The invention relates to a method for separating bulbous or tuberous plants from substantially loose pollutants present between the plants after harvesting, such as clods of earth, clay, rocks, and other tare.

From applicant's NL 9301204 a washing apparatus is known with which bulbous or tuberous plants can be stripped of loose pollutants and more persistently adhering dirt. To that end, the bulbous plants are successively led through a washing trough and a receiving trough. In the washing trough the tuberous plants are kept floating and stripped of adhering dirt under the influence of a turbulent flow generated in this trough. The coarse pollutants, such as clods and rocks, sink to the bottom of the washing trough and are there removed from the trough via discharge means provided for that purpose. The washing water polluted with the residual, finer dirt particles is led to the receiving trough, in which the washing water can calm down, so that solid particles suspended therein can sediment. These sediments are thereupon discharged, for instance, to a receiving tank, while the purified water is recirculated to the washing trough for reuse.

Although the greater part of the pollutants settles in the receiving trough within a relatively short time, for example, about 45 minutes, a residual part, in particular the finer dirt particles, needs a much longer settling time, for instance in the order of a day or more. In practice, these particles will therefore not be removed from the washing water, as a result of which the water gradually pollutes during use and in the course of time will not be able to clean the bulbous and tuberous plants adequately. The pollution process can be slowed by regularly feeding clean water to the apparatus. This, however, leads to an undesirably high water consumption. Moreover, the polluted water cannot be simply discharged, since it may include environmentally unsound substances.

In applicant's NL1016982, an apparatus and method are described where an auger is arranged at the bottom of a trough of water for

generating a vertically circulating flow in the trough. Bulbs or tubers to be cleaned are dumped into the trough at the top, together with entrained or adhering pollutants such as clay, sand, rocks and plant residues. In the current, bulbs or tubers are kept floating and driven to discharge means such as a conveyor belt, while the pollutants subside and/or are carried along in the current to the lower end of the trough, where they can settle and/or be discharged from there, for example, by a second conveyor belt. In this known apparatus, a single auger is used which extends in a length direction of the trough and substantially throughout the width thereof.

With this apparatus the bulbs or tubers can be separated from the pollutants relatively simply, but the auger brings about high flow velocities, especially at the top in the trough.

The invention contemplates the provision of an apparatus for separating bulbous and tuberous plants from substantially loose pollutants. The invention contemplates the provision of such an apparatus that is different from the known apparatuses, as an alternative thereto. The invention further contemplates the provision of such an apparatus that is suitable for many different types of bulbous and tuberous crops.

In an aspect, an apparatus according to the description is characterized in that a trough is provided, filled with water or a mixture or suspension of water and pollutants. The trough is provided with supply means for the supply of bulbous or tuberous plants mixed with pollutants and discharge means for the discharge of pollutants separated during use. Furthermore, discharge means are provided for the discharge of the bulbous or tuberous plants and means for keeping the water or the mixture or suspension of water and pollutants in motion in the trough. These means for keeping the water or the mixture or suspension of water and pollutants in motion can comprise at least two auger devices arranged next to one another and near a bottom of the trough.

In an apparatus according to the description, each of the auger devices viewed in a length direction of the auger devices can comprise at least two augers arranged behind one another. A first auger of each auger device can then be bearing-mounted at or near a free end remote from the other of the at least two augers. A first auger can be bearing-mounted at or near two opposite ends, and another of the at least two augers only at or near the end proximal to the first auger. As a result, the free end can move so as to prevent the auger from being jammed by, for instance, a hard pollutant part such as a rock.

