DIRECT INJECTION VARIABLE RATE CHEMICAL DISTRIBUTION. FIELD OF THIE INVENTION 5 The present invention relates generally to the field of crop and field spraying with chemical such as but not limited to insecticides, fertilisers and the like and more particularly relates to a method and apparatus for the controlled distribution of liquid sprays and particularly but not limited to liquids distributed by aerial spraying. 10 More specifically, the present invention relates to a system which enables controlled spraying of such liquids to apply the optimum quantity to the correct areas of the a. field. The invention further relates to a direct injection variable rate liquid application system. 15 BACKGROUND OF THE INVENTION In agriculture, farmer's require liquid spraying to either fertilise crops or to eradicate or control unwanted vegetation such as weeds or insects and the like. This activity is 20 usually conducted by aerial spraying using crop spraying aircraft. It is well known in the industry that significant losses and therefore economic loss is sustained and also inefficiencies in the distribution of sprays occurs as a result of the inaccuracy of the current distribution techniques. For instance, in a typical field of crops, it has in the past been difficult to estimate the quantity of chemical to be delivered for a particular 25 purpose be it for fertilisation of crops or spraying weedicides or pesticides. To date, the quantities which have been sprayed in a unit area can exceed or fall short of the required quantity leading to economic loss and loss of chemical or a level blow that required for the spray concentration to be suitable for the purpose for which the liquid is intended. According to conventional method, quantities required for a particular 30 job are estimated leading to potential for oversupply in one area of a paddock and undersupply in another area of the paddock. Typically, biomass of a field determines the quantity of weedicide, pesticide or the like required for a chemical treatment. Biomass varies across a field of vegetation, crops and the like so different volumes of chemical treatment are required for different parts of the filed. These 1 variations occur irregularly and not according to any geometric pattern. In fact the distribution of biomass concentration is random and varies in random patterns across 5 a field. In the past, crop growers essentially made estimates of the vegetative biomass and averaged the quantity of chemicaL Accordingly, there was in the past considerable waste of chemical due to excessive volume spray in some areas. Also there was under spray in other areas where more chemical was needed and overspray in other areas where less chemical was needed. 10 Conventional aerial spraying is conducted by means of rear wing nozzles mounted on booms which extend laterally and parallel to the wings. The number of discharge nozzles and their settings are selected according to the required task The conventional method for aerial spraying insecticides and the like in fields is as 15 follows. 'rhe first step is agronomic inspection of the field which allows a guesstimate of the quantity of insecticide required for that application. An estimate of litres per hectate is calculated and this concentration is averaged over the entire area of the paddock. This data is provided to a pilot who then sets the spray equipment to deliver liquid a 20 predetermined discharge rate. This rate is kept the same for the whole spray area. Typically, the local spray requirements in a particular paddock will vary considerably as vegetation density and chemical requirements change over the area of a paddock. Vegetation is usually irregular over the area of the paddock. Insecticide requirements consequently vary over the paddock area but presently there is no means to accurately 25 dose the insecticide according to the local requirements of a particular region of an area to be sprayed by air. In estimating liquid requirement by simply averaging the estimated concentration required over the whole area of the job at hand, this carries with it the risk that there will be an oversupply of spray in one area and an undersupply of spray in another area. This is an uneconomic, environmentally 30 detrimental and inefficient use of expensive agricultural chemicals. At present, there are no means for automatic direct injection dosing of sprayed liquids such as insecticides to overcome the losses and inefficiencies arising from the present averaging techniques. There is a need to provide a system which allows controlled variation in the application and / or dosage rate of a liquid fertiliser, 2 insecticide or the like whilst maintaining droplet size. There is a need to provide such a system which may be adapted to aerial crop spraying. Agronomy management units have become smaller in recent years and the technology now exists to expedite checking and correlation which was previously done by hand. 5 Existing systems usually put on a complete spray of only a