GB2140262A - A method for improving plant growth - Google Patents

Abstract

A method for improving plant growth comprises illuminating the plants with a source of light of wave length from 380 to 800 nanometres, which is moved over the plants and parallel to a support for the plants to provide intermittent illumination thereof. <IMAGE>

Description

SPECIFICATION Method of improving plant growth The present invention relates to a method for improving plant growth in greenhouses and climatic cells by subjecting them to inter mittent illumination.

"Greenhouses and climatic cells" will be understood, within the meaning of this text, to be any enclosures in which conditions appro priate to plant cultivation, particularly temper ature, hygrometry and lighting conditions, are reproduced artificially, in part or whole.

The use of greenhouses and climatic cells makes it possible to grow plants outside their usual cultivation season, for example in winter, while the usual cultivation season extends, in general, only over the spring/ summer period.

To achieve this, it is necessary of course to reproduce inside the greenhouse or climatic cells the best conditions appropriate to ensur ing a satisfactory development of the plant, particularly the appropriate conditions of tem perature, hygrometry and illumination. The conditions to be employed will of course be very different, depending on whether the intention is to cultivate temperate climate crops, such as wheat, or tropical or subtropical cli mate crops, such asscotton or soya.

While the provision of appropriate conditions does not present insurmountable difficulties where temperature and hygrometry are concerned, this is not the case for the provision of appropriate conditions of illumination in greenhouses and climatic cells, most particularly when the intention is to recreate the lighting conditions required for the cultivation of tropical or subtropical plants. In fact, the lighting system must then satisfy many highly exacting conditions, namely: (a) it must provide the plants with an illumination capable of reaching, if need be (that is to say depending on the crop), very high values, attaining and even exceeding 100,000 lux in the region of the plant.

(b) the illumination must be distributed very uniformly over the cultivation zone, (c) the lighting system must be placed at a sufficient height above the cultivation zone so that it does not interfere either with the plant growth or with the handling required for their cultivation, (d) finally, in the case of greenhouses, the lighting system must obstruct as little as possible the entry of sunlight into the greenhouse from outside.

For this purpose, it is usual to employ a set of fluorescent tubes fixed to the upper part of the greenhouse or the climatic cell, these tubes being mutually parallel, adjacent to each other and situtated in the same horizontal plane, very close to each other, so as to form together a rectangular source of light whose verical projection on the lower part of the greenhouse or climatic cell represents the area to be illuminated. As an example, to illuminate a ground area of 6 m x 6 m, 180 fluorescent tubes are used, each of 215 watts, placed 0.90 m above the zone in which the plants will be iocated.The main disadvantage of this system is that despite the use of a large number of tubes, it is difficult to obtain an illumination (luminous flux) attaining even as much as 40,000 lux at plant level, which is completely inadequate when it is intended to cultivate tropical or, subtropical plants.

Another disadvantage of this system is that it requires a large number of fluorescent tubes and hence involves both a major investment and also a very high energy consumption.

This high energy consumption results in a heat release, itself high, inside the greenhouse or climatic cell and it is therefore necessary to provide a more extensive system for controlling the temperature, to maintain the latter at the required value. Finally, with such a system, in the case of a greenhouse, sunlight is practically completely screened off and as a result the light from outside is not utilised at all.

Replacement of the tubes with more powerful lamps, such as, for example, discharge lamps, whose unit power can be 1 ,000 or even 2,000 watts is not wholly satisfactory either, because problems of lack of uniformity of the illumination then arise and even in this case it is hardly possible to obtain more than 50,000 lux at the plant level. The disadvantages referred to earlier and related to the consumption of energy and to the dissipation of this energy in the form of heat inside the greenhouse of the enclosure are also present of course when lamps are employed instead of fluorescent tubes.As a result of these inadequacies of the illumination in greenhouses or climatic cells, it is found that plants cultivated in such conditions have an appearance which generally differs from those cultivated in an open field under optimum conditions in respect of these plants; those cultivated in a greenhouse or climatic cells are very frequently etiolated, more fragile and less green than those cultivated in an open field. These differences are most particularly awkard when it is intended to experiment in a greenhouse or climatic cell with pesticide products which are intended for agricultural use and which will therefore be employed, as a rule, for treatments carried out in an open field; it is most particularly essential for such experiments that the trials in a greenhouse should be as similar as possible to trials in open field.

According to the present invention there is provided a method for improving plant growth in greenhouses or climatic cells, comprising.

illuminating the plants by means of a movable source of light situated above the plants and moved along a path which is substantially parallel to the surface where the plants are arranged, the source of light comprising mainly radiations of wavelengths between 380 nanometres and 800 nanometres and travelling above the plants according to a uniform motion so as to create an intermittent illumination at plant level.

