WO2004040965A1

WO2004040965A1 - Apparatus and method for measuring and controlling crop growth

Info

Publication number: WO2004040965A1
Application number: PCT/NL2003/000778
Authority: WO
Inventors: Reinier De Graaf; Arie De Gelder; Christiaan Blok
Original assignee: Praktijkonderzoek Plant En Omgeving B.V.
Priority date: 2002-11-06
Filing date: 2003-11-06
Publication date: 2004-05-21
Also published as: AU2003283861A1; NL1021856C2

Abstract

A method for measuring and controlling crop growth, comprising a cultivation through (9) containing water-absorbing growth elements for plants of crop, plant supporting means (14), watering means (33), drainage means (28) and a control device (37), wherein the cultivation through (9) and the plant supporting means (14) are suspended from at least one weighing unit (10) and wherein at least the watering means (33) and the weighing unit (10) are coupled to the control device (37).

Description

Title: Apparatus and method for measuring and controlling crop growth

The invention relates to an apparatus for measuring and controlling crop growth. In particular, the invention relates to a method for measuring and controlling crop growth in cultivation troughs, on growth elements such as substrate mats, where use is made of watering means by means of which, at suitable moments, water with growth substances can be supplied to the crop via these growth elements.

NL 1008377 describes a method and apparatus for automatically watering crop in cultivation troughs. In this known apparatus, a cultivation trough with growth elements in the form of substrate mats therein is placed on two scales by which the weight of the cultivation trough can be measured. Along the cultivation trough, a water hose extends which is connected to each of the growth elements via branches. The water hose is connected to a central valve which can be electrically controlled to open and close for supplying water to the growth elements. Above the cultivation trough, a rack is provided from which a series of force sensors has been suspended. To each of the force sensors, a wire is attached along which grows an individual plant of the crop which grows in or on the growth element. By means of the force sensors, thus, the weight of the individual plants can be measured relatively accurately, insofar as this weight is actually suspended from the wire and is not supported on the cultivation trough. At the bottom side of the cultivation trough, a drain opening is provided which connects to a collection tray in which water can be collected which, after watering via the water hose, flows away via the drain opening. The weight of the water flowing away is measured by means of a scale under the collection tray. In this apparatus, the scales and individual force sensors are coupled to a central control unit, as is the central valve. In the control unit, a program has been included which, on the basis of inter alia the cultivation trough weight, the plant weight and the drain water weight, controls watering events by opening and closing the central valve. In each watering event, an excess of water is supplied, such that the salts remaining in the substrate are washed out. The program is designed to estimate the moisture of the growth elements and to control, on the basis of this, a specific watering pattern during a growth period of, for instance, 24 hours or a multiple thereof. Here, at regular intervals, each of the growth elements is completely saturated with water, after which the weight of the cultivation trough with growth elements just when no more water flows out of the cultivation trough via the drain opening is taken as a calibration weight of the cultivation trough. On the basis of this periodically determined calibration weight, the watering pattern is controlled.

In this known apparatus, it has been found that the weight of the cultivation trough cannot always be determined sufficiently accurately, which seems to result from this weight being influenced by the plant weight, the stiffness of the crop and water freely present in the cultivation trough which has not yet flown away via the drain opening upon determination of the calibration weight. In addition, in this known apparatus, it is necessary to completely saturate the growth elements with water at least once per twenty-four hours, which is disadvantageous for the crop. A further disadvantage of this known apparatus is that the space below the cultivation trough is largely taken up by parts of the apparatus, particularly the scales, while, in addition, the scales used are relatively costly to purchase and use.

The invention contemplates an apparatus for measuring and controlling crop growth in which at least a number of the disadvantages of the known apparatus have been avoided. The invention particularly contemplates providing an apparatus for measuring and controlling crop growth in which a watering pattern can be set up automatically, in which, during use, repeated complete saturation of the growth elements is prevented. The invention further contemplates such an apparatus in which a relatively large floor surface is preserved below the cultivation trough and in which the construction of the apparatus is relatively simple.

The invention further contemplates providing a greenhouse provided with such an apparatus for measuring and controlling crop growth and a control device for use in measuring and controlling crop growth, in particular for determining a watering pattern.

The invention further contemplates providing a method for measuring and controlling crop growth, in which a watering pattern is determined on the basis of at least the difference in the amount of water supplied to growth elements on which the crop grows, the weight of the cultivation troughs in which the crop is cultivated and the amount of water discharged from the cultivation troughs.

These and other objects are achieved by an apparatus, greenhouse, control device and/or method according to the invention. In an apparatus according to the invention, the cultivation trough is suspended from at least one weighing means, with watering means and draining means being provided so that the amount of water supplied and the amount of water discharged can always be determined. From inter alia the difference between these two amounts of water, in the control unit, an estimate can be made of how much water has been used by the plants for growth and evaporation and how much water is thus still available in the growth elements for further use by the crop. If this amount of water remaining in the growth elements falls below an amount to be priorly inputted into the control unit, a new amount of water will be supplied by the watering means. Because, in an apparatus according to the invention, the cultivation trough and the plant supporting means are suspended, influencing of the weight measurement of the cultivation trough by the plant weight and in particular by, for instance, the stiffness of the crop and the relative position of the force sensors with respect to the position at which the respective plant is disposed on the growth element and/or the growth element is placed with respect to the cultivation trough, is minimized. Such influencing can lead to unacceptable measuring errors. Further, the suspension of the cultivation trough offers the surprising advantage that these cultivation troughs can be used both with plants disposed freely on plant supporting means such as the growth elements and with plants guided by wires or similar crop supporting means. A further additional advantage of suspending the cultivation trough is that the floor surface below the cultivation troughs remains substantially free, while any height of the cultivation troughs with respect to the floor can be chosen.

