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.     

Implementing irrigation: Salt and nitrate exported from the Lerma basin (Spain)

The creation of a new irrigated area influences the pollutants exported from the zone and, consequently, the quality of receiving water bodies. The aim of this study was to analyze the masses of the main pollutants exported by an area before and during its gradual transformation into irrigated land. To this end, salinity balances were carried out and the nitrate exported from the Lerma basin (752 ha, Spain) was quantified during 2004–2008. The agroenvironmental impact was evaluated through the use of pollution indices. The results revealed that the transformation of the area into irrigated land decreased salinity and increased nitrate concentration in drainage. The increase in the volume of drainage increased the masses of salt and nitrate exported, which in turn increased pollution indices during the transition. However, these indices were still lower than those quantified in other irrigated lands and therefore can still be considered to be of low contamination level. This study demonstrates the important environmental influence of introducing irrigation to an area, as pollution levels change and become mainly dependent on the management of irrigation and nitrogenous fertilization. For this reason, it is highly desirable to promote the optimization of agricultural management in a way that minimizes its impact.     

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.     

Assessment of irrigation and environmental quality at the hydrological basin level: I. Irrigation quality

Irrigated agriculture notably increases crop productivity, but consumes high volumes of water and may induce off-site pollution of receiving water bodies. The objectives of this paper were to diagnose the quality of irrigation and to prescribe recommendations aimed at improving irrigation management and reducing the off-site pollution from a 15,500 ha irrigation district located in the Ebro River Basin (Spain). Three hydrological basins were selected within the district where the main inputs (irrigation, precipitation, and groundwater inflows) and outputs (actual crop's evapotranspiration, surface drainage outflows, and groundwater outflows) of water were measured or estimated during a hydrological year. The highest volume of water (I = 1400 mm/year) was applied in the basin with highly permeable, low water retention, flood irrigated soils where 81% of the total surface was planted with alfalfa and corn. This basin had the lowest consumptive water use efficiency (CWUE = 45%), the highest water deficit (WD = 5%) and the highest drainage fraction (DF = 57%). In contrast, the lowest I (950 mm/year), the highest CWUE (62%), and the lowest WD (2%) and DF (37%) were obtained in the basin with 60% of the surface covered with deep, high water retention, alluvial valley soils, where 39% of the cultivated surface is sprinkler irrigated and with only 48% of the surface planted with alfalfa and corn. We concluded that the three most important variables determining the quality of irrigation and the volume of irrigation return flows in the studied basins were (i) soil characteristics, (ii) irrigation management and irrigation system, and (iii) crop water requirements. Therefore, the critical recommendations for improving the quality of irrigation are to (i) increase the efficiency of flood-irrigation, (ii) change to pressurized systems in the shallow and highly permeable soils, and (iii) reuse of drainage water for irrigation within the district. These management strategies will conserve water of high quality in the main reservoir and will decrease the crop water deficits and the volume of irrigation return flows, therefore, minimizing the off-site pollution from this irrigation district.     

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.     

Long-term water balances in La Violada irrigation district (Spain): I. Sequential assessment and minimization of closing errors

Long-term analysis of hydrologic series in irrigated areas allows identifying the main water balance components, minimizing closing errors and assessing changes in the hydrologic regime. The main water inputs [irrigation (I) and precipitation (P)] and outputs [outflow (Q) and potential (ET_c) crop evapotranspiration] in the 4000-ha La Violada irrigation district (VID) (Ebro River Basin, Spain) were measured or estimated from 1995 to 2008. A first-step, simplified water balance assuming steady state conditions (with error ? = I + P − Q − ET_c) showed that inputs were much lower than outputs in all years (average ? = −577 mm yr⁻¹ or −33% closing error). A second-step, improved water balance with the inclusion of other inputs (municipal waste waters, canal releases and lateral surface runoff) and the estimation of crop's actual evapotranspiration (ET_a) through a daily soil water balance reduced the average closing error to −13%. Since errors were always higher during the irrigated periods, when canals are full of water, a third-step, final water balance considered canal seepage (CS) as an additional input. The change in water storage in the system (ΔW) was also included in this step. CS and ΔW were estimated through a monthly soil–aquifer water balance, showing that CS was a significant component in VID. With the inclusion of CS and ΔW in the water balance equation, the 1998–2008 annual closing errors were within ±10% of total water outputs. This long-term, sequential water balance analysis in VID was an appropriate approach to accurately identify and quantify the most important water balance components while minimizing water balance closing errors.     