In an apparatus according to the description, preferably, in an advantageous manner use is made of the difference in specific density of the bulbous plants and the pollutants to be separated, as described in

NL 1016982, by bringing these into a liquid mixture a density of which lies between the specific densities of the two products to be separated. Thus, the heavier products, the pollutants, will subside and the lighter products, the bulbous or tuberous plants, will keep floating near the liquid surface. As a liquid mixture, preferably, water is used, in which an amount of the pollutants to be separated, in particular the finer, only slowly sinking parts, is mixed. Accordingly, in this apparatus and method the finer dirt particles actually contribute towards realizing and operatively maintaining a desired density. As these particles do not, at least not all of them, need to be separated, long settling times can be avoided. The intended separation of bulbous plants and loose pollutants comes about simply, without further intervention, relatively fast, for example within an hour, under the influence of gravity. An additional advantage of this method is that the water does not, as in the known method, need to be refreshed regularly. Accordingly, relatively little water can suffice and only at most little polluted water needs to be discharged to the environment.

By the use of two or more augers next to one another, at the bottom in the trough, an advantageous flow pattern can be generated and

maintained in the trough, while relatively much space is afforded for a volume of water above the augers, in proportion to a trough of the same size according to NL1016982.

In an advantageous embodiment, a method according to the invention is characterized by the features of claim 4 and claim 5.

Regularly discharging a part of the settled pollutants can prevent a concentration of pollutants in the mixture becoming too high. What is obviated, furthermore, is that a part of the already settled pollutants can mix again into the liquid layer above it, for instance under the influence of turbulence, which may arise in the mixture during the supply of a new charge of tuberous plants.

Separation preferably takes place near the location where the bulbous or tuberous plants are lifted. This allows the separated pollutants to be dumped back on the field they come from. This prevents useful substances possibly still present in the separated pollutants, such as soil nutrients or control agents, from being lost and also prevents these pollutants from causing (environmental) nuisance elsewhere. Moreover, it is sensible to separate the bulbs and field residues from each other as soon as possible because these residues are merely useless dead weight during transport.

In a further advantageous elaboration, in the apparatus at least an upper current and a lower current are generated.

With the current created in the liquid mass, the products to be separated can each be manipulated in a desired direction. Bulbous plants floating near the water surface can be guided by an upper current from a supply point to discharge means, while subsided pollutants can be led with a lower current in, for instance, the opposite direction to a collecting or discharge point. In addition, the current promotes a good mixing of the dirt particles suspended in the water, so that the mixture during use obtains and retains a more or less homogeneous density.

With an apparatus according to this description, in a simple manner, soil, rocks and other field residues that come along with bulbous or tuberous plants during harvesting, can be separated from each other. A part of the pollutants can then be used to bring about a desired density in a water mass, allowing the liquid mixture to function still better as a separation medium for lighter parts (the tubers) floating on it and parts to be separated (the pollutants) sinking down in it. The apparatus, because of the small size of the water trough needed, can be simply made of mobile design, allowing it to be set up on the land, near the lifting site.

In a further elaboration, an apparatus according to the invention is characterized by the features of claims 10-13.

In the further subclaims, further advantageous embodiments are described of an apparatus, assembly and a method according to the invention for separating bulbous or tuberous plants and pollutants present therebetween.

To clarify the invention, an exemplary embodiment of an apparatus according to the invention as well as a method will be described on the basis of the drawings. In the drawings:

Fig. 1 shows a side view of an apparatus according to the invention, in partial cross section;

Fig. 2 shows a perspective top plan view of the apparatus according to Fig. 1, partly in cross section;

Fig. 3 shows a cross section of an apparatus according to Fig. 1, along line I -I; and

Fig. 4 shows in top plan view an apparatus according to the invention. The Figures show an apparatus according to the invention for separating bulbous or tuberous plants from loose pollutants present between them, comprising a trough 3 filled with water. In the water trough, prior to and/or during use, such an amount of pollutants to be separated can be dissolved or mixed that the density of the resulting mixture or

suspension during use is greater than that of the bulbous or tuberous plants and less than that of the pollutants to be separated. As a result, the bulbous or tuberous plants will remain floating still better and the pollutants are separated in that in the mixture they subside below the bulbous or tuberous plants. In embodiments where bulbs and/or tubers are cleaned that float in water, use can be made of water without pollutants mixed into it. In this further description reference will be made to water, which is to be

understood to cover also, though not exclusively, the above-mentioned mixture or solution of pollutants and water.

