Crop cultivation apparatus

Abstract: A crop cultivation apparatus comprises a cultivation bed (1) having a ditch (11) formed on the bottom thereof for receiving and supplying a culture liquid, a liquid level adjusting tank (2) is provided adjacent to and communicated with the cultivation bed (1), a culture liquid tank (3) provided at a higher position than the cultivation bed (1) for supplying the culture liquid to the liquid level adjusting tank (2). A liquid absorbent sheet (6) for upwardly absorbing the culture liquid from the ditch (11) formed on the bottom of the cultivation bed (1), a mass of culture medium (8) is provided above the liquid absorbent sheet (6) for cultivating a crop. The apparatus avoids the need to provide a circulating culture liquid flow but alleviates the problems experienced with conventional one way flow systems.

Description: This invention relates to a crop cultivation apparatus, particularly to a crop cultivation apparatus of a kind in which a culture liquid is supplied from a culture liquid tank to a culture medium by virtue of gravitation and capillary action (phenomenon). In the prior art, when an operation for crop cultivation is to be conducted by the use of a culture liquid, it is necessary to utilise various large equipment, particularly to use power equipment to periodically supply the culture liquid to a cultivation bed. Usually, in a crop cultivation system using a culture liquid, one or more pumps are used to cause the culture liquid to flow from a culture liquid tank to a cultivation bed, and then from the cultivation bed back to the culture liquid tank so as to circulate the liquid. This is therefore referred to as circulation method. Alternatively, a culture liquid is just supplied to a cultivation bed in accordance with a predetermined time interval and never caused to flow back, and such an operation is therefore referred to as a one way flow method. However in both of the above mentioned conventional methods, because various large equipment is required a housing such as a glass house is needed to house the equipment, the costs for equipment purchasing and equipment installation is therefore high. Because an electric power supply is necessary in order to operate one or more pumps, and the pump and other equipment needs periodic maintenance, other costs, e.g., for equipment running and maintenance may also be too large a burden for a farmer. In the aforesaid circulation method, a large amount of culture liquid is required to keep a desired liquid circulation between the culture liquid tank and the cultivation bed, consequently a crop often absorbs too much of the culture liquid or only selectively absorbs one particular component of the culture liquid, resulting in an unbalanced composition of the culture liquid. Accordingly, in order to keep various components at desired concentrations to obtain a required composition for the culture liquid, it is necessary to check and analyse from time to time the composition of the culture liquid in the culture liquid tank and to supplement a certain component which has been found insufficient for the culture liquid. In the aforesaid one-way flow method, although it is not necessary to periodically analyse the composition of the culture liquid in the culture liquid tank nor to supplement a certain component, it is extremely difficult to supply a correct amount of culture liquid that is exactly right for consumption by the crop. In fact the culture liquid is supplied in a much larger amount than is necessary for actual consumption by the crop, as a result a considerable amount of the culture liquid has to be drained away from a cultivation bed, which not only causes a waste of the culture liquid but also contaminates the surrounding environment. The reader will be further enlightened concerning the state of the art by reading the publications referred to in the search report on this application and particularly DE-U-8814990 and US-A-5076010. Claim 1 of this application is characterised with reference to DE-U-8814990. An object of the present invention is to provide a crop cultivation apparatus adapted to be positioned on a crop field and capable of supplying only the necessary amount of a culture liquid from a culture liquid tank to a cultivation bed by virtue of gravitation and capillary action, thereby the crop cultivation may be continued without the use of any power equipment, so that the operation and maintenance of the apparatus become extremely easy. According to the present invention, there is provided a crop cultivation apparatus in accordance with claim 1. In one aspect of the invention, the liquid level adjusting tank is communicated with the ditch of the cultivation bed, said adjusting tank being provided such that an amount of the culture liquid flowing into the ditch does not exceed