Drivers and barriers in farmers’ adoption of vermicomposting as keys for sustainable agricultural waste management

ABSTRACT

The conversion of agricultural waste into organic fertilizer through vermicomposting is a sustainable waste management solution and an income source for organic fertilizer producers. Most of the agricultural waste in Iran is burned, triggering an array of negative consequences. Vermicompost production at the farm level is rarely practiced in Iran, and farmers play a central role. The study aimed to identify the factors influencing the adoption of on-farm vermicomposting and its level (number of cycles), barriers to it, and to provide adapted policy recommendations. The study used a mixed-method approach, with a survey on 142 farmers and semi-structured interviews with stakeholders. The study showed that attitude (β = 0.515, sig. = 0.01), subjective norms (β = 1.745, sig. = 0.01), vermicomposting training (β = 2.160, sig. = 0.01), safe spraying (β = 2.915, sig. = 0.01), and integrated pest management (β = 1.793, sig. = 0.01) influenced the participation in vermicomposting. Some of the barriers to vermicomposting revealed by the qualitative research were the initial investment cost, farmers’ short-term vision, lack of necessary infrastructure, and lack of subsidies. The study complements the scant information on farmers’ vermicomposting behavior and proves that its understanding is essential to remove barriers and engage farmers in vermicomposting. Practical recommendations based on findings support sustainable agricultural waste management.

KEYWORDS:

• Behavioral spillover
• biomass resources
• protection motivation theory
• environmentally friendly behavior
• sustainable agricultural practices
• theory of planned behavior
• waste

1. Introduction

Agriculture is the primary source of income for most of the world’s population, particularly in developing and underdeveloped countries (Barragán-Ocaña & del-Valle-Rivera, 2016; Guo & Liu, 2022). Agriculture is also the world’s primary food source (Fróna et al., 2019). Agricultural soil is rapidly eroding, causing irreversible damage to the environment, the agricultural industry, and, as a result, the food chain (Chalise et al., 2019). One major problem of this sector is excessive waste production (Bahrololoum et al., 2022). When this organic waste is not treated on time, it pollutes the environment, endangering the health of humans and other organisms and wasting resources such as virtual water, land, and nutrients (Munir et al., 2018). Furthermore, most of agriculture is intensive agriculture, which depletes farm soil of nutrients and destroys its texture through continuous tillage and chemical fertilizer use (Kopittke et al., 2019).

Vermicomposting agricultural waste can play a key role in alleviating the problems associated with agricultural waste (Kauser & Khwairakpam, 2022). The bioconversion of organic materials by earthworms is called vermicomposting (or earthworm technology), and the production of earthworms in organic material is knowns as vermiculture (Bhat et al., 2018). In addition to meeting farmers’ income needs, vermicomposting can help preserve resources, protect the environment and human beings (Appala et al., 2022), and improve the circularity of farm activity and its ecological footprint (Salemdeeb et al., 2021; Wang et al., 2021; Yang et al., 2022). Vermicomposting not only treats organic waste but also generates revenue and reduces costs for farmers (Yuvaraj et al., 2021).

Vermicomposting can be used in all regions of the world where agriculture is practiced and for diverse types of agricultural waste (Thomas et al., 2019). In Iran, 66.95 million tons of manure are produced yearly from large livestock (i.e. cow and calf) and can potentially be used as fertilizer (Ardebili, 2020). Compared to cow manure, vermicompost production is negligible (Taheri Rahimabadi, 2018), although it could be another source of natural fertilizer. According to Indian research, an earthworm population of 1 million per hectare may be developed in three months. Earthworms consume 12 tons of soil or organic matter per hectare per year on average, resulting in 18 tons of soil upturning each year worldwide (Sinha et al., 2010). Darwin was the first to recognize the importance of earthworms in the decomposition of organic matter in 1881 (Van Groenigen et al., 2019). Studies have comparatively analyzed the efficiency of various earthworm species to identify the best option considering the species, climatic conditions, and type of waste and thus to increase the efficiency of vermicomposting (Thomas et al., 2019).

Vermicomposting is an efficient method of converting waste into gold, a simple technique with many positive effects (Kauser & Khwairakpam, 2022). For example, it produces less pollution and is thus more environmentally friendly than other waste management methods such as landfill disposal, fermentation, and incineration (Grasserová et al., 2020). Earthworms in vermicomposting can decrease contaminants in soils and, thus, generate a non-toxic, high-value product useful in agriculture (Masciandaro et al., 2010). Vermicompost absorbs atmospheric moisture well (Appala et al., 2022). For this reason, adding vermicompost to the soil increases its water-holding capacity and reduces water evaporation, ultimately improving ecology and the hydrological cycle (Omran & Negm, 2020). In managed and natural ecosystems, increasing soil capacity to hold the water is one of the measures to control soil erosion (Pasha et al., 2020). Soil erosion is a significant threat to soil productivity and food security. Soil erosion in Iran (16.7 tons per hectare per year; Mohammadi et al., 2021) is six times higher than the global average (Borrelli et al., 2017). Vermicompost was one of the practices selected by non-government organizations Guatemala for interventions that aimed to rescue the traditional agricultural system (milpa system) and to diversify farming systems (González-Esquivel et al., 2020). In addition, vermicompost can save farmers money in the long run by eliminating the costs of chemical fertilizers (Swati & Hait, 2018). Vermicompost use can bring a marketing advantage when it is used for products sold on the market, as it was observed that consumers were willing to pay more for sustainable attributes of products (Staples et al., 2020; Yue et al., 2016) and that environmental value of products (like the one brought by the use of vermicompost) stimulated consumers’ choice of green products (Rahnama & Rajabpour, 2017). Vermicompost improves soil properties and plant growth (Oo et al., 2015). Studies that compared various organic and inorganic treatments found that vermicompost was a better organic amendment, increased crop yield by 5%, improved nutrients in the soil, and generated the least environmentally damaging gas emissions (Raza et al., 2020, 2023). It also increases productivity; for example, in India and Sierra Leone, in combination with inorganic fertilizers, it increased tef (Eragrostis tef) yields, and it significantly reduced the quantity of planting material necessary to grow turmeric (Adhikari et al., 2018). Having all these advantages, vermicomposting can be considered a suitable option to support sustainable agriculture and a sustainable farm, as they were defined by FAO (FAO, 2014) and Sustainable Agriculture Initiative Platform (Sustainable Agriculture Initiative Platform (SAI), 2022) (Mungkung et al., 2022).