proposed variable rate chemical and they simply manipulate the total volume in conjunctio with manipulating the application technique for example the nozzles to maintain a uniform droplet size. There is a long felt want in the industry to provide a system of spraying agricultural 10 chemicals in an economic and efficient way by controlling the direct injection of a chemical. either alone or in conjunction with and to supplement a base chemical . There is a need to provide a system which controls direct injection of chemicals so that an accurate dosage is delivered according to predetermined parameters of the land 15 / vegetation requirements and taking into account characteristics of the delivery vehicle. INVENTION 20 The present provides an efficient method and associated apparatuses for crop and field spraying with chemicals such as but not limited to insecticides, fertilisers and the like and more particularly relates to a method and apparatus for the controlled. distribution of chemical, including liquid sprays but not limited to liquids distributed by aerial spraying. More specifically, the present invention provides a system which enables 25 controlled variable rate direct injection spraying of such chemicals /liquids to control or eliminate wastage of the liquid and to improve overall efficiency of delivery. The present invention which is described by the name Direct Injection Variable Rate Liquid Application ( DIVRA) according to a preferred embodiment, allows a grower to apply a base chemical and variable rate liquid application ( VRA) 30 chemical simultaneously. According to one embodiment, there is provided a hopper for the DIVRA chemical and a primary hopper for the primary chemical in an aircraft which delivers the chemicals. 3 It is one object of the present to provide anl efficient method of controlled aerial distribution of liquid sprays such as but not limited to insecticides, fertilisers and the like. 5 In is another object of the invention to provide associated apparatuses for controlled crop and field spraying with insecticides, fertilisers and the like. It is a further object of the invention to provide an improved chemical delivery system which enables controlled variable rate spraying of such chemicals to control or 10 eliminate wastage of the chemical and to improve economic efficiency and efficiency of distribution. It is a further object of the present invention to provide a means for efficient distribution of insecticides, weedicides and the like and without unwanted over spray 15 or under spray in a given area. It is another object of this invention to provide a computerized distribution control system which enables predetermined dosages of a liquid delivered to a predetermined local area in a field responsive to predetermined field parameters and vehicle delivery 20 parameters. The present invention is most suited to aerial distribution of such chemicals but it will be appreciated that the system may be adapted to distribution by means other than aircraft. The present invention, according to one embodiment, provides a system which allows a grower to apply a primary chemical and VRA chemical simultaneously by a direct injection system. The direct injection system 25 includes a hopper for the VRA chemical in an aircraft. The direct injection system injects the VRA chemical through at least one nozzle orifice where it meets a base chemical prior to spray of the base chemical and which is applied to a crop or other vegetation. 30 In one broad fonrm the present invention comprises: an assembly for the controlled aerial distribution of at least one chemical from at least one spray nozzle, the assembly including; 4 a boom assembly attachable to a vehicle such as an aircraft and which supports said at least one nozzle and communicates between a supply of chemical and an outlet to said at least one nozzle; a computer including software which receives prescription data relating to spray 5 requirements of a location in an area to be sprayed with chemical; control means enabling spray operation of said at least one nozzle responsive to a control signal; wherein, the computer controls delivery of chemical according to the prescription data for a specific location in a spray area. 10 Preferably, the prescription data is created from an image of a spray area relating to a biomass in a particular location of said spray area. According to a. preferred embodiment, there are a plurality of nozzles each capable of delivering a base chemical and at least one second chemical, wherein, the second chemical is 15 delivered via the at least one nozzle at a variable rate dictated by the prescription data. A plurality of nozzles may form at least one nozzle bank for spraying the base chemical and the variable rate chemical. Each chemical is held in a separate hopper and are each delivered via supply lines to each said nozzles in said at least one nozzle 20 bank which are retained by a base chemical delivery boom and a variable rate chemical delivery manifold boom. The variable rate chemical is delivered to supply lines via the manifold boom which is in communication with the hopper holding the variable rate chemical. The apparatus preferably works in conjunction with an aircraft guidance system. in communication with the cornputer allowing the computer to 25 determine the exact location of the aircraft in a field being sprayed and allowing at the same time delivery of the variable rate chemical at a predetermined rate depending upon the delivery rate requirements for a predetermined area. The computer allows for operating parameters of the aircraft from which the chemical is sprayed. 