in fig1 a , a first embodiment of an agricultural sprayer apparatus according to the present invention is shown generally designated the reference numeral 10 . the agricultural sprayer apparatus 10 comprises a agricultural tractor 14 and a spraying unit 20 . the agricultural tractor 14 comprises a chassis 12 , a driver &# 39 ; s cab 15 and an engine 17 . at the rear part , the tractor 14 is provided with a connecting device 19 , such as an ordinary three - point coupling for establishing connection to auxiliary equipment such as an agricultural implement . alternatively , the connecting device 19 may be a hitch for connecting thereto a separate trailer ( not shown ). the tractor 14 is further provided with a power take - off ( not shown ) at the rear part . the spraying unit 20 generally comprises a frame 22 for supporting a container or tank 24 containing a fluent material , such as a chemical agent , i . e . a pesticide or a fungicide to be deposited on vegetation by spraying . the tank 24 is provided with an inlet aperture 26 for filling the tank with the chemical agent . the frame 22 is further provided with a pump unit ( not shown ) connected to the power take - off of the tractor , or to any other suitable power means , for transferring the chemical agent from the tank 24 to a plurality of nozzles from which the chemical agent is sprayed onto the crop , as will be explained in further details below . the spraying unit 20 is shown as being connected to the tractor by means of the above mentioned three - point coupling . the spraying unit may , however , be mounted on a separate trailer which is subesquently connected to the tractor 14 . the frame 22 furthermore supports a boom structure 30 which extends in a transverse direction in relation to the agricultural tractor 14 and is formed as a plane lattice structure . the boom structure 30 is preferably composed of a number of individual boom structure sections 35 , 37 e . g . four , six or even more boom structure sections . in the presently preferred embodiment shown in fig1 a total of four boom structure sections are provided . the boom structure sections 35 , 37 are interconnected by means of hinges 31 , allowing the boom structure 30 to be folded to a position ( not shown ), in which the individual boom structure sections 35 , 37 are folded against one another and assume a vertical position , serving the purpose of allowing the agriculural sprayer apparatus 10 to travel from one place to another for moving the spraying unit 20 from one place to another . in fig1 a , the boom structure 30 is shown in a position wherein the boom structure sections 35 , 37 extend in a plane parallel to the ground . alternatively , one or more boom structure sections may be raised so as to extend at an angle to the ground for the purpose of spraying special crops such as trees . moreover , the boom structure 30 supports a plurality of nozzles 40 arranged along the length of the boom structure 30 for distributing the chemical agent transferred thereto from the tank means 24 by means of the pump , via a tubing 28 , likewise supported by the boom structure 30 onto the crop by spraying . optionally , a plurality of individual air - blowers or fans 29 , may be arranged along the length of the boom structure 30 . an air - distributing device is connected to and supported by the frame and is generally designated by the reference numeral 50 . the air distributing device 50 comprises an air - blower unit 52 having an air intake 54 and including a fan for providing a pressure and / or high velocity flow of air . the air - blower unit 52 is preferably connected to a power take - off of the tractor 14 . the air - distribution device 50 further comprises two elongated air ducts 58 , 59 connected thereto , each extending laterally from the air - blower unit 52 at opposite sides thereof along the boom structure 30 . the air ducts 58 , 59 are releasably connected to the air - blower unit 52 in an air - tight manner whereby the aforementioned pressure and / or high - velocity flow of air may be guided from the air - blower unit 52 of the air - distributing device 50 and into each of the two air ducts 58 , 59 . as will be apparent , the nozzles are arranged laterally off - set from the air - duct , i . e . behind the air duct as seen in fig1 . the air ducts 58 , 59 extending along the boom structure 30 may be connected to the boom structure in numerous ways , as will be discussed in further details below , and is sectionally divided corresponding to the sections 35 , 37 of the boom structure 30 . as will be apparent , the air ducts 58 , 59 each comprises a flexible sheet 60 providing a light - weight structure , and a connecting element 62 , whereby in use , i . e . when the air - blower unit 52 of the air - distributing device 50 is activated , the air duct