**1. Introduction**

The growing demand for food and the limitation of territorial expansion of agricultural areas direct agriculture toward an increasing intensification with the rational use of resources and maximization of production [1]. For 2050, the world population is estimated at 9 billion people; this represents a need for an increase in food production around 70 to 100% that can be achieved if more efficient cultivation techniques are adopted with fewer impacts on the environment [2]. For this to be possible, it is necessary to have knowledge and control of the variables that interfere in the costs of production and productivity of crops. In this sense, precision agriculture is a tool that makes it possible to meet these needs.

Precision agriculture comprises a set of technologies that combines sensors, information systems, improved machinery, and informed management to optimize production, considering variability and uncertainties in agricultural systems [3].

This modern agriculture starts from the concept that an area of production is not homogeneous, that is, it has great variation. Thus, it is not appropriate to use agricultural inputs and management techniques equally for areas that have different characteristics. The aggregated knowledge throughout history helps to scientifically explain the variability observed and offers paths to localized management with more technique and rigor [4].

This new approach mainly benefits from the emergence and convergence of various technologies, including the global positioning system (GPS), geographic information system (GIS), microcomputers, control automation, remote sensing, mobile computing, advanced information processing, and telecommunications [5]. With these technologies, it is possible to analyze spatial variability, through data collection, information management, application of inputs at varying rate, and, finally, the economic and environmental evaluation of the results [6].

Precision agriculture allowed to perform not only the mapping of the physicochemical properties of the soil, application of fertilizers in a localized way, pest monitoring, harvesting and post-harvest operations, among others [3] but also the mapping and control of weeds, with localized sprays through mapping equipment or real-time systems and thus rationalize the use of pesticides and also minimize damage to the environment. Thus, the objective of this chapter was to address an overview of the use of herbicides in variable rate application (VRA) for weed management in PRE and POST.

## **2. Variable rate application (VRA) of herbicides**

Weed control with herbicides makes up much of the production costs of a crop. In conventional agriculture, herbicide doses are recommended for large areas, without considering many aspects of spatial and temporal variation. When the use of herbicides is made at a fixed rate, economic losses occur directly and indirectly, both due to the above—what is necessary for herbicides and for possible control failures that decrease productivity. In addition, environmental contamination may occur by leaching herbicides into groundwater and rivers. To fix these problems, it is necessary to use the precision agriculture tools and implement a VRA system [7].

VRA refers to the application of herbicides based on area, location, and soil conditions, among other characteristics. Important characteristics such as the variation in infestation and weed density in the application of herbicides in POST and in the sorption capacity that the soil exerts in the application of herbicides in PRE are considered in this system. This allows us to control weeds more efficiently and reduce environmental risks, as there are no applications of underdoses or overdoses. This technology works by integrating a variable rate control system with the sprayer for herbicide application [8, 9].

VRA systems can be different in many ways, but have components in common; the basic system deployment consists of five components that are represented in **Figure 1**: GPS receiver for location and orientation of the machinery at the time of application, a computer that will perform the data processing, a software capable of relating the data collected in the area and determine the dose to be applied, in addition to controllers that will be responsible for changing the flow and pressure of the spray syrup [7].

The application at a varied rate can be fundamentally based on maps or sensors (**Table 1**). Such methodologies require specific resources that differ greatly from each other.

**181**

**Table 1.**

**Figure 1.**

Laboratory analysis (plant and soil)

*Source: Ahmad and Mahdi [10].*

**2.1 Map-based variable rate application (VRA)**

*Comparison of the application in varied rate based on maps and sensors.*

*receiver, and control valve). Source: adapted from Grisso et al. [7].*

Methodology Grid sampling—lab analyses—site-

rate applicator

Application maps of specific areas are generated by analyzing previous georeferenced samples of soil or plants of the area to be managed. Due to the need to collect many samples to create a representative map of the area, the costs of analysis tend to increase with this method and need more time to get ready. The map-based system is highly dependent on GPS and differential global positioning system (DGPS), as it is necessary to cross-reference the coordinates of the samples collected with the

*Variable Rate Application of Herbicides for Weed Management in Pre- and Postemergence*

*Main components of a variable rate spraying system (spray rate controller, computer and software, GPS* 

Required Not required

Relevance Popular in developing countries Popular in developed countries

Real-time sensors—feedback control measures and the use of variable rate

Lack of sufficient sensors for getting crop

applicator

and soil information

**Parameter Map based Sensor based**

GPS/DGPS Very much required Not necessary

Mapping Required May not required

Time consumption More Less

Operation Difficult Easy Skills Required Required Sampling unit 2 to 3 acres Individual spot

Limitations Cost of soil testis and analysis limit the usage

specific maps and the use of variable

*DOI: http://dx.doi.org/10.5772/intechopen.93558*

*Variable Rate Application of Herbicides for Weed Management in Pre- and Postemergence DOI: http://dx.doi.org/10.5772/intechopen.93558*

#### **Figure 1.**

*Pests, Weeds and Diseases in Agricultural Crop and Animal Husbandry Production*

more technique and rigor [4].

management in PRE and POST.

implement a VRA system [7].

for herbicide application [8, 9].

the spray syrup [7].

