Usefulness and limitations of decision support systems for improving irrigation scheme management

SIMIS (the FAO Scheme Irrigation Management Information System) is a decision support system that integrates tools and performance indicators to facilitate the planning and management of irrigation schemes. The authors used SIMIS to compute performance indicators in an irrigation scheme in Southern Spain that were used to identify distribution system constraints affecting the flexibility of water deliveries and to identify scheme sectors where deliveries could not meet the predicted crop water demands. Applying SIMIS, the authors and the irrigation scheme manager evaluated measures to overcome the constraints for future irrigation campaigns, and to refine the water orders made every 2 weeks to the basin authority. On the other hand, SIMIS presented limitations to the evaluation of on-demand delivery schedules. To overcome these limitations, an external model, developed outside SIMIS, showed that the current distribution network of the scheme has the capacity to deliver water on-demand only if a slight water deficit is accepted during the peak demand period. The analysis showed that by relaxing the stringency of the quality of operation of on-demand systems, rotation systems may be transformed into on-demand systems without changing their structures. This analysis could also be done using Clément's hypothesis, but doing so resulted in overestimates of the quality of operation and of the relative irrigation supply.     

Agro-environmental evaluation of irrigation land: II. Pollution induced by Bardenas Irrigation District (Spain)

It is difficult to quantify non-point contamination caused by irrigated agriculture. As continuation to the evaluation of water use on the scale of large irrigation districts, this second part seeks: (i) to quantify the mass of salt and nitrate exported by Bardenas Irrigation District included in the Arba basin (BID-Arba; 54,438 ha); (ii) to analyze the most influential factors; (iii) to propose agro-environmental contamination indices which can be incorporated into legislation.For this, salt and nitrate balances were carried out, assigning concentration values to each of the components of the water balance between 1 April 2004 and 30 September 2006. Saline and Nitrate Contamination Indices were also quantified which correct the mass of pollutants exported from irrigation return flows by geological and agronomic factors of the irrigation area studied.For the whole period of the study the exported mass of salt was 15 kg/(ha day), of which 65% came from geological materials in the area, 34% from irrigation water and only 1% from precipitation. As for exported nitrate, it was 76 g NO₃⁻-N/(ha day), only 25% of the quantities measured in other small basins (≈100 ha) of Bardenas district without re-use of drainage water for irrigation, but double the nitrate exported in other modern irrigation districts.Water and saline agro-environmental indices of BID-Arba resemble those of well-managed modern irrigation districts indicating little margin for improvement in water use and saline contamination. But, the nitrate-contamination-index was 1.5 times higher than well-managed modern irrigation districts indicating the necessity to change nitrogenous fertilization practices to minimize nitrate contamination.     

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.     

A regional soil survey approach for upgrading from flood to sprinkler irrigation in a semi-arid environment

Increasing pressure on water resources in Spain is forcing farmers to move from flood to pressurized water application. Initial recommendations for this upgrading require soil survey information, especially in areas prone to soil salinity. In this article a 3158 ha soil survey at a scale of 1:25,000 is presented. Soil series are split in phases based on the texture of the surface layer, slope, and salinity. Available water holding capacity (AWHC), to a depth of 1.5 m or to a lithic or paralithic contact, texture and coarse components in the surface horizons, and salinity mapped as discrete soil units are combined to develop a regional soil suitability map for irrigation upgrade. To minimize soil erosion and salt mobilization in the soils, our recommendations are: (i) maintain and improve flood irrigation on 296 ha, (ii) develop standard sprinkler irrigation on 2261 ha, and (iii) move to high frequency sprinkler irrigation on 601 ha. This research demonstrates the importance of soil survey as part of the decision making process for upgrading the regional irrigation systems.     

