Assessing irrigation performance in the Gediz River Basin of Turkey: water user associations versus cooperatives

The aim of this study is to compare the performance between Water User Associations (WUAs) and cooperatives in the Gediz River Basin in Turkey by applying a set of external comparative performance indicators. The indicators allow for the comparison of irrigation performance between the two organisations. Benchmarking indicators were used to best evaluate the differences, achievements and failures. The indicators included fee collection rate, cost recovery, general meeting attendance, irrigation and personnel intensity. The data was collected over a 7-year period from 1997 to 2003, inclusive. The article clearly shows that, with respect to the selected indicators, both WUAs and cooperatives performed well. Personnel intensity is the one area that both organisations could improve upon. Overall, WUAs function better than cooperatives. The findings and conclusions drawn from this research will be beneficial to managers responsible for policy-making decisions for the future attempts on irrigation management.     

Management evaluation of Water Users Associations using benchmarking techniques

The development of different tools to evaluate the performance of Water Users Associations (WUAs) is an important practice for improving water and energy management, together with other production costs. One of these tools is the Benchmarking technique, which is based on the comparison between different WUAs to determine the best practices in each of them.In this paper, a Benchmarking process is applied to seven WUAs located in Castilla-La Mancha (Spain) during three irrigation seasons (2006-2008). The performance indicators developed by the International Programme for Technology and Research in Irrigation and Drainage (IPTRID) are used, while new indicators dealing with production and energy are proposed. The goals of this paper are to group WUAs with the same characteristics, using performance and energy indicators, and to reduce the set of indicators using statistical methods. The most important indicators, easy to obtain and yielding result in maximum information are retained for further use.Three proposals reducing the initial number of indicators were proposed, with an aim of being useful for future applications based on characterizing WUAs. Indicators results highlighted that irrigable areas can be grouped based on the application of drip irrigation systems and those with sprinkler irrigation systems. When using groundwater resources, no significant differences were observed for energy consumption between these irrigation systems. This can be explained by the indicator energy load index (ICE, m), which had similar values in all WUAs analyzed. According to annual irrigation water supply per unit irrigated area (V_TSr, m³ ha⁻¹), the highest values (between 5200 m³ ha⁻¹ and 6800 m³ ha⁻¹) were obtained in WUAs with sprinkler irrigation systems, which contained crops characterized by high water requirements, compared to the V_TSr (less than 1800 m³ ha⁻¹) of WUAs with drip irrigation systems, with crops that required less volume of irrigation water. Regarding production efficiency indicators, in drip irrigation systems the high presence of vineyards, almond and olive trees, crops with low water requirements, explained high values of gross margin per unit irrigation delivery (MBVs, € m⁻³)(close to 0.82 € m⁻³) in comparison with sprinkler irrigation systems (close to 0.36 € m⁻³).     

Evaluating planning and delivery performance of Water User Associations (WUAs) in Osh Province, Kyrgyzstan

The primary objective of an irrigation organization is to provide efficient and effective management of water resources to achieve enhanced agricultural production. Performance assessment studies provide a tool to evaluate and promote this objective. The study examines the existing planning procedures and assesses irrigation performance of four Water User Associations (WUAs) located in Osh Province, Kyrgyzstan. Performance was evaluated using indicators of adequacy, efficiency, dependability and equity. Indicators were calculated for each irrigation season over the period 2003 to 2007. In general, all WUAs were found to be strong in terms of adequacy and efficiency standards. However, performance with respect to dependability and equity was poor. The results suggest that more effort is needed to improve temporal uniformity and equity in water distribution. In order to achieve this, estimations of irrigation requirements by WUA managers needs to be improved and mechanisms developed to request water in quantities, which are needed to maintain equity across the WUA outlets and among water users. The study concludes that the establishment of WUAs in Kyrgyzstan has helped to address the problem of water distribution and allocation among a large number of farmers. However, further training of farmers and managers is required to build their capacity to share water and ensure equity among users particularly during periods of less than optimal water supply. The findings of this research suggest that application of a pre-determined set of indicators can be a useful and cost effective tool to measure the performance of WUAs. This is particularly important for Central Asia where the performance of the recently established and state initiated WUAs to replace former collective farms is now a key element in future sustainable water management. The study identified uncertainties in the estimation of WUA water demands based on previous methods and suggests more attention and care required in calculating water requirements.     

