Managing the water balance of The Fayoum Depression,Egypt

A study of the water balances of The Fayoum irrigated lands and Lake Qarun was made to investigate the management of the irrigation system and the efficiency of irrigation water use. The two water balances are strongly interrelated. The drainage flow to Lake Qarun and the water level of the Lake are in delicate balance. A rise in Lake level causes the inundation of adjacent land. Management of The Fayoum water balance assumes control over irrigation water flows, but this control has technical and organizational limitations. Also discussed is the influence of irrigation practices in The Fayoum on the water balance (e.g., the autumn flushing of fields and farmers' preference for not irrigating at night in winter). Notwithstanding a high overall efficiency, irrigation efficiency during the winter is low. The reasons for this are given, together with the constraints against improving system management. Improved uniformity of the division and application of irrigation water will enable a better technical control of flows and will result in better water management in The Fayoum. Abbreviations: FID — Fayoum Irrigation Department, 1 feddan (fe) — 0.4 ha, 1 mcm — 1 million cubic metres: an average annual flow of 3.17 m³/s gives 100 mcm, m³/fe.year — supplied volume (m³) per surface area (fe) per year: 1000 m³/fe.year equals 240 mm/year, MSL — Mean Sea Level     

Water use efficiency and economic feasibility of growing rice and wheat with sprinkler irrigation in the Indus Basin of Pakistan

With a population of more than 150 million, Pakistan cannot meet its need for food, if adequate water is not available for crop production. Per capita water availability has decreased from 5600 m³ in 1947 to 1000 m³ in 2004. Water table has gone down by more than 7 m in most parts of the country. Present need is to identify and adopt measures, that will reduce water use and increase crop production. This study was conducted in farmers’ fields during 2002–2004 to evaluate the water use efficiency and economic viability of sprinkler irrigation system for growing rice and wheat crops. Yields and water use were also measured on adjacent fields irrigated by basin flooding, which were planted with the same crop varieties. Sprinkler irrigation of rice produced 18% more yield, while reducing consumption of water to 35% of that used in the traditional irrigation system. Sprinkler irrigation of wheat resulted in a water use efficiency of 5.21 kg of grain per cubic meter of water used compared to 1.38 kg/m³ in the adjacent flooded basins. Benefit–cost analysis showed that adoption of rain-gun sprinkler irrigation for rice and wheat is a financially viable option for farmers. While these findings show large potentials for improving water use efficiency in crop production they also indicate that a large portion of the water applied in traditional flooded basin irrigation is going to groundwater recharge, which has high value near large cities which draw their water from the aquifer.     

Seasonal on-farm irrigation performance in the Ebro basin (Spain): Crops and irrigation systems

Irrigation performance assessments are required for hydrological planning and as a first step to improve water management. The objective of this work was to assess seasonal on-farm irrigation performance in the Ebro basin of Spain (0.8 million ha of irrigated land). The study was designed to address the differences between crops and irrigation systems using irrigation district data. Information was only available in districts located in large irrigation projects, accounting for 58% of the irrigated area in the basin. A total of 1617 records of plot water application (covering 10,475 ha) were obtained in the basin. Average net irrigation requirements (IR_n) ranged from 2683 m³ ha⁻¹ in regulated deficit irrigation (RDI) vineyards to 9517 m³ ha⁻¹ in rice. Average irrigation water application ranged from 1491 m³ ha⁻¹ in vineyards to 11,404 m³ ha⁻¹ in rice. The annual relative irrigation supply index (ARIS) showed an overall average of 1.08. Variability in ARIS was large, with an overall standard deviation of 0.40. Crop ARIS ranged between 0.46 and 1.30. Regarding irrigation systems, surface, solid-set sprinkler and drip irrigated plots presented average ARIS values of 1.41, 1.16 and 0.65, respectively. Technical and economic water productivities were determined for the main crops and irrigation systems in the Aragón region. Rice and sunflower showed the lowest productivities. Under the local technological and economic constraints, farmers use water cautiously and obtain reasonable (yet very variable) productivities.     

