CA1317762C - Method and structure for improved natural lighting for plant growth - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method and structure for improved natural lighting for plant growth, particularly for mass production of horticultural crops in environmental conditions where normal solar lighting may be inadequate for horticultural production within a greenhouse structure. The structure comprises a translucent shell on a base, the shell and base enclosing a predetermined space within which plants are to be grown.
reflective surface is situated adjacent major portions of the base, outside the shell and preferably below the level of the base, to reflect solar radiation into the space through the shell. The structure may also be provided with other features tending to increase the exposure of solar radiation to the plants.

Description

13:l7~2 BACKGROUN~_OF THE INVENTION

Thi~ invention relates to a method and structure for improved natural lighting for plant growth and more particularly to a method and structure for mass production of horticultural crops in environmental conditions where solar lighting under conventional conditions may be inadequate for horticultural production within a greenhouse structure.
Traditional greenhouse structures consisting of transearent panes of glass forming a roof to enclose a growing area, drawing air from the outside and having a heating system for winter months, while adequate for many purposes, possess many shortcomings which make them unsuitable for year-round production of many types of fruits and vegetables in certain climatic conditions, e.g. in climates where temperature and light conditions may be poor. Because such greenhouses often are not well sealed against the outside environment, unsuitable temperature differentials may be created within. As well, outside air which may contain substances which are not conducive to proper growth of plants, is permitted to enter.
~lso, exhaust products from the greenhouse heating system, which often is a natural gas or oil furnace may be present in the environment within such greenhouses again causing reduced plant growth. The water which is used in such greenhouses is often local water and again may contain impurities or compositions which impede plant growth. There is an incLeasing - 2 - ~

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awareness of the detrimental impact of impurities in the air or water on plant growth. In addition, the concentration of elements for plant growth such as calcium, nitrogen and phosphorous in water being fed to elants in conventional greenhouses may change Erom day-to-day, resulting in irregular plant growth.
As a result, in recent yeacs there has been a trend towards development of controlled environment horticultural or ageicultural installations. F'or example, Canadian Patent No.
1,097,075 oE Miller issued March lOo 19~1 describes and illustrates a nutrien~ supply system for such a controlled environment agricultural installation incorporating nutrient film techniques in which plant root masses are arranged to be wetted by contact with a small stream of liquid nutrient.
Capillary attraction or wicking then is relied upon to extend the nutrient-wetted area over and through the entire root mass. Nutrient supply is achieved by positioning the plant roots in long troughs and flowing a thin stream of liquid nutrient along the bottom of the trough permitting the stream to contact each of the plant root masses as i-t flows along.
Excess nutrient is recycled usually after any needed replenishment of its compositional elements.
Such attempts to control in a greenhouse the various conditions responsible for plant growth have heretofore been extremely limited in scope. Thus, for example, in Miller Canadian Patent No. 1,09~,075, only the nutrient feed is ~3~7~2 controlled. In Canadian Patent No. 982,426 of Delano et al issued January 27, 1976, a method of controlling the amount of solar heat and light which enters a glass or plastic greenhouse is described wherein a liquid is coated on the glas6 or plastic film of the greenhouse. The li~uid dries into a coating which is transparent under certain conditions and non-transparent under other conditions. In Canadian Patent No. 955,748 of Glatti et al issued October 8, 198~, the ligh~ passing through a translucent covering of a greenhouse is par-tially controlled by coating the inner surface o~ the translucent covering with a surface-active agent, which surface-active agent reduces the contact angle of water-condensate droplets formed on the inner surface thereof to below 75.
Other patents of general background interest describing different types of greenhouse structures include U.S. Patent No. 4.195,441 of Baldwin issued April 1, 19~0 (solar greenhouse in which plants are used as solar collectors to absorb solar radiation and store it in a heat reservoir benea~h the greenhouse) and U.S. Patent No. 4,352,256 of Kranz issued October 5, 1982 (greenhouse structure including a central hub and arms comprising growth chambers extending radially outwardly therefrom).
While previous attempts to provide controlled environment horticultural installations have apparently been successful for the limited purposes for which they were developed, such structures have not really addressed the ;