a predetermined level. In another aspect of the invention, the liquid absorbent sheet is provided such that the bottom area of the cultivation bed is covered by the sheet. In a further aspect of the invention, the liquid absorbent sheet is partially dipped in the ditch of the cultivation bed for upwardly absorbing the culture liquid. Crop cultivation apparatus embodying the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: Fig. 1 is a schematic perspective view, Fig. 2 is a longitudinal cross sectional view of the apparatus, taken along line D-D in Fig. 1, Fig. 3 is a cross sectional view of the apparatus, taken along line A-A in Fig. 1, Fig. 4 is a cross sectional view of the apparatus, taken along line B-B in Fig. 1, and Fig. 5 is a end view of the apparatus, taken on an arrow C in Fig. 1, Referring to Fig. 1, a crop cultivation apparatus comprises a cultivation bed 1 for cultivating a crop by means of a culture liquid, a liquid level adjusting tank 2 provided adjacent to and communicated with the cultivation bed 1 and a culture liquid tank 3 provided at a higher position than the liquid level adjusting tank 2. The culture liquid tank 3 is communicated with the liquid adjusting tank 2 through a pipe 13. As illustrated in Fig. 1, since the culture liquid tank 3 is provided at a higher position than the liquid adjusting tank 2, the culture liquid may flow automatically from the culture liquid tank 3 to the liquid adjusting tank 2, by virtue of gravitation. The cultivation bed 1 may be in various forms or shapes. Preferably, the cultivation bed 1 is constructed with its lateral cross section in a generally rectangular shape, and the entire bed in a rectangular parallelepiped shape. The liquid level adjusting tank 2 is provided at one end of the cultivation bed 1. An elongate culture liquid ditch 11 is formed on the bottom of the cultivation bed 1. As illustrated in Figs. 2 and 3, the culture liquid ditch (channel) 11 is directly communicated with the liquid level adjusting tank 2, so that the liquid level of the ditch 11 and that of the tank 2 will be the same all the time. The liquid level adjusting tank 2 is provided with a ball tap 10 which is constructed to shut off the supply of the culture liquid from the culture liquid tank 3 when the ball is raised to a predetermined level due to its buoyancy in the liquid as shown in Fig. 2. It is understood from Fig. 2 that, by adjusting the liquid level in the liquid level adjusting tank 2, the liquid level of the elongate ditch 11 is also simultaneously and automatically adjusted. In this way, the liquid level of the elongate ditch 11 may be continuously kept at a predetermined value, so as to prevent unnecessarily large amounts of the culture liquid from flowing into the ditch 11. Referring to Fig. 4, a liquid absorbent sheet 6 is arranged over almost the whole bottom area of the cultivation bed 1. Such liquid absorbent sheet 6 is made of a porous material having excellent water absorbtion. By partially dipping the liquid absorbent sheet 6 into the culture liquid ditch 11 of the cultivation bed 1, the culture liquid may be absorbed and drawn up from the ditch 11 by capillary action. Above the liquid absorbent sheet 6 there is disposed a mass of culture medium 8 made of a porous PVA (polyvinyl alcohol) material in chip form. Since the porous PVA material is also an excellent water absorber, the culture liquid can be upwardly absorbed into it through the liquid absorbent sheet 6. In order to prevent crop roots from extending through the liquid absorbent sheet 6 into the culture liquid ditch 11, a liquid penetration sheet 7, which permits the penetration of liquid but not of crop roots, is disposed to cover the bottom and side faces of the culture medium 8. Therefore, the culture liquid remaining in the ditch 11 and flowing up through the sheet 6 can be protected from being invaded by the extending crop roots, ensuring a stabilised composition. The liquid penetration sheet 7 is arranged in direct contact with the liquid absorbent sheet 6, so that the culture liquid being absorbed up through the sheet 6 may pass smoothly into the culture medium 8. The culture medium 8 not only serves to upwardly absorb the culture liquid to the upper surface thereof, but also serves to support crops growing on the culture medium 8. Referring again to Fig. 4, the mass of the culture medium 8 is covered with a permeable covering sheet 9 to prevent the culture medium 8 from scattering out. Since the permeable covering sheet 9 is excellent in light reflection and water penetration, it is possible not only to avoid a temperature rise on the surface of the culture medium 8 due to sunlight, but also to prevent a temperature rise inside the culture medium 8, by virtue of water evaporation through the permeable sheet 9. Such an evaporation is useful to remove