is inflated , thus assuming the configuration shown in fig1 in which the air ducts 58 , 59 each assumes a substantially tubular configuration . the air ducts 58 , 59 are further provided with individual air - outlets 64 on the lower side thereof and formed in the connecting element 62 , and arranged along the air duct and serving the purpose of directing the air flow generated by the air - blower unit 52 towards the crop to be sprayed . as shown , the air duct gradually tapers toward the outer ends of the boom for providing a uniform air flow or an air flow providing a specific distribution pattern predominantly determined by the position , configuration and orientation of the air outlets 64 . this , however , is not particularly required as the specific distribution pattern may solely be regulated by the position , configuration and orientation of the air outlets . during operation , the spraying unit 20 is connected to the tractor 14 by means of the connecting device 19 , and the pump unit and the air - blower unit 52 is connected to any power take - off , e . g . of the tractor , and the agricultural sprayer apparatus 10 travels across a field of vegetation or crops to be sprayed , e . g . wheat , barley or corn , the pump delivering the chemical agent contained in the tank 24 via tubes 28 to the nozzles 40 arranged along the boom structure 30 . at the same time , the air - blower unit 52 of the air - distribution device 50 generates the above mentioned air flow which is conveyed from the air - blower unit 52 along the air duct 58 , 59 , leaves the air duct through the air outlets 64 and is directed downwardly to impinge on the jet of spraying agent which leaves the nozzles 40 and is directed towards the vegetation at an angle determined by the position of the nozzles 40 relative to the crop . the impingement depends on the position , configuration and orientation of the air outlets 40 relative to the nozzles 64 , which may be varied as discussed below . in fig2 a , a first embodiment of the air duct 58 of the air distribution device 50 according to the invention is shown , illustrated in an inflated condition , the duct 58 being pressurized by means of the air blower unit 52 . as shown , the air duct 58 comprises the flexible and elongated sheet 60 made of an air - impervious material such as polyester , pvc or polyethylene . the sheet 60 and the connecting element 62 which is of a substantially flat or planar elongated configuration extends along the length of the air duct 58 . the connecting element 62 may suitably be manufactured by extrusion of a plastics material or aluminium , and is provided with two grooves or tracks 65 extending along the longitudinal edges of the conneting element 62 . the sheet 60 is provided with beads 66 extending along the longitudinal edges of the sheet 60 , and the beads 66 are received within and releasably secured to a respective groove or track 65 of the extruded element 62 . the width of the sheet 60 is adapted in such a manner to the width of the connecting element 62 that the sheet 60 forms a substantial part of the perimeter of the air duct 58 when secured to the connecting element 62 . the beads 66 are preferably formed by folding back a narrow strip of the sheet 60 along the edges thereof to form a channel receiving a wire , rope or a rod - like component 68 , which is subsequently forced into the groove 65 of the connecting element 62 , thus securing the sheet 60 in fixed relationship to the connecting element 62 . the connecting element 62 is as discussed above provided with a plurality of air outlets 64 which are arranged spaced apart along the length of the connecting element 62 . according to the invention , connecting elements 62 of different length or configurations , or having air outlets 64 of different sizes and shapes may be arranged end - to - end along the boom structure 30 shown in fig1 supporting the air ducts 58 , 59 . the connecting element 62 thus serves the purpose of ensuring the integrity of the air duct 58 , while at the same time providing a great flexibility by being releasably connected to the sheet 60 , so as to allow the replacement of one element by another , whereby the intensity and direction of the air outflow expelled from the air duct 58 may be ajusted in a particularly simple manner along the air duct 58 in accordance with the intentional intensity and direction of the air flow to be expelled by the air duct 58 . the connecting element 62 is preferably connected to the boom structure 30 , possibly by means of an adjusting device whereby the direction of the air flowing from the air outlets may be altered relative to the crop being sprayed or relative to the boom structure 30 . fig1 b shows by way of example an air duct 959 comprising four individual connecting elements 662 &# 39 ;, 762 &# 39 ;, 