GB2150403A

GB2150403A - A method and apparatus for spreading fertilizers

Info

Publication number: GB2150403A
Application number: GB08425001A
Authority: GB
Inventors: Heinz Dreyer
Original assignee: Amazonen Werke H Dreyer SE and Co KG
Current assignee: Amazonen Werke H Dreyer SE and Co KG
Priority date: 1983-10-18
Filing date: 1984-10-03
Publication date: 1985-07-03
Also published as: FR2553251A1; NL8403183A; GB8425001D0; DE3337762A1; DE3337762C2; FR2553251B1; GB2150403B

Abstract

A method is disclosed for spreading fertilizers by means of a spreader, preferably attached to the power lift of a tractor. The spreader comprises driven throwing elements which throw the fertilizer particles over an area which is substantially greater than the structural width of the spreader, and whose effective spreading width may be modified, wherein the throwing elements distribute the fertilizer particles over the ground surface to be treated in a uniform spreading pattern in laterally adjacent and overlapping spreading areas with no gaps. In order to ensure an optimum and uniform spreading of the fertilizer whilst taking into account all the conditions of use encountered in practice, the spreading pattern (28) consists of at least three adjacent and overlapping individual spreading areas (29, 31), each of the spreading areas being produced by a respective special throwing element (19, 20). The throwing elements of the spreader may be formed either as centrifugal discs rotating about vertical axes or as distributor nozzles moved with a reciprocating movement. <IMAGE>

Description

SPECIFICATION A method and apparatus for spreading fertilizers The invention relates to a method of and apparatus for spreading fertilizers.

More particularly the invention concerns a method of spreading fertilizers by means of a centrifugal spreader which is preferably attached to the power lift of a tractor, which spreader comprises driven throwing elements which throw the fertilizer particles over an area which is substantially greater than the structural width of the centrifugal spreader, and whose effective spreading width may be modified, wherein the throwing elements distribute the fertilizer particles over the ground surface to be treated in a uniform spreading pattern in laterally adjacent and overlapping spreading areas wih no gaps.

German Offenlegungsschrift 28 227 already discloses a method of this type in which effective spreading widths of different sizes may be obtained by using differently formed throwing elements in the centrifugal spreader. In the case of the centrifugal spreader used in this respect it is possible to obtain small and large throwing widths for the fertilizer particles discharged by a corresponding selection of the throwing elements which are formed, in this case, as centrifugal discs with throwing blades disposed thereon.Farming requires a method for the use of centrifugal spreaders by means of which the effective spreading width may reach 18 to 24 m and more so that the machine may be moved over the surface to be treated with the widest possible spacing so as to destroy as little as possible of the plants growing on the surface to be treated and so as to leave as few traces as possible of the machine.

The less travel required from the machine, the greater the proportion of the surface which bears no traces of the passage of the machine so that a greater yield is obtained.

The known methods have the drawback, in the first instance, that in the case of large effective spreading widths the fertilizer particles are thrown to the rear with a very wide trajectory. The spreading pattern is consequently very dependent on the wind.

In addition, at the edges of the fields unavoidable overfertilized or under-fertilized areas are produced which have a very disadvantageous effect on the yield. A further drawback of the known methods is that the effective spreading width cannot be reduced during operation or the discharge of the fertilizer.

This has a very disadvantageous effect in the case of large effective spreading widths in particular. The ground surface to be treated does not have a rectangular shape in every case and the width of the ground surface to be treated is not a whole multiple of the effective spreading width. In both cases the farmer must either take into account non-fertilized or overfertilized strips or must spread the fertilizer particles from the centrifugal spreader beyond the surface to be treated onto adjacent surfaces which are not to be treated such as ditches, paths, roads or neighbouring plots of ground. All these possibilities are undesirable. Although this situation may be improved by changing the centrifugal discs, this is time-consuming and does not always solve the problem.In the case, therefore, of an obliquely extending remaining surface area, it is unreasonable for the farmer to change the centrifugal discs several times for the final spreading passage. In addition, this method does not ensure that the spreading pattern produced by several spreading elements is uniform per se.