In use of an apparatus according to the invention with plant supporting means guiding along wires or the like, which are also suspended from weighing means, further, the advantage is achieved that irregularities in the setting of the plant supporting means with respect to the cultivation trough seem to have less influence than in the known apparatus in which the cultivation trough is supported at the bottom side by scales which are supported on the ground. Without wishing to be bound to any theory, this difference seems to result from the cultivation trough not having any freedom of movement with respect to the scales in the known apparatus, so that movements of the plant supporting means cannot be followed. In an apparatus according to the invention, movements of the cultivation trough which are relatively small compared to the outside dimensions of the cultivation trough can relatively easily be compensated for without the measurements being influenced by this. Such movements can, for instance, occμr as a result of material expansion and shrinkage, asymmetric loading of the cultivation trough by the crop, positioning errors and the like.

It is preferred that, in an apparatus according to the invention, the cultivation trough is suspended from first weighing means such as force sensors, while the plant supporting means are suspended from second weighing means. Of course, the second weighing means may also be force sensors. This yields the advantage that the load of the plant supporting means can be recorded independently. Because both means are suspended, permanent recording errors can simply be avoided. Here, it is preferred that the second weighing means are suspended from the first weighing means, so that, by the first weighing means, the full weight of the cultivation trough with crop, plant supporting means and growth elements, including water present therein, is measured, so that errors in the measured crop weight resulting from, for instance, partial support on the cultivation trough can be eliminated in further calculations.

In a particularly advantageous embodiment, an apparatus according to the invention is characterized in that in the or one or more growth elements a moisture sensor is provided, connected to the control unit. By means of such a sensor, the moisture of the or each respective growth element can always be measured. Optionally, here, on the basis of the measurement of the moisture of one of the growth elements, the moisture of the other growth elements in the cultivation trough can be estimated.

Draining means are preferably provided for collecting and measuring the weight of water flowing out of the cultivation trough. The water with growth substances present therein can then preferably be recycled.

The apparatus is preferably built-up substantially symmetrically, such that two cultivation troughs with associated plant supporting means are suspended from the same first weighing means, so that space and material are saved. In addition, in this manner, asymmetries in the crop growth can be substantially compensated for. It is further preferred that the carrying means for the crop supporting means and the cultivation troughs above the crop transmit as much light as possible. For this purpose, an apparatus according to the invention is further characterized by the measures according to claim 9. These optimize the light yield for the crop while the cultivation troughs and the crop can still be supported so as to be suspended in a simple manner and their weight can be measured.

In a particularly advantageous further elaboration, an apparatus according to the invention is further characterized in that the control device is provided with an algorithm by means of which the evaporation of water through the crop can be determined. Models for determining such evaporation are sufficiently well known and described in, for instance:

Automation of the water supply of glasshouse crops by means of calculating the transpiration and measuring of the amount of drainage water

R. de Graaf 1988, Acta Horticulturae 229, page 219-231;

Watergeven bij rozen onder glas Toepassing van het PBG-watergeefrekenmodel bij de teelt van rozen [Watering roses under glass: Application of the PBG water supply calculation model in rose growing]

R. de Graaf en L. Spaans 1998. Internal report 171, Proefstation voor Bloemisterij en Glasgroente [Research station for Floristry and Glass vegetables]; and

Transpiration of Greenhouse Crops an Aid to Climate Management. C. Stanghellini, 1987 Dissertation Wageningen University.

In this manner, the control device can be used to make an even better determination of the moisture of the growth elements and/or the absorption of water and growth substances by the crop, also if no moisture sensors are used in the or a growth element. On the basis thereof, then, a specific watering pattern can be determined, in which the intervals between the watering events and/or the amount of water per watering event can be optimized.

Unexpected changes in the measurements can be simply corrected for, for instance, changes as a result of picking, disturbances due to sprinkling the crop with, for instance, plant protection products, plant diseases and the like by determining the evaporation from the actual trough weight. This is more reliable than the evaporation determined by models, in which, in fact, ideally evaporating crop is taken as a starting point. This is particularly true if, in the control means, memory means are stored which can be used as a basis for extrapolation or for determining a new starting point.

In general, it can be stated that, under normal conditions, it is preferred to use the measurement of the trough weight for determining a watering starting signal. With brief disturbances, such as sprinkling or picking or other crop operations, an evaporation model may be used. With prolonged disturbances, for instance for a few hours, the cultivation trough weight will be used, with differences from the models providing information about the condition of the crop.

Preferably, means are provided by which movements, in particular human movements, can be sensed around the cultivation trough, so that, for instance, certain measurements can be corrected or eliminated if these are influenced or could be influenced by these human movements or operations such as picking fruits, cutting these from the crop, rearranging the crop, sprinkling and the like. In this manner, the watering pattern can be controlled even more adequately by the control device.

The invention further relates to a greenhouse provided with at least one and preferably a series of apparatuses according to the invention.