latent heat so as to keep the culture medium 8 at an appropriate temperature. As illustrated in Figs. 3 and 4, most parts (except an area over the ditch 11) of the bottom area of the cultivation bed 1 are provided with rain water collecting means 5 for collecting rain water entering the cultivation bed 1. The rain water collecting means 5 has a wave-shaped (corrugated) surface in order to facilitate water drainage. The rain water collecting means 5 is arranged so as to be inclined in the longitudinal direction of the cultivation bed 1 and to be communicated with a plurality of drainage holes 12 ( see Fig. 5 ). As illustrated in Fig. 1, there are formed a plurality of drainage holes 14 on both longitudinal side walls of the cultivation bed 1. Usually, the drainage holes 12 and 14 are closed, but will be opened during rain to drain the rain water entering the cultivation bed 1. As indicated in Figs. 2, 3 and 4, if the bottom portions of both the cultivation bed 1 and the liquid level adjusting tank 2 are not water resistant, it is necessary to dispose a liquid tight film or sheet 4 on the inner surface of the lower and bottom portions of the cultivation bed 1 and liquid level adjusting tank 2. In this way, a possible leakage of the culture liquid can be prevented. The operation of the crop cultivation apparatus according to the present invention will be described as follows, with reference to the flowing course of the culture liquid. Referring to Fig. 1, the culture liquid flows from the culture liquid tank 3 through the pipe 13 into the liquid level adjusting tank 2 by virtue of gravitation. The flow of the culture liquid into the adjusting tank 2 may be shut off by the operation of the ball tap 10 when the liquid reaches a predetermined level. On the other hand, if the liquid decreases below the predetermined level, the shut-off state may be released so that culture liquid supply may be continued until the liquid again rises above the predetermined level. Since the liquid level adjusting tank 2 is directly communicated with the culture liquid ditch 11, the culture liquid flows directly from the tank 2 into the ditch 11, and the liquid levels in both the tank 2 and ditch 11 will be kept at the same level all the time. As shown in figure 2 the predetermined level within the adjusting tank 2 is a level beyond which the culture liquid will overflow from the ditch 11. As shown in Fig. 4, the culture liquid in the culture liquid ditch 11 will then be absorbed upwardly through the liquid absorbent sheet 6 by capillary action. In this way, the culture liquid will be absorbed continuously to the culture medium 8 through the liquid penetration sheet 7. Residual culture liquid no longer to be absorbed by a crop will be evaporated from the surface of the culture medium 8 through the permeable covering sheet 9. Because the liquid penetration sheet 7 is provided to prevent the invasion of crop roots through the liquid absorbent sheet 6 and into the culture liquid ditch 11, a desired balanced composition of the culture liquid adjusted at an early time may be maintained during the whole operation period of the apparatus, thus the culture medium 8 is sure to obtain a stabilised culture liquid having a constant composition. The crop cultivation apparatus of the present invention may provide at least the following effects. Firstly, a culture liquid may be supplied from the culture liquid tank to the culture liquid ditch only by virtue of gravity, and further supplied to the culture medium only by means of capillary action. Secondly, the culture liquid may be supplied automatically through the controlling means (the ball tap) in an exactly the amount corresponding to the consumption by the crop and the evaporation from the culture medium. It is not necessary to circulate the liquid between the culture liquid tank and the culture medium as is required in a conventional method. Thus, it is possible to avoid the problem that the crop absorbs too much of the culture liquid or only selectively absorbs one particular component of the culture liquid. Therefore, the composition of the culture liquid can be maintained at a desired balanced condition during the whole of the cultivation period. Thirdly, since the cultivation bed is provided with rain water collecting means for collecting rain water entered therein, rain water may be drained away smoothly from the cultivation bed. In this way, the culture liquid in the cultivation bed may be prevented from being diluted by the rain water. Since the culture medium is covered with a permeable light reflecting covering sheet it is possible to prevent the culture medium from scattering and to alleviate a temperature rise on the surface of the culture medium and a temperature rise inside the culture medium, by virtue of water evaporation through the permeable sheet.