Assessing grain crop water productivity of China using a hydro-model-coupled-statistics approach. Part II: Application in breadbasket basins of China

We assessed the basin-scale crop water productivity (CWP) on staple grain crops, i.e. rice, wheat, maize, soybean, at major breadbasket basins of China over time periods of 1997-2004. The multiple-year average CWP was 1.06 kg m⁻³ for the selected basins (equivalents of 946 m³ water consumption in producing 1 metric ton of crop economic yield), varying from 0.97 kg m⁻³ to 1.18 kg m⁻³. Of all the water consumed in crop production, irrigation water contributes 28-41%, while soil-stored precipitation contributes 59-72%, confirming the crucial yet hitherto under-estimated role played by green water in total crop yield formation. The blue water depletion rate ranges from 0.48 to 0.87, with most of the basins exceeding 0.50, while the green water depletion rate from 0.39 to 0.85, with the majority of basins being beyond 0.60. We conclude that both blue and green water shortage will contribute to water scarcity in grain crop production. The mission of ensuring China's food security will entail multiple trade-offs among water security, ecosystem conservation, environment protection, and human development with increasing challenges in the years to come. However, increasing water productivity through research innovation and technological upgrades at river basin scale is a key to mitigating water stress that may be caused by increasing food production in the coming decades.     

Different drip irrigation regimes affect cotton yield, water use efficiency and fiber quality in western Turkey

Decreasing in water availability for cotton production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant cotton varieties or water management. A field trial was conducted to observe the effects of different drip irrigation regimes on water use efficiencies (WUE) and fiber quality parameters produced from N-84 cotton variety in the Aegean region of Turkey during 2004 and 2005. Treatments were designated as full irrigation (T₁₀₀, which received 100% of the soil water depletion) and those that received 75, 50 and 25% of the amount received by treatment T₁₀₀ on the same day (treatments T₇₅; T₅₀ and T₂₅, respectively). The average seasonal water use values ranged from 265 to 753 mm and the average seed cotton yield varied from 2550 to 5760 kg ha⁻¹. Largest average cotton yield was obtained from the full irrigation treatment (T₁₀₀). WUE ranged from 0.77 kg m⁻³ in the T₁₀₀ to 0.98 kg m⁻³ in the T₂₅ in 2004 growing season and ranged from 0.76 kg m⁻³ in the T₁₀₀ to 0.94 kg m⁻³ in the T₂₅ in 2005 growing season. The largest irrigation water use efficiency (IWUE) was observed in the T₂₅ (1.46 kg m⁻³), and the smallest IWUE was in the T₁₀₀ treatment (0.81 kg m⁻³) in the experimental years. A yield response factor (k_y) value of 0.78 was determined based on averages of two years. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use for treatments. Fiber qualities were influenced by drip irrigation levels in both years. The results revealed that well-irrigated treatments (T₁₀₀) could be used for the semi-arid climatic conditions under no water shortage. Moreover, the results also demonstrated that irrigation of cotton with drip irrigation method at 75% level (T₇₅) had significant benefits in terms of saved irrigation water and large WUE indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25.0% saving in irrigation water (T₇₅) resulted in 34.0% reduction in the net income. However, the net income of the T₁₀₀ treatment is found to be reasonable in areas with no water shortage.     