30 Preferably each spray nozzle includes a first check valve which regulates delivery of the base chemical through an outlet in the nozzle and a second check valve which regulates the delivery of the variable rate chemical through the same outlet. 5 The nozzles are preferably charged under pump action. The prescription data for a particular spray 'field is obtained from prescription maps and may be related to biomass of the field. 5 Preferably, a variable rate pump delivers the variable rate chemical responsive to a signal from the computer at a rate determined by the prescription data for a particular field location. The plurality of nozzles may be actuated either collectively in groups or individually in response to input data relating to spray requirements obtained from a prescription for a field to be sprayed. 10 An board controller operates the computer thereby allowing controlled delivery of chernical via said nozzles responsive to data in said computer based on predetermined image parameters and aircraft velocity, position and ground speed. 15 Software in said computer which receives data using a photograph whose parameters are inputted into said computer works in conjunction with an air craft GPS guidance system. Preferably a land manager associated with a flow controller sends a control signal to a flow control valve motor which activates a flow control three way valve and a flowmeter. 20 According to one embodiment, the variable rate chemical is delivered from flexible lines to an orifice holder through a check valve and into a T junction between the check valve delivering the base chemical and said delivery nozzle. The check valve may be solenoid activated 25 The chemicals are preferably distributed by aerial spraying from a crop dusting aircraft and the distribution system allows the delivery rate to change as the aircraft flies over the field. Preferably the aircraft includes a display in the aircraft showing a line diagram of the field layout and display on the screen of a variable delivery rate as the aircraft passes over different portions of the Field having different 30 predetermined delivery requirements according to the prescription for that field. A field prescription may be according to one embodiment, colour based such that a colour represents a volure of chemical spray required for a predetermined location in the field. In one example a red colour on a photographic image may require delivery 6 of spray. at the rate of 0.1. 1 /hectare, a green colour may require delivery of spray at the rate of 0.6 1 /hectare and a blue colour may require delivery of spray at the rate of 1.2 1 /hectare Preferably the base chemical and VRA chemical are liquid sprays such as insecticides, 5 fertilisers and the like applied to a crop or vegetation. delivered simultaneously by a direct injection system. In a broad form of a method aspect the present invention comprises: a method of controlled aerial spray delivery over a predetermined area of at least one 10 chemical from at least one nozzle in a spray nozzle assembly, the method comprising the steps of; a) providing a prescription for a spray regime over a selected area of a field; b) inputting prescription data into a computer in communication with said nozzle assembly; 15 c) providing means associated with the nozzle assembly enabling said nozzle assembly to operate responsive to a signal generated from the computer; di) when the aircraft is airborne, selecting from a control console a job identity relating to a particular field data prescription stored in said computer; C) allowing the computer to control operation of delivery of said at least one 20 chemical according to the prescription data for a specific location in said area. The method comprise the further step of creating a prescription is created from an image of a spray area relating to a biomass load in a particular location of said field. The nozzle assembly includes at least one nozzle for spraying a base chemical and at 25 least one second chemical wherein the second chemical is delivered via said at least one nozzle at a variable rate dictated by the prescription data for a particular job. (The prescription data may come from a number of sources for example the prescription maps that are used to control the system may be subcontracted to experts 30 who provide multi spectral images . According to a preferred