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difficulties of producing horticultural crops in any quantity using natural lighting at latitudes where solar angles are very low, e.g. during winter months. Thus, for example, even with a properly maintained greenhouse installation, during winter months the solar angle may be so low that little or no fruit or vegetable production can be achieved in plants within the greenhouse. Thus, for example in Canada and -the Northern United States, during the middle winter months when the solar angle is lowest, plants such as tomatoes and cucumbers will not produce vegetables. As well the growth rates of such elants are significantly reduced as compared to their growth rates during the summer months when the solar angle is greatest.
Hence, up till now, it has been virtually impossible to go into large scale production of fruit and vegetables in such regions, during the winter months, and virtually all of the fresh fruits and vegetables to be consumed persons inhabiting such regions during the winter months have had to be imported from more temperate regions where the solar angle is higher and fresh fruits and vegetables can be produced either in greenhouse or outdoor conditions.
Thus, it is an object of the present invention to provide a struc-ture and method for improved natural lighting for plant grow-th which will permit large scale production of horticultural crops even in conditions of relatively low solar angle such as those experienced in Northern United States or Southern Canadian areas during the winter months.

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SVMMARY OF THE INVENTION

According to the present invention, a reflective surface is provided about a structure within which to grow plants. The structure comprises a translucent shell on a base enclosing a eredetermined space within which plants are to be grown. The surface is situated adjacent major portions of the base, outside the shell, to reflect solar radiation into the space through the shell.
In a preferred embodiment of the present invention the reflective surface is created by water ponds located beside the base, and the structure comprises a plurality of elongated shells and bases radially e~tending about a central shell to which the elongated shells are interconnected to the space of the central shell. The shells are each of a shape and are positioned so as not to minimize their shadows cast at any time on another shell. The ponds are positioned between the elongated shells.
The shell of the structure may be a stressed membrane space enclosure such as is described in my U.S. Patent No.
4,137,687 issued February 6, 1979.
The structure in accordance with the present invention has significantly contributed to the winter growing, under natural lighting, of tomatoes and cucumbers at 90% of summer production rates, at the latitude of Calgary, Alberta, Canada.
Heretofore such production at that latitude in the middle oE

~3~77~2 winter was thought to be impossible. The plants were grown in a sealed environment within a translucent stressed fabric shell, the space between the base and shell being sealed against external environmental air conditions, and the temperature, humidity and carbon dioxide conditions within the space being controlled for optimum conditions for plant growth, as described in my co-pending Canadian Application Serial No. 555,398 filed December 24, 1987.
The structure and method according to the present invention provide increased plant growth, including increased yields of fruit and vegetables, over increased periods of time at low solar angles such as experienced in winter-time in Canadian or Northern United States cities.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will become apparent upon reading the following detailed description and upon referring to the drawings in which:
FIGURE 1 is a perspective view of a structure in accordance with the present invention;
FIGURE 2 is a plan view of the structure of FIGURE 1;
FIGURE 3 is a cross-sectional view along lines III-III of FIGURE 2, through a shell and base of one of the plant production areas of the structure of FIGURE 1; and 13 ~ 7 1 & ~
F'IGURE 4 is a partial view :Erom the outside of the shell of one of such areas.
While the invention will be described in conjunction with an example embodiment, it will be understood that it is not intended to limit the invention to such embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAI~ED DESCRIPTION OF THE INVENTION

