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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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The N accumulation and growth of regularly watered soybean (Glycine max. L.) plants were compared with those grown under various durations of drought stress varying from 14 to 47 days (D). The stresses were imposed between the V 3 (three nodes) and R 7 (physiological maturity) growth stages. The stress was defined as either mild, moderate or severe, corresponding to (i) a single drought cycle from V3 to R2 (18 D) or R5 to R 7 (14 D), (ii) double cycle from V 3 to R 5 (33 D) or R2 to R 7 (29 D), and (iii) three continuous cycles from V 3 to R 7 (47 D), respectively. Plants were harvested at the R 7 stage (76 days after planting). The A-values measured by the non-nodulated plants under all treatments were similar (P < 0.05), indicating that the available amount of soil N was not changed by drought. However, the A-values assessed by the nodulated plants (which included the N2 fixed) differed significantly among treatments. Except under the longest stress condition, all plants (in both genotypes) absorbed similar amounts of soil N, but N2 fixed in the nodulated plants differed significantly among treatments. The regularly-watered plants derived the highest amount (68 mg plant -t) and proportion (46.1%) of N from fixation, and the water stresses resulted in significant reductions in N 2 fixed. Although the growth of both nodulated and non-nodulated plants was adversely affected by water stress, this was not as great as was the effect on N2 fixation. Nitrogen fixation was the most sensitive parameter to drought, followed by plant growth, and the least sensitive was soil N uptake.

Displacement of chloride during infiltration was studied using soil columns for two cases: chloride initially spread on the soil surface; and chloride initially mixed with the soil. Chloride was applied as CaCl2 labeled with 36Cl. Its activity in counts per minute was scanned with a GM counter along a 2.5‐cm wide window slit in the columns. In conjunction with the chloride activity measurement, gamma‐ray attenuation measurement was used for monitoring the water content distribution during the simultaneous flow of chloride and water. Treatments included different levels of initial soil water content and different levels of water saturation at the soil surface during infiltration. With a numerical method the equations describing vertical water flow and miscible displacement of chloride were solved simultaneously. Experimental and calculated chloride distributions were in agreement. Chloride apparent diffusion coefficients estimated for pore water velocities less than 0.01 cm min‐1 were nearly equal to that for moleculer diffusion only. Initial soil water content did not influence the depth of chloride displacement for a given quantity of water infiltrated; whereas, keeping the water content at the soil surface below saturation resulted in a deeper and more complete displacement of chloride.