embodiment, the liquid is distributed by aerial spraying from a plurality of nozzles which are actuated either collectively, in groups or individually 7 in response to input data relating to spray requirements, obtained prescription of the 'field to be sprayed and which is input into said computer. Preferably in accordance with a method aspect, as an aircraft flies over a 5 predetermined area of a field, data contained in the controller computer based on a field parameter automatically determines a prescribed minimum or maximum delivery rate from said nozzles so that an accurate dose of liquid is delivered Preferably, the computer and controller is located on board an aircraft but in an 10 alternative embodiment the system of delivery may be remotely controlled. In another broad form., the present invention comprises: an assembly for controlled delivery over a. predetermined area of a liquid from at least one nozzle in a nozzle assembly attached to an aerial spraying aircraft, the 15 assembly comprising; a nozzle assembly having at least one nozzle capable of delivery of a fluid; a prescription of an area to be sprayed with said liquid; a computer in communication with a controller and comprising data relative to the aerial image; 20 means associated with a nozzle assembly enabling said nozzle assembly to operate responsive to an input from said controller; wherein said nozzle assembly operates responsive to said input data to enable controlled aerial delivery of a liquid from said at least one nozzle. Preferably, said image is obtained by infrared aerial or satellite photography and provides data relating 25 to local areas of a paddock. In another broad form the present invention comprises: 30 an assembly for controlled delivery over a predetermined area of a liquid; the assembly comprising, a source of fluid contained in a fluid reservoir input data relating to a prescription of an area to be sprayed with said liquid; 8 at least one nozzle in a. nozzle assembly capable of receiving and delivery of fluid from said source of fluid; a computer in communication with a controller capable of communicating with an operating valve; 5 a flow meter in communication with the controller for regulating the flow of a chemical to a boom assembly; a supply line for controlled delivery of at least one chemical to at least one nozzle for injection; wherein said nozzle assembly operates responsive to said input data to enable 10 controlled delivery of a liquid from said nozzle assembly at a predetennined rate. Preferably, a computer is located on board an aircraft but in an alternative embodiment the system of delivery may be remotely controlled. A method of controlled delivery over a predetermined area of at least one chemical 15 from at least one nozzle in a nozzle assembly attached to an aerial spraying aircraft, the method comprising the steps of; a) preparing input data derived from a prescription map of an area of a field to be sprayed with said chemical, b) providing an on board computer in communication with said at least one 20 nozzle and inputting said data relative to the prescription map into an on board computer; c) providing a controller associated with the nozzle assembly in communication with said computer and enabling said nozzle assembly to operate responsive to an output signal or signals from said controller; 25 d) operating said nozzle assembly responsive to said output signal/s to enable controlled aerial delivery of the at least one chemical via an outlet in each said nozzles; e) providing a flow meter in communication with a boom assembly and the controller, 30 f) regulating flow rate through said nozzles of a variable rate chemical for a particular location in a spray area based on biomass data, aircraft perfonnance and location data responsive to outputs from said computer. 9 These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments. 5 BRIEF DESCRIPTION OF DRAWINGS The present invention will now be described in more detail according to a preferred but non limiting embodiment and with reference to the accompanying illustrations: 10 wherein; Figure 1 shows a schematic layout of an assembly for delivery of liquid via aerial spraying according to one embodiment. Figure 2 shows a plan view of an aircraft showing a layout of a chemical variable rate distribution assembly according to a preferred embodiment. 15 Figure 3 shows a schematic view of a variable rate distribution assembly according to a preferred embodiment. Figures 4 show an enlarged view of a direct injection boom and nozzle assembly according to one embodiment. Figure 5 shows a typical aerial image of a paddock to be sprayed with rate defining 20 borders and which constitutes image data inserted into a computer. Figure 6 shows a boundary line image of a result of spraying according to the prescription of figure 5. DETAILED DESCRIPTION 25 The invention will be described below with reference to preferred embodiments of an assembly and associated method for variable rate chemical distribution. The system. according to one embodiment of the invention is adapted for spraying 30 cotton growth regulant by air with the objective to give growers a tool by which they could even up the biomass of their variable fields, thereby making in field management easier. 