Chapter 5. SOLAR RADIATION ENVIRONMENT
5.1 Introduction
Solar radiation is one of the most important environmental factors for plant growth.
In general it is know that radiation is generated from a material close to a blackbody,
Solar radiation received at the earth's “surface varies with the season because of the
geographical relation between the sun and the earth. Therefore, it is very important to
calculate how much of it we can utilize at a given place on the earth at a certain time of the
yeah
Coverings can improve the temperature environment by increasing inside temperature,
but they cannot enhance the solar radiation level. Shading to decrease solar radiation level
is sometimes important. but in most cases, the most important problem is minimizing the
reduction of solar radiation due to coverings.
Three properties of coverings are related to the solar radiation environment:
transmissivity, reflectivity and absorptivity. It is hard to see with the human eye, but solar
radiation is decreased by reflectivity and absorptivity as it travels through transparent films.
in a normal situation, the amount of solar radiation transmitted into the covered area is less
than that outside.
These properties are dependent on wavelength. PVC film in the early years created
serious problems for eggplant production under PVC cover, because its stabilizer absorbed
solar radiation in the ultraviolet region (290 - 360 nm) that triggers the violet coloring of
eggplants. Another problem is that the eyes of honeybees are sensitive in the ultraviolet
region (< 400 nm), and the bees cannot fly well if the covering does not transmit solar
radiation in this region. Therefore, it is essential to be careful about the spectral distribution
of the transmitted solar radiation if you are growing plants whose color is generated by
anthocyan (a pigment for red to violet color) and whose flowers are pollinated by bees.