Crooked view

After transplanting perennial crops to the field, producers face a series of challenges to keep the plants away from attack by pests, diseases and weeds. As these attacks normally result in high losses in crop productivity, it is necessary for control operations to be carried out quickly, but also efficiently. Therefore, appropriate use of sprayers and all other factors involved in the application must be made. For applications in perennial crops such as coffee, avocado and citrus, hydropneumatic sprayers stand out, as they present both good operational capacity and good penetration of the spray into the canopy of these plants, which is normally very closed.

However, often, before spraying, the operators or technicians responsible for the application only take into account the sprayer calibration stage, that is, only changes are made to the speed and/or working pressure to adjust the volume of spray that will be applied. . This way, they forget a very important procedure, which must be carried out prior to calibration. For the sprayer to be operationally prepared, it must be adjusted. This procedure consists of visual and operational checking of all sprayer components, in addition to their adjustment when necessary. In the case of hydropneumatic sprayers, it is essential to pay attention to the direction of the spray nozzles, the positioning of the air curtain conduction fins and the sizing of the fan. These aspects are directly responsible for the correct distribution and deposition of the syrup in the field. During adjustment, these settings must adapt to the product applied and the target to be achieved, that is, the insect or disease to be controlled and the characteristics of the crop in question.

Furthermore, hydropneumatic sprayers are characterized by the production of small droplets, one of the aspects that justify their good coverage and penetration of the spray into the plant canopy. However, this droplet size facilitates the occurrence of drift, which is characterized by the displacement of the drops generated by spraying the solution to different locations from where the application is being carried out. When drift reaches adjacent areas with susceptible crops, reserve or housing areas, it can cause serious damage, both environmental and financial. Studies already carried out indicate that applications made with hydropneumatic sprayers can be quite inefficient, resulting in the loss of more than half of the product applied. Another issue is that the correct assessment of these sprayers is complex, mainly because they require equipment to collect the sprayed syrup vertically, which makes this practice difficult to carry out on most agricultural properties. This equipment, in general, is expensive and not widely used in Brazil, mainly because there is no obligation in our country to carry out periodic inspections on sprayers. Therefore, it is necessary to develop alternative ways to check the quality of applications with hydropneumatic sprayers.

An evaluation of 30 hydropneumatic sprayers was carried out in the region of Alto Paranaíba (MG), in the period between May and October 2012. In summary, the general objective of the work was to evaluate the uniformity of spray solution provided by these sprayers in coffee plantations. With this purpose, a vertical liquid collection structure was built to evaluate the uniformity of vertical volumetric distribution, consisting of 20 PVC tubes with one end sealed, containing only one outlet where a silicone hose was adapted, which took the liquid to graduated cylinders. The other end was cut into a bevel shape. The collection structure was 3,2 meters high, with the tubes overlapping at a 45° angle in relation to the horizontal plane.

Before each evaluation, the structure was moistened and then sprayed simulating a normal application. To do this, the sprayer was moved in front of the structure as many times as necessary to collect enough liquid to read the test tubes.

To verify whether the volume of syrup collected was actually consistent with what was needed to be applied to the property's crops, the vegetative volume of the plants was quantified. Subsequently, the statistical test (chi-square) was used to verify whether the quantity of sprayed mixture really complied with what was necessary for the respective vegetative volume measured.

On average, the uniformity of vertical distribution observed in the sprayers evaluated was 19,5%, and in more than 60% of them there was no uniformity of spray distribution proportional to the vegetative volume of the crops. This probably occurs due to the use of hydraulic nozzles with inadequate flow. Either because they present high flow variation, do not follow the crop distribution pattern or are damaged. The tips are the most important parts of these sprayers. They are directly responsible for the fragmentation into drops of the applied syrup and in the case of hydropneumatics, together with the fan, they are also responsible for the distribution in the different strata of the crop. However, maintenance, cleaning and replacement of these components are often neglected, which can lead to great inefficiency in the spraying process. This may have contributed to the lack of uniformity detected in this work.

Comparing the height of the crop with the height reached by the sprayed syrup drops, the volume of syrup lost above the plant canopy was analyzed and quantified. The value found was on average 10% of the total volume sprayed (Graph 1). This implies higher production costs and environmental contamination. This was possibly due to the inappropriate positioning of the spray nozzles. Studies already carried out have demonstrated that the correct positioning of the nozzles is essential to avoid these losses and, thus, improve the volumetric distribution of the syrup throughout the plant canopy.

Graph 1 - Comparison of the volumetric distribution profile obtained from 30 hydropneumatic sprayers and the vegetative volume of coffee plants

It was observed in the relationship between the maximum and minimum average values ​​of vegetative volume and spray deposition (Graph 1) that, in the lower strata of the plants, the spray volume applied was much lower or much higher than what would actually be necessary for the vegetative volume in question. On the other hand, in the relationship between the average values ​​of spray deposition and vegetative volume, it can be noted that they followed the same distribution pattern, depending on the height. However, this relationship in the lower third is one of greater vegetative volume and less spray deposition, tending to be equal in the middle third and reverse in the upper third. Furthermore, in the relationship between the maximum average values ​​of vegetative volume and spray deposition in the upper strata, it is evident that spray deposition was always higher than what would be necessary for that maximum vegetative volume.

It is concluded that the proposed methodology makes it possible to measure the volumetric distribution of hydraulic sprayers using few resources and presenting satisfactory results. Most of the sprayers evaluated do not provide uniformity of vertical volumetric distribution, when taking into account the relationship with the vegetative volume of the plants. This demonstrates the existing negligence with the techniques recommended by application technology. Small adjustments to the direction of the air jet or the hydraulic nozzles would probably provide good results. Finally, the need to implement sprayer inspection policies in general is highlighted, in order to popularize techniques aimed at improving the operational quality of sprayers and increasing the efficiency of agrochemical applications.

This article was published in issue 145 of Cultivar Máquinas magazine. Click here to read the edition.