Management trends and responses to water scarcity in an irrigation scheme of Southern Spain

Improvement of irrigation management in areas subjected to periods of water scarcity requires good knowledge of system performance over long time periods. We have conducted a study aimed at characterizing the behaviour of an irrigated area encompassing over 7000 ha in Southern Spain, since its inception in 1991. Detailed cropping pattern and plot water use records allowed the assessment of irrigation scheme performance using a simulation model that computed maximum irrigation requirements for every plot during the first 15 years of system operations. The ratio of irrigation water used to maximum irrigation requirements (Annual Relative Irrigation Supply, ARIS) was well below 1 and oscillated around 0.6 in the 12 years that there were no water supply restrictions in the district. The ARIS values varied among crops, however, from values between 0.2 and 0.3 for sunflower and wheat, to values approaching 1 for cotton and sugar beet. Farmer interviews revealed some of the causes for the low irrigation water usage which were mainly associated with the attempt to balance profitability and stability, and with the lack of incentives to achieve maximum yields in crops subsidized by the Common Agricultural Policy (CAP) of the European Union. The response to water scarcity was also documented through interviews and demonstrated that the change in crop choice is the primary reaction to an anticipated constraint in water supply. Water productivity (value of production divided by the volume of irrigation water delivered; WP) in the district was moderate and highly variable (around 2€ m⁻³) and did not increase with time. Irrigation water productivity (increase in production value due to irrigation divided by irrigation water delivered) was much lower (0.65€ m⁻³) and also, it did not increase with time. The lack of improvement in WP, the low irrigation water usage, and the changes in cropping patterns over the first 15 years of operation indicate that performance trends in irrigated agriculture are determined by a complex mix of technical, economic, and socio-cultural factors, as those that characterized the behaviour of the Genil-Cabra irrigation scheme.     

A distributed agro-hydrological model for irrigation water demand assessment

The actual irrigation water demand in a district in Sicily (Italy) was assessed by the spatially distributed agro-hydrological model SIMODIS (SImulation and Management of On-Demand Irrigation Systems). For each element with homogeneous crop and soil conditions, in which the considered area can be divided, the model numerically solves the one-dimensional water flow equation with vegetation parameters derived from Earth Observation data. In SIMODIS, the irrigation scheduling is set by means of two parameters: the threshold value of soil water pressure head in the root zone, h_m, and the fraction of soil water deficit to be re-filled, Δ. This study investigated the possibility of identifying a couple of irrigation parameters (h_m, Δ) which allowed to reproduce the actual irrigation water demand, given that the study area was adequately characterized with regard to the spatial distribution of the soil hydraulic properties and the vegetation conditions throughout the irrigation season. The spatial distribution of the soil and vegetation properties of the study area, covering an irrigation district of approximately 800 ha, was accurately characterized during the summer of 2002. The soil hydraulic properties were identified by an intensive undisturbed soil sampling, while the vegetation cover was characterized in terms of leaf area index, surface albedo and fractional soil cover by analysing multispectral LandSat TM imageries. Irrigation volumes were monitored at parcel scale.A reference scenario with h_m = −700 cm and Δ = 50% (corresponding to a mean actual to potential transpiration ratio of 0.95) allowed to reproduce the spatial and temporal distribution of the actual irrigation demand at the district scale. The spatial variability of the crop conditions in the considered area had much more influence to assess the irrigation water demand than the soil hydraulic spatial variability. The proposed approach showed that, under the agro-climatic conditions typical for the Mediterranean region, SIMODIS may be a valuable tool in managing irrigation to increase water productivity.     

Long-term water balances in La Violada Irrigation District (Spain): II. Analysis of irrigation performance

The analysis of long-term irrigation performance series is a valuable tool to improve irrigation management and efficiency. This work focuses in the assessment of irrigation performance indices along years 1995-2008, and the cause-effect relationships with irrigation modernization works taking place in the 4000 ha surface-irrigated La Violada Irrigation District (VID). Irrigation management was poor, as shown by the low mean seasonal irrigation consumptive use coefficient (ICUC = 51%) and the high relative water deficit (RWD = 20%) and drainage fraction (DRF = 54%). April had the poorest irrigation performance because corn (with low water demand in this month) was irrigated to promote its emergence, whereas winter grains (with high water demands in this month) were not fully irrigated in water-scarce years. Corn, highly sensitive to water stress, was the crop with best irrigation performance because it was preferentially irrigated to minimize yield losses. The construction of a new elevated canal that decreased seepage and drainage fractions, the entrance in operation of six internal reservoirs that would increase irrigation scheduling flexibility, and the on-going transformation from surface to sprinkler irrigation systems are critical changes in VID that should lead to improved ICUC, lower RWD and lower DRF. The implications of these modernization works on the conservation of water quantity and quality within and outside VID is further discussed.     

