Move over dogs – drones are a farmer’s new best friend! In just a few years there’s been a huge rise in the use of drones in agriculture. Their popularity is set to soar globally as countries grant operators permission to also apply crop protection products.

It makes sense to use drones for spray applications – they can operate over sodden fields and tall crops where no machine could normally move, fly quickly to exact locations to treat target areas precisely, as well as be pre-programmed to navigate their own way around.

Recent equipment introductions, and regulation changes in particular, look likely to see aerial applications by UAVs to increase substantially and quickly around the globe.

Drone sales in the USA to rise by a third

In the USA sales are set to rise by a third in a year – probably thanks to new regulations that now permit drone applications. And, with John Deere showing its developments at the Agritechnica Show in 2019, it looks like drone spraying is moving into the mainstream.

John Deere revealed the giant VoloDrone at the Agritechnica Show in Hannover, last autumn. A joint development with Volocopter, it is 9.2m wide, has 18 rotors, a fully electric drive and is powered by lithium-ion batteries, which provide a flight time of about 30 minutes on one charge. Like smaller drones, it can be remotely or automatically operated and is able to follow a pre-programmed route. What sets it apart is its 200kg carrying capacity, which enables it to carry two tanks, a pump and a spray boom, offering outputs of up to 6ha per hour. It has a standardised attachment system that allows different applicators to be fitted depending on requirements. – Photo: John Deere

In countries with advanced agriculture, aerial spraying by drone completes the precision farming virtuous circle. This begins with remote crop scouting targeting treatment areas that are followed by applications on a pre-programmed route. And this, can not only be achieved remotely, but also truly autonomously.

Massive benefits for farmers in countries with developing agriculture

Drone spray applications also provide massive benefits for farmers in countries with developing agriculture. Indeed, in countries like China and India, they have essentially enabled farmers to leap from hand-held applicators, skipping vehicle-mounted boomed machines, and going straight to drones. At the same time drones improve application timeliness, reduce the need for skilled labour and cut hand-held sprayer operators’ exposure to harmful pesticides.

In November last year Chinese drone giant XAG unveiled its latest Xplanet quadrotor UAV, which has a 20kg payload. For spraying it has a 16 litre capacity tank and is equipped with rotary atomisation nozzles, fitted below the rotors, which produce 85 to 550 micron sized spray droplets. It also has variable flowrate control according to speed, as well as automatic refilling. In Rapid mode, with a 7m spray width it offers workrates up to 18ha an hour, producing a coverage of 5 droplets/m², at an application rate of 12 litres/ha and at 7m/s flying speed. The ‘Fine spray width’ mode is 4.5m wide and this produces 15 droplets/m² at the same dose and speed. – Photo: XAG

Reducing overuse

Drones are playing a major role in the Chinese government’s aims to use advanced technology to modernise its agricultural production and help combat the overuse of chemicals in the country. A report by the FAO and World Bank shows the volume of pesticides it uses is three times more than the USA per hectare of land.

Lack of regulations slowing deployment of spraying drones

Elsewhere around the world the lack of regulations is slowing the wider deployment of spraying drones on farms. This is either due to rules not keeping up with technology or simple outright bans on all aerial applications – as in the whole of the EU. While many countries are catching up by including drone use in civil aviation law, the difficulty is compliance with spraying regulations. In many places chemical applications are tightly controlled and in most circumstances this will require changes to products’ registered use.

Last November DJI, which is China’s other leading drone manufacturer, launched its latest Agras T16, six-rotor agricultural drone. This is equipped with a quick-change, 16 litre capacity tank providing workrates of up to 16ha an hour. Spray rates of up to 4.8 litres/min can be applied via four pumps supplying eight nozzles, which, depending on type and size, create droplets between 130 to 265 microns. Mounted on arms underneath the rotors, these offer working widths from 4m up to 6.5m, set between 1.5m to 3m above the crop. Flowrates are maintained by an electro-magnetic flow meter. The modular design makes it easier to swap the liquid tank and the battery, to help speed up turn-around times and boost operational efficiency. – Photo: DJI

Drone applications will also have to comply with local regulations. For example, in the Netherlands all applications can only be made with 75% drift reducing nozzles or technology. Currently, in countries with advanced agriculture, ground-based application equipment developments and product use restrictions are focused squarely on reducing drift and increasing accuracy.

Drone spraying rules vary across the globe

The restrictions on use and strictness of regulations regarding spraying from drones vary around the world, according to the type of farming and whether countries have advanced or developing agriculture.
This is perfectly illustrated by the world’s three largest economies, the USA, EU and China. First the EU. In all member states aerial spray applications, including drones, are completely banned. There are discussions between farming and industry associations and governments, but most experts predict it’s unlikely the ban will be lifted in the near future.
In the USA drone spraying is now permitted in many states, provided pilots comply with strict Federal Aviation Administration operational rules as well as separate requirements for aerial applications.
In 2018, China introduced new regulations for commercial operations with drones weighing more than 25kg. Under the same regulations, for agricultural spray applications pilots will also require Class V – Crop Protection training.
A survey across Africa in 2016 found 73% of the 79 countries did not have any rules or regulations in place, 19% have some regulations, while the remaining 8% were formulating the rules.

