Studying the effects of deficit irrigation as an on-farm strategy on carrot yield in arid environment

Abstract

The deficit irrigation (DI) as an on-farm water management strategy was tested for 3-years to determine the water requirements and productivity, soil salinity and yield for carrot irrigated with saline water (3.6 dS/m) under actual farming conditions in southern Tunisia. The irrigation regimes were full (I100) and deficit (I80 and I60) irrigated with levels of 100, 80 and 60% of ETc when the readily available water, 35% of total available water (TAW), in the I100 treatment was depleted, and traditional farmer practice (Farmer). Regulated DI regime where 40% reduction is applied only during ripening stage (I60-ripening) was also used . Higher soil salinity is observed at harvest under I60 and Farmer treatments compared to I100. Carrot yield was highest over 3 years for the I100 scheduling technique, (29.5, 28.7 and 26.8 t/ha) although no significant differences were observed with the I60-ripening strategy . However, the I80 and I60 treatments caused significant reductions in carrot yields through a reduction in roots number and weight in comparison with I100. The farmer’s method not only caused significant reductions in yield but also resulted in using 43 to 57 % more water and increased soil salinity. For all treatments, carrot yields were higher in first than the two following years. Water productivity (WP) values reflected this difference and varied between absolute extremes of 3.3 and 9.7 kg/m 3 . WP was the greatest in the I60 treatment and the least in the Farmer's strategy. I100 irrigation strategy provides significant advantage on yield and WP compared to farmer’s method in carrot production. Therefore, for water-saving purposes, the I100 irrigation scheduling is recommended to optimize the use of saline water in carrot production and to control soil salinity. Nonetheless, under water scarcity, irrigation of carrot could be scheduled using I60-ripening and I80 deficit strategies, with some yield reductions (4-15%).