The invention further relates to a control device for use with an apparatus according to the invention, characterized by the measures according to claim 15. By such a control unit, a watering pattern can relatively rapidly and accurately be calculated and controlled for crop in, for instance, a greenhouse, while watering means can be controlled for watering the crop at desired intervals and/or measuring a desired amount of water per watering event. Here, the control device is preferably set such that the moisture content of growth elements in the cultivation trough is maintained between approximately 10% and 95%, more in particular between 35% and 95% of the maximum moisture capacity of the or each respective growth element. In a particularly advantageous embodiment, the setting is chosen such that, in principle, the moisture content is controlled between 65% and 80% of the maximum capacity, for at least 80% of the time that the crop grows. Incidentally, for different substrates, this may be chosen differently. For rockwool, for instance, it will controlled between approximately 50% and 90% of the total mat volume, more in particular between 60% and 80%, which means, for instance, 52-93% and 62-83% respectively of the maximum absorption capacity. For peat, these numbers will, for instance, be between 40% and 80% of the total volume, more in particular between 50% and 60%, which, for instance, corresponds to 50-100% and 63-75% respectively of the maximum absorption capacity. This prevents the growth elements becoming too moist, which has been found to be particularly disadvantageous for many types of crop, while it also prevents the growth elements becoming too dry, so that the water capacity of the growth elements may permanently fall below an acceptable level. This is particularly true if the growth elements are formed from mineral wool such as rockwool or the like. The invention further relates to a method for determining a watering regimen for plants in growth elements in a cultivation trough in a greenhouse or similar growth room, characterized by the measures of claim 16.

By such a method, the amount of water evaporating through the crop during a period can be accurately determined, while, in addition, a good determination can be made of the growth of the crop. Further, the moisture of the growth elements can be accurately determined, at least estimated, so that the moisture balance of the cultivation trough with crop can be determined at any desired moment. From this moisture balance, it can then be determined when and/or how much water needs to be supplied in order to maintain a desired moisture of the growth elements.

In a method according to the invention, preferably, the or each growth element is prevented from being saturated in the watering events, to protect the crop. The moisture content of the or each growth element can be measured by moisture sensors, but, also from the moisture balance, an accurate estimate can be made of its moisture content. It is further preferred that the weight of the crop, in particular an increase or decrease in its weight is measured during the growth, such that the water absorption by the crop can be determined, at least estimated. By means of a method according to the invention, preferably, such a water regimen is set that the moisture of the or each growth element is maintained between, for instance, 10% and 95% of the maximum moisture capacity of the respective growth element. More in particular, the aim is to maintain this moisture between 35% and 90%, while, preferably, for at least 80% of the duration of the growth of the respective crop, the moisture of the or each growth element is maintained between approximately 65% and 85% of the maximum moisture capacity. It has experimentally been determined that, in this manner, optimal growth of the crop is obtained, while too great moisture is prevented. Too low a moisture of the or each growth element could result in a decrease of the water capacity of the respective growth element to undesirably low values.

Drainage water flowing, at least dripping, from the cultivation trough is preferably collected in a collection tray, its weight being measured or determined, while, during discharge of the water from the discharge tray, supply of water from the cultivation trough into it is prevented, so that an accurate measurement is obtained.

In a method according to claim 22, a watering starting point for a cultivation trough is determined by comparing the weight of a cultivation trough prior to watering with the weight development of the cultivation trough after watering, in relation to drainage of water from the cultivation trough and evaporation of water through the crop. The evaporation of water through the crop is determined, with a water starting point being determined by the moment when the moisture of the or each growth element in the cultivation trough falls below a predetermined value, which can vary during a day. The moisture of the or each growth element can be estimated from the difference between the weight of the drained water, the evaporated water and the weight of the cultivation trough prior to watering on the one hand and the momentary weight of the cultivation trough on the other hand. Preferably, this estimate takes into account the increase or decrease in weight of the crop over the respective period after a preceding watering event, which increase in weight can be subtracted from the momentary weight of the cultivation trough.

In a particularly advantageous embodiment, use is made of a memory in which, over a preceding period, the weight development of the cultivation trough with crop is recorded, such that, in case of sudden changes of the crop weight in a cultivation trough, the data stored in the memory can be used for recalibration, for instance by extrapolation, for determining a next watering starting point. To clarify the form of the invention, exemplary embodiments of an apparatus, greenhouse, control device and method according to the invention will be further elucidated with reference to the drawings, in which:

Fig. 1 diagrammatically shows, in front view, a part of a greenhouse with an apparatus according to the invention; Fig. 2 diagrammatically shows, in side-elevational view, a greenhouse with apparatus according to Fig. 1;

Figs. 3 A and 3B show, in side elevational and front view, a drainage device for an apparatus according to the invention; Fig. 4 diagrammatically shows a control device according to the invention;

Fig. 5 diagrammatically shows a graphically plotted possible course of the average moisture content of growth elements in an apparatus according to the invention; Fig. 6 diagrammatically shows a graphically plotted example of the average moisture of the growth elements during 24 hours;

Fig. 7 graphically shows, for one day, the momentary weights of different quantities in an apparatus and method according to the invention;

Fig. 8 shows, in a view comparable to Fig. 2, an apparatus according to the invention, in a further alternative embodiment; and

Fig. 9 shows, in top plan view, an alternative embodiment of an apparatus according to Fig. 8.

In this description, same or corresponding parts have same or corresponding reference numerals. The exemplary embodiments shown and described only serve to illustrate the invention and should not be taken as being limitative in any way. Combinations of different parts of the exemplary embodiments shown expressly fall within the scope of the invention as set forth in the claims. Herein, water is understood to mean that liquid medium that is supplied to crop, at least for stimulating its growth. This is at least understood to mean a solution of water and growth substances for crop. Its composition can be determined in a usual, known manner, depending on, for instance, the crop, the desired amount of water per watering event, salts remaining in the or each growth element and the like. Figs. 1 and 2 diagrammatically show, in front view and side elevational view respectively, a part of a greenhouse 1 according to the invention, comprising greenhouse spuds 2 with, supported thereon, a frame of greenhouse girders 3A, 3B extending parallel to each other. On the frame 4 thus formed, a roof 5 is supported having gutters 6 and ridges 7. Such greenhouses 1 are generally known in many variations with various constructions. The invention is not limited to the embodiment shown here, at least not with regard to frame 4 and roof 5.