Claims: A crop cultivation apparatus comprising a cultivation bed (1) having a ditch (11) formed on the bottom thereof for receiving and supplying a culture liquid; a liquid level adjusting tank (2) provided adjacent to and communicated with the cultivation bed (1); a culture liquid tank (3) provided at a higher position than the cultivation bed (1) for supplying the culture liquid to the liquid level adjusting tank (2); a liquid absorbent sheet (6) for upwardly absorbing the culture liquid from the ditch (11) formed on the bottom of the cultivation bed (1); a mass of culture medium (8) provided above the liquid absorbent sheet (6) for cultivating a crop characterised in that: the liquid level adjusting tank (2) is directly communicated with the ditch (11) of the cultivation bed (1) in a manner such that the liquid level in the ditch (11) and that in the tank (2) will be the same all the time; and in that the liquid level in the ditch (11) is automatically and simultaneously adjusted when adjusting the liquid level in the liquid level adjusting tank (2). A crop cultivation apparatus according to claim 1, wherein the liquid level adjusting tank (2) is communicated with the ditch (11) of the cultivation bed (1), said adjusting tank being provided such that an amount of the culture liquid flowing into the ditch (11) does not exceed a predetermined level. A crop cultivation apparatus according to claim 1 or claim 2, wherein the liquid absorbent sheet (6) is provided such that a bottom area of the cultivation bed (1) is covered by the liquid absorbent sheet (6). A crop cultivation apparatus according to any of clai 1 to 3, wherein the liquid absorbent sheet (6) is partially dipped in the ditch (11) of the cultivation bed (1) for upwardly absorbing the culture liquid. A crop cultivation apparatus according to any one of preceding claims, wherein the culture medium (8) is covered at its side and bottom faces with a liquid penetration sheet (7). A crop cultivation apparatus according to any one of preceding claims, wherein the liquid level adjusting tank (2) includes a ball tap (10), which is provided to shut off the supply of the culture liquid from the culture liquid tank (3) when the ball tap (10) is raised to a predetermined level by liquid buoyancy. A crop cultivation apparatus according to any one of preceding claims, wherein most parts of the bottom area of the cultivation bed (1) are provided with rain water collecting means (5) for collecting rain water falling on the cultivation bed (1). A crop cultivation apparatus according to claim 7, wherein the rain water collecting means (5) is formed with a wave-shaped surface. A crop cultivation apparatus according to claim 7 or claim 8, wherein the cultivation bed (1) has a plurality of drainage holes (14) communicated with the rain water collecting means (5) for draining away rain water in the cultivation bed (1). A crop cultivation apparatus according to any one of the preceding claims wherein the culture medium (8) is PVA (polyvinyl alcohol) porous material excellent at absorbing water. A crop cultivation apparatus according to any one of the preceding claims, wherein the culture medium (8) is covered with a permeable covering sheet (9) to prevent the culture medium (8) from scattering. A crop cultivation apparatus according to claim 11, wherein the permeable covering sheet (9) is excellent at reflecting light and liquid penetration.

Inventors: SAKUMA HARUSHIGE, SAKUMA, HARUSHIGE, SAKUMA, HARUSHIGE, C/O OKINAWA BR. OF JP INT.R.C.
Applicants: DIRECTOR GENERAL OF JAPAN INTE, DIRECTOR GENERAL OF JAPAN INTERNATIONAL RESEARCH CENTER FOR AGRICULTURAL SCIENCES
Application year: 1995
Main classification: A01G27
IPC codes: A01G27, A01G31