Previous studies sought to determine farmers’ or other people’s knowledge regarding vermicomposting. They did not provide a model for farmers’ behavior regarding vermicomposting, thus signaling a modeling vacuum. As a result, it is difficult to thoroughly understand the factors influencing farmers’ participation in vermicompost production for agriculture and horticulture. Farmers play a leading role in developing a particular type of agriculture – conventional, multifunctional, or other. Studies showed that in developing countries, farmer’s behavior is linked to the environmental degradation caused by agricultural activities (Yaghoubi Farani et al., 2019). In Iran, most of the agricultural waste is burned, triggering an array of negative consequences (Bahrololoum et al., 2022; Golshan et al., 2002), despite the legal barriers to it, such as the Clean Air Law (FAO, 2017). Therefore, understanding farmer behavior when vermicomposting on garden is essential for sustainable development and agricultural waste management in developing countries. As a result, assessing the factors that influence vermicomposting participation is necessary. The current study aims to fill a gap in the research on farmers’ behavior regarding vermicomposting combined with gardening. The study contributes to the theory and practice of sustainable agriculture in several ways. First, the study focuses on sustainable agricultural practices – vermicomposting – that can be beneficial for sustainable agricultural waste management and soil health. Second, the study combines elements from two established behavioral theories, the Theory of planned behavior (TPB) (Ajzen, 1991) and the Protection motivation theory (PMT) (Rogers, 1975, 1983), and the idea of behavioral spillover, thus, providing a more comprehensive understanding of farmers’ behavior compared to using only one of the theories. The TPB is a psychological framework that helps explain and predict the intention to perform a behavior, to adopt vermicomposting in this case. It casts light on the factors that influence farmers’ intention to vermicompost on garden and guides the development of strategies that target precisely the factors that help to encourage farmers to adopt vermicomposting. PTM explains how individuals make decisions to protect themselves from perceived threats or risks. It can help practitioners to increase farmers’ motivation to adopt vermicomposting through education-communication campaigns by indicating what factors to address, such as farmers’ awareness of threats posed by conventional farming practices, their confidence in implementing vermicomposting, and perceived vermicomposting effectiveness. Behavioral spillover is the phenomenon by which the adoption of one behavior increases the likelihood of engaging in other similar behaviors (Thøgersen & Crompton, 2009). By integrating the TPB, PMT, and behavioral spillover concept, the study provides insights into both motivational and cognitive factors that influence farmers’ decision-making, thus offering a more holistic and nuanced understanding of farmers’ behavior. Third, another study's contribution is that by identifying the factors that stimulate farmers’ adoption of vermicomposting and its intensity (number of cycles per year), and the barriers to it, the study can inform the development of targeted intervention strategies and policy recommendations. The study findings can guide agricultural extension programs, policymakers, and practitioners in providing trainings, technical and legal support, educational campaigns, and fostering supportive social norms to overcome barriers and encourage farmers’ adoption of vermicompost.

More precisely, the study objectives are to identify the factors that influence the adoption of vermicomposting and its level (number of cycles), to identify the barriers in front of it, and to provide recommendations adapted to study findings. Four research questions were asked to fulfill these objectives: (1) ‘What are the factors that influence the adoption of vermicomposting on garden?’ (2) ‘What are the factors that influence the number of composting cycles per year?’; (3) ‘What are the most important barriers that prevent farmers from engaging in vermicomposting?’; (4) ‘What policy recommendations can be provided based on study findings?’ Hence, the study novelty stands on the following. First, it adopts an integrated approach by combining two established theories, TPB and PMT, the behavioral spillover concept, and qualitative research to provide a deeper understanding of farmers’ adoption of vermicomposting. Second, it offers contextual relevance by focusing on the specific context of vermicomposting adoption among farmers. While TBP, PMT, and interviews have been used in other fields (e.g. health or environmental protection), their application to agricultural waste management, particularly vermicomposting, adds novelty and context-specific insights. Third, the novelty lies in the practical recommendations, adapted to the investigated context, for reducing barriers and promoting vermicomposting among farmers.