Performance assessment of small irrigation schemes along the Mauritanian banks of the Senegal River

Irrigation plays a fundamental role in world food provision but, to date, it has performed below expectations in Sub-Saharan Africa. The present study assesses and diagnoses the performance of 22 small and medium size community-managed irrigation schemes, mainly devoted to rice production, in different locations along the Mauritanian banks of the Lower Senegal River. The evaluations followed the Rapid Appraisal Process in which semi-structured interviews were held with representatives of the Cooperatives’ Boards in charge of each scheme to obtain information about the organisation of the cooperative, land tenure, irrigation system and organization, cropping pattern and soils. Additionally, for each irrigation scheme, the water-delivery service was characterized by making qualitative and comparative observations during field inspections; the pumping station's performance was diagnosed by a local specialist; the discharge at the head of the system was measured; daily irrigation time was recorded; and crop yields were determined by plot sampling. Then a set of performance indicators was computed. Water delivery capacity referred to irrigated areas was insufficient in a third of the schemes, and this insufficiency was exacerbated by poor maintenance. Irrigation intensity in habilitated areas was rather low being less than 0.66 in 50% of the schemes. The average productivity of land, irrigation water, and fuel (3.38 t ha⁻¹, 0.30 kg m⁻³ and 2.37 kg kWh⁻¹, respectively) were well below potential.     

Effects of applied water and sprinkler irrigation uniformity on alfalfa growth and hay yield

This study was conducted to investigate the effects of applied water and sprinkler irrigation uniformity on alfalfa (Medicago sativa L.) growth and hay yield in a semi-arid region. Field experiments were carried out in 2006 in Varamin, Iran, on three plots of 25 m × 30 m. Each plot was subdivided into 25 subplots of 5 m × 6 m. Different irrigation depths and sprinkler water uniformities were obtained by various scenarios of sprinkler nozzle pressure. In each plot, applied water was measured at 250 points (125 points above and 125 points below canopy) and the soil water content of 40 cm deep below soil surface was monitored at 25 points, each in the center of a subplot, throughout the irrigation season. The results showed that sprinkler water and soil water content uniformity varied between 66-78 and 88-91%, respectively. The findings revealed that soil water content uniformity was around 20% higher than sprinkler water uniformity. The irrigation uniformity below the canopy was estimated to be 2.5% greater than above the canopy, and canopy-intercepted water could account for 11-15% of the total seasonal applied water. Evaluation showed that alfalfa leaf area index relies more heavily on farm water application uniformity than hay yield and crop height. The experimental results illustrated that water distribution in sprinkler irrigation systems has a direct effect on alfalfa growth, hay yield and water productivity such that the applied water reduction and the increased sprinkler water uniformity led to an increased alfalfa water productivity of 2.41 kg m⁻³.     

Irrigation strategies to improve the water use efficiency of wheat-maize double cropping systems in North China Plain

Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm³ cm⁻³, 0.59 Mg ha⁻¹, 2.05 Mg ha⁻¹, and 0.19 kg m⁻³, respectively, for wheat; and 0.027 cm³ cm⁻³, 0.71 Mg ha⁻¹, 1.51 Mg ha⁻¹ and 0.35 kg m⁻³, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.     

Effect of brackish water irrigation and straw mulching on soil salinity and crop yields under monsoonal climatic conditions

