Effect of irrigation regimes using saline water on faba bean (Vicia faba L.) yield and water productivity in an arid environment*

A 2-year study was conducted to assess the effects of irrigation regimes using saline water on soil salinization, yield, water productivity, and net income of faba bean (Vicia faba L.) under actual farming conditions in arid regions of Tunisia. Faba bean (cvs. Luz de Otono and local) was grown on a sandy soil and drip-irrigated with water having an electrical conductivity of 6 dS m(-1). Two deficit irrigation (DI70 and DI40) and one full irrigation (FI) strategy consisting of applications of 40%, 70%, and 100% of crop evapotranspiration (ETc), respectively, were compared to the traditional farmers' irrigation method (FM) in which 16 mm irrigation were applied every 5 days from planting till harvest. Results showed that the lowest soil salinity values at harvest were observed under FI treatment, while the highest were obtained with DI40 and the FM. The maximum values of faba bean yields were obtained under FI and the lowest with the FM. No significant reduction in yields was observed with the DI70 treatment compared to FI, while DI40 and the FM significantly decreased the fresh pod yields. Using 12%-20% more irrigation water than FI treatment, the FM did not improve soil salinity but resulted in a significant yield reduction compared to FI. Total water productivity values varied between 4.9 (FM) and 14 kg m(-3) (DI40) across different years and treatments. Compared to the FM, which applies fixed amounts with the same frequency, the FI strategy, which adapts the irrigation amounts to the actual crop water requirements, was more productive and provided a significant advantage in terms of yield and net income. Under limited availability of irrigation water, adoption of the DI70 treatment was found to be a good alternative as it allowed 30% water saving and was subject to limited negative effects on soil salinity, yield, and net income.