2. Materials and methods

This research included two studies. The factors affecting vermicompost production on garden were studied in Study 1 and the barriers to vermicomposting on garden were studied in the Study 2. Study 1 used a survey to investigate factors that influence farmers’ participation in vermicomposting on garden and the level of their involvement (measured through the number of production cycles throughout the year). The selection process of participants was conducted through a multi-step random sampling procedure. As a first step, two regions were randomly selected from among four agricultural regions, and then, in a second step, a county was randomly selected: Khomeini-Shahr county (Isafahan province) [Figure 1(a)]. The study’s statistical population included 2666 farmers in Khomeini-Shahr county, and a sample 142 people were randomly selected. Third, nine villages from the Khomeini-Shahr county were randomly selected. Subsequently, interviews were conducted with individuals engaged in agricultural activities who were over 18 years old. The number of interviews carried out in each village was between ten to eighteen. To identify interview candidates, we randomly selected a starting point within each village and proceeded to interview individuals in the second house until the desired number of responses was obtained for that village. In case a village had multiple streets, we determined whether to conduct interviews on one or more streets based on the size of the village, which was determined by the number of houses present. Prior to conducting the survey, all participants were informed of the research's purpose and nature, and participation was voluntary. Data collection was done face-to-face in the mornings and evenings.

Figure 1. Study area: location on country map (a); a typical small farmer’s orchard (b); indoor vermicomposting containers at small farmer farm (c); outdoor vermicomposting (d); farmer working on vermicompost in early spring (e); vermicompost (f) [Source: (a):(Wikipedia, 2023); (b) – (f): authors’ personal archive].

The climate of Khomeini Shahr county is hot and dry, but from the east and north to the south, the air temperature becomes more balanced due to the proximity of Zayandeh River. The average annual temperature of the city is around 14°C, and the average minimum and maximum temperatures are about 6°C and 24°C, respectively. The yearly average rainfall is 216 cm. Therefore, the people of this county have practiced agriculture since ancient times. Pears, cherries, plums, and walnuts are among this county's most widespread garden products.

The questionnaire was developed starting from the TPB (Ajzen, 1991), the PMT (Kothe et al., 2019), behavioral spillover, and participants’ socio-economic characteristics. TPB assumes that intention to perform a behavior is the best predictor of that behavior. Intention is determined by attitude towards the behavior, subjective norm (it shows what interviewed people believe about the opinion of the people important to them regarding their adoption of the studied behavior), and perceived behavioral control (it shows to what degree interviewed people consider that can perform the studied behavior). PMT shows how individuals are motivated to react to protect themselves against a threat. According to PMT, the motivation to protect is determined by the threat appraisal and coping appraisal. More precisely, attitude, subjective norm, and behavior were extracted from the TPB; knowledge, training (Bagheri et al., 2019; Rastegari Kopaei et al., 2021; Yi et al., 2023), and guilt feeling (Onwezen et al., 2013; Savari et al., 2022) were added to the model based on the fact that previous studies that used an extended model of TPB found their effect relevant on farmers’ environmentally friendly behavior; perceived vulnerability (as threat assessment) was inspired by PMT; attention to safety during and after spraying, and integrated pest management (IPM) are environmentally friendly behaviors and they were added following the idea of behavioral spillover. The most reasonable, safest, most accurate and economical method of combating plant pests is IPM. To measure this issue, two questions were used, namely compliance with safety protocols during and after spraying and compliance with the IPM principles (Table A1, Appendix). Researchers explained to farmers that IPM is a holistic strategy to combat plant pests and diseases using all available methods, while reducing the use of chemical pesticides (Deguine et al., 2021). For example, IPM includes reducing workers’ exposure to chemicals; minimizing water and air pollution; using natural management methods with the least environmental harm, such as using natural fertilizers. Each variable was measured using one or more questions with answers measured on a 5-point scale or with dichotomous answers. Table A1, Appendix provides a detailed description of the questions and their answer options. The questionnaire was pretested and adjusted. A panel of experts confirmed the questionnaire's face validity, and Cronbach’s alpha coefficient was used to confirm its reliability. The final questionnaire (Table A1, Appendix) included two dependent variables and eight independent ones. It was applied through face-to-face interviews.

Study 2 used a qualitative approach through semi-structured interviews to analyze the barriers that prevented farmers to do vermicomposting. In the beginning, one of the Agricultural Extension and Education Organization specialists was interviewed in a targeted manner, and through him, the knowledgeable people related to the production of vermicompost in the garden were identified, and further interviews were conducted with other people. In this way, 11 people were interviewed so that the study reached theoretical saturation. Thus, participants were various stakeholders that were well informed about vermicomposting on farm (11 persons in total): farmers (5), promoters (3), vermicompost producers (2), and Agricultural Extension and Education Organization experts (1). Purposeful sampling was used in this case. Averagely, the interviews lasted 30 min. The researchers stopped conducting the interviews when they reached theoretical saturation. The member check method, a technique that checks the credibility of results (Birt et al., 2016), was used to confirm the findings of the part of the study. Thus, the results of this section were shown to three participants for confirmation. An overview of the research structure is presented in Figure 2.

Figure 2. Schematic diagram of the study methodology [grey: methods; light green: investigated independent variables; neon green: dependent variables investigated to respond to the first and second research question (RQ); lines: link the factors that have a significant influence to dependent variables; light red: variables linked to the third RQ; yellow: recommendations related to the fourth RQ and possible beneficiaries of vermicomposting; map: location of the study area in the country; pictures: garden (left) and vermicomposting facilities (right)].

3. Results

3.1. Determinants of farmers’ engagement in vermicomposting and its level

Results reveal that most investigated farmers practiced vermicomposting at some point [Figure 1(b)–(f)], most of them doing two or three cycles per year (Table 1). Most results concerning the motivational and environmental-related variables obtained average scores. The only exception is IPM which gathered a high score of 0.83, thus showing that most farmers declared they followed its principles.

Table 1. Vermicomposting participation and level of vermicomposting participation considering motivational, environmental, demographic and socio-economic characteristics.