10 According to one embodiment the invention provides an economically viable system which works at near constant volume. The assembly and method according to the invention may be amalgamated and work with existing equipment and apparatus. The present invention may therefore be retrofitted to existing spraying system hardware, 5 with additions required to facilitate the variable rate injection assembly. The variable rate distribution assembly may be used in a variety of applications such as but not limited to distribution of growth regulant, use as Herbicide control and on large broad acre weed control. The embodiment to be described herein is an example of an application of the 10 invention which allows a direct injection via supplementary nozzles of a chemical at a variable rate, in that the flow rate of chemical can be adjusted according to tile spray requirements for a predetermined geographical area. There are several benefits to a consumer of the Direct Injection variable rate system. to be described below in comparison to the existing Variable rate liquid 15 Application systems. 1 There are considerable cost savings to the consumer by the simultaneous application of the VRA ( variable rate liquid application ) and DIVRA ( direct injection variable rate liquid application ) chemical. 20 2 There is a tighter control on the droplet size in the DIVRA in comparison to systems that rely on variable -flow means to maintain droplet size as the total volume varies. According to a preferred embodiment of a system aspect, the invention requires the 25 use of the following hardware: a VRA computer a controller a pumping system; DIVRA Boom; and 30 Direct injection nozzles ( DIVRA nozzles) Referring to Figure 1 there is shown a schematic assembly 1 for controlled delivery of liquid chemical via aerial spraying according to one embodiment. The assembly 1 is preferably located in an air craft capable of spraying a field with pre selected 11 chemicals. Figure 1 also shows variable rate application (VRA) computer 2 on which a Program module is loaded.. The computer 2 (which is preferably a proprietary SATLOC M3) feeds the 5 required changes in application rate to the Flow controller (SATLOC Aerial Ace) by analysing a predetermined prescription for a particular job and aircraft performance parameters such as velocity, ground speed and position . The prescription is predetermined using a photographic image 3 whose parameters are inputted into computer 2 pre loaded with enabling software and which works in conjunction with 10 an air craft GPS guidance system 6. A Land manager 4 associated with a flow controller sends a control signal to a flow control valve motor 7 which activates a flow control three way valve 13 according to the prescription and a flowmeter 14. Alternatively, separate motors 11, 12 may be provided to operate one or more pumps 8, 9 and the computer 2 regulates the controller signal by gathering intelligence 15 from. the flow meter 14 associated with the pumping system 5. In a preferred embodiment, the aforesaid assembly I is integrated into the aircraft guidance system (SATLOC) and uses SATLOC proprietary software for the VRA component. Pumping system 5 is provided preferably comprising 24Vdc roller spray pumps 8 and 9 to enable more reliability and higher VRA spray volumes. The pumps 20 8 and 9 deliver a chemical into the three way valve 13 controlled by the SATLOC Aerial Ace Controller 4 via a 24V electric motor 11 and 12 respectively. According to one embodiment pumps 8 and 9 are roller pumps. The VRA chemical then passes through flowmeter 14 and is delivered to a VRA boom assembly 15 described below ( with reference to figure 4). . 25 A supplementary boom associated with boom assembly 15 is provided that injects VRA chemical to be injected into direct injection nozzles 21 described below ( see figure 4) . According to one embodiment, the direct injection VRA boom assembly 15 is essentially a % inch (19mm) stainless steel pipe with 'A inch off takes for individual injection nozzles 21. Direct injection boom assembly 15 provides a 30 VRA chemical to be injected into nozzles 21 . Direct injection nozzles 21 which are in. communication with boom assembly 15 receive via flexible hose lines 16 a VRA chemical. The VRA chemical is delivered from the flexible lines 16 to an orifice holder 17 through a check valve 18 (which may be solenoid activated) and into a T junction 19 between the check valve 12 18 delivering the base chemical 20 and delivery nozzle 21.. According to a preferred embodiment, there may be also provided ( not shown) on /off solenoids located at a direct delivery boom assembly inlet. These may be substituted for the check valves 18 upstream of the nozzles 21. An essential feature of the invention is the direct 5 injection nozzles. Under the above system the VRA chemical can be applied to virtually any Upper volume but the lower 1/3 of the requested may not be delivered effectively. i.e. If a I 1/Ha upper volume is requested the spray will be delivered at 0. 