Surface irrigation efficiency in cracking soils as influenced by water restrictions

An experimental study has been carried out in order to improve surface irrigation practices in cracking soils of the Lower Medjerda Valley. The experiments deal with soil depletion impact on the irrigation efficiencies. A comparison between border and furrow practices was conducted on wheat usually irrigated by the border technique in Tunisia. The advance infiltration process was analysed using calibration of the infiltration parameters on the advance trajectory (closed-end furrow and closed-end border practices). This calibration was conducted by means of two modelling approaches allowing hydraulic efficiencies to be estimated. The two main conclusions which can be derived from this study are : (1) water losses due to border practice under cracking soils can be significantly reduced by adopting the furrow practice without yield decreases ; (2) according to the furrow practice, the irrigation strategies optimizing the efficiencies (hydraulic and agronomic) consist of giving two water applications to the crop. The first insures crop emergence whereas the second has to be given when the soil water depletion reaches 90% of available water for the central region (low rainfall occurrence) and 30% for the northern region of Tunisia. The interest of coupling a water balance estimation with an operative furrow model in order to identify the best irrigation strategy on the whole irrigation campaign is here underlined. / Une étude expérimentale a été conduite dans le contexte des sols fissurés de la vallée de la Medjerda en Tunisie afin d'améliorer les pratiques d'irrigation gravitaire . Les essais devaient mettre en évidence l'impact du niveau d'épuisement des réserves en eau du sol sur le niveau des efficiences. Une comparaison entre la technique de la planche et celle raie a été effectuée. Deux types de modèles ont été utilisés pour estimer les efficiences. Les pertes en eau en irrigation à la planche peuvent être significativement réduites en adoptant la technique de la raie sans perte de rendement. La stratégie d'irrigation optimisant efficience agronomique et hydraulique consiste à effectuer deux irrigations. La première pour assurer l'émergence, tandis que la seconde est apportée quand le niveau d'épuisement de la réserve atteint 90% dans le centre et 30% dans le nord de la Tunisie.