Precision application onto the target area

Few areas of agricultural machinery are being confronted with such high pressure to innovate as crop protection technology. There are multiple reasons for this. Firstly, social and political objectives, for which 'minimisation' is the order of the day. Mention is being made of 'just' 50% less in the EU's 'Farm to Fork' strategy, but also in the arable farming and bee protection strategies of individual Federal States. Although the baseline quantity or the baseline period to which this figure refers and whether the active substance or frequency of treatment is meant are unclear, the message being sent is that less spraying is on the cards. For farmers, this means more prevention by means of crop rotation and the choice of variety, but also increased precision. Firstly, crops have to be kept healthy if need be, and secondly, adjacent watercourses and biotopes have to be protected by means of low-drift technology.

If you attempt to obtain an overview of this broad field, technical solutions can be classically placed into three categories. Categories 2 and 3 are to be focussed on here and explained on the basis of a few examples.

• Solutions with which virtually every new field sprayer is equipped as standard. These include automatic boom guidance and partial width systems up to and including individual nozzle control as well as highly developed flushing and cleaning systems.
• Solutions that are already technically possible with a certain degree of effort but are not (yet?) standard. These include e.g. pulse width modulation (PWM), but also the entire range of combinations of hoeing and band spraying or closed-loop filling systems.
• Solutions in connection with consistent partial area-specific application. These are usually based on the first two categories, but differ from them particularly due to the fact that emphasis is placed on the overall context of crop protection. This may mean incorporating the necessity of control directly in the treatment process but also orientation towards the individual plant rather than the crop as a whole or a 'population' of weeds, for instance. A separate category is additionally formed by automatic hoeing robots, which are not to be discussed here.

Pulse width modulation. Not only the shape of the field (e.g. cornering), but also the vehicle speed, sometimes make it difficult to always apply the same volume of water and therefore consistently dose the active substance. This is important, because constant under-dosing can easily lead to signs of resistance, at least on a part of the field. Whoever is underway at high driving speeds needs space to pick up speed or brake at the beginning and end of a tramline. Even in other cases, very different driving speeds cannot be achieved with just one nozzle calibre. Within limits, the output quantity can be kept constant by adjusting the pressure, but this then leads to changes in droplet size and drift. PWM offers a way out. In this process, the nozzle is switched on and off 10 to more than 20 times per second by means of solenoid valves (frequency). The second parameter of PWM is the pulse width. It adapts the volumetric flow. At a pulse width of 100%, the nozzle is open; at 50%, half of the application quantity is output (theoretically). PWM requires large nozzle calibres; small injector nozzles become clogged too easily. PWM initially means just one nozzle and therefore convenience; thanks to individual nozzle control, it also means precision and therefore the option of linking the sprayer with treatment maps.

Hoe plus band spraying. This is the big hope of everyone who wants to achieve less chemical crop protection without endangering the yield level. One application area of great topical relevance at present is the combination of a (possibly camera-controlled) hoe with band spraying. This system is 'ancient', but there is no comparison between the modern solutions and those of 50 years ago. Today, the operations are separated, because hoeing is best carried out in the morning when it is sunny and windy. Spraying in the morning or evening when there is no wind and not too much heat is sensible. The 'trick' is that the existing field sprayer only has to be adapted, with the result that the entire area can also be treated if required. Multiple nozzle holders or a separate band spraying line are required for this. A band spraying nozzle operates with a considerably smaller angle of 30 to 40°. Drift is a particular challenge for boom guidance. A nozzle spacing of 25 cm can be used to comfortably cover row spacings of 50 and 75 cm. The usual 45 cm beet rows make things a little trickier. Ultimate precision is achieved with RTK or camera control in combination with a moving frame on the boom or correction via the sprayer's steering.

Selective treatment. Farmers have been attempting for decades to register weeds 'in advance' and then control them 'subsequently' as required. However, this idea has only come to practical fruition in recent years. Firstly (and particularly over large areas in Eastern Europe or Australia) for controlling the use of glyphosate prior to sowing. A sensor directly detects the weed plants and actuates the nozzles. A further evolutionary stage (albeit still some way away from the state of the art) is to distinguish between weeds and crops using cameras. This is possible offline using drones, promises active substance savings of up to 50%, and additionally offers the advantage that the required quantity can be planned in advance. Online, the aim is to use self-learning systems to also determine the relationship between crop, weed type and weather and to output even less active substance – either as a tank mix or from several containers. This requires a lot of sensors on the sprayer, but may possibly lead to more precise results compared to drones and satellites.

Spot farming. These technical solutions, which will be possible in the foreseeable future, are leading to the concept of using the demands of the individual plant as a reference unit rather than the field itself. The high-performance cultivation of the largest possible areas would then no longer be the measure of all things; instead, the areas would be examined, mapped and not only treated differently, but also structured in terms of crops and biodiversity. This would result in a diverse mosaic of different crops (at least wherever the soils are not widely homogeneous). These would have to be cultivated with small, automatic robots.

Conclusion: Lots of things are technically possible, and even more are conceivable. Foreseeably, it is entirely possible to reduce the use of crop protection agents by 50% and more. However, this necessitates significantly more investment. Particularly in crop protection, farmers will have to distribute these expensive machines very 'sparingly' over the largest area possible. There is a real risk of a 'two-class society'. Numerous farms will no longer be able to keep up with the level required in the future and will leave crop protection to the professionals. While technical progress and digitalisation may solve many environmental problems, it will unfortunately come at a price. 

Thomas Preuße, DLG-Mitteilungen