1/Ha then continuously from 0.33 1/Ha to 1 I/Ha. This lower end restriction is to ensure even 10 distribution across when there is a significant change in the requested top rate of VRA chemical. The volume may also have to be changed if the total volume used with the base chemical is changed, i.e. if the main boom average working pressure is significantly increased or decreased. The bottom 1/3 restriction may be eliminated by adopting a system of paired 15 solenoids on or associated with the delivery nozzles 21. Each pair of nozzles runs on an on /off cycle . The timing of the cycle is changed to allow even pressure depending on the VRA rate at the time. Alternatively the nozzles 21 may be configured with a metering orifice similar to a carburettor jet that could keep even pressure depending on the VRA rate. In another embodiment, there are provided two booms one for the 20 top 2/3 of chemical and one for the bottom 1/3. An alternative embodiment is tie placement of a solenoid at each nozzle with individual or nozzle bank control and as the VRA rate increases bringing on line additional nozzles or banks of nozzles. In a further embodiment, there is provided a synthetic orifice that can expand and contract with changes to the VRA rate and maintain an even pressure. The aforesaid 25 description describes a schematic arrangement of hardware to implement the direct injection delivery system according to on embodiment. Figure 2 shows a plan view of an aircraft 30 showing a layout of a variable rate chemical distribution assembly 31 according to one embodiment. 30 Assembly 31 comprises a computer 32 (which is preferably a proprietary SATLOC M3) and which operates in conjunction with a Satloc M3 Guidance system 33. Computer 32 feeds the required changes in application rate to the flow controller 13 34 (SATLOC Aerial Ace) by analysing a predetermined prescription for a particular job and aircraft performance parameters such as velocity, ground speed and position. A control signal is sent to the flow controller 34. Computer 32 regulates the controller signal by gathering intelligence from the flow meter 34 associated with 5 pumping system 35. Pumping system 35 may 24Vdc roller spray pumps ( not shown) to enable more reliability and higher VRA spray volumes, The VRA chemical passes through flowmeter 36 and is delivered to a VRA boom assembly to be described below ( with reference to figure 4). A boom solenoid 37 regulates supply of chemical to the boom assembly. Hopper 38 contains spray 10 chemicals . According to a preferred embodiment, hopper 38 may contain a base chemical and a separate hopper 39 which may be contained with in or adjacent hopper 38 contains the variable rate chemical. Figure 3 shows a schematic view of a variable rate distribution assembly 40 including 15 boom assembly 41 and nozzle assembly 42 according to a preferred embodiment. Boom assembly 41 comprises a primary boom section 43 and secondary boom 44. Primary boom section 43 delivers a base chemical pumped from a. hopper ( as described in figure 2 ) and DTVRA secondary boom section 44 which transmits the variable rate chemical. Primary boom 43 communicates with a primary check valve 20 45 which regulates flow of base chemical to nozzle assembly 42. Secondary boom 44 communicates with a check valve 46 which controls delivery of the variable rate chemical in response to a signal from a controller. The variable rate chemical 47 and base chemical 48 mix upstream of nozzle assembly 42. Nozzle assembly 42 includes an outlet 49 through which mixed chemicals 47 and 48 are eventually delivered 25 Check valve 46 regulates the rate at which the variable rate chemical is distributed according to the control regime described earlier. Figures 4 show an enlarged view of a direct injection boom and nozzle assembly according to one embodiment. 30 Boom assembly 51. comprises a primary boom section 52 and secondary boom 53. Primary boom section 52 delivers base chemical pumped from a hopper located in aircraft 54 ( as described in figure 2 ) and DIVRA secondary boom section 55 which transmits the variable rate chemical. Primary boom 52 conmunicates with a primary check valve 56 which regulates flow of base chemical to nozzle assembly 57. 14 Secondary boom 55 communicates with a check valve 58 which controls delivery of the variable rate chemical in response to a signal from a controller ( not shown). The variable rate chemical and base chemical mix upstream of nozzle assembly 57. 