The trough 3 is provided with a bottom surface 10, which is surrounded by upstanding walls 11 on two longitudinal sides and a first end side, and on the second end side merges into a part 12, which may be slightly deeper than the part bounded by the bottom surface 10 and which is bounded by a fourth wall 13 sloping up obliquely. Parallel to this oblique wall 13 extend first discharge means 5, from the part 12 of the trough 3, which is preferably lower than the bottom surface 10, to beyond the upper edge 100 of this trough 3. With these, during use, settled pollutants 22, such as rocks, clods and the like, can be removed from the trough 3 and then be received in a collecting tank, not shown, or be tipped out over a field, in particular the field these pollutants 22 originally come from. Such removal takes place at least periodically and preferably continuously. Arranged opposite the first discharge means 5 are second discharge means 6, of which a free end 7 is situated under the water surface 14. This free end 7 may be height-adjustable, the usefulness of which will be reverted to later. Near this end 7, the bulbous or tuberous plants 20 in use floating on or near the water surface 14 can be scooped out of the water by the discharge means 6 and be conveyed via an oblique ascending conveyor part to outside the trough 3, to a receiving point, not shown. The discharge means 5, 6 in this embodiment are both implemented as a conveyor belt, driven by respective motors 25, 26. The surface of these conveyor belts is preferably porous, so that any water carried along by these belts is not conveyed outside the trough 3. The belts may be implemented, for example, as a rail conveyor, roller conveyor or Jacob's ladder. Also, other conveying means can be used in lieu of one or both conveyor belts, such as, for example, a screw, such as, though not hmited to, an Archimedes' screw.

Provided between the first and second discharge means 5, 6, above the open top of the trough 3, are first supply means 15, for instance in the form of a roller belt sloping down to the trough 3, a chute or a guideway. With these, the bulbous or tuberous plants 20 with the pollutants 22 present between them can be deposited in the trough 3. These first supply means 15 do not have to be part of the apparatus 1, but may also be part of, for instance, a lifter or harvester, in which case the trough 3 can be set up next to this lifter or harvester, under a terminal end of the first supply means 15. Furthermore, to the trough 3 may be coupled second supply means 16 and pumping means for the supply of water. With these, the trough 3 can be filled at the start of the method and during use be supplied with fresh water, for instance to replenish it and or to keep the density of the washing water within desired values.

On the higher-situated bottom part 10 of the trough 3 transport means are arranged in the form of a series of auger devices 8. With the aid of the auger devices 8 the water in the trough can be set into motion and held in motion. In the embodiment shown, three auger devices 8 are shown next to one another. However, other numbers may be used, for example, two, or more than three. The series of auger devices 8 at least provides the advantage over a single large auger that the flow pattern of the water in the trough 3 can be controlled better. A further advantage of a series of auger devices 8 is that even when one of the auger devices gets blocked, the other auger devices maintain flow in the water, so that the cleaning action can at least largely be preserved and moreover the blockage may be undone.

Moreover, as a consequence, the auger devices may advantageously be positioned farther below the water surface 14, as will be further elucidated later. Further, as a consequence, the advantage can be achieved that a relatively wide trough 3 can be used, without the water depth needing to be augmented accordingly. Consequently, the cleaning capacity of the apparatus can be augmented without the amount of water increasing undesirably.

The auger devices 8 have a longitudinal axis 9 extending approximately parallel to each other and/or to the bottom surface 10 and are driven by a motor 27 arranged under the bottom 10 outside the trough 3. In this embodiment the bottom surface 10 is provided with a series of juxtaposed channel elements 101, each channel element 101 accommodating one of the auger devices 8, such that at least a lower part of the latter is surrounded in the channel element by the wall of the respective channel element 101, which to that end can have, for instance, a substantially circular segment-shaped cross section and may be located at a slight distance from the augers 8A, 8B, as schematically shown in Fig. 3.

