The increasing public awareness of environmental pollution has resulted in legislation concerning pesticide application. The development of direct injection sprayers throughout Europe and how they can be used to reduce environmental pollution from pesticides is reviewed. Direct injection sprayers allow the operator to select specific pesticides for specific areas patches of different weed species or disease. The concurrent development of Geographical Positioning Systems (GPS) will aid the reduction in pesticide use. It is concluded that, as public awareness of pesticide application increases, along with more legislation, there is a considerable benefit to farmers and growers in the use of direct injection sprayers.

Keywords: Pesticide, direct injection, crop spraying, environmental pollution

DES PULVERISATEURS A INJECTION DIRECTE - UNE METHODE

POUR REDUIRE LA CONTAMINATION DE L'ENVIRONNEMENT.

L'attention grandiasante du public face a la contamination de l'environnement a abouti a des legislations concernant l'application des produits. Le developpement en Europe de pulverisateurs a injection directe et la facon dont ils pouvent reduire la contamination sont examinees. Les pulverisateurs a injection directe permettent a l'operateur de choisir le produit specifique correspondant au parasite sur une zone precise. Le developpement du systeme de positionnement geographique (G.P.S) contribuers a reduire l'usage des produits. Au moment ou le public est plus sensible a l'application des pesticides, ou la legislation se durcit, il y a un avantage confirme pour l'agriculteur a utiliser l'injection directe.

Mots-cles: produit de protection des plantes, injection directe, traitement des cultures, contamination de l'environnement.

Introduction

Pesticides may enter water supplies from several sources. Whenever pesticides are applied to field crops, a proportion of the applied dose reaches the soil. Careless overspraying of ditches, run-off from washing down areas and spillage are amongst the many sources of pollution. According to OTTER (1988) and the WATER AUTHORITIES ASSOCIATION (1988), a number of agricultural pesticides have been detected in water supplies. The EC Directive (1980) sets Maximum Admissible Concentrations (MACs) of 0.1 microgram per litre (ug/l) for any individual pesticide and 0.5 ug/l for the total of all pesticides in water intended for human consumption.

FAWELL (1991) suggested that if pesticide residues increase action should be taken to prevent contamination at source. This will only work if the manufacturers and users are prepared to play their role in seeking ways to reduce contamination. The injection sprayer is a way of reducing water pollution at source.

A survey of conventional crop sprayers was carried out to determine the amount of liquid remaining in the sprayer. The sprayers were operated using water at 2.5 bar pressure. The sprayer began to run dry, the pressure dropped to 1 bar, and the spray pattern became erratic as air became entrained in the water from the tank. Table 1 shows the quantities remaining in three sprayers. The Chafer sprayer has large bore pipes for liquid fertilizer application, but is also used for applying pesticides.

MANUFACTURER MODEL TANK BOOM QUANTITY

CAPACITY WIDTH REMAINING

(l) (m) (l)

CHAFER T2000 trailed 2000 24 83.3

HARDI TZ1500 " 1500 18 40.5

ALLMAN 625 mounted 625 12 13.5

Thus with a Chafer sprayer a farmer applying pesticides at 100 l/ha would lose an accurate spray pattern with 83 litres remaining in the 'system'. Depending on the cost of the pesticides being applied the loss of 0.83 ha worth of pesticide could be relatively expensive and this problem could occur often during the spraying season. The mounted Allman sprayer has considerably less pipework resulting in a very small amount of pesticide remaining. Besides the monetary value of the pesticide remaining in the system, there is the problem of thorough rinsing out, the correct disposal of the rinsate and the time involved.

TAYLOR et al (1988) considered the problem of decontaminating a small 600 litre sprayer. The degree of cleaning depended on the product being used. Thorough cleaning using the method outlined in the then proposed United Kingdom Ministry of Agriculture Code of Practice, MAFF(1988) took in excess of one hour, used 1500 litres of water, resulting in 5.2 ml of pesticide remaining.