5 Nozzle assembly 57 includes an outlet 59 through which mixed chemicals are eventually delivered . Check valve 58 regulates the rate at which the variable rate chemical is distributed according to the control regime described earlier. Direct injection chemical is fed to the check valve 58 via line 60 which is in communication 10 with secondary boom 55. Each nozzle assembly will have its own feed line equivalent to feed line 60. As can be seen from figure 4, there are a plurality of nozzle assemblies 61, 62, 63 and more distributed along primary boom 52. The number of assemblies maybe altered according to job requirements. 15 Figure 5 shows a. typical image of a paddock with rate defining borders to be sprayed and which constitutes image data inserted into a. computer. In a case where a cotton grower for example wishes to deliver Steward and PIX cotton growth regulant this would according to prior art VRA system methodology be 20 delivered separately in two separate spray sessions. An example of the system according to one embodiment of the invention is described below. Growers would be aware of locations is his farm where variable application of PTX regulant would have been warranted. He or his agronomist would engage a data 25 management company to acquire and interpret imagery suitable for ground truthing rhe Usual Method of doing this is that a multi spectrum image is taken of the field which reflects plant biomass. Once this has been processed the agronomist is issued with. a. preliminary copy and asked to truth the photo. Truthing is the process of tying a delivery rate to a colour in the photo which would usually take 3-5 inspections in an 30 average field, Once the photo has been truthed, the application rates are incorporated into a prescription map. The data company or the applicator usually does this. Figure 5 shows a series of rate defining borders 70 which define regions 71, 72, 73 and 74. Regions 71, 72, 73 and 74 may be colour coded according to biomass, vegetative density or like parameter. These are determined with reference to biomass of the field 1.5 and will initially be apparent from the prescription map which may be based on a NIRP ( near infra red photo) of the spray area. The variation in biomass may be represented by primary colours such as blue, green and red or shades thereof. The prescription map data is uploaded into the computer such that one colour requires a 5 particular delivery rate, another colour another delivery rate and so on with the different rates dependent upon the number of colours. The grower or the agronomist contacts the applicator to request the time of application along with instructions with regard to the primary part of the application, 10 The primary part refers to the fact that the DIVA assistance will allow a variable application to occur at the same time as the primary application. The primary application has previously taken the form of anything from water to folia, fertiliser or insecticide. Once the application has taken place, the applicator can provide a rate map showing the rates as they were actually variably applied. The grower may have 15 also engaged the data company to take an after photo which usually occurs two to three weeks after application. From. this the grower can. statistically classify the date to indicate the change in the biomass of the field. A further indication of the evening of the field can also be obtained from a yield monitor the cotton pickers use to harvest cotton in the field, 20 As the title Variable Direct Injection Rate application DIVRA suggests, the system uses direct injection technique. The site of the direct injection is in a position that is well down stream of the spray position. This is to allow the system to better cope with high ground speeds and yet maintain rapid response to rate changes. Due to the low injection rate, the DIVRA system allows the system to maintain a near 25 constant volume, which keeps the droplet sizes close to the optimum size for efficacy. The system will also allow the operator to use his current application equipment whether that is CP nozzles micronese or standard hydraulic nozzles along with some additional DIVRA equipment. The system also allows the applicator to apply a constant rate primary application along with a variable application. Growers apply 30 folia fertiliser generally at 30 litres per lectare along with a variable applicant of PIX. The DIVRA system consists of four main areas: 16 1 Currently a Satlock m3dgps system is used with a guidance variable rate application computer along with a Satlock aerial ace application flow computer. These two units have the ability to use proprietary prescription files to control the DIVRA system. The primary spray system uses a constant flow system but this can 5 be a constant rate system. The DIVRA system uses a second pump, flow meter and control valve independent of the primary spray system . The DIVRA pump is electrically driven but it will be possible to have the options of a hydraulic or wind driven pump if desired or 10 required. 