Water requirements for salt control in rice schemes in the Senegal river delta and valley

The paper estimates the water requirements for salt control in rice schemes located on saline soils in the Senegal river delta. When the fields are not cultivated, salts are transported to the top soil by capillary rise from the very saline and shallow ground water table. During the irrigation season, the large quantity of irrigation water adds additional salt to the fields. If the percolation rate of the soil is small, salts will have to be removed from the schemes by flushing the standing water from the fields when the salinity of the water reaches the threshold value of 1.5 ds m^–1. The results indicate that if the schemes are located on the river banks (fondé), flushing at the beginning of the season and the percolation losses throughout the season may be sufficient to keep the salts out of the root zone. On the less permeable soils in the depressions (hollaldé), an extra flushing is required to evacuate enough salts from the fields during the irrigation season. In total about 2,300 m³ ha^–1 of water may be needed for flushing. If flushing is not practised, the schemes have to be abandoned after a few years of cultivation due to build-up of soil salinity.     

Loquat as a crop model for successful deficit irrigation

During three consecutive seasons, two different deficit irrigation strategies were compared with control fully irrigated trees regarding their capacity to induce early bloom and harvest in “Algerie” loquat. The first strategy, a continuous deficit irrigation strategy, consisted in a uniform reduction of 20% water needs through the entire season; the second strategy, a regulated deficit irrigation approach, while accounting for the same global reduction of 20% loquat water needs, concentrated water shortages after harvest from mid-May through the end of August. Regulated deficit irrigation resulted more successful. Postharvest regulated deficit irrigation advanced full bloom 10–20 days depending on the season. Such enhancement led to more precocious and valuable yield, with an average increase of fruit value of 0.21 € kg⁻¹. The effects of continuous deficit irrigation were less noticeable and average fruit value was increased 0.08 € kg⁻¹. Yield and fruit quality were not affected for the different deficit irrigation strategies. Water savings established around 1450 m³ ha⁻¹ year⁻¹. Deficit irrigation rose water use efficiency up to more than a 40%.     

Effects of timing and duration of brackish irrigation water on fruit yield and quality of late summer melons

Brackish water (7 dS m⁻¹) is frequently utilized to drip-irrigate crops in the Negev desert of Israel, the practice being to use deep sandy soils (96% sand) to avoid soil salinization. When muskmelon (Cucumis melo L.), a moderately salt-sensitive crop species, was grown using brackish irrigation under these conditions, yields declined due to a significant reduction in fruit size, but fruit quality parameters improved markedly. In the present study, we tested the hypothesis that the use of fresh irrigation water during the early vegetative phase would increase canopy size and leaf area index (LAI) and hence the potential productivity of the melon plant. The application of brackish water during the reproductive phase, on the other hand, would improve fruit quality. Using multiple irrigations within a 24-h period, applied with drip irrigation, we examined the timing, the duration, and the concentration of brackish irrigation water as tools to optimize fruit yield and quality in late-summer melons. Indeed, the combination of fresh (1.2 dS m⁻¹) and brackish (7 dS m⁻¹) irrigation water increased the yield level to that of fresh water plants whereas it brought about the improvement of fruit quality typical to brackish water plants, thus providing an attractive approach to optimize late-summer melon production. Our results demonstrate the trade-off between fruit size and fruit quality as related to the timing and the duration of brackish irrigation water. The use of a milder (<4.5 dS m⁻¹) salinity level of irrigation water from plant emergence until harvest may be considered as well.     

The effects of irrigation methods with effluent and irrigation scheduling on water use efficiency and corn yields in an arid region

