More than a hundred years ago, in the summer of 1922, an aircraft with equipment for carrying out aerial chemical works by spraying against pests and diseases took off from the Khodynsky metropolitan airfield. Successful test flights marked the beginning of the development of agricultural aviation.
Today, the use of various aviation means for plant protection is of great economic importance, as it provides the possibility of:
— large-scale remote monitoring of agricultural crops;
- protective measures in short agro-terms and in hard-to-reach places against especially dangerous pests (locust, meadow moth, mouse-like rodents, Colorado potato beetle, harmful turtle) and diseases (brown rust, late blight, alternariosis);
- tillage with strong soil moisture, when ground equipment cannot enter the field, especially in the fight against weeds;
– processing of tall crops (corn, sunflower) and sowing of seed crops;
— processing of rice fields;
- processing of crops on slopes with a slope of more than 7 degrees, where ground spraying equipment cannot work.
In the Soviet Union, the basis of the agricultural aviation fleet was the AN-2. At present, the development of agricultural aviation is moving towards a significant expansion of the use of ultralight aircraft (ALVs) and unmanned aerial vehicles (UAVs), which are much cheaper than heavy aircraft. In accordance with the Federal Aviation Rules and the Air Code of the Russian Federation, an apparatus (aircraft) is called ultralight if it has:
- maximum takeoff weight not more than 495 kg (excluding aviation rescue equipment);
- maximum calibration stall speed (minimum flight speed) not more than 65 km/h.
Unmanned aerial vehicles (UAVs) include vehicles whose flights are controlled by pilots who are outside the board (external pilots).
Features of the right mode of use of the UAV are determined by its maximum takeoff weight:
- up to 250 g - are not subject to state registration or accounting;
- from 250 g to 30 kg - are subject to mandatory state accounting;
- from 30 kg and more - are subject to state registration.
Important advantages of using UAV and ALS are:
— no losses from damage to crops by wheels or the need to use tramlines (in comparison with ground equipment);
- high efficiency while reducing operating costs (compared to heavy aircraft, since these aircraft do not need to have equipped airfields).
The use of unmanned aerial vehicles helps in solving the following tasks:
- obtaining detailed information on the creation of a cartographic basis of agricultural land and the placement of agricultural objects with their exact coordinates for planning and controlling the technological processes of agricultural production;
– carrying out remote monitoring based on multispectral imaging of the underlying surface of agricultural land to determine the condition and development of crops, predict yields based on the calculation of the vegetation index based on the results of spectral imaging, etc.;
– real-time operational control over the operation of ground equipment and the quality of agrotechnical work;
– geocoded phytosanitary monitoring of agricultural lands to determine the level of weediness of crops, the presence of pests and manifestations of diseases at an early stage of development, including in a latent form;
The use of UAV for aerial photography of agricultural land provides, in comparison with satellite images, obtaining images with a higher resolution (up to one centimeter per point) and, most importantly, makes it possible to carry out these works in the presence of dense clouds (shooting using spacecraft during such periods is impossible ).
Let us dwell in more detail on the phytosanitary monitoring of crops. Recently, the volume of use of plant protection products in Russia has been steadily growing: according to statistics, every five years, starting from 2010, they have doubled and in 2020 reached 221 thousand tons. With the growth in the use of plant protection products, farms need to ensure the prompt collection and processing of information on the phytosanitary condition of agricultural fields. Without this information, it is impossible to solve the problems of technological support for the rational and safe use of plant protection products in a short agricultural time frame. Existing methods of ground route inspection of fields do not allow obtaining the necessary information quickly and in the proper volume. In this regard, work is being actively carried out abroad and in our country to develop high-performance remote methods for retrieving information for planning and carrying out plant protection measures. For operational remote phytosanitary monitoring, unmanned aerial vehicles are most widely used, providing geocoded video, multispectral and hyperspectral images of the underlying surface of the Earth.
It should be noted that the issues of using remote methods of information retrieval in the field of weed control (determining the location of weeds in the field, assessing crop losses, mapping zones of damage) have already been partially resolved. In this area, within the framework of an agreement on scientific and technical cooperation, research was carried out with the participation of specialists from VIZR, the University of Aerospace Instrumentation (St. Petersburg), the Samara Agrarian Academy and Ptero LLC (Moscow). Positive results have been obtained from the use of BVS for remote methods of information retrieval based on spectrometry to assess the infestation of grain crops and potato plantings for more than 20 types of weeds, including such a harmful one as Sosnowsky's hogweed. The data were obtained based on the determination and analysis of the spectral characteristics of reflection from cultivated plants and weeds in the wavelength range of 300-1100 nm.
Thus, in the course of the studies conducted to identify defining features based on the spectral brightness of reflection from cultivated and weed plants, the most informative spectral subranges of electromagnetic radiation wavelengths were established for using multispectral imaging of the underlying surface of agricultural land using modern remote sensing systems. An analysis of the spectral images of weeds and cultivated plants shows that we observe characteristic differences in the obtained spectral brightness curves in the subranges of blue, green, red, and near infrared electromagnetic radiation in the near infrared subrange of wavelengths.
A more difficult task for the widespread use of methods of remote sensing of agricultural lands is the determination of informative signs of plant diseases, and above all, in a latent form. This is due to the fact that many informative signs of diseases are similar in spectral brightness to signs of non-infectious pathology of the studied plants.