Water demand and flows in the São Francisco River Basin (Brazil) with increased irrigation

Most activities that support economic growth in the São Francisco River Basin (Brazil) need water. Allocation of the water resources to each competing use needs quantification in order to develop an integrated water management plan. Irrigation agriculture is the largest water consuming activity in the basin. It has produced large economic and social advancements in the region and has potential for further development. The local development agency in the São Francisco River has projected an increase of more than 500,000 ha in irrigation developments distributed within the basin.Water requirements of the projected irrigation expansions and their effects on river flow were quantified. A semi-distributed model was constructed to simulate the water balance in 16 watersheds within the basin. The watersheds were hydrologically characterized by the average precipitation, atmospheric demand and runoff as well as their variability. Water requirements for increased irrigated agriculture were calculated using an agronomic mass balance. A Monte Carlo procedure generated the variability of irrigation requirements and resulting decreased river flows from the multidimensional probability distribution of the hydrologic variables of each watershed.Irrigation requirements were found to be more variable during the wet season because of weather variability. In contrast to what might be expected, in drier years, irrigation requirements were often larger during the wet season than in the dry season because the cropped area is largest in the wet months and variability of precipitation is greater. Increased irrigation shifted downward the distribution of river flows but not enough to affect other strategic water uses such as hydropower. Further irrigation expansion may be limited by wet season flows.     

On-farm labour allocation and irrigation water use: case studies among smallholder systems in arid regions

On-farm measurements and observations of water flow, water costs and irrigation labour inputs at the individual parcel level were made in case studies of smallholder irrigation systems in sub-Saharan Africa and south-eastern Arabia. The systems, in which the water source supplied either single or multiple users, were analysed to address the fundamental issues of labour allocation for on-farm water management as this has important consequences for the success of such systems. Results show that the costs associated with accessing water influenced labour input, because when they were low the farmers tended to increase the irrigation rate and reduce the amount of time they spent distributing the water within their parcels. Conversely when water costs were high, lower flow rates and more time spent in water distribution were observed, and this resulted in more uniform irrigation and higher irrigation efficiency. Also, opportunities and demands for farmers to use their labour for activities other than irrigation can lead them to modify operational or physical aspects of the system so that they can reduce the time they spend distributing water within the parcels, particularly when the water is relatively cheap. Awareness and better understanding of how farmers may allocate their labour for water management will lead to more effective planning, design and management of smallholder irrigation systems.     

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.     

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 database program for enhancing irrigation district management in the Ebro Valley (Spain)

In the last decade irrigation districts in the Ebro Valley of Spain have started to use database applications to enhance their management operations. Such applications often put more emphasis on administrative issues than on water management issues. A new irrigation district management software called “Ador” is presented in this paper. This database application has been designed to overcome limitations identified in an analysis of the software used in the study area. Ador can be used in irrigation districts independently of the type of irrigation system (surface, sprinkler or trickle) and the type of irrigation distribution network (open channel or pressurised). It can even be used in irrigation districts combining different types of irrigation systems and different types of irrigation distribution networks. The software can be used with minimum district information. The goals are to manage detailed information about district water management and to promote better on-farm irrigation practices. Ador is currently used to enhance management of 62 irrigation districts accounting for some 173,000 hectares in the Ebro Valley.     

Improvement of irrigation management towards the sustainable use of groundwater in Castilla-La Mancha, Spain

The great expansion of irrigated lands using groundwater has often caused the exploitation of aquifer reserves beyond their recharge capacity. The development of management tools which can harmonize resource exploitation with reserve sustainability is the objective of an interesting experience being accomplished in the aquifer 08.29 in Mancha Oriental, Spain. This paper offers a summary of this ongoing project (GESMO), pointing out the specific role of the Irrigation Advisory Service. The general objective of the project is to create an integrated and integral management system of the aquifer as well as to prepare appropriate techniques for its adequate exploitation. Integral management means that both supply and demand management are considered, including the socio-economic and environmental perspectives. The concept of integrated management implies that the process must involve the majority of economic and social agents affected.

Management is founded on a Decision Support System (DSS) which takes into consideration different possible options. The DSS must contemplate the impacts on the environment, mainly the aquifer reserve losses and the increase of nitrates concentration in groundwater. The project directly affects more than 5000 agricultural users, irrigating about 100 000 ha with the aquifer water resources, as well as the whole population living in this region. Results of this project, including irrigation technologies developed may be useful for other areas in the Mediterranean Basin where similar cases occur.     