862 &# 39 ;, 962 &# 39 ; of a length corresponding to one fourth of the length of the boom structure shown on the right hand side of fig1 a . the connecting elements 662 &# 39 ;, 762 &# 39 ;, 862 &# 39 ;, 962 &# 39 ; are arranged in an end - to - end relationship as described above and provided with a different set or configuration of air outlets 64 for providing or allowing for a variation of the intensity and direction of the air flow which is expelled from the air duct 959 . the air duct is formed having a substantially uniform or constant cross section along the length of the air duct 959 . in fig2 b an alternative embodiment of the air duct 58 is shown . in fig2 b , elements or components similar to elements or components described above with reference to fig1 and 2a or serving the same purpose as elements or components described above with reference to fig1 and 2a are designated the same reference numerals , however , added the additional marking &# 39 ;. the elongated , u - shaped connecting element 62 &# 39 ; of fig2 b basically consists of inclined flange sections 70 , 72 converging towards a web 76 . the flange sections 70 , 72 are each provided with the tracks 65 &# 39 ; extending longitudinally along the free edges . the web 76 is provided with the air outlet apertures 64 &# 39 ;, as the inclined flanges 70 , 72 serve the purpose of directing the air towards the outlets . in use , the connecting element 62 &# 39 ; is connected to the sheet 60 &# 39 ; by means of the tracks 65 &# 39 ;, the tracks 65 &# 39 ; pointing upwards , thus forming an air duct having a large cross - sectional area . the sheet 60 &# 39 ; need not be provided with parallelly extending , longitudinal edges , but may be formed having a width at one end which is substantially smaller than the width at the opposite end of the sheet 60 &# 39 ;. when a sheet 60 &# 39 ;, formed in this way , is secured to an air - outlet element 62 &# 39 ;, having substantially parallel tracks 65 &# 39 ;, the resulting duct 60 &# 39 ; exhibits a narrowing or tapering configuration towards one end , as shown in fig1 . fig2 c shows a further embodiment of the air duct 58 . in fig2 c , elements or components similar to elements or components described above with reference to fig1 a or 2b serving the same purpose as elements or components described above with reference to fig1 a and 2b are designated the same reference numerals , however , added the additional marking &# 34 ;. the u - shaped connecting element 62 &# 34 ; is as compared to the u - shaped connecting element 62 &# 39 ; described above with reference to fig2 b connected to the sheet 60 &# 34 ; in an inverted relationship , thus forming an extremely compact air duct , the interior surfaces of the flanges 70 &# 34 ;, 72 &# 34 ; of the inverted u serving to guide the air leaving the air duct 58 &# 34 ; through the apertures 64 &# 34 ; in a predetermined direction . although the connecting elements 60 &# 39 ;, 60 &# 34 ; of fig2 b and 2c , respectively , are shown as having a generally u - shaped configuration , other configurations such as a v - shape configuration may be envisaged , the apertures being provided on one leg or both legs of the v . likewise , the connecting element may be formed having a generally curved section , the air outlets being arranged at predetermined locations for providing a directionally controlled air out - flow . in fig3 a further alternative embodiment of the air duct 58 is illustrated . the air duct 158 shown in fig3 differs from the above described embodiments shown in fig2 a , 2b and 2c in that the sheet 160 of the air duct 158 shown in fig3 is connected to a connecting element 162 which constitutes a composite structure as compared to the connecting elements 62 , 62 &# 39 ;, 62 &# 34 ; shown in fig2 a , 2b and 2c , respectively . in fig3 elements or components similar to or serving the same purpose as elements or components described above with reference to fig1 a , 2b and 2c are designated the same reference numeral , however added the prefix 1 . the connecting element 162 comprises elongated flanges or side elements 170 , 172 joined by means of narrow connecting pieces 173 extending at an angle relative to the longitudinal axis of the air duct and spaced apart along the axis . as shown , the connecting element 162 is provided with channels or grooves 165 extending long the edges of the side elements 170 , 172 . the connecting element 162 is preferably formed as an integrally cast structure having sufficient strength to support the sheet 160 . the side elements 170 , 172 of the connecting element 162 are further provided with locking means 180 , 182 adapted to releasably secure thereto a separate air - outlet element 176 to the side elements 170 , 172 , which air - outlet element are provided with apertures 164 . the separate