A great challenge for the agricultural sector is to produce more food from less water, particularly in arid and semi-arid regions which suffer from water scarcity. A study was conducted to evaluate the effect of three irrigation methods, using effluent versus fresh water, on water savings, yields and irrigation water use efficiency (IWUE). The irrigation scheduling was based on soil moisture and rooting depth monitoring. The experimental design was a split plot with three main treatments, namely subsurface drip (SSD), surface drip (SD) and furrow irrigation (FI) and two sub-treatments effluent and fresh water, which were applied with three replications. The experiment was conducted at the Marvdasht city (Southern Iran) wastewater treatment plant during 2005 and 2006. The experimental results indicated that the average water applied in the irrigation treatments with monitoring was much less than that using the conventional irrigation method (using furrows but based on a constant irrigation interval, without moisture monitoring). The maximum water saving was obtained using SSD with 5907 m³ ha⁻¹ water applied, and the minimum water saving was obtained using FI with 6822 m³ ha⁻¹. The predicted irrigation water requirements using the Penman-Monteith equation (considering 85% irrigation efficiency for the FI method) was 10,743 m³ ha⁻¹. The pressure irrigation systems (SSD and SD) led to a greater yield compared to the surface method (FI). The highest yield (12.11 × 10³ kg ha⁻¹) was obtained with SSD and the lowest was obtained with the FI method (9.75 × 10³ kg ha⁻¹). The irrigation methods indicated a highly significant difference in irrigation water use efficiency. The maximum IWUE was obtained with the SSD (2.12 kg m⁻³) and the minimum was obtained with the FI method (1.43 kg m⁻³). Irrigation with effluent led to a greater IWUE compared to fresh water, but the difference was not statistically significant.     

Effectiveness of cyclic irrigation in reducing suspended solids load from a paddy-field district

The reduction of suspended solids, nutrients, and organic matter loads in drainage water from paddy fields is an important issue for water quality management in closed water areas in Japan. We evaluated the ability of cyclic irrigation to reduce the suspended solids load from paddy fields. In 2006 and 2007, we investigated water and mass balances during the irrigation period in a low-lying paddy-field district neighboring Lake Biwa, which is the largest lake in Japan. We confirmed that cyclic irrigation reduced effluent loads during the puddling season. With cyclic irrigation, 118 kg ha⁻¹ of suspended solids was returned to the paddy fields in 2006 and 199 kg ha⁻¹ in 2007. The effect of cyclic irrigation on the net suspended solids load can be represented by three ratios: the concentration ratio, which represents the ratio of the suspended solids concentration in drainage water to that in lake water; the cyclic irrigation ratio, which represents the ratio of the volume of reused water to that of irrigation water in cyclic irrigation; and the surplus irrigation water ratio, which represents the ratio of the volume of surplus irrigation water to that of irrigation water. The cyclic irrigation ratio and the surplus irrigation water ratio interact to determine the effect of cyclic irrigation on the net suspended solids load. Simultaneously increasing the cyclic irrigation ratio and decreasing the surplus irrigation water ratio will maximize the purification effect on drainage water from paddy fields.     

Evaluation of the influence of irrigation methods and water quality on sugar beet yield and water use efficiency

Rapid urbanization and industrialization have increased the pressure on limited existing fresh water to meet the growing needs for food production. Two immediate responses to this challenge are the efficient use of irrigation technology and the use of alternative sources of water. Drip irrigation methods may play an important role in efficient use of water but there is still limited information on their use on sugar beet crops in arid countries such as Iran. An experiment was conducted to evaluate the effects of irrigation method and water quality on sugar beet yield, percentage of sugar content and irrigation water use efficiency (IWUE). The irrigation methods investigated were subsurface drip, surface drip and furrow irrigation. The two waters used were treated municipal effluent (EC = 1.52 dS m⁻¹) and fresh water (EC = 0.509 dS m⁻¹). The experiments used a split plot design and were undertaken over two consecutive growing seasons in Southern Iran. Statistical testing indicated that the irrigation method and water quality had a significant effect (at the 1% level) on sugar beet root yield, sugar yield, and IWUE. The highest root yield (79.7 Mg ha⁻¹) was obtained using surface drip irrigation and effluent and the lowest root yield (41.4 Mg ha⁻¹) was obtained using furrow irrigation and fresh water. The highest IWUE in root yield production (9 kg m⁻³) was obtained using surface drip irrigation with effluent and the lowest value (3.8 kg m⁻³) was obtained using furrow irrigation with fresh water. The highest IWUE of 1.26 kg m⁻³ for sugar was obtained using surface drip irrigation. The corresponding efficiency using effluent was 1.14 kg m⁻³. Irrigation with effluent led to an increase in the net sugar yield due to an increase in the sugar beet root yield. However, there was a slight reduction in the percentage sugar content in the plants. This study also showed that soil water and root depth monitoring can be used in irrigation scheduling to avoid water stress. Such monitoring techniques can also save considerable volumes of irrigation water and can increase yield.     

