Soil evaporation from drip-irrigated olive orchards

• Published in: Irrigation science Vol. 20; no. 2; pp. 65 - 71
• Main Authors: Bonachela, Santiago, Francisco Orgaz, Francisco J. Villalobos, Elías Fereres
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer-Verlag 01.06.2001; Springer Nature B.V
• Subjects: Drip irrigation; drying; Environmental conditions; environmental factors; Evaporation; Evapotranspiration; Ground cover; Heat transfer; Herbivores; Irrigation; Mediterranean climate; microirrigation; olives; Orchards; prediction; rain; soil; Soil surfaces; Soils; Spain, Cordoba; water conservation; water potential; Spain
• ISSN: 0342-7188; 1432-1319
• DOI: 10.1007/s002710000030

Evaporation from the soil (Eₛ) in the areas wetted by emitters under drip irrigation was characterised in the semi-arid, Mediterranean climate of Córdoba (Spain). A sharp discontinuity in Eₛ was observed at the boundary of the wet zone, with values decreasing sharply in the surrounding dry area. A single mean value of evaporation from the wet zone (Eₛw) was determined using microlysimeters. Evaporation from the wet zones of two drip-irrigated olive orchards was clearly higher than the corresponding values of Eₛcalculated assuming complete and uniform soil wetting (Eₛₒ), demonstrating the occurrence of micro-scale advection in olive orchards under drip irrigation. Measurements over several days showed that the increase in evaporation due to microadvection was roughly constant regardless of location and of the fraction of incident radiation reaching the soil. Thus, daily evaporation from wet drip-irrigated soil areas (Eₛw) could be estimated as the sum of Eₛₒand an additive microadvective term (TMA). To quantify the microadvective effects, we developed variable local advective conditions by locating a single emitter in the centre of a 1.5 ha bare plot which was subjected to drying cycles. Eₛwincreased relative to Eₛₒ as the soil dried and advective heat transfer increased evaporation from the area wetted by the emitter. The microadvective effects on Eₛwere quantified using a microadvective coefficient (Kₛw), defined as the ratio between Eₛwand Eₛₒ. A model was then developed to calculate TMAfor different environmental and orchard conditions. The model was validated by comparing measured Eₛwagainst simulated evaporation (Eₛₒ+TMA) for different soil positions and environmental conditions in two drip-irrigated olive orchards. The mean absolute error of the prediction was 0.53 mm day–¹, which represents about a 7% error in evaporation. The model was used to evaluate the relative importance of seasonal Eₛlosses during an irrigation season under Córdoba conditions. Evaporation from the emitter zones (Eₛw) represented a fraction of seasonal orchard evapotranspiration (ET), which ranged from 4% to 12% for a mature (36% ground cover) and from 18% to 43% of ET for a young orchard (5% ground cover), depending on the fraction of soil surface wetted by the emitters. Estimated potential water savings by shifting from surface to subsurface drip ranged from 18 to 58 mm in a mature orchard and from 28 to 93 mm in a young orchard, assuming daily drip applications and absence of rainfall during the irrigation season.