In the drawings, similar features have been given similar reference numerals.
Turning to FIGURES 1 and 2 there is illustrated a greenhouse structure 2 in accordance with the present invention, having elongated plant production areas 4 radially extending outwardly from a central plant immature crop development area 6 and a central control area 8. The production areas 4 are interconnected to the central shell of the immature crop development area 6 but not to each other, as illustrated in FIGURE 2. I'he production and immature crop development areas 4 and 6 are enclosed by an impermeable translucent stressed fabric shell 12 situated on a base 14, the shell and base enclosing a predetermined space (e.g. production areas 4 or immature crop development areas 6). Shell 12 is 1 3 lL 7 ~
ereferably made of a technically woven polyvinyl chloride coated polyester scrim, with about a 95% light translucency.
Such a fabric is highly effec-tive in providing natural light inside the structure. The fabric is preferably lightweight (e.g. 18 ounces per square yard), flame resistant as well as resistant ~o oil, chemicals, greases, rot, mildew and certain types of bacteria which attack eolyvinyl chlorides and which are prevalent in a moist environment. It is preferably held between arched rib members 15 which rest on the base, the rib members being spread to tension the Eabric, ~or example as described in my U.S. Patent No. 4,137,687 issued E'ebruary 6, 1979.
In addition, as can be seen in FIGURE 3, the delivery of light to the interior of the structure is further enhanced by the fact that there are very few pipes, waterlines or other physical obstructions allowed above the growing root area.
~lso, as illustra~ed in FIGURE 3 base 14 for production area 4 is elevated with respect to, and preferably surrounded by, reflective surface 16, which may be a light coloured surface e.g. of reflective plastic (not shown), or, water ponds as illustrated, ice surEaces (in below-freezing temperatures) or the like. In this manner, even when there is a low solar angle, light is transmitted by reflection, as well as diLectly, into the structure through shell 12. ~s can be seen in FIGURE 3, the sides which make up shell 12 extend upward, from base 14, in convex fashion and meet at crest 18, ~3177~
forming two sides 20 and 22 for the shells of each of the elongated production areas 4. It is preferred that shells 12 and corresponding bases 14 of each of the production areas 4 and immature crop development areas 6 seal the environment within such areas against external environmental air conditions. This makes eossible the close control of environmental conditions within each of the areas of the structure, such as humidity and carbon dioxide concentration.
Otherwise this would not be possible.
Each of the shells over production areas 4 and immature crop development areas 6 is provided with an external spray supply system 40 consisting of a series of pipes supplying water from a source 42 preferably in central con~rol area B, and feeding the water through these pipes to spray nozzles 44 (FIGURE 4) to spray a -thin film of water over the exterior surface of shell 12 to cool it as required.
To achieve this end the water is first sprayed from nozzles 44 through the air and onto the exterior of shell 12 in a dispersed pattern as illustrated. This spraying through the air provides for evaporative cooling of the water, thereby supplying additional cooling potential to shell 12. ~ensors 30 in shell 12 are electronically connected to microprocessor 10 and, either on a timed sequence or as the temperature of the shell builds up to a certain range, it activates solenoid valves (not shown) to cause water to be sprayed through nozzles 44 over exterior surface of the shell to cool it. The shape of 13~7~2 shells 12 over production areas ~ and immature crop development areas 6 is such that this water film will run down the exterioL
surface of the shells. Nozzles ~ are preferably directed to provide an even spray over most of the exterior surface of shell 12 over production areas 4 and 6, as required. Water so sprayed over shells 12 may be collected, for e~ample, in the external ponds 16 forming the reflective surface, or by any other appropriate retrieval means.
Besides cooling the shell, this water from the external vapour system cleans the fabric and also magnifies and increases the light intensity as its enters the structure.
This magnification factor increases the light intensity in such a way that it is much brighter inside the structure than outside, thus contributing to the significantly increased growth rate of plants exeerienced inside shell lZ.
Thus, the structure in accordance with the present invention is highly effective in providing maximum natural light inside the greenhouse. This natural light is provided by refraction, diffusion, magnification and reflection:
(a) Refraction - As the ligh-t passes through ~he fabric of shell 12, it is bent. I'his allows all areas to receive an equal amoun-t of light since the light waves are bent around stationary objects i.e. plants.