Positive results were obtained for the determination of potato diseases and damage to potato plants by the Colorado potato beetle using spectroradiometry. When using this method, it was found that when planting potatoes are affected by late blight (Fig. 1), on the third day after infection, we observe a sharp decrease in the spectral brightness of the reflection in comparison with healthy plants, and on the seventh day after infection, the values of the spectral brightness show that the plants are practically died. In this case, the value of the spectral brightness in plants affected by late blight is close to the values of the spectral brightness of the reflection from the soil.
When potatoes are damaged by the Colorado potato beetle, we also observe a decrease in the values of the spectral reflection brightness by two to three times compared to plants without damage by the pest. Figure 2 shows data on the spectral brightness of the reflection of potato plants, taking into account the different degree of their damage. The data obtained are of great importance for the remote method of detecting lesions of potato plants by the Colorado potato beetle.
At present, based on the studies carried out to determine informative features based on the spectral brightness of the reflection from healthy and diseased potato plants, as well as those damaged by the Colorado potato beetle, the most informative spectral subranges of electromagnetic radiation wavelengths have been established for using multispectral imaging of the underlying surface of agricultural land using BVS and SLA.
When determining diseases, it is necessary to take into account the results of studies of the Agrophysical Institute, which made it possible to determine the spectral characteristics of the reflection of plants that are deficient in nitrogen and soil moisture.
The results obtained are important for identifying informative features that make it possible to clearly distinguish, when deciphering the phytosanitary state of agricultural land, plants affected by diseases and those with pathologies caused by a deficiency of mineral nutrition or soil moisture.
The formation of libraries of spectral images of diseases of various crops, as well as spectral images of these crops that are deficient in mineral nutrition or soil moisture, will allow, based on the results of remote retrieval of information, to make reasonable and prompt decisions to stabilize the phytosanitary situation in the presence of diseases or to carry out a set of agrotechnical measures to relieve stress situations on crops caused by other factors.
The next important direction in the use of BVS is their application for plant protection measures. For the first time, UAVs in the form of unmanned remote-controlled helicopters began to be used in Japan in the early 90s for the treatment of rice fields with pesticides. At present, in China, which is the leader in the production of agricultural drones, the area under UA cultivation already exceeds several million hectares. The UAV market is also dynamically developing all over the world, the volume of use of these aircraft annually increases by 400-500%. According to experts, the use of UA technologies in agriculture in the world will reach a market value of $5,7 billion.
From agricultural drones, the Chinese company DJI dominates the market, and the most common model is the DJI Agras T16.
Due to the fact that most of the UAV parts of this model are made of composite materials, the weight of the device does not exceed 18,5 kg (without battery). With plant protection equipment, when filling the tank with working fluid, the take-off weight of the machine reaches 41 kg. The capacity of the reservoir for the working fluid is 16 liters when the boom is equipped with eight nozzles. The advantage of this drone model is that it is equipped with radars, which drastically reduces the risk of collision with obstacles, and also provides the ability to work at night, using searchlights. The optimal flight height of the drone above the field is 2,5-3 meters, and if necessary, the device can rise to 30 meters (maximum horizontal flight height). This height is necessary for the treatment of perennial plantations, plants in botanical gardens and forests from pests and diseases.
In the Russian Federation, positive results have been obtained on the use of BVS for the control of murine rodents (the studies were carried out with the participation of VIZR and the Ginus company). Production tests of remote monitoring and geocoded application of rodenticides into the burrows of mouse-like rodents showed that the accuracy of the new technology compared to manual application is 91% versus 97%.
Practical experience has been accumulated on the use of BVS for remote monitoring of the distribution areas of Sosnowsky's hogweed, as well as the use of herbicide spraying technology against this harmful species.
Despite the positive results and the prospects of using UA in agriculture, there are shortcomings, as well as unresolved issues in the field of legislation and regulatory documents on their effective and safe use for remote monitoring and plant protection, namely:
- high cost of UAV with the risk of losing the apparatus during the execution of work;
- legal restrictions on use: in most countries of the world, the UAV during the performance of work must be within the line of sight of the operator (remoteness is not more than 500 meters);
- the need to register, register the device (in most countries, if its mass exceeds 25 kg) and obtain a license to use the UAV for commercial purposes;
- the need for additional expensive equipment and qualified personnel: for the uninterrupted and efficient operation of the UAV, it is necessary to have at least three additional batteries, a generator to charge them; at least three people are engaged in servicing one car;
- great dependence on meteorological conditions. In windy weather, the control of the apparatus is very difficult, especially with a strong side wind;
- lack of legalized regulations for the use of plant protection products using BVS in accordance with the requirements of Federal Law No. 109 “On the safe handling of pesticides and agrochemicals”;
- lack of regulatory documents for the safe operation of UAVs in agriculture;
- lack of insurance risk standards for legal entities and individuals when using plant protection products with the help of BVS;
- high price and lack of software products for solving the problems of remote phytosanitary monitoring of weeds, pests and diseases, taking into account the economic thresholds of harmfulness, as well as automatic decoding of their results.
There is an urgent need to create regional centers for training operators and production approbation of technological procedures for the use of UAS for monitoring and protecting plants.
As part of the digitalization of agriculture programs, it is necessary to accelerate the development of large databases of reference samples of weeds in the most vulnerable phase of development for the use of herbicides and reference samples with characteristic informative signs of pest damage to major crops. It is equally important to complete the formation of libraries of spectral images of healthy and diseased plants, taking into account the influence of the level of mineral nutrition and agroclimatic parameters.
Anatoly Lysov, Head of the Laboratory of Integrated Plant Protection, VIZR, e-mail: firstname.lastname@example.org