From the frame 4, in particular from the greenhouse girders 3A, 3B, a cultivation apparatus 8 according to the invention is suspended, which, in the embodiment shown, comprises two cultivation troughs 9 extending parallel to each other, on both sides of the greenhouse spud 2 and the gutters 6. Preferably, a cultivation apparatus 8 is suspended such that the cultivation troughs 9 hang below a ridge 7, between two gutters 6 and between greenhouse spuds 2, which is advantageous for, for instance, the light yield.

In the embodiment shown in Figs. 1 and 2, the cultivation apparatus 8 comprises a weighing unit 10 from which the two cultivation troughs 9 are suspended by means of cables 11, such that they are freely suspended above a floor 12. In addition, from the weighing unit 10, crop carrying means 13 are suspended, which carry plant supporting means 14 in the form of crop wires 15. In the example shown, from each crop wire 15, a plant 16 has been suspended, such that the weight of the respective plant 16 is virtually completely carried by the crop carrying means 13. In the exemplary embodiment shown, the crop wires 15 are provided with wires 11 on opposite sides with respect to the greenhouse spud 2, so that a substantially symmetrical load is obtained. Alternatively, plants 16 can be attached directly to a crop girder 24, for instance with cucumber plants or paprika plants. Also, instead of the wire 25, a bar may be used, for instance with tomatoes. Especially in the case of round hanging plants, wires 15 are advantageous.

In the exemplary embodiment shown, the weighing unit 10 comprises first weighing means 17 and second weighing means 18. As Fig. 2 clearly shows, the first weighing means 17 are suspended from the greenhouse girders 3A, 3B via a supporting construction 19. The first weighing means 17 comprise two pairs of first force sensors 20, suspended from supporting constructions 19 located next to each other. From each pair of first force sensors 20, a cross girder 21 is suspended, extending approximately horizontally and parallel to the greenhouse girders 3A, 3B, approximately perpendicular to the longitudinal direction of the gutters 6 and ridges 7. To each cross girder, preferably right below a first force sensor 20, a second force sensor 22 is attached, which extends approximately perpendicular to the longitudinal direction of the cross girders 21, approximately parallel to the longitudinal direction of the gutters 6 and ridges 7. The cables 11 are attached to the cross girders 21, ^' between two second force sensors 22 attached to them, for reasons mentioned above. To the bottom side of each crop girder 24, a wire 25 is stretched, parallel to the longitudinal direction of the crop girder 24 to which the crop wires 15 are attached. In the cultivation trough 9, growth elements 26 are placed, such as substrate mats known per se, packaged in foil on four sides, for instance rockwool, with, on the top side 27, a central opening being provided in the foil in which or on which a plant 16 can be placed. Roots of the plant 16 will grow in the growth element 26 and abstract water from it for their growth. In the cultivation trough 9, one elongated growth element can be provided, but the use of shorter substrate mats is preferred, for instance one growth element 26 per plant or substrate mats with a length between, for instance, 1 and 2 m for, for instance, 2-8 plants. These dimensions and numbers should not be taken as being limitative. Fig. 2 diagrammatically shows a drainage device 28 on the right side, which is further elucidated in Fig. 3A and Fig. 3B. This drainage device 28 comprises a discharge pipe 29 which connects, by a first end 30, to a drainage opening (not shown) in the bottom of the cultivation trough 9 and, by the other end, opens into a drainage collection tray 31 resting on third weighing means 32, so that the weight of the drainage collection tray 31 with drain water collected therein can be measured. The cultivation trough 9 is suspended such that it slightly slopes down in the direction of the drainage opening so that water can flow away directly through the discharge pipe 29 to the drainage collection tray 31.

Fig. 2 diagrammatically shows a watering device 33, comprising drippers 34 provided at or inserted into each of the growth elements 26. In Fig. 2, only in the two growth elements 26 furthest left, such a dripper 34 has been drawn. It will be clear that such a dripper can be provided in each of the growth elements 26. Incidentally, water can also be supplied to the different growth elements 26 in another known manner. The drippers 34 are connected via a pipe 35 to a watering starting automatic 36, for instance a valve and/or pump to be controlled by a control device 37 to be described hereinafter. Water can be supplied from a reservoir 38 into which water can be supplied from the drainage collection tray 31 by means of a pump 39 and/or from a central water supply, such as a water conduit (not shown). Optionally, nutrients can be added in the reservoir. Via the drippers 34, per watering event, a predetermined amount of water is supplied to the growth element 26. A part of this will directly or in time flow out of the growth element 26 and flow back via the discharge pipe 29 into the drain collection tray 31. In this manner, a recirculation system is obtained.

Optionally, in a growth element 26, also, a moisture sensor 40 can be inserted. Such moisture sensors are known per se. Thus, the moisture of the growth element can be measured instantaneously, for instance related to the maximum moisture absorption capacity of the respective growth element. Such a moisture sensor can also be provided in a series of growth elements or in each of the growth elements 26.