Assessing the performance of participatory irrigation management over time: A case study from Turkey

In many countries today, irrigation systems have been transferred to the water user associations (WUAs). Accordingly, it is believed that the performance of the irrigation systems is dependent on the performance of the WUAs.In this study, the performance of participatory irrigation management (PIM) over time is assessed with regard to the Kestel WUA serving a wide area of Turkey's Aegean coast. Data relating to the WUA is obtained from both the State Hydraulic Works and WUAs’ own records. In addition, two surveys have been carried out with the members of the WUA with an 8-year interval between them. Data have been analyzed within the framework of selected irrigation performance criteria and indicators. The non-parametric Mann-Whitney U test was used to compare the perceptions of the farmers on the WUA at different survey periods. A Logit model was estimated to evaluate the relationship between the irrigation problems and the level of satisfaction from the WUA.The performance of the WUA with the indicators of utility, productivity, sustainability and financial efficiency was found to be positive; while the performance of adequacy was identified as poor. The farmers were generally satisfied of the WUA's operation, with their level of satisfaction improving over time. On the other hand, the farmers were not fully convinced that they had input with the system management. The initial design of the channel system and its maintenance were identified to be the key factors affecting user satisfaction.Overall, the Kestel WUA may be considered a successful example, thus supporting a promising future for PIM. Yet improved control and farmer education is needed for a superior performance of all indicators; and further enhanced farmer participation in management should be achieved in order to raise the level of farmer satisfaction.     

Crop water use of onion (Allium cepa L.) in Turkey

In a greenhouse pot experiment conducted in Turkey during 2001, onion seedlings were transplanted on May 31 at the density of five plants per pot. On this date the soil water content of all pots were at field capacity. The pots were weighed daily until harvest (December 2), and the data were used to determine the daily evapotranspiration and quantity of irrigation. Eight irrigation treatments were applied, designated as I₁ full irrigation (non-deficit treatment), and I₂, I₃ and I₄ no irrigation in the vegetative growth periods, yield formation and ripening, respectively, and I₅, I₆, I₇ and I₈ received 0.0, 0.25, 0.50 and 0.75 times the soil water depletion in the treatment I₁ on the same day. For each treatment, the following parameters were analysed and compared: applied irrigation depth, daily and seasonal evapotranspiration, bulb yield, yield response factor (k_y), irrigation water use efficiency (IWUE) and water use efficiency (WUE). The findings indicated that onion plants were very sensitive to lack of soil water during the total growing season and the yield formation period, but rather insensitive in the vegetative and ripening periods. High water use and water use efficiencies were observed with increasing levels of irrigation, or no irrigation in the vegetative period.     

Assessing the financial performance of water user associations: a case study at Great Menderes basin,Turkey

Management, operation and maintenance services of about 1.7 million ha irrigation areas, constructed the scheme by State Hydraulic Works (DSI) were turned over to Water User Association (WUA) in Turkey. The number of the WUAs is 330 in Turkey for 2005. There is therefore an urgent need to study methods of measurement and evaluation of financial performance of WUA in order to improve the financial performance and raise the management level of WUA. This paper proposes 12 financial indicators in order to measure and evaluate the financial performance of WUAs. Based on the results in four irrigation schemes and WUAs in Great Menderes basin, Turkey, the methods of measurement and calculation of financial performance indicators selected, and difference factor value related to each indicator are presented. Several financial performance indicators and difference factor values varied widely 1999 to 2004. Therefore, these financial performance indicators should be carefully evaluated and monitored for financial sustainability of WUAs.     