Variables	Total (n = 142)	Vermicomposting participation		Level of vermicomposting participation
	Mean	No	Yes	Low	Medium	High
	(Standard deviation)	(n=31)	(n=111)	(n=18)	(n=62)	(n=31)
Vermicomposting knowledge	61.88 (29.56)	27.41 (15.86)	71.50 (24.96)	31.59 (17.37)	73.08 (17.14)	91.53 (11.91)
Attitude about vermicomposting	3.09 (0.97)	1.97 (0.67)	3.40 (0.79)	2.27 (0.76)	3.40 (0.43)	4.08 (0.60)
Subjective norms	3.90 (0.72)	3.05 (0.63)	4.13 (0.55)	3.91 (0.60)	4.08 (0.56)	4.37 (0.45)
Perceived vulnerability	3.16 (1.08)	2.09 (0.82)	3.46 (0.96)	2.37 (0.73)	3.45 (0.75)	4.11 (0.87)
Feeling guilty	3.35 (1.35)	1.82 (0.86)	3.77 (1.14)	1.88 (0.47)	3.93 (0.70)	3.56 (0.89)
Vermicomposting training	0.66 (0.74)	0.06 (0.25)	0.83 (0.37)	0.28 (0.46)	0.90 (0.29)	1.00 (0.00)
Spraying safety	0.50 (0.04)	0.42 (0.50)	0.95 (0.22)	0.94 (0.23)	0.94 (0.24)	0.97 (0.18)
IPM	0.83 (0.37)	0.16 (0.37)	0.64 (0.48)	0.28 (0.46)	0.60 (0.49)	0.94 (0.25)
Age (years)	48.08 (10.07)	49.90 (9.63)	47.57 (10.18)	45.00 (12.28)	48.31 (10.33)	47.58 (8.50)
Horticultural experience (years)	23.37 (9.80)	25/40 (9.38)	22.82 (9.88)	20.00 (12.28)	23.76 (9.75)	22.58 (8.50)
Garden area (1000 meters)	1.84 (0.74)	1.87 (0.84)	1.83 (0.71)	1.89 (0.90)	1.79 (0.65)	1.87 (0.71)
Education (years)	12.19 (2.05)	11.96 (3.03)	12.25 (1.69)	10.83 (3.25)	12.46 (1/00)	12.64 (1.01)
Income (dollars)	62.67 (25.22)	74.59 (26.11)	59.34 (24.04)	56.25 (19.29)	56.85 (26.26)	66.12 (20.96)
Number of permanent workers (persons)	0.22 (0.41)	0.16 (0.37)	0.23 (0.42)	0.06 (0.23)	0.15 (0.35)	0.52 (0.50)

Logit regression analysis (for dichotomous dependent variable – vermicomposting participation; Model 1, Table 2) and ordinal regression analysis (for ordinal dependent variable – level of vermicomposting participation; Model 2, Table 2) were used to look at the factors that influence vermicomposting behavior. Due to the lack of a beneficial effect on the analysis, the demographic and socio-economic variables (age, horticulture experience, education, income, and number of working people in the family) were eliminated from the test. Only the rest of the independent variables are included in Table 2.

Table 2. Independent factors affecting vermicomposting.

Variables	Model 1 (Logit regression)			Model 2 (Ordinal regression)
	Vermicomposting participation (Model 1)			Level of vermicomposting participation (Model 2)
	Coef.	Std.Err.	t-value	Coef.	Std.Err.	t-value
Vermicomposting knowledge	0.024	0.029	0.726	0.097	0.027	12.51***
Attitude of vermicomposting	0.515	0.577	3.321**	2.498	0.723	11.943***
Subjective norms	1.746	0.826	4.470**	0.407	0.589	0.476
Perceived vulnerability	0.148	0.540	0.075	1.134	0.473	5.743**
Feeling guilty	0.026	0.549	0.002	0.941	0.376	6.276**
Vermicomposting training	2.160	1.031	4.389**	-0.857	1.604	0.285
Spraying safety	2.915	1.140	6.540**	0.429	2.122	0.041
IPM	1.793	1.015	3.120**	1.525	0.857	3.166*
Constant	-11.475	3.063	14.03***	-	-	-
Pseudo R2	0.529	-	-	0.757	-	-
-2 Log Likelihood	42.244	-	-	59.86	-	-

***p < 0.001; **p < 0.01; *p < 0.05.

Vermicomposting participation is influenced by attitude, subjective norms, vermicomposting training, compliance with safety rules during and after spraying, and IPM. In the neutral state, the constant coefficient also indicates that the sample people refuse to participate in such projects (β = −11.475). Variables whose t value is marked with ‘*’, ‘**’, or ‘***’ are significant. The coefficient indicates the direction of the relationship (positive or negative) and the level of influence of the independent variables on the dependent variable. For example, the feeling guilty independent variable, with a coefficient of 0.376 at 1% has a significant and positive effect on vermicomposting involvement level. In other words, the stronger the guilt feeling is, the higher the involvement in vermicomposting participation is. The R² value shows that the independent variables account for 52.9 percent of the variance changes in the dependent variable (vermicomposting participation), indicating a good prediction capacity of Model 1.

Knowledge (β = 0.097), attitude (β = 2.498), perceived vulnerability (β = 1.134), feeling guilty (β = 0.941), and IPM (β = 1.525) have a positive and significant effect on the level of vermicomposting participation. The R²= 0.757 value suggests that the independent variables can explain 75.7 percent of variance changes in the level participation of vermicomposting. This value indicated that Model 2 had a good capacity to predict the dependent variable.

