Agriculture Reference
In-Depth Information
(b)
30
Culiacán (Mexico)
25
May
Jun
Apr
20
Mar
Aug
Jul
Feb
15
Sep
Oct
Jan
Nov
10
Dec
5
0
0
5
10
15
20
25
30
Ensenada (Mexico)
30
Jul
Jun
May
Apr
Aug
25
Mar
20
Sep
Feb
Oct
15
Jan
Nov
Dec
10
5
0
0
5
10
15
20
25
30
30
Guanajuato (Mexico)
25
Apr
Mar
May
Feb
20
Aug
Jul
Sep
Jun
Jan
Oct
Nov
15
Dec
10
5
0
0
5
10
15
20
25
30
Temperature (°C)
Fig. 2.15.
Continued.
The expression VPD is the one that is used
most often from a biological point of view. It is
expressed in vapour pressure units and quan-
tifies the 'drying power of the air'. The VPD nota-
bly influences transpiration and evaporation.
Dew point is the temperature at which
the air water vapour starts to condense, due
to reaching saturation. In greenhouses, this
condensation starts on the coldest objects,
initially on the greenhouse roof cover and
walls.
The evapotranspiration (ET) inte-
grates the water evaporated from the soil
and that transpired by the vegetation. It
will vary with the climate conditions
VPD =
e
s
−
e
a
(2.4)
The atmosphere is normally sub-saturated, i.e.
the
e
a
is usually lower at ambient temperature
than its corresponding saturation value (
e
s
).