Estimation of crop evapotranspiration of irrigation command area using remote sensing and GIS

This paper describes the use of satellite-based remote sensing (RS) data and geographic information system (GIS) tools for estimating seasonal crop evapotranspiration in Mahi Right Bank Canal (MRBC) command area of Gujarat, India. Crop coefficients (K_c) for various major crops grown in MRBC were estimated, empirically, from the RS derived soil adjusted vegetation index (SAVI) values. A reference crop evapotranspiration (ET₀) map was generated from point meteorological observations. The K_c and ET₀ maps were combined to generate seasonal crop evapotranspiration (ET_crop) map which highlighted spatial variation in ET_crop ranging from more than 600 mm for healthy tobacco crops to less than 150 mm for very poor wheat crops.     

Methods for estimating irrigation needs of spring wheat in the middle Heihe basin,China

Understanding reference crop evapotranspiration (ET₀) is essential in planning the most effective use of water resources in the arid northwest China. The objective of the present work in the middle Heihe River basin were: (1) to determine the best model for calculating the areal distribution of reference crop evapotranspiration in this region, and (2) to estimate the spatial distribution of the irrigation requirements of spring wheat. Note that eight commonly used formulates were tested and that FAO-Penman was the best.The irrigation amount of spring wheat in 2000 was estimated by three steps. First, DEM-based and GIS-assisted methods were employed to estimate the spatial distribution of reference crop evapotranspiration (ET₀) according to FAO-Penman model. Then, spring wheat evapotranspiration (ET) was calculated by ET₀ and crop-coefficient (K_c). Finally, the maximum irrigation amount of spring wheat was estimated with the spring wheat evapotranspiration and precipitation in the different growing stage. The maximum irrigation has temporal–spatial variation. Temporally the irrigation amount appears the largest in June when it is the peak period of spring wheat development. The irrigation amount is the smallest in July because spring wheat was in late-season stage. In April, spring wheat was in seedling stage during which the water demand is also small. Spatially the irrigation amount increases from southeast to northwest.     

Estimation of dwarf green bean water use under semi-arid climate conditions through ground-based remote sensing techniques

Determination of temporal and spatial distribution of water use (WU) within agricultural land is critical for irrigation management and could be achieved by remotely sensed data. The aim of this study was to estimate WU of dwarf green beans under excessive and limited irrigation water application conditions through indicators based on remotely sensed data. For this purpose, field experiments were conducted comprising of six different irrigation water levels. Soil water content, climatic parameters, canopy temperature and spectral reflectance were all monitored. Reference evapotranspiration (ET₀), crop coefficient K_c and potential crop evapotraspiration (ET_c) were calculated by means of methods described in FAO-56. In addition, WU values were determined by using soil water balance residual and various indexes were calculated. Water use fraction (WUF), which represents both excessive and limited irrigation applications, was defined through WU, ET₀ and K_c. Based on the relationships between WUF and remotely sensed indexes, WU of each irrigation treatments were then estimated. According to comparisons between estimated and measured WU, in general crop water stress index (CWSI) can be offered for monitoring of irrigated land. At the same time, under water stress, correlation between measured WU and estimated WU based on CWSI was the highest too. However, canopy-air temperature difference (T_c − T_a) is more reliable than others for excessive water use conditions. Where there is no data related to canopy temperature, some of spectral vegetation indexes could be preferable in the estimation of WU.     