3.2. Barriers to vermicomposting

Study 2 revealed a series of barriers to vermicomposting. They can be grouped into three main categories: financial and market, institutional and political, and informational and behavioral (Table 3).

Table 3. Barriers to the development of vermicomposting in garden.

Barriers to vermicomposting on garden
Financial and market barriers	Institutional and political barriers	Informational and behavioral barriers
Initial investment (high interest rates to set up drip irrigation or subsurface irrigation in the garden; cash for the purchase of necessary equipment – shredder, etc.); Time required to monitor production; Short term view; Lack of necessary infrastructure; Difficult sales	No support subsidy; The existence of legal barriers to production; Absence of permanent promotion policy; Lack of sufficient and continuous political will to support it	Lack of knowledge; Lack of experience; Fear of weed and disease risk; Uncertainty of the quality of the produced fertilizer; Lack of understanding of profitability

4. Discussion

4.1 Factors that influence vermicomposting participation and its level

Farmers’ participation in the vermicomposting can increase farmers’ income and improve organic waste management. Variables that stimulate vermicomposting participation and the level of involvement in vermicomposting, as well as barriers, should also be determined to develop and expedite the growth of vermicomposting among farmers.

Farmers have a moderate amount of acquaintance with vermicompost in terms of process and advantages (Table 1), which is a favorable situation because it means that for an activity that is not widespread (vermicomposting), the education-information efforts do not have to start from zero. As a result, it appears that most surveyed farmers have a sufficient understanding of vermicomposting. On the one hand, this is encouraging because in other countries, such as Ethiopia, small farmers were less aware of vermicompost benefits. They considered earthworms not useful for degrading organic wastes although they believed that they were good for soil fertility improvement (Gebrehana et al., 2022). On the other hand, it reveals space for improvement, especially when the aim is to increase the level of involvement in vermicomposting (because Model 2 showed knowledge stimulated the involvement level). The attitude towards vermicomposting has average level. Similarly, in China, about half of surveyed farmers had a positive attitude towards various agricultural waste management activities (Xu et al., 2022).

Results revealed both commonalities and differences between the two models that aimed to reveal the factors that predict involvement in vermicomposting (Model 1) and its level (Model 2). The differences between the sets of variables that predict the two vermicompost behaviors confirm that it was correct to analyze them separately.

The findings of the present study are in line with previous research that demonstrated that components of the TPB can assist recycling activity or predict the intention towards it (Edgerton et al., 2009; Tucker & Speirs, 2003; Zhang et al., 2021). Attitude toward vermicompost and IPM are major common determinants for vermicomposting participation (Model 1) and level of vermicomposting participation (Model 2). Results show that a positive attitude is the first step towards vermicomposting and a determinant of increasing the number of cycles, indicating that creating a favorable attitude is the entry point for developing this activity. This is in line with Zheng et al.’s (2019) results about Chinese farmers’ reaction to new technology (because we can consider vermicomposting involves a new activity and technology for farmers), who showed that farmers’ attitudes play the most important role in technology acceptance. Paul et al. (2017) analyzed the factors influencing farmer acceptance of technology. The findings revealed that socio-economic variables, level of education, and experience of farmers had a positive impact on technology acceptance, while age and specialized organizations had a negative effect. Attitude can be improved by showing the benefits of vermicomposting, such as a cheaper way to eliminate agricultural and also vegetal household food waste (Burke et al., 2023), economic benefits from its selling, improved soil health, etc.

The influential power of social norms on adopting vermicomposting suggests that it is necessary to highlight the positive opinion of important others about vermicomposting. The involvement of influential people in practical demonstrations for farmers and farmers sharing experiences about vermicomposting and its promotion through social media can help in this direction. Studies showed how social media increased awareness of environmental issues (Bentley et al., 2019; Wu et al., 2020).

In Model 1, the results show that vermicomposting training is beneficial for adopting vermicomposting. Similarly, a study on the results of training on women in the Indian Central Himalayas showed they adopted vermicomposting after training (Maikhuri et al., 2011). However, vermicomposting training cannot determine the level of involvement (Model 2). As a result, training is only effective for adopting vermicomposting, and other circumstances, the ones revealed by Model 2 and others, such as resource availability, may influence the level of involvement. Currently, training is mostly theoretical and should be extended to include a practical part. This will improve the training efficiency by allowing farmers to benefit from adapted guidance when they take action. Vermicomposting knowledge increases the level of vermicomposting participation. Previous studies suggested that knowledge ensures active participation in vermicomposting (Loan et al., 2019). Knowledge and attitude were found to be important for other sustainable waste behaviors, such as waste separation in Shanghai, China (Xiao et al., 2023). Among studied people, fact sheets (educational brochures) and educational booklets can help people assimilate more knowledge about vermicomposting and, thus, increase the level of participation. The existence of one environmentally friendly behavior (under the form of practicing IPM) stimulates the adoption of vermicomposting and increases its level. Similar results were revealed by Loan et al. (2019). This implies that when individuals are concerned about the environment, they are likely to support measures like vermicomposting. Therefore, efforts towards stimulating IPM can have a double positive effect by increasing both IPM and vermicomposting development. However, following spraying safety instructions has prediction power only in Model 1. In other words, farmers who manifest their care about their health and the environment through safe spraying are more likely to use a vermicomposting scheme in their yards. In exchange, perceived vulnerability and feeling guilty have prediction power only in Model 2. As Soorani and Ahmadvand (2019) implied, it is possible that not taking advantage of the available opportunities makes them feel guilty and try to avoid this feeling by increasing the vermicomposting level. These findings suggest that vermicompost promotion programs should focus on intensifying the feelings of vulnerability and guilt among people who already adopted vermicomposting along with using other factors (such es economic ones) that target to increase the level of vermicompost adoption. Subjective norms affect the behavior only in Model 1 (i.e. vermicomposting participation), demonstrating that the influence of peers is essential in the decision to get involved in vermicomposting, but after this happens, this factor is not powerful enough to determine farmers to increase the number of cycles.