In addition German Patent Specification 28 53 011 discloses a method in which the supply of fertilizer to the individual spreading elements of a centrifugal spreader may be switched off independently and the actual spreading width may be halved, the arrange ment of a deflector plate adjacent to the throwing element producing a spreading pattern with a steep drop on one side. This reduction of the effective spreading width and the simultaneous production of a spreading pattern with a steep drop on one side is advantageous when spreading the edges of fields.

However, one drawback of this method is that, in the case of large spreading widths, the fertilizers are thrown to the rear with a very wide trajectory with the result that areas which are greatly overfertilized or are not fertilized are produced at the edges of the field. In addition the centrifugal spreader is subject to the same drawbacks as the centrifugal spreader for carrying out the method described above, if a large effective spreading width is to be achieved, despite the possibility of halving the effective spreading width.

The invention seeks to provide an improved method such that an optimum and uniform spreading of the fertilizer is achieved, whilst taking into account all the conditions of use encountered in practice.

According to one aspect of the invention, there is provided a method of spreading fertilizer by means of a centrifugal spreader comprising driven throwing elements which throw the fertilizer particles over an area which is substantially greater than the structural width of the centrifugal spreader and whose effective spreading width may be modified, wherein the throwing elements distribute the fertilizer particles over the ground surface to be treated in a uniform spreading pattern in laterally adjacent and overlapping spreading areas with no gaps, the spreading pattern consisting of at least three adjacent and overlapping individual spreading areas each spreading area being produced by a respective special throwing element.

As a result of this measure, the spreading pattern may be combined, from the individual spreading areas, into a whole which matches the respective conditions and requirements for use. It is, for example, possible, in the case of a remaining area of the surface to be treated which has a pointed shape, to remove the spreading areas produced by individual throwing elements from the spreading pattern, without modifying the spreading density in the remaining spreading pattern which is produced by the other spreading areas, in the case of a reduced, possibly on one side only, effective spreading width.

In this respect it is crucial that fertilizer particles are only discharged by several throwing elements in the area of the overlapping zones in the spreading sector or spreading strips of each spreading area.

In addition, it is preferable that the spreading pattern is composed of the spreading areas produced respectively by the individual throwing elements in such a way that the spreading areas produced by the inner throwing element(s) extend to the rear and in terms of their width, looking away from the spreader, whilst the spreading areas produced by additional and preferably outer throwing elements extend substantially in terms oftheirwidth to the side of the spreader, looking away from the spreader. This leads, on one hand, to a major reduction in the effect of the wind and, on the other hand, to a spreading area which is kept short, looking in the direction of travel. Consequently, even in the case of large effective spreading widths of the centrifugal spreader, the spreading areas do not extend very far to the rear.

In addition, in a preferred form of the invention, the production of the spreading areas during the operation of the machine is adjusted such that the effective spreading width of the spreading pattern is modified in steps measured from the centre of the machine. The effective spreading width may therefore be enlarged or decreased whilst the spreading density remains the same. This enables a very good adaptation to conditions of use in the simplest possible way. In order to ensure that the wind has as little effect as possible on the spreading pattern and in order to provide a spreading density which is as uniform as possible at the edges of the field, the width of throw of the fertilizer particles to the rear is substantially smaller than the width of throw of the fertilizer particles to the side, in relation to the effective spreading width.

According to another aspect of the invention, there is provided a centrifugal spreader for carrying out the method according to the first aspect of the invention, which comprises a frame and a storage container provided with adjustable and closable outlet apertures and in which the throwing elements are disposed below the storage container, wherein at least three throwing elements are disposed below the storage container and wherein the outlet apertures associated with respective throwing elements may be closed independently of the outlet apertures associated with the other throwing elements.

