In Tunisia, the expansion of irrigated area and the semiarid climate make it compulsory to adopt strategies of
water management to increase water use efficiency. Subsurface drip irrigation (SDI), providing the application of
high frequency small irrigation volumes below the soil surface have been increasingly used to enhance irrigation
efficiency.
At the same time, deficit irrigation (DI) has shown successful results with a large number of crop in various
countries. However, for some crops like potatoes, DI is difficult to manage due to the rapid effect of water stress
on tuber yield. Irrigation frequency is a key factor to schedule subsurface drip irrigation because, even maintaining
the total seasonal volume, soil wetting patterns can result different during the growth period, with consequence
on crop yield. Despite the need to enhance water use efficiency, only a few studies related to deficit irrigation of
horticultural crops have been made in Tunisia.
Objective of the paper was to assess the effects of different on-farm irrigation strategies on water use efficiency
of potatoes crop irrigated with subsurface drip irrigation in a semiarid area of central Tunisia. After validation,
Hydrus-2D model was used to simulate soil water status in the root zone, to evaluate actual crop evapotranspiration
and then to estimate indirectly water use efficiency (IWUE), defined as the ratio between crop yield and total
amount of water supplied with irrigation.
Field experiments, were carried out in Central Tunisia (10◦ 33’ 47.0” E, 35◦ 58’ 8.1◦ N, 19 m a.s.l) on a potatoes
crop planted in a sandy loam soil, during the growing season 2014, from January 15 (plantation of tubers) to May
6 (harvesting). Soil water status was monitored in two plots (T1 and T2) maintained under the same management,
but different irrigation volumes, provided by a SDI system. In particular, irrigation was scheduled according to the
average water content measured in the root zone, with a total of 8 watering, with timing ranging between one and
three hours in T1, and between about half-an-hour and one-hour and a-half, in T2.
The validity of Hydrus-2D model was initially assessed based on the comparison between measured and estimated
soil water content at different distances from the emitter (RMSE values were not higher than 0.036). Then,
model simulations allowed to verify that it is possible to enhance irrigation water use efficiency by increasing
the frequency of irrigation even maintaining limited water deficit conditions during the full development stage
subsequent the crop tuberization. Experimental results, joined to model simulations can therefore provide useful
guidelines for a more sustainable use of irrigation water in countries characterised by semi-arid environments and
limited availability of water resources