4.2 Barriers to vermicomposting on garden

The initial investment was one of the most powerful barriers to vermicomposting participation highlighted by participants to Study 2. Farmers cannot carry out vermicomposting without a diagonal or subsurface irrigation system, and vermicompost cannot be produced in gardens without irrigation. Vermicomposting requires sufficient space. Other studies mentioned this fact as a barrier to vermicompost (Sarpong et al., 2019). However, this is not the main problem in the studied population because space is usually available between the trees in orchards. The problem is that the orchards in the area are irrigated using a flooding system. The use of flood irrigation system limits the possibility of fertilizer production by the farmer because the necessary space for this purpose is not available for the farmer among the garden trees. As a result, farmers cannot participate in vermicomposting in a long-term manner. Using drip and subsurface irrigation to produce vermicompost and horticultural products simultaneously is particularly efficient in terms of project implementation and water conservation. As a result, one of the barriers to the development of vermicompost production in orchards is the lack of initial cash required to set up a drip and subsurface irrigation system. While the weather is partially a barrier to vermicomposting because it imposes the need for irrigation, it is favorable to producing worms for vermicompost production. For example, Eisenia Fetida worm, used for this purpose, is easily available on the market. Because of this, specialized companies that sell composting worms are operating in Iran, including in the studied region. In addition, the investment must include machines, such as a shredder. The option of low-interest rates for loans was also not available. Moreover, during the interviews, it was revealed that many farmers ceased to produce vermicompost after just one batch. The insufficiency of garden facilities for the generation of vermicompost was one of the reasons.

According to most participants, the lack of subsidies to start this activity on garden is one of the existing institutional and legislative hurdles to its development and one of the main barriers to starting this activity. Other studies also pointed to the lack of a legal framework for supporting equipment acquisition in the case of composting in general (Zhou et al., 2022). To be effective, a subsidy system for vermicomposting should consider the scale of the operation and offer support to the specific need of each scale, from small garden composting to big producers; it should also be conditioned by compliance with regulations and best practices; furthermore, it can incentivize partnership between stakeholders, sharing resources, and cooperative efforts.

Another major barrier to vermicompost production on garden, according to interviewees, is farmers’ perception of vermicompost’s low profitability. They assumed that making vermicompost was significantly more expensive than buying it already manufactured. Having a long-term perspective on the subject of vermicompost on garden can be very advantageous compared to a short-term outlook. In addition, the lack of customers for farmers’ vermicompost prevents them from taking action in this direction. According to the interviews, an important barrier to long-term participation in vermicompost production on garden is that farmers are unaware of the profitability and benefits and how these can develop in time. Various studies assessed the profitability of compositing and found it can be profitable in the long term, even for small farmers, and that it can bring substantial revenues to big vermicompost producers (Lim et al., 2016; Zhou et al., 2022) and that there can potential for scaling up following the examples in other countries (Furlong et al., 2017), which points to the suitability of the creation of community centers for vermicomposting.

The results of this study should be considered in the context of several limitations. One is related to the limited setting of our study, because only one geographical area was investigated. Although this is an important agricultural location of the country, and others are unsuitable for this activity, a future study can consider more agricultural regions. However, despite the findings being based on a case study in the Khomeini-Shahr county, Iran, they can be relevant to an international audience. One reason is that the mixed method approach of this study, combining the survey and interviews, can be used in other regions, too. Furthermore, the research findings can be transferred to other regions or countries with similar agricultural contexts, thus serving as a valuable reference point for researchers, practitioners, and policymakers. The localized context about specific drivers and barriers that influence vermicomposting adoption can inform the design and implementation of policies and interventions at various levels beyond the studied area. The study can also serve as input for a comparative analysis with other regions or countries. It can, thus, contribute to cross-regional knowledge sharing and identification of best practices and unveil the influence of local contexts on adopting vermicomposting, hence, supporting the efforts to promote sustainable farming practices worldwide. Because of the large number of variables, some have only one item, and a future study can consider more items and variables. A research direction worthy of investigation is to observe differences between the factors influencing vermicompost participation for people who do this for the first time and factors that influence its re-adoption after abandoning this activity. Another research direction is to study the recommendations suggested here regarding their support by stakeholders and their impact on the agricultural sector.

5. Conclusion

The study identified the factors influencing the adoption of vermicomposting, its level, and the barriers in front of it using a mixed-methods approach with a TPB-PMT integrated model and interviews. Thus, the study brings to light the specific challenges and motivations the Iranian farmers face in adopting vermicomposting, a sustainable agricultural waste management practice. The findings of this study can be used by decision-makers to adopt policy measures that support vermicomposting on garden.

According to the study results, many farmers were enthusiastic about vermicomposting at some point, with 78% of the sample participating in the vermicomposting on garden during a certain period, while 22% did not. The survey results revealed what factors predict farmers’ adoption of vermicomposting and the level of their engagement. More to the point, attitude toward vermicomposting, subjective norms, training, and environmentally friendly behavior (safe spraying and IPM) influence farmers’ decision to get involved in vermicomposting. The relevant local organization should strengthen the positive attitude towards vermicomposting by emphasizing the benefits of vermicomposting, not only for personal gain but also for a cleaner environment, in addition to employing flyers to improve awareness and attitudes about vermicomposting. While vermicomposting training has a statistically significant effect on farmer participation, this component does not appear to help boost participation levels, while knowledge does. Theoretical vermicompost training should be translated into practical training events for farmers, such as field classes. Those in charge might consider arranging for experts to visit the gardens regularly to increase engagement. Furthermore, environmentally friendly behaviors (such as IPM) can increase the level of vermicomposting participation.

