Crop protection products can amount to as much as half the overall cost of production. With growing concerns about their potential environmental impact, using these products efficiently and effectively has never been more important. A new study, “Spray technologies in precision agriculture,”* from award-winning crop spraying expert, Dr. Paul Miller, examines the findings of recent research and looks to future trends that could offer farmers more options in the use of these products.
The Precision Agriculture Approach
While Dr. Miller’s review focuses on field crops, the principles of precision agriculture can also apply to other tree, glasshouse, and specialist crops. Precision agriculture depends on controlled product applications to maximize effectiveness and minimize losses in non-target areas; effectively applying different treatments only where they are needed and successfully targeting single plants or small groups of plants. The application equipment and its speed, product application pressure, droplet size, and weather conditions can all affect results.
Controlling the Delivered Dose
In most conventional crop spraying systems nozzle size and flow rate are used to control the dose volume and concentration. Changes in speed are usually managed by adjustments to the pressure at the nozzle, but only limited adjustment options are available.
To improve accuracy at a wider range of speeds a number of approaches have been tested. These include on/off valves with rapid response times that allow more precise targeting. To give a wider range of outputs, multiple nozzles in a single holder can allow single or multiple switching. More sophisticated arrangements can be used to support a wider range of adjustment to both nozzle output and droplet size at lower flow rates. This can help to reduce the risk of products drifting into neighboring areas. Another approach to varying dose concentrations is to store water and protection products separately until the point of application.
MORE BY PRECISIONAG
When specific areas of weeds, diseases, or pests need to be treated in a wider crop, spatial targeting is needed. For stable patches of grass in arable crops, straightforward mapping can allow accurate use of herbicides. However, for more varied problems, investment in accurate mapping and complex equipment can outweigh the benefits, with a minimum resolution of at least 4m. With spraying boom lengths increasing, the need for sophisticated solutions that allow variable pressure control or dose concentrations for different boom sections are likely to be needed in the future.
Minimizing Drift in the Wider Environment
Various nozzle types will change spray quality and droplet size. This can affect the amount of product retained on different crop and weed types. For example, trials have shown more effective control of grass weeds in cereal crops when treated with finer sprays. However, the increased risk of drift could restrict this approach to patches of grass weeds only.
Buffer zones at the edges of cropped areas are now a well-established control measure for unwanted exposure to pesticides. One way to reduce the width of buffer zones is to use nozzles and spraying arrangements that have been shown to reduce drift. Implementing treatment zones across a field or plot will allow drift-reduction approaches to be focused in the margins to meet environmental protection requirements without compromising wider crop treatment.
Case Study: Spot Treatment to Control Volunteers
Volunteer potatoes remaining from the previous year’s planting in crops such as onions, leeks, and carrots can seriously affect yield, quality, and harvesting. European regulations now mean that the herbicides traditionally used for repeated overall spraying to control this problem are no longer available. Spot treatment is a possible alternative. A project to develop an effective spot spraying approach used a camera system to identify the outline of weeds. This information allowed spray nozzle schedules to be defined. The nozzles in the prototype system were able to apply existing herbicide formulations to spots less than 100mm square. Overall results from field trials in a range of crop, weed, and weather conditions showed that the prototype results were comparable with alternative approaches.
Dr. Miller concludes that the costs and complexity of equipment and mapping have delayed the uptake of precision agriculture systems. However, in the last decade, technical advances have reduced the costs and improved performance and reliability. Options for the future include the use of autonomous robots to apply chemical and non-chemical treatments to individual plants. This could be suitable for high-value crops grown in small areas. Real-time detection of weeds using ultrasonic detectors to identify height differences could also allow more effective spot spraying.
Use of computer-based control systems is likely to increase, managing a wide range of parameters to produce treatment maps for individual fields and control algorithms for delivery systems. Drift risk could be managed automatically, taking account of both crop and weather conditions. As an additional benefit, compliance requirements could all be met automatically.
*The paper “Spray technologies in precision agriculture” by Paul Miller, Silsoe Spray Applications Unit Ltd, UK, appears in the new book Precision Agriculture for Sustainability, Stafford, J. (ed.), published by Burleigh Dodds Science Publishing Limited, 2019.