The UK Code of Practice, MAFF/HSC (1990), suggests that the volume of washings produced when cleaning out equipment can be reduced significantly by using an efficient flushing system. Researchers at the Scottish Centre of Agricultural Engineering developed the Rotaflush, a spinning disc for inserting into the sprayer tank to enable cascading water to flush the tank. The Code of Practice, MAFF/HSC (1990), suggests that, within the terms of the product approval, contaminated water may be applied to the treated crop, recognising that the efficacy of the previous application of pesticide may be impaired. The time taken to rinse out the sprayer and return to the headland of the field sprayed could take a long time and therefore be expensive in labour costs and missed spraying time. The operation of rinsing out a sprayer tank with a water hose also puts the operator at risk from splashes of pesticide.

Conventional tank rinsing, unless performed thoroughly can also result in carry-over of pesticide to the next crop. BCPC (1986) noted in its 1985 Annual Review of Herbicide Usage that a minute amount of a herbicide as a contaminant in a subsequent spray could damage a susceptible crop resulting in leaf yellowing or scorch through to complete plant death. Thorough decontamination is vital, particular care is needed when washing out residues of hormones, glyphosate or the sulphonyl-ureas.

Direct injection crop sprayers

A conventional crop sprayer, fitted with an injection system, usually comprises of one to four pumps which will dispense pesticide at a known rate into the water stream in the sprayer pipeline. The main tank of the sprayer holds clean water only. The pesticide is mixed with the water, either in a manifold or at the main water pump and the resultant mix flows to the booms and nozzles. An electronic controller adjusts the pesticide injection pump according to changes in operating requirements, e.g. changes in application rate and pesticide required.

Direct injection sprayers have been designed and developed in many countries. The majority of these use some form of mechanical pump to inject pesticide into the pressure line after the main water pump. The alternative low pressure pumps, e.g. peristaltic pumps, meter pesticide into the suction side of the water pump to overcome the pressure problems and to obtain good mixing of pesticide and water in the main pump.

The materials from which injection sprayers are made are subject to attack from the pesticide formulations being used, and for example, organic solvents attack plastics and rubber. AMSDEN and SOUTHCOMBE (1977) discussed the problems associated with chemical and physico-chemical attack and noted that the severity of attack falls as the pesticide is diluted but over a period of time the cumulative effect can still be devastating.

One way of reducing some of the problems associated with pumping pesticides, such as high viscosity and chemical attack, is to use a pressure source to inject the pesticide. The use of pneumatic pressure for an injection sprayer was developed by IMAG in Holland, (HOENDERKEN, 1976), originally using propane gas which was potentially dangerous and could contaminate the pesticide, IMAG subsequently developed the use of compressed air to apply phenmedipham to sugar beet. The use of compressed air to inject pesticides into a field sprayer was developed by SCHMIDT (1982). Pesticide was contained in a replaceable pesticide tank and flow was adjusted according to the pressure difference between the water line and the pesticide tank. A German farmer, Herr Schonlebers, developed a device which uses the compressor on the tractor to pressurise a stainless steel pesticide container, (PREUSSE, 1991). The farm-built system can inject one to three products.

LANDERS(1992a) described the recent development of injection sprayers in Europe and noted 5 systems which are commercially available:

Other systems are under development including one by the Dutch sprayer manufacturer, Vicon, whose injection sprayer uses a novel peristaltic pump, (BEIJAARD, 1988). In this system the dual pipe peristaltic pump allows a wide variation in application rates due to the use of a combination of small and large bore pipes. The French sprayer manufacturer, Tecnoma, is investigating the use of the Dosatron injector/dilutor, (DOSER, 1989). A similar dilutor is being developed at the University of Firenza, Italy (VIERI and SPUGNOLI, 1992).

The use of electronic controllers

A number of direct injection sprayers use in-cab electronic controller which may operate one to four injection pumps. Each pump is connected to a pesticide container or tank. Any combination of pumps may be used, resulting in an on-the-move alteration of the products being applied.

The electronic controller, allows the operator to adjust the quantity of pesticide being injected whilst on the move to accommodate different levels of infestation, soil types and headlands. This advantage results in less pesticide being applied. An example of a farmer applying chloridizan to sugar beet can be used. As the operator moves from medium or heavy soil to light soil the application rate can be reduced from 5kg to 1.7 kg/ha. Besides the environmental advantage in reducing pesticide use there is a financial benefit to the farmer.