Each of the auger devices 8, viewed in the length direction 9 of the auger devices, can comprise at least two augers 8A, 8B arranged behind one another. A first auger 8A of each auger device 8 may be bearing-mounted at or near a free end 102 remote from the other 8B of the at least two augers. Preferably, the first auger 8A is bearing-mounted at or near two opposite ends 102, 103 and the other auger 8B of the at least two augers is only bearing-mounted in a bearing 104 at or near the end 105 proximal to the first auger 8A. This bearing 104 is preferably a flexible bearing which allows some tilting of the auger 8B. Accordingly, the free end 106 of the second auger 8B proximal to the first discharge means 5 and located in the trough 3 can thereby move slightly with respect to the relevant channel element 101, at least upwards, such that more space is created between the channel element 101 and the auger 8B. This prevents, for example, rocks or like large and/or hard pollutants from jamming between the auger 8B and the channel element wall, which could result in the auger 8B coming to a halt and/or getting damaged. In normal condition the auger 8B will be urged into the channel element as a result of inter alia the rotation about the

longitudinal axis, gravity, and the flow of the water. More generally, the augers 8A and/or 8B and/or auger devices 8 may be, at least partly, flexibly mounted in the trough 3 to provide room for larger pollutants. For the different auger devices 8 it holds that, preferably, they all have the same structure, while the free ends 106 can move independently of each other.

At least one of the augers 8A, 8B and preferably the first auger 8A is at least substantially located under the second discharge means 6. This substantially eliminates the chance of relatively large pollutants such as rocks, branches and the like, ending up in this auger. This means that at least of this auger 8A the full capacity can be used for displacing water in the trough. Preferably, the bearing 105 is also located under the discharge means 6, so that it, too, is protected from pollution. Especially in the use of the apparatus for cleaning bulbous and/or tuberous plants where stringy pollution is involved, as, for instance, by tops, this additionally provides the advantage that these strings such as tops cannot end up in the bearing of the augers, so that jamming of the auger due to that is prevented as well. This applies to the free end 106 of the auger 8B all the more, since there is no bearing provided there.

As shown in the Figures, the augers 8A, 8B have a maximum diameter D, determined by the spiral-shaped blade, which is relatively small with respect to the height of the trough 3 above the bottom 10. The diameter D can, for instance, be chosen such that the auger devices 8 are arranged in a lower half of the trough 3, in particular a lowermost one-third part of the trough 3 based on the part above the bottom 10. The diameter D can be, for instance, between about one-third and one-tenth of the water depth above the bottom 10, more particularly between one-third and one-fifth, such as, for instance, approximately one quarter thereof. Thus, as indicated earlier, the water depth W between the water surface 14 and the top of the auger devices 8 can be augmented relative to an apparatus having the same dimensions with just a single auger along the full width of the trough, without the total water volume in the trough having to be appreciably augmented. Moreover, the width B of the trough can then increase without the water depth needing to be adapted, through adaptation of the number of auger devices 8.

During use, these auger devices 8 generate a calm circulatory current in the water, whose direction is indicated in Fig. 1 by arrow A.

During use, this current carries tuberous plants 20 floating near the water surface 14 in the direction of the second discharge means 6, and pollutants 22 sunk below the tuberous plants 20 in the direction of the first discharge means 5. The rotary speed of the augers 8 is preferably set such that the current thereby produced effects a good mixing of the dirt particles suspended in the water, without bringing already-settled pollutants 22 into circulation again. Surprisingly, it has been found that with an apparatus according to this description a substantially homogeneous distribution of the particles can be obtained in the water volume, especially in an upper current and lower current. The motors may be controlled, for instance, with the aid of a frequency control. The augers 8 preferably rotate all in the same direction, but may also have opposite rotary directions. As a result of opposite rotary directions, unwanted collisions of currents may occur, and unwanted turbulences and/or density differences may arise in the