Figs. 3A and 3B diagrammatically show, in two different views, a drainage device 28 comprising a drainage collection tray 31, placed on a table 42 carried by two load cells 41. The load cells 41 are disposed on a carrying plate 43 which is carried by legs 44 by means of which the table 42 can accurately be set horizontally. Above the drainage collection tray 31, free from it, the end of the discharge pipe 29 is shown, from which the drainage water coming from the cultivation trough 9 can flow into the drainage collection tray 31. Because this pipe 29 hangs freely from the drainage collection tray 31, its weight is not included in the measurement by the load cells 41. In the pipe 29, a valve 45 is provided behind a filter 46, so that contaminations can be filtered from the drainage water, while the pipe 29 can be closed off by the valve 45. Further, a drainage pipe 47 is shown which connects to the pump 39 as shown in Fig. 2 for periodically discharging water from the drainage collection tray 31. During this discharge, the valve 45 can be closed, so that, during discharge, drainage water is prevented from flowing into the drainage collection tray 31, so that the weight of the drainage water can accurately be measured. Fig. 4 shows a control device 37 for use with a cultivation device 8, which can at least be used in a method according to the invention. This control device 37 comprises a central control unit 49 to which the first weighing means 17, in particular the first force sensors 20 and the second weighing means 18, in particular the second force sensors 22 are connected, as well as the third weighing means 32, in particular the load cells 41. Further, the pump 39 and the valve 36, at .least the dose-measuring automatic, are coupled to this. In addition, the moisture sensors 40, if they are provided, and a movement sensor 50 which may be disposed in the room of the greenhouse 1 near the cultivation troughs 9, by means of which movements of, for instance, people near the cultivation trough 9 can be recorded, can be coupled to it. The purpose of this will be returned to in more detail.

To the central control unit 49, further, a memory 60 is provided in which data coming from the sensors or calculations carried out with them, as well as environmental data, can be stored. To the central control unit 49, further, recording means known per se and not shown can be coupled for measuring, for instance, relative humidity in the greenhouse 1, the ambient temperature, radiation and the like. To the control unit 49, a computer 51 or the like can be coupled for manual or automated input and reading out of data.

Fig. 8 shows, in side elevational view, an apparatus 1 according to the invention, in an alternative embodiment. Only the differences compared to an apparatus according to Figs. 1 and 2 will be discussed here.

In Fig. 8, a gutter 9 is shown, suspended from two first force sensors 20, via wires 11. In this manner, the gutter is fixedly positioned in the sense that it will not move during normal use. The apparatus below the gutter 9 and the watering apparatus are equal to those as shown in Fig. 1. The crop girder 24 is suspended from a guide 52 by means of second force sensors 22. In the exemplary embodiment shown, as guide 52, a span wire is used from which the crop girder 24 is suspended by means of eyes 53. This makes the crop girder 24 slidable in the direction M along the guide 52. The guide 52 is attached to spaced apart trusses 3B, preferably such that the distance between the attachment points is at least larger than the distance between the eyes 53. A braking mechanism 54 is provided for temporarily locking the crop girder 24 with respect to the guide 52.

An apparatus according to Fig. 8 has the advantage that the crop girder 24 is slidable so that, when the plants 16 reach a great length, these can simply be guided further, without the wires 15 needing to be rehanged and/or reattached. This is because, by the displacement of the crop girder 24 with the upper ends of the crop wires 15 relative to the stationary trough 9, the distance between them is increased, so that the growth can be allowed for. Yet, the weight measurements can simply be carried through.

Fig. 9 shows an alternative embodiment, in which a crop girder 24 is placed on two opposite sides of a gutter 9. In the exemplary embodiment shown, the length of the crop girders 24 is great compared to the gutter 9, so that, when the plants 16 grow, they can be moved along the crop girders. The plants are, for instance, led alternately to the opposite crop girders. The force sensors 20, 22 are all attached to the structure 3 of the green house. Also in this embodiment, of course, guides 52 can be used in a manner as described with reference to Fig. 8, with the directions of movement M of the two crop girders 24 being preferably opposite. These can move along during the growth of the crop.

In an apparatus according to the invention, the gutter 9 can also be suspended from brackets extending between the crop and resting on the floor 12 of the greenhouse, thus considerably reducing the sensitivity to vibrations of the greenhouse caused by, for instance, the wind. In addition, more light influx is admitted to the crop. In addition, suspension of the trough offers the advantage that it can simply be checked whether the trough is still free from the environment and that, thus, no incorrect weight measurements are carried out as a result of, for instance, friction, deformation, reduced freedom of movement or the like.

By means of an apparatus according to the invention, a water balance can be determined continuously or periodically, in, for instance, the following manner, in which water balance is at least understood to mean the balance between the supply of water to the crop, at least into the cultivation trough, and the consumption of water.