The use of an accurate injection pump and controller allows the operator to select the exact dose rate of pesticide required per hectare, thus avoiding the environmental and operational problems, associated with tank, pump and pipe residues, The ability to select the dose rate overcomes the problems of calculating the quantity of pesticide required for an unknown field size and minimises the dangers associated with spillage and contamination.

In their final form injection sprayers will be used in conjunction with large, returnable, pesticide containers. This will reduce the risks associated with spillage of pesticides whilst filling sprayers. Spillage of pesticide can kill the crop and cause environmental problems.

The operator will set the application rate on the cab-controller. Any pesticide remaining in the container at the end of spraying will be returned to the store. In an ideal world the containers would be returned to the manufacturer/filler, thus eliminating the need to rinse out and bury containers. The time taken to measure and decant pesticides can be longer than the time to fill the water tank.

On some injection sprayers the operator refers to the distance remaining on the electronic controller and switches over from pesticide to rinse water, thus rinsing out the sprayer pipes before leaving the field. Washing out is expensive in terms of labour and the time available for spraying.

CAPA- Computer Aided Pesticide Application.

Blanket or overall spraying of fields wastes pesticide and time, the use of spot treatment leads to a reduction in pesticide use which can only benefit the environment. The use of direct injection sprayers in conjunction with satellite positioning will allow the operator to spot treat patches of weeds (LANDERS 1992c). The use of satellites for marine use has enabled many sailors to find their exact position anywhere on the globe and as military and as other systems are developed, so satellite positioning will become affordable.

A hand held data logger can be used with a position indicator, resulting in weed identification and location for spot treatment of weeds and disease patches in fields. For example, the crop walker logs in the beginning of a patch of wild oats (Avena fatua) and presses the location switch on; when the patch finishes the walker presses the location switch off (the spot treatment injection sprayer will carry out the instructions when it passes over the positions).

A 'smart card' system could be developed which allows information about the weeds and disease status and its position in the field. A patch of weeds or disease could be spot treated with pesticide as the sprayer passes. As the weed infestation is passed the sprayer could be switched off. Satellite positioning would indicate the grid reference. The 'smart card' could contain information on the level of infestation, allowing the pesticide to be applied at varying levels according to the degree of infestation.

The controller of the injection sprayer enables the farmer to carry out these functions manually at present, the development of a control board to allow automation is quite feasible.

Computer aided pesticide application (CAPA) will result in better use of pesticides and less pesticide being used, thereby satisfying environmentalists, legislators and farmers. CAPA will enable the farmer to be better informed regarding his pesticide application strategy and enable him to sharpen his decision making skills.

Legislation

Current UK and EC legislation has prompted significant moves towards safer practices for the storage, handling, application and disposal of pesticides. The development of the 'single market and common laws' within the Community, in January 1993, will result in further legislation.

The UK Code of Practice, MAFF/HSC (1990) gives farmers and growers guidance on meeting their responsibilities under Part III of the Food and Environment Protection Act, 1985 (FEPA) and in particular the Control of Pesticides Regulations 1986 (COPR) and the Control of Substances Hazardous to Health Act (COSHH).

The parallel development of injection sprayers and closed transfer systems meets with the approval of legislators as engineering controls. The use of returnable containers will further protect the operator. The elimination of tank washing and subsequent rinsate disposal with direct injection sprayers overcomes the operator and environmental problems at source.

The Governments of Sweden and Norway aim to reduce pesticides by 50% states NORDBY (1989). In Denmark the Government aimed at a reduction of 25% of active ingredients in pesticides by 1990 and a further 25% cut before 1997, THONKE (1988). In Holland there is a similar move to reduce pesticide use by 50%. The Swedish Government levies a tax on each pesticide treatment.

Conclusions

Injection sprayers will reduce environmental pollution due to the elimination of tank and pipeline washing.

There will be a reduction in the operator contamination which occurs with conventional sprayers. Ideally the pesticide would arrive on the farm in large 25-35 litre containers and be

connected directly to the pesticide injection pump, resulting in a closed system.

The use of the injection sprayer with a controller to adjust dose rate on the move and to switch on /off pesticides whenever a patch of weeds or disease appears, will help the farmer reduce his pesticide requirement and reduce thee pesticide load on the environment.

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