Water scarcity, prices and quotas: a review of evidence on irrigation volumetric pricing

Underpricing of irrigation water is frequently identified as a primary cause of excessive use of water for irrigation. Higher prices are believed to have the potential to promote conservation. Changes in user behavior are predicated on a quantitative relationship between water charges and the volume use, but volumetric management is quite rare in practice. This paper reviews irrigation schemes that combine conditions of water scarcity and volumetric pricing, either at the bulk or individual level, and provides clear evidence that scarcity is almost invariably dealt with through the definition of quotas. In contrast to the large theoretical literature that has promoted price-based regulation as a key instrument of water demand management, it appears that prices are mostly used to regulate use at the margin, beyond the quota, rather than for rationing scarce water. This is an important role but one that falls short of efficiency pricing. The advantages and drawbacks of quotas are discussed, and an interpretation of why they are selected in practice is given.     

Irrigated agriculture in the Guadiana River high basin (Castilla-La Mancha, Spain): environmental and socioeconomic impacts

This article is concerned with the management of the Guadiana River high basin's water resources. The region of Castilla-La Mancha in general, and Western La Mancha and the Campo de Montiel in particular, are areas where agriculture has great economic importance. This activity is the principal water consumer, but it is necessary to take account of ecological and social considerations if two important objectives are to be achieved. Firstly, to keep wetlands and biodiversity. Secondly, to maintain natural resources which are vital if the area's future is to be assured. The paper criticizes the mechanical and partial methodological focus which has been used by conventional economics and agriculture. Thus, it supports an integrated and multidisciplinary view that recognises the region's biophysical and social characteristics in such a way that policies applied respect it.     

Assessment of irrigation and environmental quality at the hydrological basin level: II. Salt and nitrate loads in irrigation return flows

Irrigation return flows may induce salt and nitrate pollution of receiving water bodies. The objectives of this study were to perform a salt and nitrogen mass balance at the hydrological basin level and to quantify the salt and nitrate loads exported in the drainage waters of three basins located in a 15,500 ha irrigation district of the Ebro River Basin (Spain). The main salt and nitrogen inputs and outputs were measured or estimated in these basins along the 2001 hydrological year. Groundwater inflows in the three basins and groundwater outflow in one basin were significant components of the measured mass balances. Thus, the off-site impact ascribed solely to irrigation in these basins was estimated in the soil drainage water. Salt concentrations in soil drainage were low (TDS of around 400–700 mg/l, depending on basins) due to the low TDS of irrigation water and the low presence of salts in the geologic materials, and were inversely related to the drainage fractions (DF = 37–57%). However, due to these high DF, salt loads in soil drainage were relatively high (between 3.4 and 4.7 Mg/ha), although moderate compared to other areas with more saline geological materials. Nitrate concentrations and nitrogen loads in soil drainage were highest (77 mg NO₃⁻/l and 195 kg N/ha) in basin III, heavily fertilized (357 kg N/ha), with the highest percentage of corn and with shallow, low water retention flood-irrigated soils. In contrast, the lowest nitrate concentrations and nitrogen loads (21 mg NO₃⁻/l and 23 kg N/ha) were found in basin II, fertilized with 203 kg N/ha and preponderant in deep, alluvial valley soils, crops with low N requirements (alfalfa and pasture), the highest non-cropped area (26% of total) and with fertigation practices in the sprinkler-irrigated fields (36% of the irrigated area). Thus, 56% of the N applied by fertilization was lost in soil drainage in basin III, as compared to only 16% in basin II. In summary, a low irrigation efficiency coupled to an inadequate management of nitrogen fertilization are responsible for the low-salt, high-nitrate concentrations in soil and surface drainage outflows from the studied basins. In consequence, higher irrigation efficiencies, optimized nitrogen fertilization and the reuse for irrigation of the low-salt, high-nitrate drainage waters are key management strategies for a better control of the off-site pollution from the studied irrigation district.     

Farmer participation in irrigation management: The case of Doroodzan Dam Irrigation Network, Iran

The importance of farmer participation in system design and management has been emphasized in previous studies. The purpose of this study was to identify the factors affecting farmer participation in irrigation management using survey research. The study was conducted in Doroodzan Dam Irrigation Network in Fars province, Iran. Multistage stratified random sampling was used to collect data from 270 farmers as the research sample. Results reveal that farmers’ attitudes toward participation in irrigation management, attitudes toward personnel of the State Water Authority and the Agricultural Extension Service Centers (AESCs), family size, the problem perception, dependence on the dam for water, and educational background have influenced their participation in irrigation management. By contrast, contact with information sources, animal units, sociability, age and agricultural experience did not affect farmers’ participation. Moreover, based on farmers’ perspectives, unequal water distribution among farms, dissatisfaction with Water Authority operators and high water fees and charges were the main problems and obstacles toward farmer participation in irrigation management.     