The method of the present invention can largely overcome the disadvantages of the known techniques and promote to the maximum extent the phenomenum of photo-synthesis in the plants, thereby producing plants with a high chlorophyll content, and developing to the maximum extent the capability of the plants to assimilate carbon dioxide from the atmosphere and to produce oxygen.

With the method of the invention it is possible to produce under greenhouse conditions plants whose growth is as close as possible to the growth in the open field, as much in respect of the height, as size, vigour, branching, budding and flowering.

The method of the invention can be carried out employing apparatus which is simple and expends the minimum of energy. The luminous energy incident on the leaves can be distributed in a homogeneous manner, whatever the inclination of the leaves and whatever the location of the leaves on the plant (outside or inside the foliage).

It is also possible to reduce significantly invisible radiations, particularly ultraviolet radiations. Besides the hazards which such radiations introduce to the people tending the plants, these radiations are frequently the cause of degradation of agricultural chemical products applied to the plants, which annihilates the beneficial effect of these products and interferes with the experiments where experiments are involved.

Preferably, the radiations have a wavelength between 450 and 750 nanometres. While the plants could be arranged on a concave or convex support and the source of light moved along a curved path, advantageously the plants are arranged over a substantially flat horizontal area and the source of light moves in a substantial horizontal plane parallel to said area.

One way of carrying out the invention is for the plants to be arranged over an area of a substantially rectangular shape and the source of light also to be the shape of a rectangle, one of whose dimensions is substantially equal to one of the sides of the zone of a substantially rectangular shape which is to be illuminated.

The source of light may move in a direction parallel to one of the sides of the rectangular zone to be illuminated (the source of light having a dimension in common with the other side of the zone to be illuminated).

In practice, during its travel, the rectangular source of light gradually illuminates all the points of the substantially rectangular horizontal area over which the plants are arranged.

The source of light preferably travels with a regular motion at constant speed, either in one direction or in another. A reciprocating motion may be involved.

Where the area to be illuminated, which is of a rectangular shape, in fact consisted of a series of rectangles capable of forming a closed circuit, the source of light would then be able to travel along each of these rectangles and itself also follow a closed circuit.

In such a situation, for a given rectangle to be illuminated the source of light always moves in the same direction above it.

As stated above, the rectangular source of light generally comprises several lamps. These lamps are advantageously arranged inside a reflecting housing with a substantially rectangular cross-section.

In order that the invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which: Figure 1 is a schematic plan view of one embodiment of apparatus for carrying out the method of the invention; and Figure 2 is a similar view of a second embodiment.

In the construction of Fig. 1 a rectangular source of light, formed by a reflecting housing 1 in which are arranged four discharge lamps 2, each of 1,000 watts which are shown in phantom inside the housing, travels in the direction shown by the arrows above a bench 3 of a substantially rectangular shape on which will be arranged the plants to be cultivated (not shown in Fig. 1). The rectangular source of light is moved with a regular to-andfro or reciprocating motion, first from an end position A to the opposite end position B, then from B towards A, and so on.

For the sake of simplicity, we have not shown in Fig. 1 the means for electrical connection permitting the electric current to be conducted to the lamps, nor the mechanical means permitting the source of light to be moved. In practice, it is possible advantageously to provide for this purpose two guide rails situated above the longitudinal sides of the bench 3 and to fit conveyor rollers at both longitudinal ends of the housing 2 so that the housing can travel on these guide rails in the direction shown.

Fig. 2 shows another embodiment, in which the reflecting housing 1 situated above the bench 3 is movable in the directions shown by the arrow, and comprises ten discharge lamps each of 1,000 watts, shown in broken lines. The source of light, consisting of the lamps and the housing, travels with a regular reciprocating motion from A towards B then from B towards A. It is possible, of course, to employ a greater or smaller number of lamps then that shown in Figs. 1 and 2 and the invention must not therefore be restricted only to the arrangements shown in these figures.

As will readily be understood from the em bodiments illustrnted by these figures, the method of the invention makes it possible to "sweep" in a regular manner the whole of the rectangular horizontal area referred to above, supplying the intended quantity of light to it in a very uniform manner.

The distance separating the plane in which the source of light travels from that of the rectangular horizontal area on which the crops are placed can be determined depending on the power of the source of light and on the desired luminous flux at plant level. Thus, as an example, for a 1.6 m distance between planes, the source of light shown in Fig. 1 supplies, at each pass, 50,000 lux to the plant situated vertically below it, while that shown in Fig. 2, more especially intended for a climatic cell, supplies nearly 100,000 lux per pass.

In a greenhouse, such a system produces only a very slight screening of the external light, which can therefore be advantageously used in addition.

The travelling speed of the source of light can be chosen within wide limits, although it has been found that, whatever the plants cultivated, the best results were obtained with speeds ranging from 2 m/min to 8 m/min and preferably at a speed of 4 m/min.