suspension. By the use of a series of auger devices 8 having a relatively small diameter D, as well as a relatively great water depth W above the augurs 8, in particular above the second augurs 8B, there is preferably created a lower current Ao near the bottom 10 and an upper current Ab near the water surface 14, such that between them a volume V of water is obtained that exhibits lesser movement or is even substantially stagnant. Such a relatively calm volume V of water can lead to a better settlement of especially smaller pollution particles such as sand. Moreover, as a result, the displacement of the tubers and/or bulbs in the upper current is hardly, if at all, hindered. Several auger devices 8 that are relatively small in diameter D then offer the advantage that the water current can be distributed more equally over the width of the trough 3 and that, for instance, temporary local accumulations of pollutants and/or bulbs and/or tubers will disturb the working of the apparatus less than in the case of a single large auger. The auger devices 8, in particular the second augers 8B, contribute to the displacement of settled pollutants towards the discharge means 5, the lower part 12 and/or, if provided, a second auger device 107, as will be further discussed later. The series of relatively small diameter D auger devices 8A, 8B here take care of a good transport and distribution of the pollutants.

For monitoring a density of the water, at least the mixture of water and dirt particles suspended therein, such as a maximum allowable density, the density can be determined. To this end, as shown, a float 17 may be arranged in trough 3. This float 17 has a specific weight that is equal to or just a bit less than this upper limit to be monitored, which upper limit in turn is less than the specific weight of the pollutants 22 to be separated, for example, between about 1200 and 1700 kg/m ³ . Furthermore, control means 21 are provided, which, in the event the maximum allowable density is exceeded, through the float 17, can for instance augment the supply of fresh water and/or the discharge of settled pollutants, so that the density is controlled to a desired value. Optionally, a second float 18 can be used for monitoring a lower limit of the density. To that end, this second float 18 has a specific weight that is equal to or greater than the minimum desired density, which minimum density is at least greater than the specific weight of the tuberous plants 20 to be cleaned, for example, between about 1000 to 1200 kg/m ³ for onions, for example between about 1500 to 1700 kg/m ³ for iris bulbs, and, for instance, between about 1000 to 1200 kg/m ³ for potatoes. Similarly to float 17, float 18 can be coupled to control means 21 to augment the supply of pollutants, at least to reduce discharge thereof and/or diminish the supply of fresh water in order to adjust the density back to a minimum desired value.

Other means and/or methods for measurement and control of the density may be used as well, such as, though not limited to, measurement of electrical conduction, acoustic measurement, vibration attenuation, optical sampling or mechanical density measurement. For instance, a density meter can be used, such as a DMA35, supplied by Scientific BV, Sliedrecht

Nederland or Anton Paar GmbH, Graz, Austria.

The apparatus described can be used as follows. After trough 3 has been filled with water via the second supply means 16, possibly, if desired, the density thereof can be adjusted to a desired value. To this end, for instance, an amount of pollutants 22, for example clay, can be added to the water, which with the aid of the auger devices 8 is uniformly mixed into the water. Preferably, just so much sand or clay is added that a minimally required density is achieved. At this density the second float 18 will just begin to rise towards the water surface 14. Optionally, a greater initial density may be set, by mixing more pollutants 22 into the water, but considering that the density will increase during use, it is preferred to begin with a lowest possible density at which the tuberous or bulbous plants just remain floating, which, in the separation of pollutants from, for example, potatoes, may be at approximately 1000 to 1200 kg/m ³ . It is noted, incidentally, that the water to be used does not have to be mains water but can also be, for example, water from a nearby ditch. Possibly, water alone is started with.

Next, harvested bulbous or tuberous plants 20 with among them the loose pollutants 22, such as clods of earth, loose sand, rocks, and other tare, are supplied to trough 3, via first supply means 15 suitable for that purpose. Once in the water, the bulbous plants 20 will remain floating on or just below the water surface 14, while the heavier pollutants 22 go down. While this separation is taking place, the bulbs 20, under the influence of the current A created by the augers 8A, 8B, and in particular the upper current At _> , float towards the second discharge belt 6, and the wholly or partly sunk dirt parts 22 are carried along towards the first discharge belt 5.