Thus, the effective spreading width may been- larged or decreased whilst maintaining the spreading density.

A particularly symmetrical and uniform spreading pattern may be achieved, if at leastfourthrowing elements are disposed below the outlet apertures of the storage container.

The throwing elements may be formed either as rotating centrifugal discs or as distributor nozzles provided with a reciprocating movement In order to produce a spreading pattern with the minimum possible rearward projection, the throwing elements are arranged adjacent to one another, seen transverse to the direction of travel and the width of throw of the fertilizer particles discharged by the inner throwing elements is substantially smaller than the width of throw of the fertilizer particles discharged by the outer throwing elements.

in order to be able to adapt the effective spreading width of the centrifugal spreader to different existing passage systems, throwing elements may be replaced by other throwing elements in a manner known per se.

In this respect it is possible to achieve, in accordance with the passage system, by the use of corresponding throwing elements, the required effective spreading widths of, for example, 15, 18, 20 or 24 m with no difficulty.

A particularly good supply of the fertilizer particles to be discharged to the individual throwing elements may be achieved if the storage container comprises a number of container outlets corresponding to the number of throwing elements, if each container outlet comprises adjustable and closable outlet apertures and if a throwing element is disposed below each container outlet. In this respect it is advantageous for the container outlets to be separated by inverted V-shaped (roof-shaped) components.

Preferably, the outlet apertures are closed by closure elements, such that the outlet apertures associated with the individual throwing elements may be closed independently of one another by the closure elements. in this respect, it is particularly advantageous, in order to be able to actuate the closure elements during the operation of the tractor, for the closure elements to be operated by remote control.

So that the fertilizer particles discharged by different throwing elements are not deflected by one another and in order to enable the production of individual spreading areas having the required shape, preferably the throwing angle, measured with respect to horizontal, of the fertilizer particles discharged by the outer throwing elements is greater than the throwing angle, measured with respect to horizontal, of the fertilizer particles discharged by the inner throwing element(s). The same advantage is achieved if the outer throwing elements are vertically offset with respect to the inner throwing element(s).

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 'is a rear view of a centrifugal spreader designed to carry out a method according to the invention.

Figure 2 is a rear view of a further centrifugal spreader designed to carry out a method according to the invention.

Figure 3 is an outline drawing representing a method according to the invention with reference to the spreading pattern of a centrifugal spreader with four discs, Figure 4 is an outline drawing representing a method according to the invention with reference to the spreading pattern of a centrifugal spreader with three discs, Figure 5 is an outline drawing representing a method according to the invention with reference to the spreading pattern of an oscillating spreader with three distributor nozzles.

In orderto be able to use the centrifugal spreader shown in Figure 1 in thick lines, which is formed as a centrifugal spreader with two throwing elements 1 and a storage container 2, in a method embodying the invention the storage containers 3 with the throwing elements 4 shown in dashed lines are attached laterally to the storage container 2. Four throwing elements 1 and 4 are therefore disposed below the storage container which is combined into a whole. The outlet apertures 7 which may be closed by closure elements 6 are disposed in container bases 5 of the storage containers 3 and 4. The fertilizer particles are supplied in adjustable amounts to the throwing elements by means of these closure elements 6. The throwing elements 1 and 4 are formed, in this spreader formed as a centrifugal spreader, as centrifugal discs 8.Two respective throwing blades 9 are disposed on the centrifugal discs 8.

The centrifugal discs 8 are driven, in a known manner which is not therefore described in detail, to rotate about a vertical axis by a power shaft of a tractor supporting the fertilizer spreader. In this respect two outer elements are driven by the extended shaft which drives the inner throwing elements and by respective interposed mitre gears.

The fertilizer particles discharged from the centrifugal discs 8 with the throwing blades 9 are uniformly distributed on the ground surface in accordance with the spreading pattern shown in Figure 3.

