2.4.1 Phase 1 (Qualitative analysis of baseline and endline interview data).

As recommended by Jenkins et al. (2018) [18], a detailed field log was used to document and track interactions with farmers, record personal market observations, plan interviews, and compile lists of recurring research topics. The key informant interviews (KIIs) were then transcribed and coded using MAXQDA 24, which supported a thematic, deductive approach [53]. An inductive coding process was then conducted, analyzing each transcript line by line to generate focused codes and develop a systematic category framework. Using this rigorous qualitative approach, two main theoretical themes (TAM, TPB) and 3,632 different codes were identified, ensuring a nuanced understanding of the baseline and endline data and enhancing the depth of the study. The initial codes were systematically reviewed, refined, and clustered into approximately 300 refined codes, grouped under the main theme constructs.

2.4.2 Phase 2 (Quantitative analysis of pre-post-intervention data).

Both pre- and post-intervention data on overall yield and intention to adopt were analyzed using a quantitative approach. To assess the effect of training on OFSP yield among adopter farmers, a two-way mixed analysis of variance (ANOVA) was performed using SPSS. This technique allows us to examine the interaction between training status and prior intention to adopt on OFSP adoption behavior. A similar strategy has been applied in previous studies to assess the impact of interventions on agricultural productivity [54,55]. In this study, experimental conditions (trained vs. not-trained) and adoption status (adopter vs. non-adopter) were considered fixed factors. As such, we assessed the main effects, i.e., the direct effect of training (trained vs. not-trained) and adoption status (adopter vs. non-adopter) on OFSP yield, as well as the interaction effects, i.e., how the combination of training and adoption status influenced adoption behavior and yield. To identify specific group differences, Tukey’s post hoc test was conducted for pairwise comparisons. Before conducting the ANOVA, key assumptions were verified. Normality of residuals was assessed using the Shapiro–Wilk and Kolmogorov–Smirnov tests, which indicated no significant deviations from normality (p > 0.05). Homogeneity of variances was tested using Levene’s test, which confirmed equal variance across groups (p > 0.05) [56]. These results validated the use of ANOVA for the analysis. Therefore, the test results presented in the results section are based on data that met the underlying statistical assumptions. This integrated approach, combining qualitative and quantitative insights, provided a comprehensive understanding of how training influenced OFSP adoption (intention) and OFSP yield of smallholder farmers in Ethiopia.

3.1.1 Experience with OFSP.

In the study area, farmers were already familiar with cultivating white-fleshed sweet potato varieties before OFSP was introduced. These conventional varieties were mainly grown for household consumption and as a supplementary food source, especially during lean seasons. This prior experience with sweet potato cultivation provided a useful reference for farmers when evaluating OFSP, helping them compare its agronomic performance, taste, and market value with traditional varieties.

Pre-intervention farmers’ engagement with OFSP varied substantially. Some had never cultivated it (n = 29), citing priorities for cash crops, a lack of planting material, or the absence of formal agronomic training. Others learned informally, such as by observing neighboring farms or relying on traditional knowledge. A few received nutrition-related training from initiatives like the Train-the-Trainer program from Haramaya University, the regional government, covering the process from planting to harvesting. Extension services and community knowledge-sharing played a significant role in disseminating effective cultivation practices, including pest control and harvesting methods. A male respondent aged 34 noted: “Yes, I have grown OFSP on my farm in the past. Although I have not received any formal training, I have gained practical experience and knowledge by interacting with other experienced farmers in my community”. The experiences of the farmers in this study are consistent with the results of previous research on the adoption of biofortified crops. Studies have shown that access to high-quality planting material and effective extension services are critical factors for adoption. Bouis & Saltzman (2017) [59], for example, it has been highlighted that biofortification efforts need to be supported by robust seed distribution systems and farmer training programs to ensure successful adoption.

3.1.2 Consumption.

Prior to the intervention, farmers who consumed OFSP appreciated its flavor, nutritional benefits, and ease of preparation. Many reported eating it regularly due to its early maturity, food security benefits, and dietary variety. A 33-year-old female farmer noted: “We eat OFSP several times a week for its taste and health benefits”, while another highlighted its reliability during food shortages. However, non-adopters cited unfamiliarity, lack of traditional integration, and limited knowledge about preparation methods. Some farmers remained reliant on staple crops like maize and beans, indicating a need for more awareness of OFSP’s dietary versatility. These responses align with studies that emphasize cultural acceptance and awareness as key factors in the adoption of biofortified crops [60,61].