air - outlet element 176 serves the purpose of providing a desired outflow of the air expelled from the air duct 158 . as shown , the separate air - outlet element 176 is formed as a substantially planar or flat elongated component having edges formed to engage the locking means 180 , 182 of the side elements 170 , 172 in a releasable manner . the separate air - outlet element 176 may provide a further strengthening or reinforcing of the connecting element 162 when the air duct is subjected to forces due to the pressure of the air flowing through the air duct 158 or when the agricultural sprayer apparatus 10 moves across a bumpy piece of land . the connecting element 162 may be provided with a number of separate air - outlet elements 176 , 177 arranged end - to - end along the air duct 58 , the air outlet element 177 being formed without air outlets , thus forming a blind of particular use when spraying row crops , i . e . to be secured to the connecting element 162 i areas where no outward airstream is desired . in this case , the connection between the connecting element 162 and the sheet 160 may be permanent . fig4 a - 4c show different configurations or embodiments of the connecting elements 62 of fig2 a and having any convenient length , e . g . 0 . 1 - 8 m , preferably 0 . 5 - 2 m and provided with air - outlets arranged according to different configurations , e . g . elongated perforations 90 extending at an angle to the main axis of the air duct , as shown in fig4 a , or as rectangular openings 95 , as shown in fig4 b . the air outlets may alternatively be formed as circular apertures 98 arranged in two rows extending along the length of the duct , but displaced in relation to one another , as shown in fig4 c . furthermore , connecting elements 62 having no air outlets may be provided for use when no air outflow is desired , e . g . when spraying row crops . the configuration of the air - outlets illustrated in fig4 a - 4c may also be employed in connection with any other connecting elements described herein . the air - outlets of the connecting element 62 may further be provided with separate nozzle - like elements for directing the air stream in a specific and angular relationship in relation to the ground . in fig5 a tubular nozzle element 100 and an angular nozzle element 104 are shown which are provided with flanges 102 and 106 , respectively , to be inserted through the apertures 64 and secured thereto by snap - like engagement . fig6 shows a further embodiment , in which an elongated nozzle element 99 is secured to the connecting element 62 and in which a tapering nozzle element 112 is also secured to the connecting element 62 . in fig7 an alternative further embodiment of a connecting element 110 is shown which is formed as the connecting element 62 described above with reference to fig2 a , but further provided with integrally formed , downwardly extending flanges or side plates 130 , 132 for directing the flow of air in a predetermined direction and orientation . fig8 shows a connecting element 110 &# 39 ; similar to the connecting element 110 of fig7 . the connecting element 110 &# 39 ; differs from the connecting element 110 of fig7 in that the connecting element 100 &# 39 ; is connected to an actuator 135 , such as a motor or a hydraulic or electric cylinder through a shaft 138 and a crank arm 139 . the shaft 138 is connected to the connecting element 110 &# 39 ; for allowing the connecting element 110 &# 39 ; and the sheet 60 of the air duct assembly to be pivoted round the shaft 138 for pivoting or turning the connecting element 110 &# 39 ; relative to the supporting boom structure such as the boom structure 30 shown in fig1 . like the connecting element 110 &# 39 ; shown in fig8 any of the described embodiments of the connecting element and also the air duct may be provided with pivoting means for pivoting the air duct relative to the supporting boom structure . alternatively , the boom structure such as the boom structure 30 described above with reference to fig1 may in its entirety including the air duct 58 and 59 be pivoted relative to the air - blowing unit 52 . alternatively , one or both side plates 130 , 132 of fig7 and 8 may be rotatably connected to the connecting element , the actuator 135 serving to produce a rotation of the side plates 130 , 132 relative to the connecting element thus varying the velocity of the air stream . in fig9 a further embodiment 258 of the air duct is shown . the air duct 258 is secured to a boom section 235 and comprises a connecting element 262 which has air outlets 264 and is connected to a flexible sheet 260 by means of a bead 268 inserted into grooves 265 of the connecting element 262 . the connecting element 262 is basically a substantially flat , planar extruded component as described with reference to fig2 