(1) Field of the Invention
This invention relates to a method for cultivating a plant. More particularly it relates to a method for cultivating a plant while the plant is irradiated with an artificial light using a light-emitting lamp for plant cultivation whereby growth of the plant is promoted.
(2) Description of Related Art
Light-emitting technology has heretofore been adopted for growing seedlings or promoting growth of plants whereby a cultivation period of plants can be shortened and frequency of harvesting in the same farm can be increased. Plants can be grown to a large size within a predetermined period of time, and the crop yield can be enhanced.
As a plant cultivation technique utilizing artificial light irradiation, an illumination facility for irradiating a plant alternately with green light and white light has been proposed, for example, in patent document 1. In this illumination facility, plants are irradiated alternately with green light having a wavelength of 500 to 570 nm and white light having a wavelength of 300 to 800 nm whereby simulated day and night are created. Consequently the sugar translocation within plant bodies is smoothly effected and growth of plants is enhanced.
Another proposal has been proposed in patent document 2, which comprises an illumination lamp facility equipped with a light emitting diode (LED) for irradiating plants alternately or concurrently with blue light having a wavelength of 400-480 nm and red light having a wavelength of 620-700 nm to supply light energy for cultivation, growth, and tissue cultivation of plants. This illumination lamp facility is characterized as irradiating plants selectively with light having a wavelength corresponding to the light absorption peak of chlorophyll, i.e., in the vicinity of 450 nm and the vicinity of 660 nm whereby the plants are cultivated with an enhanced energy efficiency.
It is stipulated in patent document 2 that blue light and red light may be irradiated either concurrently or alternately (see patent document 2, claim 1). More specifically it is described in this patent document that single radiation of blue light, single radiation of red light and concurrent radiation of blue light and red light are compared with each other, and it was verified that the concurrent radiation of blue light and red light exhibited an enhanced effect on healthy growth of plants, which is similar to the growth achieved by sun light radiation, whereas the single radiation of blue light or red light brings about unhealthy growth such as spindling growth of plants (see patent document 2, paragraph [0011]).
It is further described in patent document 2 that blue light and red light are alternately irradiated by blinking by means of a blinking pattern at a high frequency of several megahertz or more (see patent document 2, paragraph [0006]). However, patent document 2 is silent on a method of alternately conducting a blue light irradiation step and a red light irradiation step, and thus growth promoting effects achieved by the alternate light irradiation method are not verified.