The construction of the centrifugal spreader of Figure 2 corresponds to that of Figure 1, when the two additional centrifugal discs with the associated storage containers are attached laterally with respect to the central storage containers of the centrifugal spreader shown in this Figure. The centrifugal spreader of Figure 2 comprises a frame 10 and a storage container 11. The centrifugal spreader is attached in a known manner, which is not therefore described in detail, to the three-point power lift of a tractor by means of the coupling elements disposed on the front side of the frame. The lower area of the storage container 11 is divided into four container outlets 13 separated by three inverted V-shaped components 12. Each container outlet 13 comprises a flat base plate 14 in which outlet apertures 15 are provided.Below the base plates 14 there are disposed respective closure elements 16, formed as slides, by means of which the size of the outlet apertures 15 may be adjusted and closed. The closure elements 16 may be operated independently of one another by a remote control. A horizontally extending and driven agitator shaft 16 is disposed in the lower areas of the container outlets 13. This agitator shaft 16 is mounted and sealed in the wall portions of the container outlets 13. In addition, the agitator shaft 16 projects into all the container outlets 13. The agitator shaft 16 is provided with agitator pins 17 in the region of the container outlets 13.

Respective throwing elements 19 and 20 are disposed adjacent to one another, in a direction transverse to the direction of travel of the centrifugal spreader, below the outlet apertures 15 of the container outlets 13, each container outlet 13 being associated with a throwing element. The two inner throwing elements 19 are disposed with an identical spacing from the centre of the machine. Respective additional outer throwing elements are disposed adjacent to the inner throwing elements 19. The throwing elements 19 and 20 are formed as centrifugal discs having throwing blades 21 disposed on the centrifugal discs. The centrifugal discs 19 are driven via toothed-wheel gearing 22 by the tractor power take-off shaft, so that the centrifugal discs 19 rotate about their vertical axes.The outer centrifugal discs 20 are driven via V-belt drives 23 by rotatable shafts 24 of the inner centrifugal discs 19. In addition, the agitator shaft 17 is driven via a chain drive 25 by the toothed-wheel gearing 22. The centrifugal discs 19 and 20 are disposed on shafts 24 and 26 respectively so that they may be readily detached, enabling their simple replacement, when necessary, by other differently formed centrifugal discs.

The angle of throw a, measured with respect to horizontal, of the fertilizer particles discharged by the outer centrifugal discs 20 is greater than the angle of throw ' measured with respect to horizontal, of the fertilizer particles discharged by the inner centrifugal discs 19. The throw trajectories of the individual fertilizer particles do not therefore come into conflict.

The outer throwing elements 20 are spaced from one another in such a way that the spacing A between the outer portions, formed by the throwing blades 29, of the outer throwing elements 20 is smaller than or equal to 3 m both in the operating and the rest positions. The machine can therefore be transported on public roads and paths without any modification.

The spreading pattern of the invention, which is produced by the centrifugal spreaders of Figures 1 and 2, is shown in further detail in Figure 3: The upper half of Figure 3 shows a plan view of the spreading areas produced by the throwing elements 19 and 20 which are formed as centrifugal discs, these spreading areas being combined to form a spreading pattern. The lower half of Figure 3 is an outline illustratin of the uniform spreading density S produced by the individual spreading areas or the spreading pattern. The two inner centrifugal discs 19 and the two additional outer centrifugal discs 20 are shown at the upper edge of Figure 3. The spreading pattern 28 reaches an effective spreading width E while the maximum spreading width M of the spreading pattern 28 is greater than the effective spreading width E by the size of the overlap. The two inner centrifugal discs 19 discharge the fertilizer particles over a respective area which corresponds to the spreading areas 29 shown by continuous lines. In the embodiment of Figure 3, an effective spreading width of 12 m is therefore achieved.

In addition, Figure 3 shows, in dashed lines, the spreading areas 30 which are produced by a centrifugal spreader having two centrifugal discs, when an effective spreading width E of 24 m is to be achieved.