Fresh water shortages are severally restricting sustainable agriculture development in the North China Plain. The scarcity of fresh water has forced farmers to use brackish water from shallow underground sources, which helps to overcome drought and increase crop yields but also increases the risk of soil salinization. To identify safe and effective ways of using brackish water in this region, field experiments were conducted to evaluate the effect of brackish water irrigation and straw mulching on soil salinity and crop yield in a winter wheat-summer maize double cropping system. The experiment was in a split-plot design. Six rates of straw mulching (0, 4.5, 6.0, 7.5, 15.0 and 30.0 Mg/ha) were assigned to the main plots and two irrigation water qualities (i.e. brackish water with salt content of 3.0-5.0 g/L and fresh water with only 1.27 g salt/L) were applied to subplots. The brackish water irrigation significantly increased the salt content at different soil depths in the upper 1 m soil layer during the two growing seasons. Straw mulching affected the vertical distribution of salt in the brackish water irrigation plots and the average salt content of straw mulch treatments (4.5, 6.0, 7.5, 15.0 and 30.0 Mg/ha) within the 0-20, 20-40 and 0-100 cm soil depths was 10.2, 14.0 and 1.8% lower than that without straw mulch (A₀). No salt accumulation occurred to a depth of 1 m in the brackish water irrigation plots and there was no correlation between the value of SAS (salt accumulated in 1 m of soil) and straw mulch rate. In 2000 and 2001, the salt content within the 0-40 cm soil layer in brackish water irrigation plots increased due to high evaporation rates during April-June, and then decreased up to September as salts were leached by rain. For the fresh water irrigation plots, the salt content remained relatively stable. Straw mulching affected the salt content in the 0-40 cm soil layer in brackish water irrigation plots in different periods of 2000 and 2001, but no correlation between salt content and straw mulch rates was observed except in September of 2000. Unlike for wheat, the yield of maize increased as the straw mulch rate increased according to the equation, y = 0.1589x + 5.3432 (R² = 0.6506). Our results would be helpful in adopting brackish water irrigation and straw mulching in ways that enhance crop yields and reduce the risk of soil salinization. However, long-term effects of brackish water irrigation and straw mulching on soil salinity and crop yield need to be further evaluated for sustainability of the system.     

Agro-environmental evaluation of irrigation land: I. Water use in Bardenas irrigation district (Spain)

Non-point agrarian contamination makes its allocation to a specific territory difficult. This first part of the study seeks to analyze contamination resulting from water use in 54,438 ha of Bardenas irrigation district included in the Arba basin (BID-Arba). To this end, water balances were carried out in BID-Arba by means of measuring or estimating the main inputs, outputs and water storage between 1 April 2004 and 30 September 2006. Also, the spatial-temporal variability in water use was analyzed.The semester error balances were acceptable (between 11% and −6%), which permits the attribution of the mass of pollutants exported in drainage to the irrigation area evaluated, the objective of the second part of the study. Irrigation efficiency (IE) in BID-Arba was high (90%) despite the fact that Irrigation Sub-District VII (ISD-VII), with considerable flood irrigation drainage (27%), and ISD-XI with considerable losses due to evaporation and wind drift in sprinkler irrigation systems (15%), brought down the average (IE_VII = 73%; IE_XI = 83%). Irrigation management was inadequate as there was a water deficit (WD) of 9%, partly affected by the 2005 drought (WD_{Apr-05/Sep-05} = 21%) and the low irrigation doses applied in ISD-XI (WD_XI = 12%).To sum up, intense re-use of water caused a water use index (percentage of water used by the crops) of 85% which surpassed 90% in periods of drought. Nevertheless, irrigation management should be improved in order to annul the water deficit and to maximize the productivity of the agrarian system.     

Effects of water infiltration and storage in cultivated soil on surface irrigation

Surface irrigation analysis and design require the knowledge of the variation of the cumulative infiltration water Z (L) (per unit area) into the soil as a function of the infiltration time t (T). The purpose of this study is to evaluate water infiltration and storage under surface irrigation in an alluvial clay soil cultivated with grape yield, and to determine if partially wetted furrow irrigation has more efficient water storage and infiltration than traditional border irrigation. The two irrigation components considered were wet (WT) and dry (DT) treatments, at which water applied when available soil water reached 65% and 50%, and the traditional border irrigation control. Empirical power form equations were obtained for measured advance and recession times along the furrow length during the irrigation stages of advance, storage, depletion and recession. The infiltration (cumulative depth, Z and rate, I) was functioned to opportunity time (t_o) in minute for WT and DT treatments as: Z_WT = 0.528 t_o^0.6, Z_DT = 1.2 t_o^0.501, I_WT = 19 t_o^−0.4, and I_DT = 36 t_o^−0.498. The irrigation efficiency and soil water distribution have been evaluated using linear distribution and relative schedule depth. Coefficient of variation (CV) was 5.2 and 9.5% for WT and DT under furrow irrigation system comparing with 7.8% in border, respectively. Water was deeply percolated as 11.88 and 19.2% for wet and dry furrow treatments, respectively, compared with 12.8% for control, with no deficit in the irrigated area. Partially wetted furrow irrigation had greater water-efficiency and grape yield than both dry furrow and traditional border irrigations, where application efficiency achieved as 88.1% for wet furrow irrigation that achieved high grape fruit yield (30.71 Mg/ha) and water use efficiency 11.9 kg/m³.     