Concerns about drift

There are questions about the quality, efficacy and safety of applications from drones and rising unease among researchers and experts in the more ‘traditional’ spraying community. It’s a concern shared by Tom Wolf, an independent spray expert from Canada, where pesticide applications from drones remains illegal. “My primary concern is around spray drift,” he explains. “Low drone payloads mean they are unable to carry much liquid, so by necessity they must use low application volumes to provide any sort of productivity.”

Drones4Agro, which is supported by the EU in an EFRO project, aims to produce a fully certified, 150kg drone – a ‘flying tractor’. It offers custom designs on a novel platform that, unlike other proprietary designs, comes in widths from 3m to 9m, equipped with eight to 24 rotors, distributed across the width. These various sizes can support payloads from 15kg right up to 80kg. This, it says, allows users to tailor the drone to suit their operations – from vineyards to open field applications. At the same time it offers different spray application techniques creating very fine, mist droplets from rotary atomisers up to standard, regular pressure nozzles. – Photo: Drones4Agro

Drones expand to increase productivity

Size and carrying capacity of popular agricultural drones is definitely a limitation on output. But their dimensions are often determined by local regulations, with many countries granting varying degrees of ‘permission of operation’ depending on weight, often up to just 25kg.
For operators willing to invest in the necessary training and certification required for larger capacity UAVs, there is now a growing choice of heavy haulers. One recent example is from Tactical Robotics, an Israeli aerospace company partnering with crop protection company Adama to develop an agricultural version of its Cormorant. This drone has two internal rotors that enable vertical take-off and land and is powered by a 977hp engine. It has 500kg payload capacity (764kg including fuel) and can fly for 2.6 hours with a 300kg payload.

The only way to provide sufficient coverage with very low volumes is to use nozzles that produce finer droplets. “ASABE fine to very fine droplets will have problematic effects on off-target movement and evaporation. These fine droplets are also more prone to the aerodynamic eccentricities of aircraft,” he adds.

Failure to control movement of a spray is, and should be, a problem

Entering these finer sprays into the models to assess drift from applications from conventional, manned aircraft results in buffer zones that are hundreds of times wider. “Failure to control movement of a spray is, and should be, a problem,” he adds.

Cormorant spraying drone from Tactical Robotics. Drones can’t carry large volumes of spraying fluids, so they use smaller droplets for good coverage. This creates drift risks. – Photo: Tactical Robotics

Research ongoing

While research into drone spraying is progressing, most of this relates to coverage and deposition as well as spraying speeds and heights. The USDA is, however, currently conducting trials looking at drift. Wolf is part of a working group in Canada researching drone applications, including drift analysis. While drones employ the latest, highest technology for flying, control and autonomous operation, some of the application technology is quite basic, particularly compared with modern vehicle-based boom sprayers. Drone manufacturers are addressing these issues with more sophisticated technology, such as rotary atomising nozzles, electro-static systems and other developments.

Still a lot to learn about aerial applications by drones

Drone spraying has taken off quickly across the globe, and independent research is struggling to catch up with what’s happening in terms of the application efficacy, coverage, deposition and, particularly, drift. Current drift modelling (for other aerial applications) doesn’t take account of the fact drones are commonly equipped with four to eight rotors. This introduces huge complexities into the airflow around drones, because the rotors turn in opposing directions and at different speeds and angles. At the same time drift will be exacerbated by the drone’s movement through the air, its speed and any cross winds.
Spray application expert Tom Wolf explains current regulatory models used for aerial drift assessment in North America – AgDISP and AgDRIFT – are not yet able to simulate drone applications. “But, by entering finer sprays into these models for their conventional manned rotary wing aircraft, we can see that buffer zones will be higher, much higher if finer sprays are used with drones,” he says. “I’m encouraged by experts’ comments that drone applications should only be conducted with spray qualities and under conditions where spray drift risk is acceptable,” he adds.
In the USA researchers have recently looked at the ability of existing spray drift modelling algorithms to predict the drift and deposition of sprays released by rotary wing UAV. To do this they combined two spray models currently used by regulators – CHARM, a proven airflow model for helicopters and AgDISP, a proven spray deposition model. “It’s important to note that this study does not aim to pass judgement on drift from drones, but to assess the capabilities of the model,” explains Wolf. “It does, however, include some important observations.”
The first: ‘It appears the proximity to the ground and/or flight speed and/or occasional crosswind can cause the released spray to be lofted above the UAV, producing significant airborne drift.’ Elsewhere the report states: ‘The potential complexity of the UAV wake, i.e. the impact of multiple rotor blades, is the randomiser in this behaviour. What is especially critical is to understand the pattern and behaviour of the multiple rotor wake and its possible ability to loft released spray droplets, an effect not present with full-sized helicopters because of their higher altitudes, flight speeds, and spray boom positions.’
“It seems a lot of work may be needed to fully understand the conditions during which drones will cause more, or less, drift potential. Although we don’t know the droplet size being modelled, some of the ‘airborne drift’ and ‘downwind deposition’ values (in the CHARM – AgDISP models) are very high, indeed,” comments Wolf.