In this case the spreading areas 30 extend a long way to the rear. In accordance with the invention, the larger effective spreading width E is achieved by the spreading areas 31 produced by the additional outer centrifugal discs 20, i.e. the spreading pattern 28 is formed by four adjacent and overlapping spreading areas 29 and 31, each spreading area 29 or 31 being produced by a respective special centrifugal disc 19 or 20. This means that the spreading areas 29 designed for a lower effective spreading width E' remain unchanged whilst achieving a greater effective spreading width E of the spreading pattern 28 and that the iarger effective spreading width E of the spreading pattern 28 is achieved by means of the spreading areas 31 produced by the additional outer centrifugal discs 20 whilst the spreading density S remains uniform.

In contrast to the spreading patterns for larger effective spreading widths which may be obtained using centrifugal spreaders provided with two centrifugal discs, in which the spreading areas 30 extend very far to the rear, in the case of the centrifugal spreaders having four centrifugal discs 19 and 20 a spreading pattern 28 is achieved from the combination of the spreading areas 29 and 31 produced by individual centrifugal discs 19 and 20 in such a way that the spreading areas 29 produced by the inner centrifugal discs 19 extend, looking away from the spreader, substantially to the rear and in terms of their width, whilst the spreading areas 31 produced by the additional outer centrifugal discs 20 extend, looking away from the spreader, substantially in terms of their width and laterally with respect to the spreader.

In this respect the width of throw W of the fertilizer particles discharged by the inner centrifugal discs 19 is smaller than the width of throw W' of the fertilizer particles discharged by the outer centrifugal discs 20. This is due to the fact that the fertilizer particles are discharged at a lower speed from the inner centrifugal discs 19 than from the outer centrifugal discs 20. This may be achieved by selecting corres ponding external diameters of the centrifugal discs or the throwing blades or by selecting correspond ing speeds for the centrifugal discs, so that the centrifugal discs have different peripheral speeds.

As a result ofthe above-described particular construction of the spreading pattern 28 by the spreading areas 29 and 31 produced by individual centrifugal discs 19 and 20, it is possible, whilst maintaining the uniform spreading density S, to reduce the effective spreading width E to the small effective spreading width E' or to the smaller spreading width e or vice versa to increase the widths. The reduction of the effective spreading width E by the closure of the outlet apertures 15 in the container outlets 13 by the closure elements 16 which are formed as slides, and may be operated independently of one another is carried out such that no further fertilizer particles are supplied to the centrifugal discs. The effective spreading width E can obviously be reduced on both sides.It is also possible to discontinue the supply of fertilizer particles to the inner centrifugal discs 19, so that only the outer spreading areas 31 are produced. This would be useful, for example, when fertilizing fruit crops.

In the case of a method according to the invention and the centrifugal spreader designed to carry out this method, the production of the spreading areas 29 and 31 during operation of the machine may be adjusted by closing the outlet apertures in such a way that the effective spreading width E, E' ore of the spreading pattern 28 may be modified in steps.

This requires the production of individual spreading areas produced by individual centrifugal discs. In this respect it is of great importance that fertilizer particles from several centrifugal discs are only thrown into the area of the overlapping zones in the spreading sector of each of spreading area. The individual areas are therefore produced indepen deftly of one another by particular spreading discs.

The illustration of Figure 4 corresponds to that of Figure 3. The central spreading area 25 is produced by the inner centrifugal disc 33. In this embodiment a small effective spreading width E' of 12 m is achieved by this spreading area 35. Further additional centrifugal discs 34 are disposed laterally adjacent to and on opposite sides of the inner centrifugal disc 32. These centrifugal discs 34 each produce, when fertilizer particles are supplied via the outlet apertures whose size may be adjusted and which may be closed, a respective outer spreading area 36, so that a spreading pattern 32 having a large effective spreading width of 24m is produced. The spreading pattern 32 is therefore produced from three adjacent and overlapping spreading areas 35 and 36, each spreading area 35 and 36 being produced independently by a particular centrifugal disc 33 and 34.

