., salts in the soil profile and/or groundwater due to 1982). Soil salinization results from accumulation of human activities (Greiner, 1997) and practices which water soluble salts in the soil surface and sub-surface include cultivation of marginal lands, inappropriate Agric. Biol. J. N. Am., 2012, 3(3): 105-116 irrigation practices, deforestation and mining may reach values up to 8-10 dS m-1 near to the activities. south-east sebkha. The hydraulic conductivity varied between 0,2 cm/h and 3,6 cm/h. Soil pH ranged from In order to control and monitor the process of 7.3 to 8.9. The average bulk density of the soil is salinization for the purpose of recovering damaged 3 about 1.5 g/cm . Shallow water tables of about 1.4 m land and preventing further expansion, information on depth are present in the lower parts of the district, its spatial distribution, its trends of expansion and with very high salinity values that make them severity levels is essential (Metternicht, 2001). A unsuitable for irrigation or other municipal and number of computer models have been developed industrial uses. which are useful in making predictions of soil salinity accumulation. The SALTMOD program was Properties of SaltMod: In order to estimate the root developed to predict the long-term effects of varying zone salinity, the SaltMod simulation model was water management options on desalinisation or salt used. The hydro-salinity model "SALTMOD" accumulation in the soil of irrigated agricultural lands. developed by Oosterbaan and Pedrose de Lima The water management options include irrigation, (1989), computes the salt and water balance for the drainage, and the reuse of surface drainage water or root zone, transition zone and aquifer zone. It is a subsurface drainage water from pipe drains, ditches computer-based model for simulating the salinity of or wells for the irrigation. In addition, predictions are soil and drainage waters, water table depth, and made on the depth to water table, the salt drain discharge in irrigated agricultural lands under concentration of the groundwater and of the drain or different hydrological and geo-hydrological well water. In Tunisia, Kalâat El Andalous irrigated conditions, varying water management options, and district is one of the most affected area by salinization several crop rotation schedules. due to shallow groundwater level. The objective of The model was developed to make long-term the present study was to predict the root zone salinity predictions of the impact of water management using the SaltMod simulation model. In addition, programs (including drainage) on the level of the investigations were made to study the impact of water table, and on the salt content of the soil, varying drain spacing and drain depth on root zone ground water, and drainage effluent. It can also salinity and water table depth and drain discharge. assess the impact of re-used drainage water. It MATERIALS AND METHODS includes area frequency distributions of salinity. SaltMod can also simulate farmers’ agricultural and Site description: The irrigated area of Kalâat El water-management responses to changes in water Andalous (latitude: 36° 37’ and 37°2’ N; longitude: table depth and soil salinity, which, in turn, can 10°5’ and 10° 10’ E) is located on the end part of the influence the salt and water balance (Oosterbaan, Medjerda watershed (Figure 1), with an average 1998). The program aims at using input data that are annual ETP of 1400 mm and an average annual generally available, or that can be estimated with rainfall of 490 mm. Irrigation area of Kalâat El reasonable accuracy, or that can be measured with Andalous was launched since 1992 on a flood area. It relative ease. covers an area of 2905 ha and the effectively irrigated area changes from season to season and In order to use SaltMod some factors should be the maximum was observed in the summer (about determined first. Determination of the data required 1000 ha). The irrigated area was divided into plots of could be done by entering different values for 5 ha supplied by a flow rate of 3 l/s. All the irrigated leaching efficiency (Flr), and natural drainage (Gn) area was equipped by a pressurized irrigation into SaltMod until values that match the actual network and a subsurface drainage system with a measured soil salinity and water table depths are length of 180 m and a depth of 1.8 m and spaced at obtained. Some of the data used as input parameters intervals of 40 m. The irrigation water is taken from in SaltMod were estimated or determined with in situ, the Mejreda River. Irrigation water salinity ranges laboratory, while the others were calculated by the between 3.1 g/l and 2.5 g/l in winter and between 2.3 model. g/l and 2.4 g/l in summer. The drainage outlet is Measurements: This study was carried out from Jun below sea level, and the drainage waters are 2008 to May 2010 in a farm plot of 2.38 ha (170 m x discharged to the Mediterranean Sea through a 140 m) equipped by three subsurface drainage pipes pumping station (SP4). The soils have a fine texture, D1, D2 and D3 and by drip irrigation system. There ranging from silty-clay to clayey-silt. Most soils have -1 are two cropping seasons per year i.e. winter electrical conductivity values above 2 dS m , and 106 Agric. Biol. J. N. Am., 2012, 3(3): 105-116 Water shed of Mejerda Irrigated areas Wadi of Mejerda Governorate of Alegria Bizerte Tunisia Douar Amar Ben Hamda Bizerte Kalâat El Governorate of of Governorate Andalous Legends Watershed Douar boundary Khchim Sea Mediterranean Irrigated area Bridge of Bizerte Douar Gbar Ejjahli Ennahli Régional road Highway Delegation National Highway Délégation Sidi of Raoued THABET Linear hydrography Perennial stream Temporary stream Irrigated area Public Echelle: 1/120 000 Private Used water treated Urban area Garaat Ben Ammar Wetland Fig. 1. Irrigated area of Kalâat El Andalous (December to May) and summer (June to (Cucumis mela) (1 ha) and squash (Cucurbuta September) with a fallow season in between (October maxima) (0, 38 ha) and rain fed wheat occupy the to November).