Page 9 - index

Israel Agriculture 2015

100%
85%

70%

55%

Fig. 3: Evapotranspiration from a banana plantation. Blue (EC): Fig. 4: Mean annual banana yield as a function of the mean annual
Measured ET; Red (PM-sc): Modelled ET from a plantation inside a irrigation, for the years 2004-2007. Percentage indicates the irrigation
screenhouse; Green (PM-ref,out): Modelled ET of a banana plantation amount relative to open banana plantations in this region.
outside the screenhouse; Dashed line: Irrigation.

the modifed ET model for internal screenhouse conditions, but this reduction was not statistically signifcant. The lowest
previously developed by Möller et al. (2004). Figure 3 presents irrigation level of 55% did cause a signifcant reduction in yield.
daily evapotranspiration over a period of 14 days in June Hence, water use efciency can be increased by about 20-30%
2005. The results show that the screenhouse model is close by reducing irrigation when growing bananas in screenhouses
to the measurements. However, the model for reference ET in this region.
under external conditions is signifcantly higher, illustrating Our research group also examined the potential to increase
the efect of the screenhouse in reducing evapotranspiration. water use efciency by covering other crops with screens.
The results of Fig. 3 further show that irrigation (dashed Preliminary results in apple orchards demonstrated that an
horizontal line) was consistently higher than the actual crop increase in WUE of about 15% is attainable. Future projects
water use. Note that this irrigation level was already about will study WUE of other orchard and vegetable crops covered
70% of the irrigation supplied to open banana plantations in with screens.
this region. Although irrigation was increased from JD (Julian
day) 166, actual crop water consumption did not change, Acknowledgements
suggesting the possibility of water savings. The research was funded by grants from the Chief Scientist
Sensitivity analysis was applied to the reference of the Ministry of Agriculture, and from BARD The
evapotranspiration model. The analysis showed that the main United States-Israel Binational Agricultural Research and
factors contributing to the reduced ET in the screenhouse Development Fund.
were radiation and wind. Radiation reduction by the screen
was the major factor in reducing the ET between 07:30 and References
14:00, whereas wind speed reduction by the screen was most Allen, R. G., Pereira, L.S., Raes, D. M., (1998). Crop
signifcant for the ET reduction during late afernoon (afer evapotranspiration, guidelines for computing crop water
15:00). Air temperature and humidity modifcations by the requirements. FAO Irrigation and Drainage Paper 56, FAO,
screenhouse had a much smaller efect on reducing ET. Rome, Italy.
Water use efciency is an important agricultural parameter Möller, M., Tanny, J., Li, Y., and Cohen, S., (2004). Measuring and
because it tells the farmer the expected yield per plant water predicting evapotranspiration in an insect-proof screenhouse.
consumption. Water use efciency (WUE) can be defned as Agric. For. Meteorol., 127, :35-51.
the ratio between yield and applied irrigation. In an irrigation Tanny, J., Haijun, L., Cohen, S. (2006). Airfow characteristics,
trial conducted in a large banana screenhouse in the Jordan energy balance and eddy covariance measurements in a
Valley, diferent levels of irrigation were applied (100%, 85%, banana screenhouse. Agric. For. Meteorol., 139, (1-2), 105-
70% and 55%) and yield was measured for each treatment. 118.
The 100% irrigation level was based on that used for open
banana plantations in the region. The results (Fig. 4) showed
that at 85% irrigation the yield did not decrease as compared
to the 100% level. Irrigation at 70% reduced the yield slightly tanai@volcani.agri.gov.il

9