Yield and Water-Use Efficiency of Pearl Millet (Pennisetum glaucum (L.) R. Br.) under Deficit Irrigation with Saline Water in Arid Conditions of Southern Tunisia

摘要

A 2-years experiment (2005-2006) was conducted in Southern Tunisia to determine the effect of deficit irrigation regimes with saline water on soil salinity, growth, yield and water use efficiency of millet (Pennisetum glaucum (L.) R. Br.). Millet was grown in a commercial farm during summer season on a sandy soil and drip-irrigated with water having an ECi of 7.6 dS m-1 for both experiments, a complete randomized block design with four replicates was used to evaluate four irrigation regimes. Irrigation treatments consisted in water replacements of accumulated crop Evapotranspiration (ETc) at levels of 100% (100 L) 80% (80 L) 60% (60 L) and 40% (40 L), when the readily available water in the control treatment (100 L) is depleted. Findings are globally consistent between the two experiments. Results show that salinity was lowest under emitters and highest midway to the margin of wetted bands. Under emitters it increased gradually between 100 and 40 L from 2.75-6.10 dS m-1 in 2005, from 1.95-4.92 dS m-1 in 2006. Highest ECe values were found to occur at about 20 and 7 cm from emitters, respectively for 100 and 40 L. For both experiments, LAI decreased significantly as the amount of applied water decreased from 100-40% of ETc. Yields were highest under 100 L. From values of 26.70 and 27.65 q ha 1, respectively for 1st and 2nd year, yields decreased almost linearly when applied water was reduced. However, reduction in quality was significantly important for 60 and 40 L. The analysis outcome of the crop sensitivity to salt indicated that threshold are close to the value calculated from published salt tolerance data (3.46 vs. 3.65 dS m-1) but the slope are considerably steeper (17 vs. 6.7%), apparently because of the combined effect of salinity and water stresses. Water Use Efficiency (WUE) was found to vary significantly among treatments, where the highest (7.60 kg/ha/mm) and the lowest (6.4 kg/ha/mm) values were obtained from 60 and 100 L treatments, respectively. Finally, results support the practicality of using the 100% of ETc methodology to optimize irrigation with saline water for millet production and to control soil salinity. Under situations of water shortage, the deficit irrigation strategy (80% of ETc) is recommended as a tool to schedule irrigation of millet crop in arid regions of Tunisia.