In order to clarify the advantages of a spreading pattern 32 composed of three spreading area 35,36 with respect to a pattern composed of a spreading area 37, shown by dashed lines, with an identical effective spreading width, this spreading area 37 is also shown in Figure 4. This spreading area 37 would have to be produced by providing the inner centrifugal disc 33 with a high peripheral speed. It is obvious from this Figure that a spreading pattern composed of the spreading areas 35 and 36 projects substantially less to the rear than a spreading pattern composed of the spreading area 37, with the same effective spreading width.

As a result of the division of the spreading pattern into three spreading areas 35 and 36 produced independently of one another by particular centrifugla discs 33 and 34, a spreading pattern is produced in that the spreading area 35 produced by the inner spreading disc 33 extends, looking away from the spreader, substantially in terms of its width to the rear, whilst the spreading areas 36 produced by the additional outer spreading discs 34 extend, looking away from the spreader, substantially in terms of their width to the side of the spreader. In this respect the width of throw W of the fertilizer particles discharged by the inner centrifugal discs 33 is smaller than the width of throw W' of the fertilizer particles produced by the outer centrifugal discs 34.

As a result of the above-described construction of the spreading pattern 32 by the spreading areas 35 and 36 produced by individual centrifugal discs 33 and 34, it is possible, whilst maintaining the uniform spreading density S to reduce the effective spreading width E to the small effective spreading width E' or to the smaller spreading width e or, vice versa, to increase these widths. The reduction of the effective spreading width E is achieved by the closure of the outlet apertures in the container outlets by the closure elements formed as slides, which elements may be operated independently of one another so that no further fertilizer particles are supplied to the centrifugal discs 33 and 34. The effective spreading width E may obviously be reduced from both sides.

It is also possible to discontinue the supply of fertilizer particles to the inner centrifugal disc 33 so that only the outer spreading areas 36 are produced.

This is useful when fertilizing fruit crops for example.

Figure 5 shows a spreading pattern 38 produced by a centrifugal spreader of the oscillating type, which pattern is composed of the three spreading areas 39 and 40. The spreading areas are produced by the throwing elements which are formed as offset distributor nozzles 41 and 42 provided with a reciprocating movement about vertical axes. The inner distributor nozzle 41 produces the inner spreading area 39 and the two outer distributor nozzles 42, which are disposed laterally with respect to the inner distributor nozzle 41 each produce a spreading area 40. The outer spreading areas 40 are adjacent in each case to the inner spreading area 39.

In addition, the inner and outer spreading areas overlap, so that a spreading pattern 38 with a uniform spreading density S is produced.

An effective spreading width E' of 12 m is achieved with the inner spreading area 39. By adding the outer spreading areas 40 to the inner spreading area 39 a larger effective spreading width E of 24 m is achieved. By switching off the supply of fertilizer particles, it is also possible in the case of this oscillating spreader, to reduce the spreading width E in the same way as in Figure 4. The description and details of this embodiment relate to the oscillating spreader of Figure 5.

Claims

1. A method of spreading fertilizer by means of a centrifugal spreader comprising driven throwing elements which throw the fertilizer particles over an area which is substantially greater than the structural width of the centrifugal spreader and whose effective spreading width may be modified, wherein the throwing elements distribute the fertilizer particles over the ground surface to be treated in a uniform spreading pattern in laterally adjacent and overlapping spreading areas with no gaps, the spreading pattern consisting of at least three adjacent and overlapping individual spreading areas, each spreading area being produced by a respective special throwing element.

2. A method as claimed in Claim 1, wherein the spreading pattern is made up of the spreading areas produced individually by respective throwing elements in such a way that the spreading area(s) produced by the inner throwing element(s) extend, looking away from the spreader, substantially to the rear and become wider, whilst the spreading areas produced by additional, preferably external, throwing elements extend, looking away from the spreader, widthwise substantially laterally with respect to the spreader.