Tuber yield, water and fertilizer productivity in early potato as affected by a combination of irrigation and fertilization

Excessive amounts of irrigation water and fertilizers are often utilized for early potato cultivation in the Mediterranean basin. Given that water is expensive and limited in the semi-arid areas and that fertilizers above a threshold level often prove inefficacious for production purposes but still risk nitrate and phosphorous pollution of groundwater, it is crucial to provide an adequate irrigation and fertilization management. With the aim of achieving an appropriate combination of irrigation water and nutrient application in cultivation management of a potato crop in a Mediterranean environment, a 2-year experiment was conducted in Sicily (South Italy). The combined effects of 3 levels of irrigation (irrigation only at plant emergence, 50% and 100% of the maximum evapotranspiration - ETM) and 3 levels of mineral fertilization (low: 50, 25 and 75 kg ha⁻¹, medium: 100, 50 and 150 kg ha⁻¹ and high: 300, 100 and 450 kg ha⁻¹ of N, P₂O₅ and K₂O) were studied on the tuber yield and yield components, on both water irrigation and fertilizer productivity and on the plant source/sink (canopy/tubers dry weight) ratio. The results show a marked interaction between level of irrigation and level of fertilization on tuber yield, on Irrigation Water Productivity and on fertilizer productivity of the potato crop. We found that the treatments based on 50% ETM and a medium level of fertilization represent a valid compromise in early potato cultivation management. Compared to the high combination levels of irrigation and fertilization, this treatment entails a negligible reduction in tuber yield to save 90 mm ha⁻¹ year⁻¹ of irrigation water and 200, 50 and 300 kg ha⁻¹ year⁻¹ of N, P₂O₅ and K₂O, respectively, with notable economic savings for farmers compared to the spendings that are usually made.     

Model for performance based land area and water allocation within irrigation schemes

This paper focuses on irrigation schemes under rotational water supply in arid and semiarid regions. It presents a methodology for developing plans for optimum allocation of land area and water, considering performance measures such as productivity, equity and adequacy. These irrigation schemes are characterized by limited water supply and heterogeneity in soils, crops, climate and water distribution network, etc. The methodology proposed in this paper, therefore, uses a previously developed simulation–optimization model (Area and Water Allocation Model, AWAM) that considers the heterogeneity of the irrigation scheme in the allocation process, and modifies this to take account of equity and adequacy of supply to irrigated areas. The AWAM model has four phases to be executed separately for each set of irrigation interval over the irrigation season: 1. generation of irrigation strategies for each crop–soil–region combination (CSR unit), 2. preparation of irrigation programmes for each irrigation strategy, 3. selection of specified number of irrigation programmes for each CSR unit and 4. optimum allocation of land area and water to different parts of the irrigation scheme (allocation units) for maximizing productivity. In the modified AWAM model, the adequacy is included at Phase-2 (by including only the irrigation programmes for full irrigation of each CSR unit) and equity is included at Phase-4 (by including the constraints for equity). The paper briefly discusses the applicability of the modified AWAM model for a case study of Nazare medium irrigation scheme in Southern India. The results of the case study indicated that the performance measures of productivity, equity and adequacy conflict with each other.     

Faecal contamination and hygiene aspect associated with the use of treated wastewater and canal water for irrigation of potatoes (Solanum tuberosum)

