Agriculture Reference
In-Depth Information
Box 1
Water use efficiency
Water use efficiency (WUE) of agricultural and horticultural production
can be generally defined as the ratio of the volume of water used productively
(Stanhill
1986
). It is also termed as water productivity and expressed in units
of product weight per volume of water applied. From a physiological point
of view, WUE can be defined as the ratio between CO
2
assimilation flux, and
transpiration rate on the plant level. It can also be defined as the ratio between
CO
2
flux and the rate of water applied.
As reviewed by Castilla (
1999
), protected cultivation can improve the
water productivity due to the ET reduction, and using advanced technolo-
gies like drip irrigation, sophisticated climate control and soilless culture.
Pardossi et al. (
2004
) summarized typical values of WUE for Mediterranean
greenhouse crops. Mean values presented were 21.8, 14 and 30.3 kg m
−3
, for
tomato, cucumber and sweet pepper, respectively (Pardossi et al.
2004
and
von Zabeltitz
2011
). These values were lower by more than 50 % than cor-
responding values of 58.2, 28 and 77 kg m
−3
, obtained for the same crops
in sophisticated greenhouses in the Netherlands. Van Kooten et al. (
2004
)
reported that for a kilogram of tomatoes produced in the field, on average
used about 200 ± 100 L of water. Using drip irrigation, this amount is reduced
to about 60 L per kg, (e.g. in Israel). In high-tech greenhouses in The Nether-
lands, the average use at that time was approximately 20 L per kg. However,
applying new techniques and new irrigation methods as well as modifying the
environmental management can significantly improve water use efficiency.
The techniques include the use of light selective shading or movable screens
as well as the use of the evaporative cooling system. According to van Kooten
et al. (
2004
), it is possible to get WUE of 1.5 L water per kg tomato by closing
the greenhouse and regaining the condensed evaporated water.
Water use efficiency of screenhouse crops was estimated as the ratio be-
tween yield and applied irrigation. In an irrigation trial conducted in a large
banana screenhouse in the Jordan Valley, different levels of irrigation were
applied (100, 85, 70 and 55 %) and yield measured for each treatment. The
100 % irrigation level was actually 70 % of the irrigation supplied to open ba-
nana plantations in this region. The results of Tanny et al. (unpublished data)
showed that at 85 % irrigation the yield did not decrease as compared to the
100 % level. Irrigation at 70 % reduced the yield but this reduction was statis-
tically insignificant. The lowest irrigation level of 55 % did cause a significant
reduction in yield. Hence, the results showed that water use efficiency can be
increased by about 20-30 % by growing the banana in screenhouses in this
region of the country.
Dicken et al. (
2013
) defined WUE of a screenhouse banana plantation in
two ways. One definition was the ratio between total daily values of net CO
2
uptake and ET as measured by the Eddy Covariance system (
WUE
ET
), and
the second was the ratio between total daily net CO
2
uptake and applied daily