Upon arrival of the bulbs 20 at the discharge belt 6, they are scooped from the water near the end 7. For that purpose, this end 7 is arranged at such a depth under the water surface 14 that the tubers 20 are thereby scooped up and not yet completely subsided dirt parts 22 are not. The end 7 therefore lies preferably above the interface between the subsided dirt parts and the mixture of water and finer particles located thereabove. The position of this interface is determined, for one thing, by the speed with which the dirt parts subside, which is related to the density of the water mixture. Since this density varies during use, the position of the interface will also vary. By virtue of the adjustability of the end 7, these variations can be accommodated and the position of this end 7 can always be set such that only bulbous plants 20 are scooped from the trough 3. Possibly, such setting may be done with the aid of second control means 23, engaging the end 7, which can adjust the position of this end 7 below the water surface 14 on the basis of a density signal produced by the first and/or second float 17, 18. The bulbous or tuberous plants 20 scooped from the trough 3 by the end 7 are then passed out of the apparatus, for example to a collecting bin, or a washing apparatus, for removing persistent dirt such as adhering clay.

In an advantageous embodiment, the end 7 lies approximately in the volume of water V between the lower current Ao and the upper current Ab. Any dirt particles that are carried along with the bulbs and/or tubers on the discharge belt 6 will flow through the belt along with the water and be fed back towards the first discharge means 5.

The continuously changing density of the water is preferably held within a minimum and maximum value with the aid of the first and second floats 17, 18 and the control means 21 connected thereto. As long as the density remains below a predetermined upper limit, at which density the pollutants to be separated will just settle, for example, 1700 kg/m ³ , the first float 17 will be near the bottom 10, at least below the water surface 14, and the second float 18 will float on or near the water surface 14. When the upper limit is exceeded, in that during use fine dirt particles are taken up in the water, the first float 17 will go up. This vertical displacement can be simply detected, on the basis of which the control means 21 can be activated. These can increase the supply of fresh water and/or the discharge of pollutants 22, so that the density will fall. In lieu of intervening with the control means 21, an alert signal may be produced, after which the desired density can be manually adjusted. The second float 18 is especially useful at commencement of the method, when effecting a correct initial density. As long as the density of the water is less than the minimum desired density, the second float 18, just like the first float 17, will be on or near the bottom. Not until sufficient pollutants 22 are mixed into the water to cause the density to increase to the desired minimum density will the second float 18 float to the surface. When during use the density falls below the minimum density, the float 18 will sink and in the manner described above an alert and/or control signal may be generated and the density controlled back to a desired value, either manually or automatically, by adding extra pollutants. As indicated, the auger devices 8 will conduct settled pollutants 22 towards the discharge means 5 and a possibly provided second auger device.

Near the lower end of the first discharge means 5, in or adjacent part 12, in embodiments a second auger device 107 may be provided having a transport direction Z which includes an angle a with a transport direction X of the first auger devices 8. The angle a can be, for example, an angle of about ninety degrees. The second auger 107 and its transport direction Z are preferably approximately horizontal in normal use of the apparatus, at approximately the lowest point of the trough 3. The second auger 107 lies preferably in a generally U-shaped trough part, such that at least a lower part of the second auger 107 is enclosed thereby at a small distance. The second auger 107 is preferably shaftless and is driven by a motor 109.

Pollutants 22 can fall from above into the second auger 107, at least settle, so that in and around the second auger a slightly condensed mass is formed. The second auger 107 connects in transport direction Z to a valve

mechanism 108 with which the mass can be at least partly carried off to outside the apparatus 1, periodically or continuously. Preferably, the density of the mass is then such that draining of water from the trough 3 is at least substantially prevented. The second auger 107 may be non bearing- mounted, at least in the trough. By designing the second auger 107 to be shaftless and without bearings in the trough 3, the second auger 107 can be prevented from jamming in the trough, for example due to pollutants in the water, in particular, again, for example, strands such as tops.