` ~3~62 (b) Diffusion - As the light enters the structure it is diffused and scattered in all directions. As a result thexe is an equal amount of light from one side to the other for all plants. This diffusion factor also reduces any shadows that may be cast over the plants by people, plants, cable, etcetera.
(c) Maqni~ication - The water from the external spray system 40, which cleans and cools the fabric, will also tend to magnify and focus or concentrate light rays as they enter the structure. This magnification factor increases the light intensity in such a way that it is much brighter inside the structure than outside. This increased light contributes to the improved growth rate inside the structure.
(d) Reflection - The light reflected into the structure from the ponds 16 surrounding the complex in the summer months, and snow on top of these ponds in the winter months, accounts for a large portion of the increased light intensity inside the structure. ~s well, ice on the ponds in winter-time not only re~lects light into the space under shell 12 as well as the water in the summer, but also maintains snow, in the spring-time, on its surface a longer time than 1 3 ~ 2 otherwise would be the case. Snow is an excellent reflector of light.
~dditionally the level of light that is obtained inside the structure is substantially increased by the fact that very few piees, waterlines or other physical obstructions, required for normal operation in the production and immature crop development areas, are allowed above the growing root area of the plants. ~s a result approximately 18% more light is obtained in applicant's s-tructure as opposted to a conventional greenhouse. Also the base lg within the structure is reflective - e.g. of white or other light reflective colour.
The actual radial layout of production areas 4 (FIGURES l and 2) was developed in order to maximize all available light. The distance between the structures themselves and their shape and orientation minimize the shading of the production areas 4 or immature crop development areas 6 by other areas. Since minimization of light interception i8 the main objective, any form of shading is undesirable. The shells thus cast shadows only at the lowest of solar elevations which only occur for a very short period of any day.
In addition, this arrangement of the structures allows for a large empty region in between each building, which, through ponds 16, is maintained full of water or ice or snow.
Incidental light in these regions is thus reflected back towards eroduction areas 4 or immature crop development areas 6. The actual amount of light which thus reaches the growing ~3~7~2 areas is greater than that which is purely incidental. In addition, because the reflected light tends to come into from below base 14 (FIGURE 3), a more uniorm pattern of light intensity is realized within the production areas. This low angle light enables a second crop to grow and perform under a more mature crop. Without this total light pattern, the interception of the primary incidental light by the mature plants would prevent the young plants from developing normally.
It should be noted that each of the ponds 16 is in fluid communication with adjacent ponds 16. In this manner if the water level in one pond or ano-ther, for some reason, becomes low so that pond would otherwise tend to dry out, water is supplied to that pond from the other ponds. The ponds also receive and collect water passed over the exterior surface of shells 12 by the external vapour system 40.
In one application of the invention, a series of temperature monitors 24, carbon dioxide moni-tors 26 and relative humidity monitors 28 are provided for the interior atmosphere within each of the production areas 4 and immature crop development areas 6 in question (FIGURE 3). As well, in the shell covering each of the areas 4 and 6 are embedded temperature sensors 30. Carbon dioxide delivery systems 32 and nutrient delivery systems 34 (FIGURE 1), the systems delivering respectively carbon dioxide and nutrient solution from sources preferably located in central control area 8 are provided for each of the production areas 4 and immature crop development 13~7~
areas 6. Microprocessor 10 (FIGURE 2), electronically connected -to monitors 24, 26, 28 and 30, controls the delivery of carbon dioxide from a source 36 and nutrient from reservoir tanks 38 in central control area 8 to areas 4 and 6.
The temperature and relative humidity within each of the production areas 4 and immature crop development areas ~ is controlled by a sophisticated and sometimes interrelated series of systems. First of all, for temperature control, each of the shells over production areas 4 and immature crop development areas 6 is provided with an external spray system 40 (F'IGURES