The interviews in Study 2 revealed a high number of barriers that hinder farmers’ engagement in vermicomposting in orchards, pointing to the complexity of the problem and the need for a well-structured strategy to overcome them. The initial investment in irrigation systems, the purchase of necessary equipment, a short-term vision, the time required to monitor production, difficult sales, the lack of subsidies, the lack of experience, knowledge, and awareness of profitability, fear of weeds and disease, confusion regarding fertilizer quality, the lack of a permanent promotion policy, and the lack of sufficient and consistent willpower are factors to be removed or at least diminished through coherent programs. Understanding what are the specific barriers farmers experience is valuable for informing policy decisions, guiding educational activities, fostering collaboration among farmers, and supporting sustainable agricultural practices.

5.1 Practical and policy recommendations

Finally, five types of recommendations are offered based on the findings of the quantitative and qualitative studies to remove the identified barriers. The first recommendation is to look at different vermicomposting methods, such as industrial, semi-industrial, or small-size at the small farm level and identify improvement possibilities. Currently, vermicompost is nearly entirely produced by semi-industrial firms or farmers in their gardens. Outsourcing the garden vermicompost production process to a service provider is one possibility. These service groups will regulate and supervise the vermicomposting process on the garden. This production method eliminates some barriers, such as the need for the farmer to devote a significant amount of time to vermicompost production and the need to purchase appropriate equipment, such as shredders and other machinery. Furthermore, it eliminates the information barrier, i.e. the lack of knowledge and experience, highlighted by Model 2, to influence the level of involvement in vermicomposting. Collaboration between diverse farmers, environmental experts, and other stakeholders interested in environmental management could be another potential approach to producing vermicompost. Biomass that is not ideal for a vermicomposting company (due to seasonality, small production volumes, or lengthy transportation distances) can be concentrated in a ‘local biomass center’ or a cooperative where the biomass of various partners is vermicomposted. Individual farmers may benefit from reducing time and production and transportation costs by organizing vermicompost production. Furthermore, the cost of obtaining the necessary vermicomposting equipment, initial fixed investments, and other required tasks can be split among the participants. A bigger amount of supplemental biomass (green / brown) can be delivered to the cooperative with the assistance of relevant partners. Farmers who do not want to join participatory activities can still provide vermicompost and manure or do individual activities such as establishing worm towers among garden trees and feeding earthworms. Two policy suggestions related to this practical recommendation appear. One is to develop the legal framework that facilitates the collaboration between the current big producers of vermicompost and small farmers by making vermicomposting more attractive financially and raising awareness of its environmental benefits among small farmers. Another is to elaborate regulations and provide incentives for creating and functioning a ‘local biomass center’ or cooperative.

The second recommendation is that farmers use biomass from tree cutting and weeding to produce biofertilizers through vermicomposting. Currently, this biomass is mainly burned. More restrictive regulations regarding the burning of this biomass associated with their enforcement and provision of solutions for their disposal, such as delivering biomass to certain producers or contributing to a ‘local biomass center’ or a cooperative, can foster vermicomposting.

The third recommendation is to improve the current policies and institutional structures regarding vermicompost production and application. This can be done by adapting them to the current situation, increasing their flexibility, and simplifying their implementation. Simple and feasible legal and administrative procedures that support vermicompost production on garden should be elaborated.

A fourth recommendation is to create market support and incentives for vermicompost products. An important policy and institutional need is the creation of a legal classification of biomass types based on their intended use (by the end-user) (especially when farmers intend to sell their vermicompost). Furthermore, package labels indicating the properties of the biofertilizer might assist and persuade the end-user to select the appropriate product. This approach has been used in the Netherlands since 2016. They utilized labels to distinguish between biofertilizers, which allowed the farmer-producer and farmer-user to understand better the properties of vermicompost (Viaene et al., 2016). As a result, farmers will better understand the quality of biofertilizer, potentially lowering price variations for all types of biofertilizers.

The fifth recommendation is to improve farmers’ vermicomposting knowledge and experience. Farmers are sensitive to educational and information activities provided by the agricultural extensions. Thus, these bodies should carry out awareness-raising activities and programs to boost farmers’ acquaintance with vermicompost and vermicomposting on garden. Policies can prioritize awareness-raising campaigns about vermicomposting and its benefits for crop productivity and soil health, and provide technical support and training programs for farmers. Policy support for technical assistance, workshops, and demonstrations can increase farmers’ confidence and skills in implementing vermicomposting, thus, facilitating its adoption. By implementing these policies, decision-makers can create an enabling environment for farmers to adopt vermicomposting, leading to sustainable agricultural waste management.

Declaration of interest statement

The authors report there are no competing interests to declare.

Acknowledgments

This paper was partially elaborated within the research program ‘Identification of composting opportunities from the point of view of consumer behavior to promote and develop the circular economy’, selected within the bilateral cooperation between the Romanian Academy and Wallonia – WBI, FRS-FNRS. ‘La présente publication a été rendue possible grâce à l’Accord qui lie WBI, le FRS-FNRS et l’Académie Roumaine.’

