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1 2 Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean 3 basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) 4 techniques and relate it to the physical characteristics and irrigation management of four Mediterranean 5 irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water 6 inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or 7 estimated in each district. Soil salinity (EC e ) maps were obtained through electromagnetic induction surveys 8 (EC a readings) and district-specific EC a -EC e calibrations. Gravimetric soil water content (WC) and soil 9 saturation percentage (SP) were also measured in the soil calibration samples. The EC a -EC e calibration 10 equations were highly significant (P < 0.001) in all districts. EC a was not significantly correlated (P > 0.1) with 11 WC, and was only significantly correlated (P < 0.1) with soil texture (estimated by SP) in Spain. Hence, EC a 12 mainly depended upon EC e , so that the maps developed could be used effectively to assess soil salinity and 13 its spatial variability. The surface-weighted average EC e values were low to moderate, and ranked the 14 districts in the order: Tunisia (3.4 dS m

Field experiments were conducted for 3 years from 2000 to 2002 to assess proportional crop yield differences obtained under conventional deficit irrigation (CDI) and partial root zone irrigation (PRI) practices, compared with full irrigation (FULL) where plant water requirements were fully met. The experimental crops included vegetables (tomato and pepper), field crops (maize and cotton) and citrus. The fruit yield of greenhouse-grown tomato with FULL irrigation was higher than with PRI (7-22% lower) but was not significantly different. The PRI treatments had 7-10% additional tomato yield over CDI receiving the same amount of water. The yield of pepper, however, decreased in proportion to the level of irrigation deficit with no increase of irrigation water use efficiency (IWUE). No seed yield decrease was evident for cotton with the deficit treatments (PRI and CDI) compared with FULL irrigation. Similarly, the PRI treatment did not give any yield benefit for maize compared with CDI. The ranking of fruit yields of mandarin, FULL > PRI > CDI, was the same as that of other crops; however, the differences were not significant. Although the deficit treatments (PRI and CDI) had as high as 39% increase in IWUE, compared with FULL treatment, some adverse effects on fruit quality were evident such as smaller size of fruits under the deficit treatments.

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Simulated annual values were in general more accurate than simulated monthly values. 13 APEX predicted that improving irrigation management (change of irrigation system 14 and/or scheduling) will decrease N loads in IRF over current values by 45% (Akarsu), 15 40% (La Violada), and 8% (Sidi Rached). However, improved N fertilization only will 16 reduce N loads in IRF by 17% (Akarsu) or below 5% (La Violada and Sidi Rached). 17Improving irrigation management will increase IRF NO 3 -N concentrations by 19% in La 18 Violada and will decrease or will remain the same in the other two watersheds. APEX 19 simulations identified the main soils (shallow and low water holding capacity soils) and 20 crops (heavily fertilized or shallow-root crops) N polluters within the studied watersheds. 21Overall, APEX simulated that the improvement of irrigation performance was the best 22 management strategy to decrease off-site N pollution while maintaining or increasing crop 23 yields in the three studied Mediterranean watersheds. 24

This study attempts to find out the best-fit probability distribution function to low flows using the up-to-date data of intermittent and non-intermittent rivers in four hydrological basins from different regions in Turkey. Frequency analysis of D = 1-, 7-, 14-, 30-, 90- and 273-day low flows calculated from the daily flow time series of each stream gauge was performed. Weibull (W2), Gamma (G2), Generalized Extreme Value (GEV) and Log-Normal (LN2) are selected among the 2-parameter probability distribution functions together with the Weibull (W3), Gamma (G3) and Log-Normal (LN3) from the 3-parameter probability distribution function family. Selected probability distribution functions are checked for their suitability to fit each D-day low flow sequence. LN3 mostly conforms to low flows by being the best-fit among the selected probability distribution functions in three out of four hydrological basins while W3 fits low flows in one basin. With the use of the best-fit probability distribution function, the low flow-duration-frequency curves are determined, which have the ability to provide the end-users with any D-day low flow discharge of any given return period.