Abstract
This study is targeted to the assessment of the saturation risk in sprinkler irrigation. For this purpose, in situ field trials were carried out to infer the saturated hydraulic conductivity (Ks) and sorptivity (S) using the disc infiltrometer method. Since the measured values of Ks are very close to prescribed application rate, caution is required. In a first step, the pressure head at the wetting front (hf) and the useful porosity (θs – θi) are assumed to be constant. Thus, the logarithmic derivation of the sorptivity provides a relation between relative variations of S and Ks. The ponding time (Ts) is estimated from Green and Ampt (1911) and Philip (1957b) infiltration equations. The risk of saturation is deemed to be inexistent inasmuch as simulated values of Ts are greater than the irrigation times practiced in the zone. In a second step, the values of the pressure head at the wetting front and saturated water content were assumed to be variable with soil texture. Simulations of the ponding time were carried out based on Rawls and al. (1981) data. For the recommended sprinkler spacing in the Cherfech perimeter (12 m × 12 m), the simulations show a good agreement between Ts values generated from Green and Ampt and Philip equations for Ks ranging from 1.5 to 6 mm/h. Moreover, it was established that saturation risk due to a gradual texture variation is virtually inexistent in the conditions prevailing in Cherfech perimeter.
Highlights
The fair distribution of water under sprinkler irrigation is a major concern
It is obvious that perfect uniformity is an idyllic schematization of the reality. This is why we investigated the impact of an eventual texture change on the ponding time
Field trials showed that optimal application rate is equal to 9 mm/h for a sprinkler spacing of 12 m × 12 m
Summary
The fair distribution of water under sprinkler irrigation is a major concern. Irrigation network should be adapted to the soil texture, crop, available water discharge, water quality and environmental conditions. The assessment of sprinkler irrigation performance was widely analyzed (Merriam & Keller, 1978; Heermann et al, 1990; Keller & Bliesner, 1990; Burt et al, 1997; Pereira, 1999). Tiercelin (1998) and Keller and Bliesner (1990) emphasized that distribution uniformity is a prominent factor in the design and management of sprinkler irrigation systems. The unfair water distribution induces harmful impact on crop yield and environment. Under irrigation may induce crop yield reduction and soil salinization. Excess of irrigation may induce crop yield reduction by asphyxia as well as a leaching of fertilizers and pesticides. Excess of irrigation may induce crop yield reduction by asphyxia as well as a leaching of fertilizers and pesticides. Solomon (1983) indicated that water stagnation and runoff has a prejudicial impact on soil and crop
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