Evaluating irrigation performance in a Mediterranean environment

Characterizing water use and management in irrigated agriculture is a prerequisite for conserving agricultural water. We carried out a detailed analysis of irrigation performance by documenting the water use of about 840 parcels in an irrigation scheme (Genil–Cabra irrigation scheme; GCIS) located in Andalusia, southern Spain, from 1996 to 2000. Performance indicators based on the water balance detected two water-management strategies, depending on the crop: (1) cotton, garlic, maize and sugar beet had average ratios of measured irrigation supply to the simulated optimum demand (ARIS) ranging between 0.73 and 0.91 and (2) winter cereals, sunflower and olive had a much lower average ARIS (with a 4-year average of 0.28–0.39). We found a large variability in water usage among the management units in all cases. For instance, in cotton, even though the average ARIS was around 0.8, about 50% of the fields were not irrigated adequately (41% with deficit, 9% with excess). Water productivity (WP) in the GCIS was highest for the horticultural crops (garlic, olive; from 1.13 €/m³ to 6.52 €/m³) while it varied among the field crops, being lowest in maize (4-year average of 0.28 €/m³) and highest in sugar beet (4-year average of 1.04 €/m³). Large year-to-year variations in WP were observed in all crops, particularly in sunflower and garlic due either to fluctuating prices for garlic or to the effects of the 1998/1999 drought for sunflower. In fact, WP was lowest in all crops in that year, because seasonal irrigation depths were much higher than in the other 3 years. The combination of ARIS and other performance indicators allowed for determining performance levels and improvement measures. It was found that if more irrigation water is used in the GCIS, garlic and olive will be the crops that profit most from the additional supply. However, it was concluded that, given the wide range in water use and management encountered at the parcel level, improvement policies at the scheme level should always consider individual performance when designing measures for water conservation in irrigated agriculture.     

Increasing water productivity of irrigated crops under limited water supply at field scale

Borkhar district is located in an arid to semi-arid region in Iran and regularly faces widespread drought. Given current water scarcity, the limited available water should be used as efficient and productive as possible. To explore on-farm strategies which result in higher economic gains and water productivity (WP), a physically based agrohydrological model, Soil Water Atmosphere Plant (SWAP), was calibrated and validated using intensive measured data at eight selected farmer fields (wheat, fodder maize, sunflower and sugar beet) in the Borkhar district, Iran during the agricultural year 2004-2005. The WP values for the main crops were computed using the SWAP simulated water balance components, i.e. transpiration T, evapotranspiration ET, irrigation I, and the marketable yield Y_M in terms in terms of Y_MT⁻¹, Y_M ET⁻¹ and Y_M I⁻¹.The average WP, expressed as $ T⁻¹ (US $ m⁻³) was 0.19 for wheat, 0.5 for fodder maize, 0.06 for sunflower and 0.38 for sugar beet. This indicated that fodder maize provides the highest economic benefit in the Borkhar irrigation district. Soil evaporation caused the average WP values, expressed as Y_M ET⁻¹ (kg m⁻³), to be significantly lower than the average WP, expressed as Y_MT⁻¹, i.e. about 27% for wheat, 11% for fodder maize, 12% for sunflower and 0.18 for sugar beet. Furthermore, due to percolation from root zone and stored moisture content in the root zone, the average WP values, expressed as Y_MI⁻¹ (kg m⁻³), had a 24-42% reduction as compared with WP, expressed as Y_M ET⁻¹.The results indicated that during the limited water supply period, on-farm strategies like deficit irrigation scheduling and reduction of the cultivated area can result in higher economic gains. Improved irrigation practices in terms of irrigation timing and amount, increased WP in terms of Y_MI⁻¹ (kg m⁻³) by a factor of 1.5 for wheat and maize, 1.3 for sunflower and 1.1 for sugar beet. Under water shortage conditions, reduction of the cultivated area yielded higher water productivity values as compared to deficit irrigation.     