GIS user-interface based irrigation delivery performance assessment: a case study for Tanjung Karang rice irrigation scheme in Malaysia

Various indicators are used for evaluating the performance of different aspects of an irrigation system, and assessments also differ in terms of the types of performance indicators used. This paper describes a GIS-based assessment system which utilizes a new concept and evaluated the inadequacy of a widely used Relative Water Supply (RWS) concept to characterize the irrigation delivery performance for a rice irrigation system as the season advances. Development of this GIS-based assessment system resulted in the creation of new indicators, viz., the Rice Relative Water Supply (RRWS), Cumulative Rice Relative Water Supply (CRRWS) and Ponding Water Index (PWI). These indicators were determined from field tests and evaluated in a Malaysian Tanjung Karang Rice Irrigation Scheme (TAKRIS). The RWS concept was found to be inaccurate for characterizing the oversupply condition on irrigation deliveries for rice irrigation; and difficult to correctly quantify the oversupply condition for irrigation supplies. Besides, it was found that the RRWS indicator can distinctly characterize the oversupply condition for RRWS > 1.0 and undersupply condition for RRWS < 1.0 on irrigation delivery for any given period. A value of 1.0 for RRWS indicates an irrigation delivery that matches perfectly the actual field water demand. This study presents a cumulative RRWS plot that provides important information on irrigation supplies for any given time interval for management decisions. An increasing slope in the actual CRRWS curve with CRRWS = 1.0, means that irrigation supply can be slightly curtailed in the next period. On the other hand, if the slope is negative, supply has to be increased. If a computed CRRWS line follows the CRRWS = 1.0 line, it means that irrigation deliveries are perfectly matched with the field water demand. A graphical user-interface was developed for structuring the assessment tool within an ArcGIS platform. The system can instantly provide information on the uniformity of water distribution and the shortfall or excess, and provides vital information in terms of decisions that need to be made for the next period. The system helps to maintain continuous updating of input and output databases on real field conditions. Results are displayed on the computer screen together with color-coded maps, graphs and tables in a comprehensible form. The system is likely to be adopted for evaluating various water allocation scenarios and water management options. It can also be used as an analytical and operational tool for irrigation managers.     

Modelling for maize irrigation scheduling using long term experimental data from Plovdiv region, Bulgaria

Independent historic datasets on irrigated maize, collected over seven years (1984-1990), were used to parameterize the irrigation scheduling model ISAREG. Experimental data were obtained under rainfed, deficit, and full irrigation conditions in an alluvial soil at Tsalapitsa, Plovdiv region, in the Thracian plain, Bulgaria. Crop coefficients and depletion fractions for no-stress were calibrated by minimizing the differences between observed and simulated soil water content. The calibration was performed using data from full irrigation and rainfed treatments while deficit irrigation treatments were used for validation. The modelling efficiency was high, 0.91 for the calibration and 0.89 for the validation. The resulting average absolute errors of the estimate for the soil water content were smaller than 0.01 cm³ cm⁻³. The model was also tested by comparing computed versus observed seasonal evapotranspiration. Results for dry years show a modelling efficiency of 0.96 but the model slightly underestimated evapotranspiration for other years. The yield response factor was derived from observed yield data of the hybrid variety H708 when relative evapotranspiration deficits were smaller than 0.5. The value K_y = 1.32 was obtained. The relative yield decreases predicted with this K_y value compared well with observed data. Results support the use of the ISAREG model for developing water saving irrigation schedules for the Thracian plain.     

Temporal irrigation performance assessment in Turkey: Menemen case study

During the recent decades, there has been an increasing effort to transfer the management of irrigation schemes from government organizations to non-governmental organizations as decentralization gained momentum and as states started to devolve some of their functions to different groups in the society. Irrigation management in Turkey was also affected by these developments. Since 1993, approximately 90% of the public irrigation schemes were turned over to the locally managed farmer organizations.This study was conducted in the Menemen Irrigation Scheme, to assess the temporal variations of agricultural, water use, environmental and financial performance indicators for the pre-transfer (1984–1994) and the post-transfer (1995–2004) periods.Results showed, after 10 years of transfer, a continued improvement in irrigation performance. The most important finding of the study was a considerable increase in output per unit of land and per unit of water after turnover. Irrigation management transfer (IMT) provided a dramatic achievement in water fee collection efficiencies and more financially self-sustaining organizations. Therefore, it can be safely concluded that the transfer process created more sustainable management for irrigation.     