Factors affecting the economic benefits of sprinkler uniformity and their implications for irrigation water use

Adoption of more uniform sprinkler systems involves a trade off between increased capital expenditure on equipment and the benefits associated with reduced water application when application is uniform. An empirical analysis of the economics of lettuce production, grown using sprinkler systems under the windy conditions of the Swan Coastal plain in Western Australia is presented, where the yield response to water exhibits eventual declining marginal productivity. A range of sprinkler designs that have been field-tested for performance were examined. The optimal per-crop water application for the least efficient system was up to double the application rate of the most efficient system. However, the economic analysis demonstrates that there are clear incentives for adopting more water-efficient systems despite the higher capital cost, because of the yield depressing effect of over-watering. Sensitivity analysis demonstrates substantially poorer incentives for improving irrigation efficiency when yield relationships follow a Mitscherlich functional form.

Water reuse for irrigation in Jordan: Perceptions of water quality among farmers

The reuse of treated wastewater (reclaimed water) for irrigation is a valuable strategy to maximise available water resources, but the often marginal quality of the water can present agricultural challenges. Semi-structured interviews were held with Jordanian farmers to explore how they perceive the quality of reclaimed water. Of the 11 farmers interviewed who irrigate with reclaimed water directly near treatment plants, 10 described reclaimed water either positively or neutrally. In contrast, 27 of the 39 farmers who use reclaimed water indirectly, after it is blended with fresh water, viewed the resource negatively, although 23 of the indirect reuse farmers also recognised the nutrient benefits. Farmer perception of reclaimed water may be a function of its quality, but consideration should also be given to farmers’ capacity to manage the agricultural challenges associated with reclaimed water (salinity, irrigation system damage, marketing of produce), their actual and perceived capacity to control where and when reclaimed water is used, and their capacity to influence the quality of the water delivered to the farm.     

Yield and quality response of drip irrigated broccoli (Brassica oleracea L. var. italica) under different irrigation regimes, nitrogen applications and cultivation periods

The experiment aimed at evaluating the yield and quality response of broccoli (Brassica oleracea L. var. italica) to applied irrigation water and nitrogen by drip irrigation method during the spring and autumn cultivation periods of 2007. Irrigation water was applied based on a ratio of Class A pan evaporation (k_cp = 0.50, 0.75, 1.00 and 1.25) with 7 days interval. Also, the effect of four nitrogen levels (0 kg ha⁻¹, 150 kg ha⁻¹, 200 kg ha⁻¹ and 250 kg ha⁻¹) was compared with each treatment. The seasonal evapotranspiration in the treatments varied from 233 mm to 328 mm during the spring period and from 276 mm to 344 mm during the autumn period. The highest broccoli yield was obtained in the spring period as 11.02 t ha⁻¹ and in the autumn period as 4.55 t ha⁻¹. In general, there were statistical differences along nitrogen does with respect to yield and yield components while there were no statistically significant differences in the yield and yield components among irrigation regimes. Both yield and yield parameters in the spring period were found to be higher than that of the autumn period due to the low temperature and high rainy days in autumn. Irrigation water use efficiency (IWUE) ranged from 3.78 kg m⁻³ to 14.61 kg m⁻³ during the spring period and from 1.89 kg m⁻³ to 5.93 kg m⁻³ during the autumn period. On the other hand, nitrogen use efficiency (NUE) changed as 37.32-73.13% and 13.08-22.46% for spring and autumn season, respectively.     

River basin closure: Processes, implications and responses

Increasing water withdrawals for urban, industrial, and agricultural use have profoundly altered the hydrology of many major rivers worldwide. Coupled with degradation of water quality, low flows have induced severe environmental degradation and water has been rendered unusable by downstream users. When supply of water falls short of commitments to fulfil demand in terms of water quality and quantity within the basin and at the river mouth, for part or all of the year, basins are said to be closing. Basin closure is an anthropogenic process and manifested at societal as well as ecosystem levels, and both its causes and consequences are analyzed. Implications in terms of increased interconnectedness between categories of users and between societal processes and ecosystems in different parts of river basins are emphasized. Finally, several possible responses to the challenges posed by the overexploitation of water resources are reviewed.