Abstract
Agricultural water reservoirs (AWRs) are commonly used to guarantee water supply throughout the whole irrigation season in arid and semiarid areas. An important fraction of the total stored water is lost through evaporation, substantially decreasing overall irrigation efficiency. In this study, the effects of suspended shade cloth covers (SSCCs) on reducing evaporation and on the quality of the stored water have been experimentally assessed. To this aim, an AWR located in south-eastern Spain was monitored during two consecutive years. During the first year, the AWR remained uncovered, while during the second year it was covered with a black polyethylene SSCC. The evaporation rate, the water temperature profile and the driving meteorological variables determining evaporation were measured to assess the technical viability of the cover. Evaporation measurements for covered conditions were compared with estimations obtained from an openwater evaporation model which was validated during the first year of experimentation. A reduction close to 85% in the evaporation rate was found. To assess the effects on water quality, water samples and measurements with a multiparametric instrument were monthly collected during the two-year experimental period. Electrical conductivity, chlorophyll concentration and turbidity were measured using this equipment. Results indicate that the reduction in solar radiation (1% transmission through the cover) dramatically reduced the photosynthetic activity; hence algal bloom was highly limited. Finally, the main benefits and costs associated with the cover installation were identified in order to analyse economic viability under different scenarios representative of the current irrigated farming situation in south-eastern Spain.
Highlights
In arid and semi-arid regions, where water is scarce and its availability varies seasonally, Agricultural Water Reservoirs (AWRs) for irrigation are commonly used to guarantee water supply throughout the whole irrigation season (Daigo and Phaovattana, 1999; Martínez Alvarez et al, 2006; Ali et al, 2008)
Annual rainfall averages 350 mm, with high seasonal and inter-annual variability; most precipitation occurs during the fall and winter months
The polyethylene mesh achieved an annual evaporation reduction factor (FR = 1-electrical conductivity (EC)/E) of 84%, similar to the one found by Martínez Álvarez et al (2006) in previous trials with Class-A evaporation pans
Summary
In arid and semi-arid regions, where water is scarce and its availability varies seasonally, Agricultural Water Reservoirs (AWRs) for irrigation are commonly used to guarantee water supply throughout the whole irrigation season (Daigo and Phaovattana, 1999; Martínez Alvarez et al, 2006; Ali et al, 2008). Craig et al (2005) estimated that in many areas of Australia, up to 40% of the water stored in on-farm reservoirs can be lost to evaporation These figures indicate that in regions facing water shortages, the implementation of techniques to reduce evaporation from AWRs is as important as promoting highly efficient on-farm irrigation systems and techniques. Craig et al (2005) evaluated the efficiency of a porous shade cover on a shallow dam (3.8 ha, 3 m depth) located in south-eastern Queensland (Australia), where the evaporative demand is very high (2,200 mm year–1). They achieved evaporation reductions up to 87% for summer months. Martinez-Alvarez et al / Span J Agric Res (2010) 8(S2), S122-S133 viability of SSCCs under different scenarios representative of the current farming situation in south-eastern Spain is analyzed
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