The pass cycle time of the source of light can also vary within wide limits, but it is advantageous nevertheless to carry out a pass of the source of light above each plant per period of 45 seconds to 3 minutes, preferably one pass per period of 1 to 2 minutes.

The following examples, given without implying a restriction, illustrate the invention and show how it can be put to use.

Example 1 A source of light (4 X 1,000 watts) such as shown in Fig. 1 is used for a greenhouse test.

The reflector 1 (or light-shade) serving as lamp carrier is fitted, at both of its ends, with rollers (not shown) permitting it to travel in the direction shown by the arrows, on horizontal rails, (not shown) situated 1.6 m above the long sides of the bench 3 the length of which is 6 m. This source of light emits radiations in the visible range only.

Seeds of wheat, mustard and soya are sown in seed pans on this bench and are kept in the usual conditions of temperatures and hygrometry. The lamps are switched on. The source of light travels with a reciprocating motion above the bench at a speed of 4 m/min from 7 o-clock in the morning to 9 o-clock in the evening. It is switched off the remainder of the time. After 35 days under these conditions it is found that the plants produced have an appearance which is completely similar to that of the same plants obtained in the open field.

Example 2 Example 1 is reproduced by cultivating bean plants in pots under illumination from the beginning of the sowing of seeds.

One half of the bean plants is subjected to an intermittent illumination (movable source of light) as in Example 1. The other half is subjected to an illumination which is identical from the point of view of the source of light but not intermittent (fixed source of light).

After 1 5 days, 1 5 leaves are sampled from each of the two bean populations and chlorophylls A and B are extracted by means of a water/acetone mixture and these chlorophylls are then determined by spectrophotometry.

It is found that the plants under fixed illumination contain 0.67 mg of chlorophyll per gram of bean leaf, while plants under mobile illumination contain 0.89 mg/g, i.e.

approximately 33% more.

Example 3 Example 1 is reproduced with various types of plants by carrying out a comparative experiment with plants subjected to a fixed illumination by the same lamps.

1 5 days after the start of the experiment the following observations are made in respect of bean and soya plants: Bean The average height of the plants obtained under movable illumination is reduced by 35% relative to the height of the plants obtained under fixed illumination. The plants obtained under movable illumination are therefore shorter but more vigorous, markedly green and similar to those obtained in an open field; the plants obtained under fixed illumination, on the other hand, are etiolated, i.e. they are excessibely high and thin; furthermore, they have a high tendency to lie down the stem having insufficient vigour to remain upright.

Soya: The average height of the plants obtained under mobile illumination is reduced by 25% relative to the plants obtained under fixed illumination. However, these plants obtained under mobile illumination are more vigorous and have a habit or bearing, as well as a colour, which are similar to that of plants obtained in an open field.

Millet (Echinocloa crus galli): The germination or shoot formation is obtained in 4 days after sowing under mobile lamps and in 8 days after sowing under fixed lamps.

Claims (14)

1. A method for improving plant growth in greenhouses or climatic cells, comprising illuminating the plants by means of a movable source of light situated above the plants and moved along a path which is substantially parallel to the surface where the plants are arranged, the source of light comprising mainly radiations of waveiengths between 380 nanometres and 800 nanometres and travelling above the plants according to a uniform motion so as to create an intermittent illumination at plant level.

2. A method according to claim 1, wherein said radiations have a wavelength between 450 and 750 nanometres.

3. A method according to claim 1 or 2, wherein the plant are arranged over an substantially flat horizontal area and the source of light moves in a substantially horizontal plane parallel to said area.

4. A method according to claim 1, 2 or 3, wherein the plants are arranged over an area of a substantially rectangular shape and the source of light is also in the shape of a rectangle one of whose dimensions is substantially equal to one of the sides of the zone of substantially rectangular shape to be illuminated.

5. A method according to claim 4, wherein, the source of light moves in a direction parallel to one of the sides of the rectangular zone to be illuminated the source of light having one dimension in common with the other side of the zone to be illuminated.

6. A method according to claim 4 or 5, wherein during its travel, the rectangular source of light gradually illuminates all the points of the substantially rectangular horizontal area on which the plants are arranged.

7. A method according to any preceding claim, in which the source of light travels at a substantially constant speed.

8. A method according to any preceding claim in which the source of light travels with a reciprocating motion.

9. A method according to any preceding claim, in which the zone to be illuminated consists of a series of rectangular zones.

10. A method according to claim 8, in which the source of light follows a closed circuit.

11. A method according to any preceding claim, in which the source of light passes above the plants once per period of 45 seconds to 3 minutes.

1 2. A method according to claim 11, in which the source of light passes above the plants once per period of 1 to 2 minutes.

1 3. A method of improving plant growth substantially as hereinbefore described with reference to and as illustrated in Fig. 1 of the accompanying drawings.

14. A method of improving plant growth substantially as hereinbefore described with reference to and as illustrated in Fig. 2 of the accompanying drawings.