In general, the water balance satisfies the following formula:

W=V+D+(R+G+S) (1) wherein W = water supply per time unit or irrigation event V = amount of water intended for compensation for evaporation through the crop D = amount of water intended for rinsing out undesirably accumulated salts around the roots of the crop R = remaining amount of water, for instance evaporation through the substrate G = amount of water absorbed by the crop S = amount of water fixed in the substrate

The water balance can be considered a substantially closed system, and so can the cultivation trough. For this, it holds true that the water supply can be equated to the sum of the crop growth, the evaporation and the drain, i.e. the water which flows out of the cultivation trough via the pipe 30. In the method known from the state of the art according to

NL1008377, deviations from the terms mentioned in (1) are not noted, at least not recorded, but ascribed to the evaporation V through the crop and/or the substrate moisture content S. Because, at night, an excess of water is supplied (W> V+D+(R+G+S)), it is assumed that the moisture content of the substrate of the growth elements returns to a maximum value determined for the cultivation. It has been found that, with most substrates, at least growth elements, this is probably not achieved each time again, resulting in deviations. In addition, for the crop, it is not advantageous to reach the maximum moisture content around the roots. Further, in this known method, it is assumed that the suspension of the plants from the individual force sensors will not influence the measured weight of the cultivation trough. It has been found, however, that the measured weights are temporally influenced by varying stem stiffnesses, shapes, asymmetric load of the crop by fruits and the like, while such a method is unsuitable for freestanding plants having upright, relatively stiff stems, such as roses or paprika, because the weight of the crop is not at all, at least not accurately, measurable in this manner. A further disadvantage of the known apparatus and method is that, during the pumping out of the drainage collection tray, there is a chance that drain water still flows into it, so that the weight of the drain water is not measured accurately, especially not if the drainage water flows relatively rapidly. In addition, in this known method, for the moisture content determinations of the substrate elements, either the moment that no drops come out of the drainage opening anymore or the moment when, conversely, the first drop comes out of it, is taken as a starting point. In both cases, the water still freely present in the cultivation trough is left out of account.

In a method according to the invention, the water balance given by (1) is taken as a starting point. Here, each time, a known amount is taken for the water supply, W = pi. The weight of the cultivation trough system at a given point in time, Gt, is determined by means of the force sensors and is checked by determining whether the change in weight during a water supply is equal to the weight of the water W supplied. The value of D is determined, at least checked, by measuring the change in the weight of drainage collection tray 31 during a water supply. The value of R is set at zero, assuming that the evaporation during the water supply is virtually equal to 0, which is plausible in view of the short time taken up by the water supply. The absorption of water into the substrate can be determined by determining the increase in weight of the cultivation trough during the water supply, which is approximately equal to the amount of water W of the water supply reduced by the weight of the drainage water. After a watering event, the moisture content S will decrease by evaporation V, absorption of water by the crop G and further drainage D', given that R=0. The increase in the crop weight G can be determined by reading out the second force sensors 24. If it is assumed that the individual plants 16 will grow approximately the same amount, the individual plant weight can be determined by dividing the joint crop weight determined by the second weighing means 18 by the number of plants.

For the total evaporation V of water through the crop, an estimation model can be used, as described above. If the moisture of a or each growth element 26 can be measured using a moisture sensor, V can, incidentally, also be read directly from the water balance. By using a model, from the water balance, the average moisture of the joint growth elements 26 may be calculated.

By a method according to the invention, the moisture content of the growth elements can be determined, on the basis whereof it can be determined when a next water supply needs to take place and/or how much water needs to be supplied to the growth elements in a next watering event, in order to maintain the moisture content within desired limits. Figs. 5 and 6 show examples of desired limits for the average moisture of the growth elements for a year and a day respectively, with the upper limit being indicated by a dotted line and the lower limit by a dash-dotted line. It is clear from Fig. 5 that, here, in the periods when the crop needs relatively less water, in spring and autumn and particularly in winter, the growth elements are, on average, maintained less moist, decreasing to, for instance, approximately 60 to 65% of the maximum capacity of the growth elements, while, in summer, when the crop needs more water as a consequence of, particularly, radiation, the average moisture content is maintained higher, for instance 75 or 80 to 85% of the maximum capacity. It appears from Fig. 6 that the moisture will also vary during a twenty -four hour period, between for instance 65 to 70% of the maximum capacity during the night and 75 to 85% during the afternoon, while, preferably, a difference of, for instance, 8% is maintained between day and night. Of course, these limits will slightly shift during the year (as shown in Fig. 5). These limits can, of course, be different for different crops. In a method according to the invention, an estimated or determined evaporation can be compared to an evaporation expected to be achievable through the crop, so that, for instance, stress can be determined in the crop, if the evaporation falls short of expectation, or a better growth than expected, if the evaporation is higher than expected. Then, for instance, the radiation in the greenhouse can be influenced by, for instance, sunscreens, in order to regulate the evaporation.

Because, in a method according to the invention, the growth of the crop can be accurately measured, particularly when moisture sensors are used in the growth elements, a better insight into the production can be gained. Growth deviations can be properly observed, so that adjustments can be made in time.

A further advantage of an apparatus and method according to the invention is that, on the basis of the water supply and the estimated evaporation, the amount of nutrients in the water can simply be adjusted, so that, in case of high evaporation, relatively fewer nutrients need to be provided in the water. This prevents the waste of nutrients while accumulation of salts in the growth elements is better counteracted and supersaturation of the crop is prevented. In a general sense, in a special method according to the invention, by use of a moisture sensor, the moisture content of the growth elements is measured or, optionally, estimated, the evaporation through the plants is calculated and compared to an estimate coming from an estimation model for evaporation mentioned, on the basis whereof, then, an optimum watering starting point and/or amount can be determined, as well as the desired amount and composition of the nutrients.

By way of illustration, which should not be taken as being limitative in any way, for instance, on a summery day, a water supply is carried out approximately 50 times, of approximately 100 ml per dripper. In all, thus, for instance, 11 liters per square meter are supplied, approximately 3 liters of which flow out via the drainage pipe and approximately 8 liters are absorbed and evaporated (substantially evaporated). During a wintry day, for instance, watering is carried out only 3 times, 100 ml per water supply per dripper, so that, on the same surface, 660 ml of water are applied. Of this, for instance, 440 ml are evaporated and absorbed by the crop

(approximately 40 ml) and 220 ml are discharged by the drainage pipe.