Sensitivity analysis of optimal operation of irrigation supply systems with water quality considerations

A model for optimal operation of water supply/irrigation systems of various water quality sources, with treatment plants, multiple water quality conservative factors, and dilution junctions is presented. The objective function includes water cost at the sources, water conveyance costs which account for the hydraulics of the network indirectly, water treatment cost, and yield reduction costs of irrigated crops due to irrigation with poor quality water. The model can be used for systems with supply by canals as well as pipes, which serve both drinking water demands of urban/rural consumers and field irrigation requirements. The general nonlinear optimization problem has been simplified by decomposing it to a problem with linear constraints and nonlinear objective function. This problem is solved using the projected gradient method. The method is demonstrated for a regional water supply system in southern Israel that contains 39 pipes, 37 nodes, 11 sources, 10 agricultural consumers, and 4 domestic consumers. The optimal operation solution is described by discharge and salinity values for all pipes of the network. Sensitivity of the optimal solution to changes in the parameters is examined. The solution was found to be sensitive to the upper limit on drinking water quality, with total cost being reduced by 5% as the upper limit increases from 260 to 600 mg Cl l^–1. The effect of income from unit crop yield is more pronounced. An increase of income by a factor of 20 results in an increase of the total cost by a factor of 3, thus encouraging more use of fresh water as long as the marginal cost of water supply is smaller than the marginal decrease in yield loss. The effect of conveyance cost becomes more pronounced as its cost increases. An increase by a factor of 100 results in an increase of the total cost by about 14%. The network studied has a long pipe that connects two distinct parts of the network and permits the supply of fresh water from one part to the other. Increasing the maximum permitted discharge in this pipe from 0 to 200 m³ h^–1 reduces the total cost by 11%. Increasing the maximum discharge at one of the sources from 90 to 300 m³ h^–1 reduces the total cost by about 8%.     

Evaluating irrigation performance in a Mediterranean environment

Assessment of irrigation performance is a prerequisite for improving water use in the agricultural sector to respond to perceived water scarcity. Between 1996 and 2000, we conducted a comprehensive assessment of the performance of the Genil–Cabra irrigation scheme (GCIS) located in Andalusia, southern Spain. The area has about 7,000 ha of irrigated lands distributed in 843 parcels and devoted to a diverse crop mix, with cereals, sunflower, cotton, garlic and olive trees as principal crops. Irrigation is on demand from a pressurized system and hand-moved sprinkler irrigation is the most popular application method. Six performance indicators were used to assess the physical and economic performance of irrigation water use and management in the GCIS, using parcel water-use records and a simulation model. The model simulates the water-balance processes on every field and computes an optimal irrigation schedule, which is then checked against actual schedules. Among the performance indicators, the average irrigation water supply:demand ratio (the ratio of measured irrigation supply to the simulated optimum demand) varied among years from 0.45 to 0.64, indicating that the area is under deficit irrigation. When rainfall was included, the supply:demand ratio increased up to 0.87 in one year, although it was only 0.72 in the driest year, showing that farmers did not fully compensate for the low rainfall with sufficient irrigation water. Nevertheless, farmers in the area made an efficient use of rainfall, as indicated by the relatively high values (0.72–0.83) for the ratio of actual:attainable crop yields. Water productivity (WP) in the GCIS oscillated between 0.72 €/m³ and 1.99 €/m³ during the 4 years and averaged 1.42 €/m³ of water supplied for irrigation, while the irrigation water productivity (IWP) averaged 0.63 €/m³ for the period studied. WP is higher than IWP because WP includes production generated by rainfall, while IWP includes only the production generated by irrigation.Communicated by A. Kassam     