Semi-empirical approach for estimating actual evapotranspiration in Greece

Reliable estimation of actual evapotranspiration rates (ET) may be achieved if extensive information on the soil–plant–atmosphere system is available. Agricultural and irrigation engineers facing the problem of rational irrigation planning, rarely have at their disposal such information. Therefore, there is a demand for simpler approaches to estimate actual evapotranspiration. In this paper, a semi-empirical approach is proposed for estimating actual water losses from crops. It is assumed that the ratio of actual to maximum evapotranspiration (ET/ET_m) is an exponential function of the water content w in the root-zone, of the form: ET/ET_m=exp[c(w−w_fc)/(w−w_wp)], where c is a constant introduced to adjust the decrease of the ratio ET/ET_m according to what is observed for the climatic conditions, soils and crops of Greece, w_fc the water content at field capacity and w_wp denotes the water content at wilting point. Verification of the above approach for estimating actual evapotranspiration was achieved by comparing ET-values obtained by the soil moisture profile changes and the ET-values obtained by the above equation. Meteorological, crop and soil data required were collected from experimental fields of the Agricultural University of Athens (38°23′N, 23°6′E). The agreement of actual versus computed ET-values for three widely grown crops in Greece (cotton, wheat and maize) may be considered as satisfactory.     

Early morning fluctuations in trunk diameter are highly sensitive to water stress in nectarine trees

The sensitivity to water stress of different plant water status indicators was evaluated during two consecutive years in early nectarine trees grown in a semi-arid region. Measurements were made post-harvest and two irrigation treatments were applied: a control treatment (CTL), irrigated at 120 % of crop evapotranspiration demand to achieve non-limiting water conditions, and a deficit irrigation treatment, that applied around 37 % less water than CTL during late postharvest. The plant water status indicators evaluated were midday stem water potential (Ψ _stem) and indices derived from trunk diameter fluctuations: maximum daily shrinkage (MDS), trunk daily growth rate, early daily shrinkage measured between 0900 and 1200 hours solar time (EDS), and late daily shrinkage that occurred between 1200 hours solar time and the moment that minimum trunk diameter was reached (typically 1600 hours solar time). The most sensitive [highest ratio of signal intensity (SI) to noise] indices to water stress were Ψ _stem and EDS. The SI of EDS was greater than that of Ψ _stem, although with greater variability. EDS was a better index than MDS, with higher SI and similar variability. Although MDS was linearly related to Ψ _stem down to ?1.5 MPa, it decreased thereafter with increasing water stress. In contrast, EDS was linearly related to Ψ _stem, although the slope of the regression decreased as the season progressed, as in the case of MDS. Further studies are needed to determine whether EDS is a sensitive index of water stress in a range of species.     

General irrigation efficiency for field water management

On-farm water management systems are traditionally evaluated using a set of performance indices which are inconvenient for evaluation and comparison. We propose a general efficiency (E_g) which is defined as the ratio of crop transpiration to the sum of the volume of applied water and the volume of deficit. E_g combines the characteristics of traditionally used irrigation efficiencies: application efficiency (E_a), storage efficiency (E_s) and the Christiansen's coefficient of uniformity (U_c). Thus, it is possible to compare the performance of different water application systems and/or design and management scenarios using a single index. The relationships of E_g vs. E_a, E_s and U_c are also presented using a transpiration fraction (α) which is defined as the ratio of transpiration to evapotranspiration.     

