Andrew Landers

Royal Agricultural College, Cirencester, Glos., U.K.

Increased pesticide legislation and falling margins have resulted in farmers looking for ways to reduce pesticide use on farms. The advent of direct injection crop sprayers, combined with information technology, offers a solution to the problem. Crop walkers using hand-held data loggers and satellite positioning can provide field information for comparing with computer-based crop models. A smart-card can be used to provide information to the electronic controller of the injection sprayer resulting in less pesticide being used and lowering production costs.

Farmers are under great pressure when applying pesticides. The increasing awareness of environmental pollution, along with worries about pesticide residues on food has resulted in increased legislation concerning pesticide use. The decrease in profit margins requires closer attention to the production costs.

Traditionally, farmers have used pesticides to 'blanket' spray the whole field. The advent of direct injection sprayers and computer based information systems will allow them to spot treat patches of weeds or disease. Cussans et al (1987) suggests that many fields are treated at weed levels far lower than the economic threshold due to poor herbicide performance and differing infestation levels. The quantification of these risk elements would be a vital practical step in rationalising pesticide use.

A conventional crop sprayer is fitted with an injection system comprising 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 the 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. Figure 1 shows the basic concept of a direct injection system. There are four systems commercially available in Europe and six systems under development. Landers (1988 and 1989) states the major advantages of injection sprayers are:-

i) the reduction in environmental pollution due to the elimination of tank and pipeline washing.

ii) a reduction in the operator contamination which occurs with conventional sprayers. Ideally the pesticide would arrive on the farm in large 35 litre containers and be connected directly to the pesticide injection pump, resulting in a closed system.

iii) an electronic controller which allows each pesticide pump to deliver each product. The injection pumps can be switched on / off as and when required to spray a patch of weeds.

iv) the amount of pesticide applied (dose rate) can be adjusted on the move, allowing a higher dose rate to be applied to a high infestation of weeds or disease and vice-versa.

Figure 2 shows the role of information technology for a computer aided application system.

Information technology can be used to help the farmer gather information about the health status of his crop and compare field conditions with a computer model. The resulting farm management information can be used to develop a crop spraying programme. CAPA comprises the following:

i) computer based information systems

There are several new information based programmes available to the farmer using human logic to help solve problems such as planning strategy, pesticide application and machine selection. Information technology can be used to record data from field observations on soil type, crop response to pesticides and crop yield.

Computer models can be used to simulate crop production, allowing the farmer to compare the model with the field information, (Baandrup and Ballegaard, 1989). Smith and Webster (1986) concluded that simulation models should display more than just 'spray' or 'dont spray', they should include monetary values of alternate strategies e.g. the opportunity cost of labour. Farmers are more interested in the expected loss rather than the variability of loss. Machinery selection models are available for comparing spraying systems. Landers (1992) devised a model to examine the effect on sprayer output of a changes in the operating parameters of a spraying system e.g. increasing tank or boom size and filling time.

ii) Data acquisition in the field.

There are a number of systems available for data capture and retrieval.

a) Soil mapping.

Detailed soil maps can be constructed for the farms. A soil survey will result in a detailed plan of the various soil types so that the farmer can appraise the land, cropping and fertilizer policy. Pesticide requirement varies from one soil type to another, certain pesticides are used at different rates on organic soils compared to sand soils, and weed growth is often more vigorous on organic soils compared with other soil types.

b) Crop reporting.

Hand held data capture systems are being developed by a number of manufacturers. The introduction of a data logger will eliminate transcription errors, provide the opportunity to review assessments immediately and cut down time delays between information collection and the final report, greatly reducing costs. An integrated approach to information technology was reported by Dickson and Talbot (1985). The hand held data logger can be used with a position indicator, Figure 3, so that weed or diseased patches can be identified and located for spot treatment. 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 then carry out the instructions when it passes over the positions. The data can also be downloaded into an office computer.

c) Down the row identification of soil organic matter

Gaultney et al (1989) developed a real-time soil organic matter sensor which used a narrow band light source and measured reflectance from the soil with a photodiode. Sudduth et al (1990) developed a prototype sensor using near infrared reflectance techniques to determine the organic matter content of the soil surface. The application rates of soil acting herbicides must often be increased on high organic matter soils because the cation exchange capacity of the organic matter increases the adsorption of a herbicide and decreases its effectiveness. A microprocessor can be developed to interface with the controller of an injection crop sprayer.

d) Down the row identification of weeds.

Petry and Kuhnbauch (1988) developed a technique for the discrimination and quantative registration of a weed population. Different spectral information of the plant and soil was used. A video camera ra was used to deliver separate image signals for the red, green and blue parts of the spectrum which then became digitised in a video card and a weed cover gradient was devised. Thompson et al (1990) concluded that a weed detection system based on finding plant material between rows of cereal crops was very sensitive to crop canopy cover; detection was only possible when crop density was low.

e) Crop yield meters.

A number of combine harvesters have been fitted with grain yield meters. The operator is able to monitor crop yield and obtain a print out of the results. Selected areas of the field can be monitored and farm trials carried out. The farmer is able to use this information in developing a cereal model on his office computer and thus the effect of pesticides applied to any particular part of the field can be closely monitored.

f) Satellite positioning.

The position of a crop walker when recording data on the health status of a crop is very important for the spot treatment of weed patches. Similarly the position of the combine harvester is also important when measuring grain yield from trial plots. As the injection sprayer drives towards the patch of weeds or disease a vehicle position indicator can inform the sprayer controller and switch on a particular injection pump and spray pesticide as and when required.

Shmulevich et al (1987) and Gorham and MacLeod (1991) developed a field machinery guidance system using a scanning laser based upon triangulation geometrical positioning. Choi et al (1990) described an automatic guidance system based upon two position sensors designed to follow a predetermined path. The use of satellites for marine use has enabled sailors to find their exact position anywhere in the world. Satellites are used extensively for military purposes and systems exist which give pinpoint accuracy. As more systems are made available by the military and as other systems are developed, so satellite positioning will become affordable.

The farmer is able to use the data acquisition systems information to help in the decision making process. The farmer can compare the ground data with the computer simulation and decide on a pesticide strategy.

A 'smart card' system could be developed which allows information to be downloaded from the office computer. The card would contain 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, but the development of of a control board to allow automation is quite feasible. A printer could be installed to allow the farmer to know the exact quantities of pesticide applied and the area sprayed which would enable precise financial control to be retained.

i) Direct injection sprayers enable the farmer to rationalize his pesticide use, reduce environmental pollution and reduce operator contamination.

ii) Computer aided pesticide application (CAPA) will result in more appropriate use of pesticides and rates being used, with an overalll reduction in application rates, thereby satisfying environmentalists, legislators and farmers. CAPA will enable the farmer to be better informed regarding his pesticide application strategy and enable him to improve his decision making skills.

iii) Information technology systems already exist to allow computer aided pesticide application technology to be developed.

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