a and comprises a flange 270 extending perpendicularly thereto along the length of the connecting element 262 together with a first tongue 272 formed as an extension of the connecting component , extending beyond the flange 270 alongside the connecting element 262 . the connecting element 262 is furthermore provided with a second tongue 273 serving the purpose of supporting the sheet 260 when the duct is deflated . as shown , the boom section 235 comprises a framework formed from tubes or elements 236 extending parallel to one another and serving two purposes , viz . firstly the purpose of supporting a series of nozzles 240 and tubings 245 for distributing the chemical agent contained in the tank 24 and secondly the purpose of supporting the air duct 258 comprising the sheet 260 and the connecting element 262 . the elements 236 are of rectangular cross section , allowing the flange 270 and the tongue 272 to rest against two sides of the elements in supported relationship . the air duct 258 is fixated in relation to the boom section 235 by means of fixation means ( not shown ) possibly by securing the connecting element 262 directly to a tube 236 . the direction of the air flowing from the air duct 258 through the air outlets 264 may be varied in relation to the crop by rotating the entire boom section about its longitudinal axis . fig1 shows an alternative embodiment 358 of the air duct according to the present invention . in fig1 , elements or components similar to or fulfilling the same purpose as elements or components described above with reference to fig1 a , 2b and 2c are designated the same reference numerals , however with the prefix 3 added . thus , the air duct 358 comprises a connecting element 362 similar to the connecting element 62 described above with reference to fig2 a . the connecting 362 is , however , provided with a downwardly protruding channel - like section 367 receiving a shaft 338 which is connected to a crank arm 339 and further to an actuator 335 , such as a motor or a hydraulic or electric cylinder , serving the same purpose as the actuator 135 described above with reference to fig8 . the air duct 358 shown in fig1 is further connected to the boom section 235 described above with reference to fig9 by means of suitable bearings . the actuator 335 serves the purpose of rotating the connecting element 362 and the sheet 360 of the air duct 358 relative to the supporting boom section 235 . by rotating the connecting element 362 , the angle of impingement of the air expelled from the air outlets 364 of the connecting element 362 is altered relative to the jet of atomized fluid material expelled from the nozzles 240 . the rotational motion may be transmitted between adjacent ( end - to - end ) connecting elements 362 by means of separate connectors ( not shown ) which may be inserted in the channel - like section 367 . the nozzles 240 may be rotatably secured to the boom section 235 , e . g . for rotation about an axis extending parallel to the boom section 235 , the rotation being effected by means of any simple linking system joined to the connecting element 362 for ensuring a coordinated rotation of the nozzles 240 and the connecting element 362 . fig1 illustrates in greater details a part of a connecting element 462 which differs from the above described connecting element 362 shown in fig1 by the provision of a through - going flange 436 which is formed as an integral part of the connecting element , and which supports a number of brackets 485 which further support tubings 445 and nozzles 440 similar to the tubings 245 and the nozzles 240 described above with reference to fig9 and 10 . the brackets are provided with a section 482 which engages the flange 436 by snap - action whereby the nozzle - supporting brackets may be secured to the connecting element 462 . as shown , the connecting element 462 is provided with a section 430 to which a shaft 438 is connected which shaft 438 together with a crank arm 439 and an actuator 435 correspond to the shafts 138 , 338 , the crank arms 139 and 339 and the actuators 135 and 335 described above with reference to fig8 and 10 , respectively . thus , through the operation of the motor 435 , the connecting element 462 and the nozzles 440 are pivoted or rotated relative to the supporting boom section ( not shown ), while being fixed relative to one another . in fig1 , a connecting element 562 is shown which connecting element is very much similar to the connecting element 162 described above with reference to fig3 however differing from the connecting element 162 in two aspects to be described below . thus , the connecting element 562 and the individual elements or components thereof are designated the same reference numerals as the corresponding components of the connecting element 162 , however amended by the