The first auger devices 8 can be jointly driven by a single motor 27 and driving unit. In the embodiments shown, each of the auger devices 8 is driven by its own motor 27. With this, at least the advantage is achieved that the rotation speed of the different auger devices 8 can be individually controlled. For instance, the rotation speed of each of the auger devices 8 about the longitudinal axis 9 can be kept constant, regardless of, for instance, resistance being exerted thereon by water and/or pollutants, the rotation speed of, for instance, the outermost auger devices 8 can be adjusted relative to intermediate auger device(s) 8, for instance, be raised or lowered, in order to influence the flow pattern of the water in the trough 3. For the control of the speed of the motors, for instance, a frequency control can be used. A transmission 110 between the motor(s) and the auger devices 8 and/or 107 can be provided in a known manner, for instance, a right- angled transmission and/or a transmission with protection from damage of the motor, should the respective auger device 8 driven by it experience increasing resistance to rotation. To this end, the transmission 110 can comprise, for example, a slip-action coupling.

In embodiments, above the first conveyor belt 5 near or in the water surface 14 a brush element 111 may be suspended, which prevents bulbs and/or tubers which may temporarily, for instance after feed-in, move in the direction of the first discharge belt 5, from being carried along and discharged thereby. Above the second belt conveyor, preferably near the end 7, above the water surface 14, a sprayer 112 may be provided for spraying the tubers and/or bulbs on the belt 6, so that any residual adhering pollutants are flushed off therefrom.

With the above-described apparatus and method, bulbous and tuberous plants 20 can be simply and rapidly separated from loose pollutants 22 present therebetween. For this method, relatively little water is needed, so that a small trough 3 can be employed and moreover, afterwards, only little polluted water needs to be discharged. A small trough 3 provides the advantage that with it a relatively light apparatus 1 can be built, which can be simply made of mobile design. Such a mobile apparatus can be set up near a harvester or even drive along next to it during harvesting. In that case, the harvested bulbous and tuberous plants 20 can be brought from the harvester directly into the trough 3. The immediate separation of the bulbous and tuberous plants 20 from tare is favorable because the separated residues can simply be tipped back onto the field from which they originate. As a result, no substances such as nutrients, control agents, and like substances possibly contained in the tare are lost, and these substances are prevented from giving rise to any environmental problems elsewhere. Moreover, since such pollutants 22 would otherwise merely form unnecessary dead weight during further transport of the bulbous or tuberous plants 20, it is advantageous to separate these residues from the bulbous plants as early as possible. Especially when the field from which the bulbous or tuberous plants 20 are lifted consists chiefly of sandy soil, it is preferred to further add to the trough 3, besides this sandy soil, a clay mineral. The clay mineral suspends readily in the mixture or suspension contained in the trough 3 and thus helps adjust the density thereof to a desired level and/or keep it at such level.

The invention is not limited in any way to the exemplary embodiments shown in the description and the drawings. Many variations thereon are possible within the scope of the invention as outlined by the claims.

Thus, the bulbous and tuberous plants can be moved from the supply means to the discharge means by a water-permeable conveyor belt extending at least partly under water, instead of by a current created in the water. The water may be set into motion by other means than the auger shown, for instance, by means of one or more screws arranged in the trough. The density can be monitored or measured with other measuring means than the floats described, for instance by leading a representative part of the mixture periodically or continuously through a bypass with a defined volume and measuring the mass thereof, which is a direct measure of the density of the mixture. Furthermore, the settled pollutants can be

discharged, instead of via a conveyor belt, by means of a cell wheel or separator arranged near the lowest point of the trough. The wheel can be rotated periodically, or when a cell is full, through an angle such that an empty cell comes to lie at the top and the full cell can be emptied outside the trough.

Screw spindles can be used with equal or different pitch and/or different thread hands.

These and many variations are understood to be within the scope of the invention outlined by the claims.