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The datasets generated during and/or analyzed during the current study are available from the first author upon reasonable request.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

No funding was received to assist with the preparation of this manuscript.

Notes on contributors

Hamid Rastegari

Hamid Rastegari holds a master in Rural Development (2016) from Yasouj University, Iran, and a PhD in Agricultural Development (2022) from Yasouj University, Iran. His research interests include behavior change and sustainable consumption, mainly related to agricultural practices, food, and waste.

Mehdi Nooripoor

Mehdi Nooripoor holds a master in Agricultural Extension and Education from Shiraz University, Iran, a PhD in Agricultural Extension and Education from Shiraz University, Iran. He is associate professor at Yasouj University, Iran. His research interests include climate changes, vulnerability, and sustainability.

Maryam Sharifzadeh

Maryam Sharifzadeh holds a master in Agricultural Extension and Education from Shiraz University, Iran, a PhD in Agricultural Extension and Education from Shiraz University, Iran. She is associate professor at Yasouj University, Iran. Her research interests include social issues in agriculture and natural resources.

Dacinia Crina Petrescu

Dacinia Crina Petrescu holds a master in Marketing (2001) from Complutense University, Spain, a PhD in Economics (2003) from Babes-Bolyai University, Romania, and a Habilitation in Business (2021) from Bucharest University of Economic Studies, Romania. She is professor at Babes-Bolyai University, Romania, and associate researcher at Liege University, Belgium. Her research interests include behavior change and sustainable consumption, mainly related to food, agricultural practices, land use, and waste.

Appendix

Table A1. Variable used in the study and related questions in the questionnaire.

	Variabactles	Question in the questionnaire	Answer options/ Answer codes
	Dependent variables
	Vermicomposting participation	Are you producing vermicompost on your land?	0 = I am not producing vermicompost 1 = I am producing vermicompost
	The level of vermicomposting participation	How many times are you producing vermicompost on your land?	1 = Once a year = low level of participation 2 = Twice or three times a year = medium level of participation 3 = Four or more times a year = high level of participation
	Independent variables
	Vermicomposting knowledge	Definition: ‘Vermicomposting technology is recycling organic matter’ ^1 ‘Earthworms are a key role in vermicomposting’ ^1 ‘There is no need of bed with shade, raw organic material, earthworms, and water in prepare the vermicompost’ ^1 Process: ‘The bed should not be on a raised platform’ ^1 ‘The bed should not have shade over it’ ‘We can use large riffage, cereal straws, dry leaves, animal dung, fresh green leaves, etc. as raw material’ ^1 ‘These materials can be used directly in the bed without any pretreatment’ ‘A special variety of earthworms responsible for vermicomposting’ ^1 ‘Water is not needed in preparation of vermicompost’ ‘We can add raw material in the bed daily’ ‘Humidity required for the bed is 60–70%’ ^1 ‘Vermicompost is ready when earthworms come on surface of the prepared compost and has black color’ ^1 Advantages: ‘Vermicompost can be use as soil amendment to increase organic matter in the soil’ ^1 ‘Vermicompost does not feed microbial life in the soil’ ‘Vermicompost provides nutrients for plants’ ^1 ‘Vermicompost respects organic farming principles, providing safe food’^1	0 = Farmer gave the wrong answer 1 = Farmer gave the correct answer
	Attitude towards vermicomposting ^2	‘Vermicomposting is good for the environment’ ‘Vermicomposting should be more promoted’ ‘Vermicomposting is a useful activity’ ‘I have a favorable attitude toward vermicomposting’	1 = I strongly disagree, … ., 5 = I strongly agree
	Guilt feeling related to less friendly environmental behavior ^3	‘If I leave recyclable materials on garden, I feel guilty’ ‘If I do not follow the principles of harvesting, storage, and product transportation, I feel guilty’	1 =  I feel very low guilt feeling, … , 5 = I feel very high guilt feeling
	Subjective norms ^4	How much do the following persons encourage you to produce vermicompost? Family Other farmers Agricultural magazines Agricultural service companies Agricultural promoters Vermicompost companies	1 =  I receive very low encouragement from them, … , 5 = I receive very high encouragement from them
	Perceived vulnerability to chemical fertilizers and pesticides ^5	‘I use chemical pesticides at a standard amount’ ‘I do multifunctional agriculture on my garden’ ‘I use chemical fertilizer at a standard amount’ ‘I should use more organic fertilizers (vermicompost and compost) because the farm is damaged regarding soil, crops, and water consumption’	1 = I strongly disagree, … ., 5 = I strongly agree
	Vermicomposting training	Have you followed training about how to do vermicompost and its benefits?	0 = I did not follow a training 1 = I followed a training
	Attention to safety during and after spraying	Have you followed the safety protocols during and after spraying for yourself and the surroundings?	0 = I did not follow the safety protocols 1 = I followed the safety protocols and
	IPM	Do you practice integrated pest management (IPM)?	0 = I did not practice IPM 1 = I practiced IPM
	Demographic and socio-economic variables
	Age (years); Horticultural experience (years); Garden area (1000 meters); Education (years); Income (million Rials); Number of permanent workers (persons).

¹ These are true statements.

² Cronbach's alpha coefficient was used to assess attitude reliability, and it was found to be 0.64, indicating a correlation between cases.

³ The correlation between the two guilt questions was determined using Cronbach's alpha coefficient (α =  0.94), demonstrating the questions’ reliability.

⁴ Cronbach's alpha coefficient, α = 0.80, indicated questions’ reliability.

⁵ Cronbach's alpha coefficient, α = 0.89, indicated good reliability.