Clean water has become one of the main limiting factors in agricultural food production in Europe, especially for countries around the Mediterranean, who now face more severe and frequent seasonal water shortages. In order to overcome water shortages the European Water Framework Directive encourages and promotes the use of treated urban wastewater in agriculture. However, the use of poor quality water in agriculture poses potential health risks. The application of wastewater through subsurface drip irrigation lines could possibly overcome public health concerns by minimizing contact with wastewater by farmers, farm workers but it is uncertain if the risk for consumers of wastewater irrigated produces would be acceptable. The objective of the current study was therefore to assess whether subsurface irrigation of potatoes with low quality water was associated with higher food safety and reduced human health risks as compared with surface irrigation. The microbial quality of soil and potatoes irrigated by sprinkler, furrow and subsurface drip irrigation, using treated urban wastewater, canal water and tap water were compared at experimental sites near Belgrade, Serbia and in Bologna, Italy. Water, soil and potato samples were collected from March 2007 to September 2008 and their faecal contamination estimated by enumeration of the faecal indicator Escherichia coli. In addition, water and potatoes in Italy were analysed for the presence of helminth eggs, another important indicator of faecal pollution. A quantitative microbial risk assessment (QMRA) model combined with Monte Carlo simulations was used to assess whether the different irrigation practices and associated health risks complied with guidelines set by the World Health Organization (WHO). The study found low levels of E. coli in irrigation water (Italy mean value: 1.7 colony forming units (cfu)/ml and Serbia 11 cfu/ml), as well as in soil (Italy mean: 1.0 cfu/g and Serbia 1.1 cfu/g). Similar low concentrations of E. coli were found on potatoes (Italy mean: 1.0 cfu/g and Serbia 0.0 cfu/g). The vast majority (442/516) of the collected different samples were free of E. coli. No helminth eggs were found in any types of irrigation water or on the surface of potatoes. The risk assessment models found the use of treated wastewater to exceed the levels of risks for gastro-intestinal disease (1.0 × 10⁻³ disease risk) as recommended by the World Health Organization (WHO) for the accidental ingestion of soil by farmers (Serbia: 0.22 and Italy: 5.7 × 10⁻²). However, samples that exceeded disease risks set by the WHO were collected before initiation of wastewater irrigation and were limited to a few numbers of samples, which would indicate environmental contamination not linked to irrigation practice. Disease risk from consumption of potatoes in Italy and in Serbia was found to be within acceptable levels. No relationship was found between E. coli concentrations in irrigation water, soil and produce. Similar lack of association was found for E. coli findings in sprinkler, furrow or subsurface drip irrigated soils and produce. This indicates that subsurface drip irrigation can be practiced while ensuring food safety and protecting the health of consumers and farmers.     

Assessing yield optimization and water reduction potential for summer-sown and spring-sown maize in Pakistan

Agricultural food production in arid and semi-arid regions faces the challenge to ensure high yields with limited supply of water. This raises the question to which extent irrigation supply can be reduced without detriment to yield. Our study focuses on the yield-water uptake relationship for maize in the moderate water stress range in order to determine the onset of stress-induced dry-matter and yield losses. Compensatory plant responses under moderate stress levels are discussed in relation to seasonal climatic conditions.Summer-sown and spring-sown maize were irrigated with a decreasing amount of water in a field experiment in Pakistan. Water supply ranged from 100% water required to maintain soil at field capacity (FC) to 40% of FC. The average dry-matter and yield levels were slightly higher for summer-sown (15.0 Mg ha⁻¹) compared to spring-sown maize (13.1 Mg ha⁻¹). The onset of significant dry-matter and yield reduction started at the least irrigation treatment in both seasons. The amount of water required to avoid production losses was 272 mm in the summer-sown maize during the autumn growing season, and 407 mm for the spring-sown maize in the summer season, when the evaporative demand of the atmosphere was +27% higher. Water use efficiency (WUE_ET), normalized by vapour pressure deficit, of the summer-sown maize which was 10.0 kg kPa m⁻³, was +15% higher compared to the spring-sown crop; while the irrigation water productivity (2.9 kg m⁻³) was +11% more. WUE_ET increased over the whole range of applied water deficits for summer-sown maize, while the spring-sown crop showed a decreasing WUE_ET in the less irrigated treatment. Due to the higher efficiency in summer-sown maize, the potential in irrigation reduction without production losses (129 mm) was higher compared to the spring-sown maize (57 mm). Our results showed that in Pakistan water saving irrigation practices can be applied without yield loss mainly during the cooler growing season when the crop can efficiently compensate a lower total water uptake by increased use efficiency. For spring-sown maize the increasing evaporative demand of the atmosphere towards summer implies a higher risk of yield losses and narrows the range to exploit higher irrigation water productivity under moderate water deficit conditions.     