3, 4) consisting of a series of pipes 42 supplying water which may be, for example from a source (not shown) in central control area 8 or from ponds 16, and feeding the water through these piees to spray nozzles 44 (FIGURE 4) to spray a thin film of water over the exterior surface of shell 12 to cool it as required. Sensors 30 in shell 12 are electronically connected to microprocessor 10 and, either on a timed sequence or as the temperature of the shell builds up to a certain range, it activates solenoid valves (not shown) to cause water -to be sprayed through nozzles 44 over exterior surface oE the shell to cool it. The shape of shells 12 over production areas 4 and immature crop development areas 6 is such that this water film will run down the exterior surface of the shells. Nozzles 44 are preferably directed to provide an even spray over most of the exterior surface of shell 12 over production areas 4 and 6, as required. Water so sprayed over shells 12 may be collected, 13~ 7~2 for example, in the external eonds 16 forming the reflective surface, or by any other approeriate retrieval means.
In-ternally, temperature control is achieved through internal mist generation system 4B (FIGURE 3) which comprises water supply pipes 50 feeding fog nozzles 52, which nozzles produce, as required, a fine mist or cloud in the atmosphere in the space over plants 54. This internal mist generation system is activated by temperature monitors 24 elec-tronically connected to microprocessor lO,, which microprocessor activates -the internal mist generation system when -the temperature within the immature crop development or production area exceeds a predetermined level or on a timed sequence. The production of the mist or cloud causes cooling in two ways. Firstly, it impedes the passage of rays of sunlight to the plants, thereby cooling by shading. Secondly, as the mist or cloud evaporates under the heated conditions within the shell, the evaporation draws heat from the environment in the space in the shell. The evaporated water vaeour condenses on the cooler shell surface (cooled if necessary by external spray system 40), passing the heat of condensation into the shell Eabric. The shell fabric is of a heat conductive material and heat is thereby passed from the internal to the external side of the shell and out of the internal environment of production area 4 or immature crop development area 6.
Water vapour thus condensing on the interior surface of shell 12 ~which may include wa-ter vapour from transpiration ~ 3 ~ ;J\
- of the elants 5~) travels down the sides of the shell and i6 collected by means of collection skirts 56 passing into slots 57 in collection pipes 58 (F'IGURE 5), collection pipes 5~
returning this condensed water to a central location where it may be used as required, preferably being mixed with nutrient in tanks 38 (FIGURE l). This system ~hus acts as a large scale water distillation system, the water received by the plants in solution with the nutri.ent having been purified by means of this distillation process.
As well, as one can imagine, one of the problems of adapting a greenhouse structure in which the internal environment is sealed against external environmental air conditions, when applied to large scale production from crops within the greenhouse, is the build up of water vapour in the air. This build up results from transpiration from the plants. If it is eermitted to continue unchecked, the relative humidity in the greenhouse structure will build up to the eoint that transpiration of the plants is significantly impeded. As plants LeqUire transpiration for example to cool their leaves and to draw nutrient solution through the plant system, the growth of the plant is thus adversely affected. While the structure could be opened to the outside environment to permit the humidity which has become built up within the structure to escape, this may create unwanted temperature differentials within the greenhouse structure and be quite impractical, for example in winter conditions. It will be readily understood, therefore, that the condensation of water vapour on -the interior surface of shell 12 and the removal of that condensed water by means of collection skirts 56 and collection pipes 58 helps to control the humidity conditions within the greenhouse structure so tha-t proæer transpiration of the plants i8 continuously permitted without requiring the greenhouse structure to be opened ue to the outside environment.
The cooling of the areas 4 and 6 is most important because of the tremendous heat build up which occurs in such areas during solar radiation of structure 2 particularly during summer, spring and fall months. During winter or cool external conditions however, where heating is required, that heating is provided by appropriate furnaces 60 (FIGURE 3). These may be gas, oil or electric preferably. Again, in order -to minimize obstructions to light passing to plants 54, these furnaces are positioned in basement channel 62 below the floor of base 1 (FIGURE 3).
Humidity conditions within each of the areas 4 and 6 may also be controlled by microprocessor 10 as required, as dictated by relative humidity sensors 28, by passing water through supply pipes 50 and passing it into the atmosphere as a cloud or mist through fog nozzles 52. Alternatively separate sets of supply pipes or valves may be used for controlling relative humidity.
It will be understood tha~ nutrient delivered through nutrient delivery system 34 is passed to trays 55 in which sit 3~ 3 :~1. 7 ~ ~ r~
the roots o-E plants to be g~own (in production aLeas ~) or inert blocks o seeds or seedlings (immature crop development areas 6). ~s is conventional in the art, excess nu-trient not required by the plants, seeds or seedlings is collected and returned to nutrient tanks 38. Thus it is preferred -to slope base 1~, earticularly in each production area 4 downwardly from the centre towards the sides and from the outer ends to the inner ends to facilitate collection of excess nutrient and water fLom these areas.
Because of the computerized control of the various aspects of the internal environment in production areas 4 and immature crop development areas 6, nutrient concentrations, carbon dioxide concentrations, relative humidity and temperature may be adjusted to suit the earticular type of plant being grown or the stage of growth of that plant.
Microprocessor 10 may be appropriately programmed to modify these environmental conditions for the plants over the life of the plants, to ensure optimum plant growth. As well, it is preferred to provide an appropriate alarm signal so that when such environmental conditions exceed a desired range for proper plant growth, the alarm will sound and, if required, a manual override and manual adjustment of such conditions may take place.
Using the light reflecting feature of the eresent invention in conjunction with the comeuterized control of the various factors of the internal environment such as carbon ` ~.3:~7~2 dioxide concentration, temperature and relativé humidity in the air and concentration of the nutrient delivered to the plants (where a nutrient film system is used) in production areas 4 and immature crop development areas 6 as described and illustrated in my co-pending Canadian Patent Application Serial No. 555,398, significantly improved results in yrowing tomatoes and cucumbers have been achieved over traditional greenhouse technoloyy. Not only has it been possible to produce such veyetables on a year round basis in parts of Canada where, previously, even under controlled environment greenhouse conditions, it was difficult or not possible to produce them during the winter months, but also significant, large scale production has been achieved. That production has, even during winter months, been 90% of summertime production.