The viability of irrigating mandarin trees with saline reclaimed water in a semi-arid Mediterranean region: a preliminary assessment

The effect of irrigation water quality was investigated in a commercial mandarin orchard during four growing seasons using fresh water (EC ≈ 1 dS m^?1), irrigators’ association water (EC = 1–3 dS m^?1) and reclaimed water (RW) (EC ≈ 3 dS m^?1). RW had higher concentration of macro- and micronutrients, especially potassium, and the phytotoxic elements, boron, sodium and chlorides. The microbiological load in the different irrigation water sources showed a high seasonal variability, and all water sources occasionally exceeded health standards to irrigate fruit trees. In the RW treatment, an increase in soil salinity and leaf boron concentration was observed. The nutritional contribution of RW was high, providing 24 and 15 % of the annual nitrogen and phosphorus (N and P₂O₅) fertilizer requirement for mandarin oranges, respectively, and RW treatment satisfied the entire potassium requirement (K₂O). An important fluctuation in the crop production was observed during the 4 years in the different water quality treatments. In general, quality parameters of mandarins were not affected. The results provide additional evidence that long-term effects must be studied to test sustainability when using RW irrigation on fruit trees.     

Soil salinity related to physical soil characteristics and irrigation management in four Mediterranean irrigation districts

Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) techniques and relate it to the physical characteristics and irrigation management of four Mediterranean irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or estimated in each district. Soil salinity (EC_e) maps were obtained through electromagnetic induction surveys (EC_a readings) and district-specific EC_a-EC_e calibrations. Gravimetric soil water content (WC) and soil saturation percentage (SP) were also measured in the soil calibration samples. The EC_a-EC_e calibration equations were highly significant (P < 0.001) in all districts. EC_a was not significantly correlated (P > 0.1) with WC, and was only significantly correlated (P < 0.1) with soil texture (estimated by SP) in Spain. Hence, EC_a mainly depended upon EC_e, so that the maps developed could be used effectively to assess soil salinity and its spatial variability. The surface-weighted average EC_e values were low to moderate, and ranked the districts in the order: Tunisia (3.4 dS m⁻¹) > Morocco (2.2 dS m⁻¹) > Spain (1.4 dS m⁻¹) > Turkey (0.45 dS m⁻¹). Soil salinity was mainly affected by irrigation water salinity and irrigation efficiency. Drainage water salinity at the exit of each district was mostly affected by soil salinity and irrigation efficiency, with values very high in Tunisia (9.0 dS m⁻¹), high in Spain (4.6 dS m⁻¹), moderate in Morocco (estimated at 2.6 dS m⁻¹), and low in Turkey (1.4 dS m⁻¹). Salt loads in drainage waters, calculated from their salinity (EC_dw) and volume (Q), were highest in Tunisia (very high Q and very high EC_dw), intermediate in Turkey (extremely high Q and low EC_dw) and lowest in Spain (very low Q and high EC_dw) (there were no Q data for Morocco). Reduction of these high drainage volumes through sound irrigation management would be the most efficient way to control the off-site salt-pollution caused by these Mediterranean irrigation districts.     

The contribution of shallow groundwater by safflower (Carthamus tinctorius L.) under high water table conditions, with and without supplementary irrigation