Irrigation planning in cotton through simulation modeling

Experiments were undertaken at CCS Haryana Agricultural University Farm, Sirsa (India) to estimate the optimum irrigation schedule for cotton resulting in minimum percolation losses. The sprinkler line source technique was adopted for creating various irrigation regimes at different crop growth stages. The SWASALT (Simulation of Water And SALT) model after calibration and validation provided water balance components. The wa-ter management response indicators (WMRI's) such as transpiration efficiency E_t/(Irr + P), relative transpiration E_t/E_tp, evapotranspiration efficiency ET/(Irr + P), soil moisture storage change ΔW/W_int (deficit/excess) and percolation loss Perc/(Irr. + P) were evaluated using water balance components as estimated by the simulation study. Under limited water supply conditions, the optimum irrigation depth was found to be 57 mm at crop growth stages with pre-sowing and 1^st irrigation of 120 mm and 80 mm respectively for sandy clay loam underlain by sandy loam soil (Type I). The corresponding values of relative transpiration, transpiration efficiency and evapotranspiration efficiency were 0.65, 0.65 and 0.89 respectively. The crop yield varied linearly with increasing irrigation depth which was evident from increase in relative transpiration with increasing depth of water application. However, increased depth of irrigation resulted in less moisture utilisation from soil storage (20% depletion at 40 mm depth and 4.4% moisture built up at 100 mm depth). The extended simulation study for sandy soil underlain by loamy sand (Type II) indicated that two pre-sowing irrigations each 40 mm and subsequent irrigations of 40 mm at an interval of 20 days depending upon rainfall were optimum. This irrigation scenario resulted in zero percolation loss accompanied by 74% relative transpiration and 14 per cent soil moisture depletion. Received: 20 November 1995     

Temporal and spatial variations of evapotranspiration for spring wheat in the Shiyang river basin in northwest China

The methods for estimating temporal and spatial variation of crop evapotranspiration are useful tools for irrigation scheduling and regional water allocation. The purpose of this study was to develop a method for mapping spatial distribution of crop evapotranspiration and analyze the temporal and spatial variation of spring wheat evapotranspiration in the Shiyang river basin in Northwest China in the last 50 years. DEM-based methods were employed to estimate the spatial distribution of spring wheat evapotranspiration (ET_c). Reference crop evapotranspiration (ET₀) was calculated with the Penman–Monteith equation using meteorological data measured from eight stations in the basin. Crop coefficient (K_c) was determined from measured evapotranspiration in spring wheat season in the region. The results showed that ET_c gradually increased in the upper reaches of the basin in the last 50 years, while the middle reaches showed a significant decreasing trend, and in other regions, no significant trend was found. These changes can be attributed to expansion of irrigation areas and climate change. The multiple regression analysis between ET_c and altitude, latitude, and aspect were carried out for eight weather stations and the relationships were used to map ET_c for the basin. The spatial variations of ET_c were analyzed for three typical growing seasons based their precipitation. Results showed that long-term average ET_c over cultivated land was increasing from 270 mm in southwest mountainous area to 591 mm in northeast oasis of the basin, and the relative error between the estimated ET_c in spring wheat growing season by reference evapotranspiration (ET₀) and crop coefficient (K_c), and the interpolated ET_c was within 11.1%.     

Agricultural water management in a humid region: sensitivity to climate,soil and crop parameters

A sensitivity analysis of irrigation water requirements at the regional scale was conducted for the humid southeastern United States. The GIS-based water resources and agricultural permitting and planning system (GWRAPPS), a regional scale, GIS-based, crop water requirement model, was used to simulate the effect of climate, soil, and crop parameters on crop irrigation requirements. The effects of reference evapotranspiration (ET_o) methods, available soil water holding capacities (ASWHC), crop coefficients (K_c), and crop root zone depths (z) were quantified for 203 ferneries and 152 potato farms. The irrigation demand exhibited a positive relationship with K_c and z, a negative relationship with ASWHC, and seasonal variations depending on the choice of ET_o methods. The average irrigation demand was most sensitive to the choice of K_c with a 10% shift in K_c values resulting in approximately 15% change in irrigation requirements. Most ET_o methods performed reasonably well in estimating annual irrigation requirements as compared to the FAO-56 PM method. However, large differences in monthly irrigation estimates were observed due to the effect of the seasonal variability exhibited by the methods. Our results suggested that the selection of ET_o method is more critical when modeling irrigation requirements at a shorter temporal scale (daily or monthly) as necessary for many applications, such as daily irrigation scheduling, than at a longer temporal scale (seasonal or annual). The irrigation requirements were more sensitive to z when the resultant timing of irrigation coincided with rainfall events. When compared with the overall average of the irrigation requirements differences, the site-to-site variability was low for K_c values and high for the other variables. In particular, soil properties had considerable average regional differences and variability among sites. Thus, the extrapolation of site-specific sensitivity studies may not be appropriate for the determination of regional responses crop water demand.     