**2. Variable rate application (VRA) of herbicides**

results [6].

This modern agriculture starts from the concept that an area of production is not homogeneous, that is, it has great variation. Thus, it is not appropriate to use agricultural inputs and management techniques equally for areas that have different characteristics. The aggregated knowledge throughout history helps to scientifically explain the variability observed and offers paths to localized management with

This new approach mainly benefits from the emergence and convergence of various technologies, including the global positioning system (GPS), geographic information system (GIS), microcomputers, control automation, remote sensing, mobile computing, advanced information processing, and telecommunications [5]. With these technologies, it is possible to analyze spatial variability, through data collection, information management, application of inputs at varying rate, and, finally, the economic and environmental evaluation of the

Precision agriculture allowed to perform not only the mapping of the physicochemical properties of the soil, application of fertilizers in a localized way, pest monitoring, harvesting and post-harvest operations, among others [3] but also the mapping and control of weeds, with localized sprays through mapping equipment or real-time systems and thus rationalize the use of pesticides and also minimize damage to the environment. Thus, the objective of this chapter was to address an overview of the use of herbicides in variable rate application (VRA) for weed

Weed control with herbicides makes up much of the production costs of a crop. In conventional agriculture, herbicide doses are recommended for large areas, without considering many aspects of spatial and temporal variation. When the use of herbicides is made at a fixed rate, economic losses occur directly and indirectly, both due to the above—what is necessary for herbicides and for possible control failures that decrease productivity. In addition, environmental contamination may occur by leaching herbicides into groundwater and rivers. To fix these problems, it is necessary to use the precision agriculture tools and

VRA refers to the application of herbicides based on area, location, and soil conditions, among other characteristics. Important characteristics such as the variation in infestation and weed density in the application of herbicides in POST and in the sorption capacity that the soil exerts in the application of herbicides in PRE are considered in this system. This allows us to control weeds more efficiently and reduce environmental risks, as there are no applications of underdoses or overdoses. This technology works by integrating a variable rate control system with the sprayer

VRA systems can be different in many ways, but have components in common; the basic system deployment consists of five components that are represented in **Figure 1**: GPS receiver for location and orientation of the machinery at the time of application, a computer that will perform the data processing, a software capable of relating the data collected in the area and determine the dose to be applied, in addition to controllers that will be responsible for changing the flow and pressure of

The application at a varied rate can be fundamentally based on maps or sensors (**Table 1**). Such methodologies require specific resources that differ greatly from

**180**

each other.

*Main components of a variable rate spraying system (spray rate controller, computer and software, GPS receiver, and control valve). Source: adapted from Grisso et al. [7].*


#### **Table 1.**

*Comparison of the application in varied rate based on maps and sensors.*

#### **2.1 Map-based variable rate application (VRA)**

Application maps of specific areas are generated by analyzing previous georeferenced samples of soil or plants of the area to be managed. Due to the need to collect many samples to create a representative map of the area, the costs of analysis tend to increase with this method and need more time to get ready. The map-based system is highly dependent on GPS and differential global positioning system (DGPS), as it is necessary to cross-reference the coordinates of the samples collected with the coordinate occupied by the machinery at the time of application. Thus, the operational difficulty of map-based systems is greater.

Although it has some disadvantages referring to operating costs and complexity, the map method is very efficient when used correctly and with accurate equipment. **Figure 2** shows a mapping of weed distribution in a given area and correlated with the required amount of herbicide needed to control weeds according to their density. The result of this crossing of information is a varied rate application map. In the area, there were infestations ranging from 0 to >30 plants m−2; so, it is not necessary to apply the same dose at all levels of infestations [11]. Areas with higher infestation will receive more herbicide than areas with low infestation. In the specific case, the volume of syrup varies from 100 to 250 L ha−1, which corresponds to a variation of 150%. If the volume of syrup was kept constant, there would certainly be herbicide wasting due to excess or lack in certain places. In the example of **Figure 2**, the VRA allowed uniform yield of the crop that was implanted, reduced environmental impacts, and provided savings of 29% in the amount of herbicide.
