Drift is one of the main complications of spraying, a phenomenon that requires a lot of attention and technique to be minimized in operations.
The increase in agricultural production in the world occurs in response to the growing demand for food for nutritional needs and raw materials for industry. Optimizing the productive potential of crops is a determining condition for the existence of the activity as a business, as it maximizes yield with the least use of resources in the cultivated area.
These resources can be local, such as soil, water and light, or imported, such as seeds, fertilizers and agrochemicals. Regardless of whether it is local or not, these resources must be used rationally so that exploration does not constitute a waste of resources, does not anticipate their scarcity and does not increase production costs.
In addition to rational use, agricultural production must not condition the use of one resource that compromises another. Therefore, a fertilizer cannot be used in a way that contaminates the soil, even increasing production. Likewise, an agrochemical cannot contaminate the environment outside the site of application, even if it effectively controls a certain damaging agent.
Although this premise is logical, it is not easy to follow, especially when it comes to agricultural production. This difficulty is due, among other reasons, to the variable local conditions in which this activity is practiced and the time, normally scarce, to carry it out.
Given the size of the Brazilian territory, the great variability of climatic, operational and cultural conditions existing in different regions can be considered, which requires the producer to have in-depth knowledge or good guidance on the agricultural techniques necessary for sustainable production.
Among the risks of negative impacts on the environment, the drift of agrochemicals is one of the most worrying, as it is characterized by the transport of the applied product to an unwanted location. This drift can occur within the area where the agrochemical was sprayed, either by runoff, overflow or non-interception of the droplet on the target, in this case called endodrift. The transport of the droplet outside the spray area is called exoderivation.
The latter, in addition to subjecting people, animals and other crops to risks of discomfort, compromised health or decreased production, also reduces the amount of product applied in the agricultural area, minimizing the level of control over the damaging agent and reducing the period residual product in crop protection.
There are several factors that can increase the risks of agrochemical drift, among them some are well known and will be highlighted here, such as: the environmental condition at the time of spraying, the spectrum of drops produced by the equipment and the composition of the spray solution. pulverization.
Among the environmental variables, wind speed, temperature and air humidity are the most relevant. Although the occurrence of wind is often attributed the greatest responsibility for drift, it must be considered that the wind will move out of the application area only the drops that did not fall in the direction of the target, characterizing the drift as horizontal transport.
The absence of wind can also favor drift, as in moments of heat release from the ground or heat deflection from its surface, whether day or night, the absence of wind intensifies the transfer of heat to the air close to the ground. , reducing its density and promoting the upward displacement of air masses, called convective currents, which delay or prevent the fall of the lightest spray droplets in the area that was treated, characterizing vertical drift.
Air temperature and humidity act in combination, accelerating the evaporation of volatile compounds from the droplets (Figure 1). In this way, the water that makes up the drop is removed into the environment in the form of vapor, making the drop lighter, exposing it to the convective action of heat or to being carried by the wind, which will move this drop to an unwanted location. This location could be the neighboring area, a city or a water source, near or far.
The micronization of droplets in spraying can be achieved in different ways, promoting droplet classes of different sizes, the most common classes being fine, medium and coarse. Each class of drops must be used considering local application conditions such as product, climatic conditions, leaf area index, among others. Each of these droplet classes is characterized by a certain diameter range, but this does not mean that all drops in the spectrum will fall within this range. Those finer spray droplets represent those at greater risk of drift.
Studies are carried out to identify how some factors affect the droplet spectrum. Among those that can have the most effect on their quality are spray tips and operating pressure. Broad-use flat jet tips are recognized as those with the greatest droplet variability, increasing the potential for drift in a spray due to the high percentage of very fine droplets. Air-induction tips produce low levels of fine droplets, allowing products with greater environmental risk to be used with low risk of drift (Figure 2).
Associated with the spray tip performance parameters is the working pressure. It can be modified according to the desired flow and application rate, these parameters being directly proportional to the operating pressure. The higher the operating pressure, the more intense the shock of the jet or sheet of liquid projected through the tip orifice with the air in the atmosphere, intensifying the micronization of the liquid and the formation of finer drops.
Thus, although increasing pressure also increases flow to promote corrections in the application rate, its adoption can increase the risk of drift (Figure 3), warning that the safest way to increase the application rate is to replace a given spray tip with another with a higher absolute flow rate, not requiring an increase in pressure.
The composition of the spray solution also has a high influence on the risks of drift. Research has shown that some agrochemical formulations can reduce the environmental impact of these applications (Figure 4). Currently, the industry develops specific formulations or products that allow producers to spray safely, minimizing losses to the environment and enhancing efficiency.
Among the most used products are some spray additives with anti-drift characteristics and low volatility formulations with a low potential for the formation of very fine droplets. These products are widespread in agriculture and are recommended when the risk of losses due to evaporation or drift is imminent, and should be chosen for their safety.
Some factors that enhance drift may act in association with its occurrence. Thus, high temperatures and low air humidity can quickly reduce the mass of the drops by evaporating the volatile portion, delaying their fall, exposing these drops to fluctuation by convective action which, combined with strong winds, end up dragging these drops to other locations. .
Likewise, safer formulation technology, associated with the most suitable spray tip, can also reduce these losses to minimum levels, compensating them even in periods of greatest risk.
A technology already studied that could bring safer applications to agriculture is the use of air assistance associated with electrostatic systems. The assistance is an artificially generated air current at the spray bar that projects the droplet downwards. The electrostatic system, in turn, charges the drops with an electrical charge that aims to provide electromagnetic attraction between the drop and the plant. The rapid fixation of the droplet on the plant reduces its exposure time in the environment, reducing losses due to evaporation and drift.
If drift is a harmful factor in the application because it reduces deposits in the desired location, knowledge and the use of safer application technologies are recognized alternatives for reducing it. Technical knowledge for its adoption must be sought and disclosed in its entirety. This condition is essential for the growth of agricultural production to occur in a safe and fair manner, allowing the consumption of healthy food in an environment free from contamination.
Marco Antonio Gandolfo, Ulisses Delvaz Gandolfo, Dashen Agricultural Research Institute
Article published in issue 164 of Cultivar Máquinas.
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