Water requirement of drip irrigated tomatoes grown in greenhouse in tropical environment

Four different levels of drip fertigated irrigation equivalent to 100, 75, 50 and 25% of crop evapotranspiration (ET_c), based on Penman–Monteith (PM) method, were tested for their effect on crop growth, crop yield, and water productivity. Tomato (Lycopersicon esculentum, Troy 489 variety) plants were grown in a poly-net greenhouse. Results were compared with the open cultivation system as a control. Two modes of irrigation application namely continuous and intermittent were used. The distribution uniformity, emitter flow rate and pressure head were used to evaluate the performance of drip irrigation system with emitters of 2, 4, 6, and 8 l/h discharge. The results revealed that the optimum water requirement for the Troy 489 variety of tomato is around 75% of the ET_c. Based on this, the actual irrigation water for tomato crop in tropical greenhouse could be recommended between 4.1 and 5.6 mm day⁻¹ or equivalent to 0.3–0.4 l plant⁻¹ day⁻¹. Statistically, the effect of depth of water application on the crop growth, yield and irrigation water productivity was significant, while the irrigation mode did not show any effect on the crop performance. Drip irrigation at 75% of ET_c provided the maximum crop yields and irrigation water productivity. Based on the observed climatic data inside the greenhouse, the calculated ET_c matched the 75–80% of the ET_c computed with the climatic parameters observed in the open environment. The distribution uniformity dropped from 93.4 to 90.6%. The emitter flow rate was also dropped by about 5–10% over the experimental period. This is due to clogging caused by minerals of fertilizer and algae in the emitters. It was recommended that the cleaning of irrigation equipments (pipe and emitter) should be done at least once during the entire cultivation period.     

Determination of evapotranspiration from an alfalfa crop irrigated with saline waste water from an electrical power plant

Summary Investigations were carried out in 1989 to determine the evapotranspiration (ET) of alfalfa when irrigated with saline waste water coming from the evaporation of fresh water in the cooling towers of Utah Power and Light Company Electrical Power Plant at Huntington in central Utah, U.S.A. The primary goal is to dispose of the waste water from the power plant by irrigation and to maximize salt deposition in the soil, maximize crop ET, minimize runoff from the soil surface, and minimize leaching to the ground water. Using the Bowen ratio-energy balance method, alfalfa evapotranspiration was measured at an experimental site for each 20-minute period during the 1989 irrigation season. Using a simplified seasonal water balance, the results showed that cumulative irrigation plus rain was less than evapotranspiration for the 1989 irrigation season. This means that for the long term in addition to irrigation and precipitation some water was withdrawn from the soil for alfalfa crop water requirements (ET_a). Short term evaluations showed that because of unforeseen heavy rain (thunder showers) in this mountainous area between irrigations, ET_a was occasionally less than irrigation plus rain. This means the excess water was stored in the soil for later use. The average value for ET_a/ET_p (potential ET) for the 1989 irrigation season was 0.47 but occasionally the ratio was greater than unity. Short-term studies (Hanks et al. 1990 a) indicate that yield and ET_a are likely to decrease only slightly for the coming years if saline irrigation water is applied. This method of investigation can be applied to any industrial processes which produce waste water.