Fig. 7 diagrammatically shows, for a day in autumn, the course of water consumption by crop (cucumber plants) shown as mass plotted against time. In this Figure the following have been drawn in: I water supply

II sum of water absorption

III evaporation through crop

IV sum of drainage water

V trough VI crop

It can be read from Fig. 7 that water supplies of a fixed amount have been carried out, with the intervals between the water supplies decreasing towards noon and increasing after noon, which particularly results from more evaporation due to increased radiation. For the growth elements, zero is taken as a target weight (as a measure for its moisture), while this weight will increase due to increase of water absorption. This means that the amount of water absorbed into the growth element can be read out in relation to the average moisture percentage desired for that day of the year as shown in Fig. 5. With each water supply, the weight of the trough rapidly increases (water supply amount) and rapidly decreases (drainage) directly afterwards, after which the decrease will proceed more slowly until the new water supply, as a result of decreasing evaporation. The total weight of the cultivation trough (measured by the first weighing means, corrected for the "dry weight", so before use, before the first watering event) increases slowly and to a limited degree during the day, as a result of the increasing plant weight and, possibly, an increase in the water absorbed and retained in the growth elements. It is clear that, over the whole day, the crop increases in weight, while, during the afternoon, its weight slightly decreases, as a result of stronger evaporation. It has been found that, at the beginning of a twenty-four hour period, the mat weight is lower than the target weight and that, until, for instance, the end of the morning (in Fig. 7 approximately 11 o'clock), virtually all water supplied is absorbed by the growth elements. Not surprisingly, the drain during this period is virtually zero. It can also be seen from Fig. 7 that the increase of the plant weight is virtually equal to the difference between the sum of the water absorption (II) and the sum of the evaporation (III).

In a method according to the invention, preferably, estimates and calculations are carried out in the central control device, in particular by means of an algorithm suitable for the purpose, in which known estimation models may be used for estimating, for instance, evaporation, growth and the like, while, for this purpose, data may be used from external sensors such as radiation meters, atmospheric humidity meters and the like. In addition, movement sensors may be used by means of which external influences can be recognized, for instance picking, sprinkling and the like. By recording historic values in the memory means, by extrapolation, the progress can be estimated if particular extreme values or transitions, for instance sudden changes in weight resulting from picking, fruits or leaves falling off and the like occur and need to be left out of account or need to be compensated for.

In a method according to the invention, of course, in a usual manner, use can be made of other relevant data, such as pH value of growth elements and water, nutrients and nutritional supplements, sprinkling means used, artificial illumination and the like, which can, in an obvious manner, be used in a control device according to the invention, for instance for still more accurate estimate of evaporation.

The invention is by no means limited to the exemplary embodiments shown and described in the description and the drawing. Many variations of these are possible within the scope of the invention as set forth in the claims.

For instance, means may be used for measuring the weight of the cultivation trough or troughs and/or the plants, for instance pressure sensors or the like. Also, an apparatus 8 according to the invention may contain a different number of cultivation troughs, for instance one, while the cross beams 21 may be omitted. Also, with freestanding plants, the crop weighing means may be omitted. The pressure sensors 20, 22 and/or 41 are preferably thermally insulated or designed such that fluctuations of temperature are compensated for. The suspension means, in particular the crop suspension means, preferably have, in top plan view, a smallest possible surface and are, in side elevational view, preferably light-transmitting, for instance in that openings are provided which comprise, for instance, 30%, more particularly more than 40% and preferably more than 60% of the total surface of the carrying means. This can, for instance, be achieved by using girders having an open honeycomb structure. In this manner, an optimum light yield is maintained.

In order to minimize influencing of the cultivation trough weight by the crop weight, a supporting lath or the like may be provided approximately horizontally, near the growth elements, suspended from the second weighing means. Since both the cultivation troughs and the plants are suspended from weighing means, the crop can be hung round in a usual manner, in particular when two cultivation troughs are provided in one apparatus 8. Because only two load cells, at least force sensors, are provided in the first, second and third weighing means, mutual influencing is prevented. The measurements per day are preferably carried out between, for instance, the first watering event of a twenty-four hour period and the first watering event of a next twenty -four hour period, so that the measurements will be accurate. The length of the cultivation troughs is preferably kept relatively small, for instance approximately 4 m or less, so that water only has to cover a short distance between a growth element and the drainage pipe.

Claims

1. An apparatus for measuring and controlling crop growth, comprising a cultivation trough containing water-absorbing growth elements for plants of crop, plant supporting means, watering means, drainage means and a control device, wherein the cultivation trough and the plant supporting means are suspended from at least one weighing unit and wherein at least the watering means and the weighing unit are coupled to the control device.

2. An apparatus according to claim 1, wherein the weighing unit comprises at least first and second weighing means, wherein the cultivation trough is suspended from the first weighing means and the plant supporting means are suspended from the second weighing means.

3. An apparatus according to claim 2, wherein the second weighing means are suspended from the first weighing means via intermediate weighing means.

4. An apparatus according to any one of the preceding claims, wherein moisture measuring means are included for determining the moisture of the growth elements.

5. An apparatus according to any one of the preceding claims, wherein drainage means comprise a collection element, supported such that its weight can be measured, which collection element is mechanically separated from the cultivation trough, such that the weight of the collection element and water possibly received therein can be determined independently of the weight of the cultivation trough, growth elements and plants possibly disposed therein, wherein, further, discharge means are provided for discharging water from the collection element, preferably in the direction of the watering means.