2 The DIVRA system preferably has a hopper located within the primary hopper as previously described. This facilitates keeping the weight and balance of the air craft within correct limits. It has been constructed so that in an average primary 1 5 application of 30 litres per hectare and variable application of two litres per hectare, both hoppers will run out of chemical at a similar time, There is also the variable boom co located with the primary boom which delivers the DIVRA chemical to the injection point. A hopper loading system has been developed to pump ie DIVRA chemical into the DIVRA hopper. 20 3 The final component in the DIVRA system is the DIVRA nozzles. These nozzles allows injection of the DIVRA chemical into the primary spray line just before the primary chemical goes out through the primary nozzles. 25 In use, the grower, his agronomist or his data management company will supply the applicator with a VRA map in digital form. The most usual form of this is a shape file. The SatJock program mapstar is used to take the shape file with the rates attached and converts it to the proprietary PMH PMD file foimat. The PMH PMD files are then loaded into the root directory of the PC card used in. the Satlock n3 30 system of the aircraft being used in a particular application. . When the pilot first selects a prescription for the job which has to be done, a prescription map in paper form. is also given to the pilot so he can monitor the application to ensure the DIVRA satlock system is delivering the correct rates. The data provider will also provide a data sheet with the amount of DIVRA chemical 17 which will be needed to finish the application in accordwice with the prescription, Once the right job is established the prescription for that job can be entered into the computer. The pilot can then proceed with the application as he would in any normal situation. Apart from starting the DIVRA pump periodically monitoring the DIVRA 5 application, the pump would normally be started at a similar time to the normal application pump. A display in the plane shows a line diagram of the field layout and display on the screen the variable delivery rate as the plane passes over different portions of the 10 field having different predetermined delivery requirements according to the prescription for that field. The delivery rate changes as the plane flies over the field. Once the application as been completed a log file may be loaded for review and filing. Broad scale commercial use of variable rate application by air is close to 15 becoming a reality by use of the DIVRA system. Where a cotton grower elects to apply a cotton growth regulant ( PIX) to the field a photographic image 3 of the field to be treated is prepared having internal borders which signify liquid delivery rate. A grower is provided with a prescription 20 map which may be prepared from an infra red photo NIRP - Near Infra Red Photo which is typically supplied by a third party. The image is studied by an agronomist who identifies a locations on the image within the crop to be sprayed to establish a delivery rate associated with a particular colour. As indicated by figure 5 rate boundaries are imposed on the map around areas of approximately the same colours 25 so as not to over extend the prototype set up avoiding the system having to change application rate too frequently. Once a prescription is created for a particular job the map details are uploaded into the aircraft The SATLOC M3 is used to load in the prescription maps (PM) . A prescription according to this example might be for example: 30 Red requires 0.1 1/Ha. PIX Green requires 0.61/H PIX Blue requires 1.21/H PIX 18 .61/H1 is put into the main hopper so tile actual rates of PTX applied are the map rates plus a further 0.61/-J. ). 0.81/H of Steward is also applied through the main hopper. Map rate required 0.61/Ha of PIX to be applied to areas green & blue can require additional application as above. 5 The application is carried out and the result of the application is shown in a completed application map. which was obtained is shown in a recoloured Figure 5. As can be seen in figure 6 individual blocks represent approximately one second of 10 travel. From this image it is possible to determine if the actual application is as per prescription. As an example blue green may show heavier application and orange/red lighter application with white areas showing that the flow meter was getting no feedback at these points ( i.e 01/Ha). 15 A further NIRP photograph maybe taken to verify the results about 114 days or thereabouts after spraying. Again colour coding will show such parameters as continual growth, minimal growth . For instance, colour red may show minimal growth and blue continued growth. It may be seen from a comparison of the before and after photos that a highest application rate is shown mainly as red confirming that 20 the growth has been retarded as prescribed. It will be recognised by persons skilled in the art that numerous variations and modifications may be made to the invention broadly described herein, such as but not limited to fire control without departing from the overall spirit and scope of the 25 invention. 30 1i9