COMPAR~TIVE TESTING

In experiments conducted growing tomatoes and cucumbers in accordance with the present invention, in Calgary, Alberta, Canada, significantly improved results including continuous production, higher densities and faster growth during winter months over traditional greenhouse technology have been achieved. Indeed, before the present invention, mass production of such veyetables during winter months at such a latitude had been unknown.

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Compared with conventional greenhouse systems, the controlled environment system according to the present invention permits a production line (e.g. Alpha production units) which will eroduce for a peak production period. ~s this period phases out, a neighbouring production line (Beta production unit) enters its peak production period. The Alpha line is then removed and ceplaced with a young Alpha production line which will come into peak productlon as Beta -production line phases out. This rotation allows for continuous peak eroduction 365 days a year. Conventional systems, while sometimes having two production lines, do not allow for continuous production from the lines, a gap in production occuring between the termination of production of one line and the commencement of production of the o-ther. As well, the production cycle is not for the peak period but ra-ther for a much longer cycle. Production over the year is not 365 days a year. Several months are non-productive periods, particularly during winter months.
In addition, for example with cucumbers, applicant's system permits higher density production. Cucumbers for example may be grown in a 1.75 square foot spacing whereas, with conventional greenhouse nutrien-t feed systems, that spacing is 6 square feet at the latitude in question.
As for faster growth, over a period of January to May, cucumber plants grown in accordance with applicant's invention have produced 50 cucumbers per plant (at much higher densities ~ 3 ~ 7 ~
than conventional nutrient feed systems). Conventional nutrient feed systems at this latitude have produced 2S
cucumbers eer plant over this period of time. Prior to mid-February, cucumber crops according to conventional nutrient feed technology do not produce and, by mid-February, such systems have been producing 5 to 8 cucumbers per plant.
Cucumbers grown in applicant's invention have produced 25 cucumbers per plant during the entire winter.
Thus it is apparent that there has been provided in accordance with the invention a method and structure for improved natural lighting for plant growth that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. ~ccordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the invention.

Claims (24)

1. In a land-based greenhouse structure comprising a shell on a base, the shell and base enclosing a predetermined space within which plants are to be grown, the improvement comprising the shell being translucent and a reflective surface being situated adjacent major portions of the base, outside the shell, for enhanced reflection of solar radiation into the space through the shell for plant growing purposes.

2. A structure according to claim 1 wherein water ponds are located beside the base to provide the reflective surface.

3. A structure according to claim 2 wherein the surfaces of the ponds are positioned slightly below the level of the base.

4. A structure according to claim 2 wherein the shell and base are elongated and the ponds are positioned on either side thereof.