3. A method as claimed in Claim 1 or Claim 2, wherein the formation of the spreading areas during the operation of the machine is adjusted such that the actual spreading width of the spreading pattern is modified in steps measured from the centre of the machine.

4. A method as claimed in anyone of Claims 1-3, wherein the throwing width of the fertilizer particles towards the rear is substantially smaller than the throwing width of the fertilizer particles towards the side, in relation to the actual spreading width.

5 A centrifugal spreader for carrying outthe method of Claim 1, which comprises a frame and a storage container provided with adjustable and closable outlet apertures and in which the throwing elements are disposed below the storage container, wherein at least three throwing elements are disposed below the storage container and wherein the outlet apertures associated with respective throwing elements may be closed independently of the outlet apertures associated with the other throwing elements.

6. A centrifugal spreader as claimed in Claim 5, wherein at least four throwing elements are disposed below outlet apertures of the storage container.

7. A centrifugal spreader as claimed in Claim 5 or Claim 6, wherein the throwing elements are disposed adjacent to one another, in a direction transverse to the direction of intended travel of the centrifugal spreader, and wherein the throwing width of the fertilizer particles spread from the internal throwing element(s) is substantially smaller than the throwing width of the fertilizer particles spread by the external throwing elements.

8. A centrifugal spreader as claimed in Claim 7, wherein the throwing elements are replaceable by other throwing elements.

9. A centrifugal spreader as claimed in anyone of Claims 5-8, wherein the storage container comprises a number of container outlets corresponding to the number of throwing elements, wherein each container outlet comprises adjustable and closable outlet apertures and wherein that a throwing element is disposed below each container outlet.

10. A centrifugal spreader as claimed in Claim 9, wherein the container outlets of the storage container are separated from one another by inverted V-shaped components.

11. A centrifugal spreader as claimed in anyone of Claims 5-10, wherein the outlet apertures are closable by means of closure elements and wherein the outlet apertures associated with the individual throwing elements are closable independently of one another by the closure elements.

12. A centrifugal spreader as claimed in Claim 11, wherein the closure elements are actuable by means of a remote control.

13. A centrifugal spreader as claimed in anyone of Claims 5-12, wherein the throwing angle (ops), measured with respect to horizontal of the fertilizer particles discharged by the outer throwing elements is greater than the throwing angle (a'), measured with respect to horizontal, of the fertilizer particles discharged by the inner throwing element(s).

14. A centrifugal spreader as claimed in anyone of Claims 5-13, wherein the outer throwing elements are offset, looking vertically, with respect to the inner throwing element(s).

15. A centrifugal spreader as claimed in anyone of Claims 5-14, wherein the outer throwing elements are drivable, via V-belts, by the inner throwing element(s).

16. A centrifugal spreader as claimed in Claim 9 or anyone of Claims 10-15 when dependent on Claim 9, wherein an agitator shaft extends horizontally and transversely to the direction of intended travel and projects into all of the container outlets.

17. A centrifugal spreader as claimed in anyone of Claims 5-16, wherein the throwing elements are centrifugal discs drivable about in use vertical axes and wherein discharge blades are disposed on the centrifugal discs.

18. A centrifugal spreader as claimed in anyone of Claims 5-16, wherein the throwing elements are discharge nozzles which are displaceable about in use vertical axes with a reciprocating movement.

19. A centrifugal spreader as claimed in anyone of Claims 5-18, wherein the outer portions of the outer throwing elements are spaced from one another in the operating position by a distance which is smaller than or equal to 3 m.

20. A method of spreading fertilizer substantially as hereinbefore described with reference to Figure 3, Figure 4 or Figure 5 of the accompanying drawings.

21. A centrifugal spreader substantially as hereinbefore described with reference to, and as shown in, Figure 2, or Figure 2 as modified by Figure 4 or Figure 5, of the accompanying drawings.