substitution of the first integer 1 by the integer 5 . the connecting element 562 shown in fig1 firstly differs from the above described connecting element 162 in that the element is integrally connected to brackets 585 serving the same purpose as the brackets 485 described above with reference to fig1 , viz . the purpose of supporting the tubings 445 and the nozzles 440 described above with reference to fig1 . secondly , the integral structure of the connecting element 162 and the tubings and nozzles support brackets 585 is rotatable round a shaft 538 on which the integral structure is supported relative to the boom structure of the spraying unit 20 allowing the integral structure comprising the connecting element 562 and the nozzles 440 supported by the brackets 585 to be rotated relative to the longitudinal axis of the boom structure . in fig1 the air ducts 58 and 59 are supported by the supported boom structure and extend in inflated state upwardly from the supporting boom structure . in fig1 , an alternative embodiment of the air duct is shown designated the reference numeral 658 and differing from the above described air duct 58 shown in fig1 in that the air duct 658 is consealed within the supporting boom structure which is designated the reference numeral 630 which consequently serves the additional purpose of protecting the air duct , which similar to the above described air ducts comprise a sheet 660 apart from supporting the air duct 658 . the air duct 658 shown in fig1 comprises a connecting element 662 which is of a structure similar to the structure of the connecting element 62 &# 39 ; described above with reference to fig2 b , however additionally provided with an outwardly protruding shaft 638 serving the purpose of allowing the air duct 658 to be rotated by means of an actuator , such as a motor or a hydraulic or electric cylinder ( not shown ) relative to the supporting boom structure 630 . the actuator serving the purpose of rotating the air duct 658 relative to the supporting boom structure 630 may be implemented in accordance with the techniques described above with reference to fig8 and 11 . in fig1 , a nozzle 640 is further shown which is supported by the boom structure 630 and serves the purpose of expelling the atomized spraying agent supplied to the nozzles from the supplied tank of the spraying unit 20 . fig1 shows by way of example the air duct 59 of the air distribution device 50 being fitted with connecting elements 62 and 962 and ready to use for spraying crops arranged in rows or for spraying areas where no air discharge is desired from the interior part of the air duct 59 , i . e . the part of the air duct 59 situated close to the air blower 54 . one or several connecting elements 62 may thus be arranged in an end - to - end relationship in the outermost part of the air duct 59 and being provided with apertures 64 allowing the air flowing in the air duct of the air distribution device 50 to be expelled . socalled blinds or connecting elements 962 having no air outlets are provided extending along a part of the air duct 59 close to the air blower 54 , the blinds 962 serving the function of ensuring the integrity of the air duct 59 in this region . this application or arrangement of connecting elements is particularly useful when applying the spraying unit according to the invention in the spraying of trees , as shown in fig1 wherein a spraying unit according to the invention in shown as passing by a tree 1 , the boom structure being raised to a position in which the boom structure and the air duct 59 extends at an angle relative to the horizontal on which the spraying unit according to the invention travels . in this case only the outermost part of the air duct 59 and the nozzle means 40 are active , thus ensuring that the spraying agent and the air flow is directed towards the crown or top of the tree 1 . for spraying row crops formed by bushes , cucumber plants , the boom structure may alternatively be provided with a plurality of vertical and downwardly extending air ducts comprising the same elements as the air ducts 58 , 59 described with reference to fig1 - 15 i . e . comprising connecting elements and a flexible sheet and being connected to a separate boom structure . although the present invention has been described above with reference to presently preferred embodiments , it is to be understood that numerous modifications are easily deduced by a person having ordinary skill in the art without departing from the scope and spirit of the present invention . these modifications or alternative embodiments are to be considered part of the present invention , as the scope of the present invention is by no means to be construed limited to the above - described embodiments , but rather be considered defined by the scope of the appending claims .