5. A structure according to claim 2 comprising a plurality of elongated shells and bases radially extending about a central shell on a corresponding base, the central shell and corresponding base enclosing a predetermined central space, the spaces within the elongated shells being interconnected to the space of the central shell, the shells each of a shape and being positioned so as not to case a shadow at any time on another shell, the ponds positioned and taking up most of the area between the elongated shells.

6. A structure according to claim 1, 2 or 5 wherein the shell consists of a fabric of technically woven polyvinyl chloride coated polyester scrim having about a 95% light translucency.

7. A structure according to claim 1, 2 or 5 wherein the base is of a light, reflective colour.

8. A structure according to claim 5 wherein the base is of a light, reflective colour.

9. A structure according to claim 1, 2 or 5 wherein means are provided to elevate the plants above the base, and wherein the structure is provided with heater means and means to provide nutrient to the plants, the heater means and plant nutrient supply means being positioned below the plants to minimize any shading thereby on the plants.

10. A land based controlled environment structure within which to grow horticultural plants, comprising:

(a) a translucent impermeable stressed fabric shell on a base, the shell and base enclosing a predetermined space within which horticultural plants are to be grown, the shell and base to seal the environment within the space against external environmental air conditions:
(b) temperature monitor and temperature control means for the space;
(c) humidity monitor and humidity control means for the space;
(d) carbon dioxide monitor and carbon dioxide control means for the space;
(e) microprocessor control means electronically associated with the temperature monitor and control means, humidity monitor and control means and carbon dioxide monitor and control means and programmed to provide optimum -temperature, humidity and carbon dioxide conditions for the plants being cultivated in the space, and a reflective surface being located adjacent major portions of the base, outside the shell, to reflect solar radiation into the space through the shell.

11. A structure according to claim 10 further comprising:
(f) plant root nutrient solution monitor means and plant root nutrient solution control means for plants grown within the space, the microprocessor control means also electronically associated with the plant root nutrient solution monitor and control means and programmed to provide optimum nutrient concentration conditions for the roots of the plants being cultivated in the space.

12. A structure according to claim 11 wherein water ponds are located beside the base to provide the reflective surface.

13. A structure according to claim 12 wherein the surfaces of the ponds are positioned slightly below the level of the base.

14. A structure according to claim 12 wherein the shell and base are elongated and the ponds are positioned on either side thereof.

15. A structure according to claim 12 comprising a plurality of elongated shells and bases radially extending about a central shell on a corresponding base, the central shell and corresponding base enclosing a predetermined central space, the spaces within the elongated shells being interconnected to the space of the central shell, the shells each of a shape and being positioned so as not to cast a shadow at any time on another shell, the ponds positioned between the elongated shells.

16. A structure according to claim 11, 12 or 15 wherein the shell consists of a fabric of technically woven polyvinyl chloride coated polyester scrim having about a 95% light translucency.

17. A structure according to claim 11, 12 or 15 wherein the base is of a light, reflective colour.

18. A structure according to claim 15 wherein the base is of a light, reflective colour.

19. A structure according to claim 12 wherein the shell is elongated and is centrally peaked along its elongated direction, and a spray means for controlled spraying of a film of water over the external surface of the shell is mounted to the shell to spray water in a film down both sides of the shell.

20. A method of growing horticultural crops in conditions of low solar angle which comprises growing plants in a sealed environment within a translucent shell on a land-supported base enclosing a predetermined space within which the crops are to be grown, and locating a reflective surface adjacent major portions of the base outside of the shell to reflect solar radiation into the space through the shell.

21. A method according to claim 20 wherein the reflective surface is a pond located beside the base to provide the reflective surface.

22. A method according to claim 21 wherein the pond is positioned slightly below the level of the base.

23. In a land-based greenhouse structure comprising a plurality of shells on bases, each such shell and base enclosing a predetermined space within which plants are to be grown, the improvement comprising the shells and bases being positioned so as to extend radially outwardly so as to provide large areas of generally triangular configuration between adjacent shells, said areas comprising reflective surfaces positioned slightly below the level of the adjacent bases for enhanced reflection of solar radiation into the spaces through the shells for plant growing purposes.

24. A structure according to claim 23 wherein said triangular areas comprises water ponds.