Theory of Planned Behavior

In recent years, many models have been presented by different scholars to investigate people behavior and recognize the socio-psychological components that connect with behavior. In this respect, one of the most applicable models is the TPB, which is being increasingly used in the wide range of various fields, particulary in the context of sustainable agriculture.
A literature review indicates that the TPB has long been successfully applied to investigate a broad variety of farmers’ behavior and intention such as conservation technology adoption decisions (Lynne et al., 1995), diversification of agricultural production (Senger et al., 2017), identifying main beliefs farmers’ intention to apply improved natural grassland (Borges et al., 2016), using best management practices by farmers (Reimer et al., 2012; Hyland et al., 2018), increasing soil organic matter (Hijbeek et al., 2018), farmers and forest conservation (Dolisca et al., 2009; Meijer et al., 2016), applying pro-environmental activities in the farm (van Dijk et al., 2016), adoption of soil conservation practices (Wauters et al., 2010), engagement in sustainable agricultural practices (Fielding et al., 2008). Kaiser and Gutscher (2003) believed that TPB can predict human behavior in different fields and its application field is not limited to a specific context.
TPB is developed theory of reasoned action theory by Ajzen (1991). Ajzen presented “perceived behavioral control” to complete people’s behavioral framework (Zhou et al., 2016). In addition to perceived behavioral control, there are four other variables in the model: attitude, subjective norms, intention and behavior (Figure 1). Intention bodes individual readiness to carry out a given behavior (Ajzen, 2002) and is identified as the stimulus which is essential for engagement in a specific behavior.

The intention is considered as the main predictor of behavior (Clayton, 2004; Ataei and Izadi, 2014; Hoseininia et al., 2017) and is assumed to be an immediate antecedent of behavior (Ajzen, 2002). The more one intends to commite in a behavior, the more likely will be its performance (Clayton, 2004). According to the TPB model, an individual’s intention to carry out a behavior is a function of that individual’s attitude, perceived behavioral control and subjective norms (Ajzen, 1991).
Attitude is an individual’s negative or positive assessment of specific behavior performance (Ajzen and Fishbein, 1980). According to the TPB, it should be stated that the more favorable attitude toward a particular behavior, the more possibility that the individual will carry out that certain behavior (Ajzen, 1991; Ataei et al., 2018).
PBC can be defined as “an individual’s perceived convenience or difficulty of a specific behavior performance” (Ajzen and Fishbein, 1980). Fielding et al. (2005) stated that PBC implies “the extent to which that an individual perceives a behavior to be under his/her volitional control”. Sometimes a person feels that he/she can easily conduct and control a behavior (internal control), and sometimes he feels that a behavior is completely out of control and depends on factors such as time or circumstances, etc (external control).
The subjective norms are formed by beliefs about the normative expectations of other people to perform the behaviour (Meijer et al., 2015). People intend to carry out a behavior when they feel that the people who are important for them confirm their behavior (Shin and Hancer, 2016). Group consistency in social norms obliges individuals to behave same to others in the similar group.