3.1.3 Barriers and drivers to OFSP adoption.

Prior to the intervention, the study revealed that peer pressure within the farming community played a significant role in influencing adoption (intention), as summarized in Table 2. Both adopters and non-adopters observed others successfully cultivating OFSP, which encouraged them to plant the vines, fostering a sense of community expectation and shared learning. This aligns with previous studies highlighting the role of social influence in agricultural technology adoption [62]. In addition, their children’s enthusiasm and fondness for the crop motivated several farmers, emphasizing the importance of growing a crop that their families like and find useful, as noted in previous research [61]. The economic potential and nutritional benefits of OFSP were also important motivating factors [63,64], especially when the availability of free vines reduced the initial investment costs, reducing financial barriers to adoption, which aligns with findings from previous studies on input subsidies and technology uptake in smallholder farming [65].

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 2. Perceived barriers and drivers of farmers’ intention to adopt OFSP.

https://doi.org/10.1371/journal.pone.0340709.t002

Despite the recognized benefits of OFSP, several barriers hinder its widespread adoption among both OFSP adopters and non-adopters. Most farmers reported difficulties in obtaining OFSP vines, which are primarily sourced from research institutions, universities, or neighboring farms. The lack of high-quality planting material restricts new farmers from trying the crop and limits the expansion of existing cultivation. While some OFSP adopters gained knowledge through extension services or informal networks, many lacked formal training in OFSP cultivation. The absence of structured guidance on planting techniques, pest control, and post-harvest handling posed challenges, making farmers hesitant to adopt the crop. Some OFSP adopters prioritized high-value cash crops over OFSP, viewing them as more profitable and marketable. The perception that OFSP is primarily for household consumption rather than commercial sale reduced its appeal to farmers seeking immediate economic returns. OFSP adopters identified pest infestations and the need for careful early-stage management as obstacles to successful OFSP cultivation. Unlike traditional staple crops, with which adopters are more familiar, managing OFSP requires additional effort, thereby discouraging adoption. Farmers also faced challenges in selling OFSP due to limited market linkages and fluctuating demand. Some reported difficulties in finding buyers, while others struggled with the perishability of the crop, which necessitated timely marketing and efficient storage solutions. Non-adopters cited unfamiliarity with OFSP and a lack of traditional integration into local diets as barriers to consumption. Some farmers and consumers preferred staple crops such as maize and beans, which are deeply embedded in their food culture. Limited knowledge of preparation methods further reduced interest in OFSP adoption. These findings align with previous research on biofortified crop adoption, which emphasizes the importance of robust seed distribution systems, extension services, and community networks [62,64]. Studies in Mozambique and Tanzania similarly found that nutritional benefits, yield stability, and economic potential drive OFSP adoption [15,60,65,66]. As noted by Sheoran et al. (2022) [67] and Mwiti et al. (2020) [14], sustainable adoption of OFSP depends on quality inputs and support. As Sulaiman et al. (2020) and Samuel et al. (2025) suggest, collaboration between stakeholders is critical to overcoming these barriers and positioning OFSP as a key crop for improving food security and nutrition in similar regions.

3.2.1 Knowledge.

Pre-intervention farmers recognized the nutritional and agronomic benefits of OFSP, particularly its high vitamin A content, economic advantages, and cost efficiency. Knowledge about OFSP was primarily disseminated through fellow farmers, agricultural extension workers, university staff, and various media channels, including radio. Extension agents played a vital role in introducing OFSP; some farmers learned about it through formal programs, while others received information informally through community interactions. The resilience of OFSP, characterized by its adaptability to various soil and climate conditions, as well as its low input requirements, was often cited as a reason for interest in the crop. This perception aligns with existing literature that emphasizes OFSP’s resilience to drought, low fertilizer requirements, and minimal need for intensive farming methods, ultimately reducing production costs and labor demands [67]. Additionally, the crop’s good flavor was frequently cited as a factor enhancing its appeal for both household consumption and marketability, confirming earlier findings by (Laurie et al., 2018) [68]. Despite these advantages, some farmers had limited familiarity with OFSP, underscoring the need for more comprehensive awareness-raising interventions. Moreover, the significance of indigenous knowledge transfer and community networks in agricultural innovation is well-documented. [69] emphasized in his theory of the Diffusion of Innovations (DOI) that interpersonal networks are essential for the spread of new agricultural practices. The fact that farmers in this study relied on traditional knowledge and community interactions supports this theory, suggesting that enhancing these informal networks could promote greater adoption of OFSP. After the intervention, trained farmers perceived they had a better understanding of proper cultivation techniques, including optimal planting times and methods for OFSP. They stated to have gained knowledge on pest and disease control, improving soil fertility, and the effective use of fertilizers. This aligns with previous studies that emphasize the importance of training and knowledge dissemination in improving agricultural practices and productivity [70,71].