Lysimetric experiments were conducted to determine the contribution made by groundwater to the overall water requirements of safflower (Carthamus tinctorius L.). The plants were grown in 24 columns, each having a diameter of 0.40 m and packed with silty clay soil. The four replicate randomized complete block factorial experiments were carried out using different treatment combinations. Six treatments were applied during each experiment by maintaining groundwater, with an EC of 1 dS m^?1, at three different water table levels (0.6, 0.8 and 1.10 m) with and without supplementary irrigation. The uptake of groundwater as a part of crop evapotranspiration was measured by taking daily readings of the water levels found in Mariotte tubes. The supplementary irrigation requirement for each treatment was applied by adding water (EC of 1 dS m^?1). The average percentage contribution from groundwater for the treatments (with and without supplementary irrigation under water table levels of 0.6, 0.8 and 1.10 m) were found to be 65, 59, 38% and 72, 70, 47% of the average annual safflower water requirement (6,466 m³ ha^?1). The increase in groundwater depths under supplementary irrigation treatments from 0.6 to 0.80 and 1.10 m caused seed and oil yield reductions of (7, 23.10%) and (48.23, 65.40%), respectively.     

A model for computing date palm water requirements as affected by salinity

Irrigation of crops in arid regions with marginal water is expanding. Due to economic and environmental issues arising from use of low-quality water, irrigation should follow the actual crop water demands. However, direct measurements of transpiration are scant, and indirect methods are commonly applied; e.g., the Penman–Monteith (PM) equation that integrates physiological and meteorological parameters. In this study, the effects of environmental conditions on canopy resistance and water loss were experimentally characterized, and a model to calculate palm tree evapotranspiration ET_c was developed. A novel addition was to integrate water salinity into the model, thus accounting for irrigation water quality as an additional factor. Palm tree ET_c was affected by irrigation water salinity, and maximum values were reduced by 25 % in plants irrigated with 4 dS m^?1 and by 50 % in the trees irrigated with 8 dS m^?1. Results relating the responses of stomata to the environment exhibited an exponential relation between increased light intensities and stomatal conductance, a surprising positive response of stomata to high vapor pressure deficits and a decrease in conductance as water salinity increased. These findings were integrated into a modified ‘Jarvis–PM’ canopy conductance model using only meteorological and water quality inputs. The new approach produced weekly irrigation recommendations based on field water salinity (2.8 dS m^?1) and climatic forecasts that led to a 20 % decrease in irrigation water use when compared with current irrigation recommendations.     

Production and water use in lettuces under variable water supply

The effects of a variable water supply on the water use, growth and yield of two crisphead and one romaine (i.e., Cos) lettuce cultivar were examined in a field experiment using a line source sprinkler system that produced a range of water regimes that occur in growers fields. Four locations at increasing distances from the main line were monitored through the season (i.e., from thinning to harvest, 28–63 days after planting (DAP)). These locations at the end of the season corresponded to: (1) rewatering to field capacity (FC); (2) watering with a volume 13% below that required in the field capacity treatment (0.87*FC); (3) 30% below FC (0.70*FC); and (4) 55% below FC (0.45*FC). A linear production function for dry matter accumulation and fresh weight vs. crop evapotranspiration (ET_c) was determined for lettuce during this period, giving a water use efficiency for dry matter of 1.86 g m^–2 mm^–1 and for fresh weight of 48 g m^–2 mm^–1 . For lettuce irrigated to field capacity, ET_c between thinning and harvest was 146 mm; maximum crop coefficients of 0.81–1.02 were obtained at maturity (55–63 DAP). For the three irrigation treatments receiving the largest water application, ET_c was higher in the Cos culivar than in the two crisphead lettuce cultivars which had similar ET_c. Plant fresh weight was more sensitive than dry weight to reduction in water supply. In the FC treatment, root length density and soil water extraction were greatest in the top 0–45 cm, and decreased rapidly below 45 cm depth. Soil water extraction by roots increased at lower depths when irrigation was reduced. Instantaneous rates of leaf photosynthesis and leaf water potential showed no response to the irrigation treatments in this study, despite differences in biomass production. Evaporation was determined to be the major component of ET_c for 45 of the 63 days of the growing season. The large loss of water by evaporation during mid-season and the apparent insensitivity of lettuce to the volume of irrigation during this period may provide an opportunity for reducing irrigation applications.