Agricultural and environmental changes after irrigation management transfer in the Develi Basin,Turkey

Develi Basin is a semi-arid basin in central Turkey where water sustains both irrigated agriculture and an internationally important wetland, the Sultan Marshes. Agricultural and environmental changes in the Develi Basin have occurred since irrigation management was transferred in 1994 from a state authority (DSI) to irrigation associations (Kovalı and Ağcaaşar IAs). In this paper we evaluate the practices of the IAs using extensive data from interviews with farmers and IA officials, as well as data from reports prepared by DSI and the IAs, using comparisons with case studies reported in the scientific literature. Irrigated areas and surface water use in the Develi Basin showed significant fluctuations from 1995 to 2003. The area allocated to high water-consuming plants increased. Maintenance activities became dependent on fee collection rates. Quality of the irrigation water did not changed significantly. Ground-water levels, flow rates from springs, and water levels in the Sultan Marshes all dropped. Overall analyses indicate that the water requirements of the Sultan Marshes have not been met, while water use for irrigation has been effective but not efficient. To reconcile agricultural and wetland water requirements, a basin-wide approach in water planning is recommended. Amounts of water to be allocated to the IAs and wetlands need to be clearly defined. DSI has to monitor canal maintenance by the IAs more closely, and IAs need to be given more responsibilities for future rehabilitation of the canals. Realistic water pricing, increased reliability of irrigation scheduling, higher on-farm irrigation efficiency, and in the long-term, modernization of the irrigation system need to be considered.     

Water and salt balance at irrigation scheme scale: A comprehensive approach for salinity assessment in a Saharan oasis

Salt balance methods are generally applied in the root-zone and at local scales but do not provide relevant information for salinity management at irrigation scheme scales, where there are methodological impediments. A simple salt balance model was developed at irrigation scheme and yearly time scales and applied in Fatnassa oasis (Nefzaoua, Tunisia). It accounts for input by irrigation, export by drainage and groundwater flow, and provides novel computation of the influence of biogeochemical processes and variations in the resident amount of salt for each chemical component in the soil and shallow groundwater. Impediments were overcome by limiting the depth of the system so that the resident amount of salt that remained was of the same order of magnitude as salt inputs and allowed indirect and reliable estimation of groundwater flow. Sensitivity analyses as partial derivatives of groundwater salinity were carried out according to non-reactive salt balance under steady-state assumption. These analyses enabled the magnitude of the salinization process to be foreseen as a function of hydrological changes linked to irrigation, drainage, groundwater flow and extension of the irrigated area. From a salt input of 39 Mg ha⁻¹ year⁻¹ by irrigation, 21 Mg ha⁻¹ year⁻¹ (54%) and 10 Mg ha⁻¹ year⁻¹ (26%) were exported by groundwater flow and drainage, respectively. 7 Mg ha⁻¹ year⁻¹ (18%) were removed from groundwater by geochemical processes, while a non-significant 2 Mg ha⁻¹ year⁻¹ were estimated to have been stored in the soil and shallow groundwater where the residence time was only 2.7 years. The leaching efficiency of drainage was estimated at 0.77. With a water supply of 1360 mm by irrigation and 90 mm by rainfall, drainage, groundwater flow and actual evapotranspiration were 130, 230, and 1090 mm, respectively. The current extension of date palm plantations and salinization of groundwater resources are expected to significantly increase the salinity hazard while the degradation of the drainage system is expected to be of lesser impact. The approach was successfully implemented in Fatnassa oasis and proved to be particularly relevant in small or medium irrigation schemes where groundwater fluxes are significant.     

WaDI (water delivery for irrigation): A simulation tool to address strategic interaction of water demand and supply in irrigation schemes

The WaDI (water delivery for irrigation) model deals with the relations between the collective water supply and the demand within irrigated schemes. It is based on a separate modelling of the water supply and demand, including (i) a simplified representation of the hydraulic structure, characteristics and organizational parameters of the scheme, (ii) an assessment of the water demand of farms based on their total irrigated area, cropping pattern and irrigation practices, (iii) a farm typology, (iv) a confrontation between water demand and supply at each node of the scheme from pumping plants to tertiary canals, and (v) calculation of response factors between supply and demand during the peak demand period. “What-if” scenarios are simulated in order to enhance the stakeholders’ capacity to plan strategic decisions such as water delivery allocation rules or infrastructure investments. WaDI was implemented on two Brazilian schemes. It allowed broadening the stakeholders’ limited representation of collective water supply and demand into a more comprehensive understanding of these relations. The approach however showed some limits, along with the difficulty of assessing the real impact on the stakeholders’ capacity for strategic planning.