Agriculture Reference
In-Depth Information
characteristics, as well as the duration
of the day and night are primary ele-
ments of the climate.
The qualitative characteristics of solar
a certain delay, the evolution of solar
radiation.
Soil temperature follows, with smaller
•
•
differences, the evolution of the air
temperature. The daily oscillations of
soil temperature decrease as the depth
increases.
Wind conditions are very important for
radiation, especially the proportions of
diffuse and direct radiation, are impor-
tant for greenhouses.
Solar radiation or global solar radiation,
•
•
is basically composed of: (i) UV radia-
tion, which accounts for 2-4% of the
total of the solar energy; (ii) PAR radia-
tion (photoactive radiation) which
accounts for 45-50% of the total solar
energy and is indispensable for photo-
synthesis; and (iii) IR radiation which
accounts for the remaining 50% of solar
energy.
The solar constant is the global radi-
greenhouses. The wind force is a basic
consideration in the design of green-
house structure while the wind direc-
tion and velocity are important for
ventilation and the energy balance.
The composition of the atmosphere is
•
very important particularly regarding
water vapour content and CO
2
content.
The water vapour content of the atmos-
•
•
phere is usually represented by the RH
of the air, but it is more precise to quan-
tify it by the water vapour pressure of
the air or its VPD.
The CO
ation intensity outside the Earth's
atmosphere and has a value between
1360 and 1395 W m
−2
. At the Earth's
surface, the intensity of radiation is
only in the order of 75% of the solar
constant, due to absorption, dispersion
and reflection of the solar radiation in
the Earth's atmospheric layer.
Solar radiation varies greatly with lati-
•
2
concentration in the air has
risen in the last half century from 300
to 360 ppm.
Rainfall influences the design of green-
•
houses as it affects the collection, evac-
uation and storage devices of rainfall
water.
Altitude affects the quality of the solar
•
tude; throughout the year, it varies
depending on the season, being minimum
in winter and maximum in summer.
The Earth emits long-wavelength radi-
•
radiation (affecting the proportions of
direct and diffuse radiation).
Topography may affect solar radiation
•
ation (far IR), known as the 'Earth's
radiation'.
Air temperature varies in 24 h cycles.
•
because of the shadows that may be
produced, but it also affects the wind
and thermal regimes.
•
The average temperature follows, with
