Agriculture Reference
In-Depth Information
risk of several common plant diseases, which may also lead to a reduced pesticide
application (Baille 2001 ).
In the literature different approaches for greenhouse heating, and their effects on
air temperature, were investigated. For example, Bartzanas et al. (2005) have dem-
onstrated that in a tunnel where tomato was grown, combining heating pipes with
air heaters increased the temperature difference between inside and outside from 10
to 15 °C during night. It was also shown that with the air heater, although the mass
transfer conductance to the cover was higher, the condensation flux was smaller
which resulted in less condensation at the inner surface of the cover.
In 2000 Kempkes and co-workers (Kempkes et al. 2000 ) developed a simulation
model to predict the effects of the heating system on the vertical distribution of crop
temperature and transpiration. The simulation model predicted crop temperature
distribution as a function of the position and temperature, of the heating pipes, as
well as the vertical distribution of crop evaporation. In addition Teitel and Tanny
( 1998 ) investigated the effects of pipe positioning and pipe surface temperature on
radiative heating of the crop and found that the best pipe position was near the crop
at its mid-height and that at low pipe surface temperatures, the radiative heating ef-
ficiency increased sharply with the surface temperature.
Screenhouses and Screen Covers
In screenhouses, due to the strong interaction between the inside and outside, heat-
ing or cooling is non-practical. It is commonly accepted that climate control in
screenhouses is passive, namely, it is governed by factors such as screen type,
screen deployment, and structural and canopy properties that cannot be actively
manipulated by the grower (Tanny 2013 ).
Tanny et al. ( 2009b ) demonstrated the effect of shade in reducing the air tem-
perature in an apple orchard in northern Israel. Results showed that during daytime,
air temperature under the screened plots and near the foliage were lower by about
1.4 °C than at the exposed plots (Fig. 10.8 ). During night-time, air temperature un-
der the screened treatments was larger by about 0.3 °C than under the exposed ones
due to the reduced long wave radiative cooling effect under the screens. The air hu-
midity under the screens was found to be higher than that in the exposed treatments
during daytime, which may lead to lower ET and hence water saving.
Kittas et al. ( 2012 ) measured both air and leaf temperature of tomato plants un-
der different shading treatments and showed that although the air temperature un-
der the shade was almost similar to that without shade, leaf temperature of shaded
plants was nearly 5 °C lower than un-shaded plants. This temperature reduction was
associated with a 50 % reduction in VPD of the shaded plants in comparison with
the un-shaded ones. The equality of air temperature under the shaded and exposed
treatments was attributed by Kittas et al. ( 2012 ) to the fact that the shading screens
they used were deployed only on the roof and not on the sidewalls, and that the
measurements were done near the coast where sea breeze is significant. Both fac-
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