6. An apparatus according to any one of the preceding claims, wherein at least two carrying elements are provided, each suspended from two force sensors belonging to first weighing means, wherein, on each carrying element, suspension means for at least one and preferably two cultivation troughs are provided, wherein second force sensors are provided on the carrying elements, belonging to second weighing means, from which second force sensors, plant carrying means are suspended.

7. An apparatus according to claim 6, wherein the carrying elements are girders extending substantially parallel to one another, wherein the plant carrying means comprise at least one substantially elongated crop carrying element whose longitudinal direction extends approximately perpendicular to the girders, which longitudinal direction is approximately equal to a longitudinal direction of the or each cultivation trough, wherein the distance between the girders is relatively large in proportion to the length of the cultivation trough.

8. An apparatus according to claim 7, wherein two cultivation troughs are suspended next to each other from two girders, wherein two crop carrying elements extend approximately parallel to each other below the girders, wherein the distance between the girders is considerably larger than the distance between the crop carrying elements.

9. An apparatus according to claim 7 or 8, wherein, in top plan view, the carrying elements have a surface which is small compared to the surface in side elevational view, wherein, in side elevational view, each crop carrying element has an open structure, such that light-transmitting openings are provided therein which together have a surface larger than approximately 30% of the total surface of said side elevational view, more particularly more than 40% and preferably more than 60%.

10. An apparatus according to any one of the preceding claims, wherein the drainage means comprise closing means between the cultivation trough and a collection element.

11. An apparatus according to any one of the preceding claims, wherein the control device comprises an algorithm for estimating evaporation of water through plants in the cultivation trough.

12. An apparatus according to any one of the preceding claims, wherein the control device comprises recognition means for recognizing movements in the surroundings of the cultivation trough, in particular human movements.

13. A greenhouse provided with at least one apparatus according to any one of the preceding claims, wherein the or each apparatus is suspended from a frame construction of the greenhouse.

14. A greenhouse according to claim 13, wherein means are provided for recording climate parameters in the greenhouse, such as temperature and atmospheric humidity, which means are coupled to the control device.

15. A control device for use in an apparatus according to any one of claims 1-12 or in a greenhouse according to claim 13 or 14, wherein the control device is provided with at least one algorithm for estimating evaporation of water through plants and one algorithm for determining a watering starting moment and/or watering amount per watering event for plants, wherein an estimated value for the evaporation is used for determining said watering starting moment and/or said watering amount.

16. A method for determining a watering regimen for plants in growth elements in a cultivation trough in a greenhouse or similar growth room, comprising the steps of: planting crop in or on the growth elements, in relatively dry condition; determining a calibration weight of the cultivation trough with the growth elements and plants; supplying a predetermined amount of water to the growth elements, at least to the cultivation trough; measuring the amount of water which drains from the cultivation trough during a chosen period; and determining, at least estimating, the amount of water which is evaporated through the crop during said period, wherein at least on the basis of the difference between the calibration weight, the weight of the cultivation trough after supplying the water, the weight of the drained water and the evaporation through the crop, a moment is determined when, in a new watering event, an amount of water is supplied to the crop and/or the amount of water supplied during that watering event.

17. A method according to claim 16, wherein the amount of water which is supplied to the crop per watering event is determined such that the or each growth element is not completely saturated by this.

18. A method according to claim 16 or 17, wherein the moisture content of the or each growth element is measured.

19. A method according to any one of claims 16-18, wherein the weight of the crop, in particular an increase or decrease in the weight of the crop, is measured, at least during said period, from which the water absorption of the crop is determined, at least estimated.

20. A method according to any one of claims 16-19, wherein, on the basis of at least the said steps, measurement data and/or estimates, the watering regimen is determined, wherein time intervals between watering events and/or the water amount for each watering event is/are determined, wherein the watering regimen is chosen such that the moisture of the or each growth element is maintained substantially between a minimum of approximately 10% and a maximum of approximately 95% of the maximum moisture capacity, more in particular between approximately 35% and 90% and, preferably, for at least approximately 80% of the duration of the growth of the respective crop, between approximately 65% and 85%.

21. A method according to any one of claims 16-20, wherein water is drained from the cultivation trough and is collected in a collection tray, wherein the weight of the drained water is measured, wherein, during the discharge of the water from the collection tray, drainage of water from the cultivation trough, at least inflow thereof into the collection tray, is stopped.

22. A method for determining a watering starting point for a cultivation trough, in particular with use of a method according to any one of claims 16-21, wherein the weight of a cultivation trough prior to watering is compared to the weight development of the cultivation trough after watering, in relation to drainage of water from the cultivation trough and evaporation of water through the crop, wherein a determination, at least estimate, is made of the evaporation of water through crop in the cultivation trough, wherein a watering starting point is determined by the moment when the moisture of the or each growth element falls below a predetermined value, wherein the moisture of the or each growth element is determined from the difference between, on the one hand, the weight of the drained water, the evaporated water and the weight of the cultivation trough prior to watering and, on the other hand, the momentary weight of the cultivation trough.

23. A method according to claim 22, wherein the increase in weight of the crop over the period after a preceding watering event is measured, which increase in weight is subtracted from the momentary weight of the cultivation trough.

24. A method according to any one of claims 16-23, wherein, in a memory, at least the weight development of the cultivation trough with crop is recorded and, upon sudden change of the crop weight in a cultivation trough, for instance due to picking, pruning or the like, an extrapolation is made from data recorded in the memory for determining a next watering starting point.