3.2.2 Perceived ease of use.

Before the intervention, both the adopters and non-adopters considered certain aspects of OFSP cultivation to be manageable, citing good land suitability, low labor requirements, and simple preparation methods as advantages. After the intervention, the PEOU changed among trained adopters and non-adopters. These farmers highlighted access to agronomic training and trusted sources of vines, the ease of production and propagation of the crop, and its resilience to environmental conditions as key enablers. Trained farmers perceived that the training provided practical skills to overcome previously challenging aspects of OFSP cultivation, which is consistent with the findings in past literature Devaux et al. (2018) and Mwangi and Kariuki (2015) [72]. Although some challenges remained, such as the lack of local vine propagation centers, limited irrigation, and land constraints to larger-scale production, farmers perceived that the intervention established the foundation for improved adoption and better yields, supporting the conclusions of Feder et al. (1985). In contrast, untrained adopters and non-adopters primarily associated ease of use with factors such as cost-effectiveness, perceived nutritional benefits (awareness motivating adoption despite limited technical knowledge), and cultural acceptability. Although they received free vines, they continued to struggle with technical knowledge gaps and limited access to planting material. Their perceptions of simplicity continued to focus on the availability of inputs rather than improved cultivation practices, indicating limited understanding of agronomic techniques among untrained farmers. These findings support the existing literature, which emphasizes the need to combine input provision with agronomic training to ensure effective and sustainable adoption [73].

3.2.3 Perceived usefulness.

Before the intervention, both OFSP adopters and non-adopters recognized several key attributes of OFSP, including its high nutritional quality (particularly the beta-carotene content), pleasant taste, vibrant color, and early maturity, which enables multiple harvests within a season. These characteristics were valued for their potential to enhance food security and address malnutrition. This aligns with previous research that emphasizes the significance of high-yield potential, nutritional value, and adaptability in crop selection, as these attributes support food security, economic growth, and sustainable agricultural practices [15,16,18,19,51]. After the intervention, farmers’ practices and perceptions improved. Trained farmers began to associate OFSP more strongly with concrete yield improvements, economic returns, and broader nutritional benefits. This shift reflects a deeper and more practical appreciation of the crop’s value, as training equipped farmers with agronomic knowledge that translated perceived crop potential into observed or anticipated outcomes. This positive change in perception is consistent with studies that emphasize the value of agricultural education in increasing productivity and market access [74–76]. In contrast, the untrained farmers’ perceptions remained unchanged, focused on the crop’s inherent characteristics (e.g., yield and nutrition) rather than enhanced practices or market access. This suggests that training was instrumental not only in reinforcing existing perceptions but also in expanding farmers’ understanding of OFSP’s broader utility and performance in real farming conditions, confirming the role of training as a driver of both perception change and potential behavior change.

3.2.4 Attitude toward OFSP and OFSP adoption.

Prior to the intervention, farmers’ attitudes toward adopting OFSP, particularly among non-adopters, were mainly influenced by external influences, such as community perceptions and peer acceptance, rather than direct experience with the crop. However, in line with literature [30], these attitudes were often not consistent with adoption behavior, as socially entrenched resistance to new crops required a critical mass of community members who accepted or expected the cultivation of OFSP for attitudes to effectively predict adoption. The adopters associated OFSP’s bright color with nutritional benefits, particularly for eyesight and well-being, and expressed optimism about OFSP’s potential to improve household nutrition, consistent with findings [14]. After the intervention, both trained adopters and non-adopters perceived OFSP as a valuable economic opportunity, reporting improved attitudes toward its ease of cultivation, short growing cycle, and adaptability. These findings align with findings from previous research [17,21].

3.2.5 Subjective norms.

Prior to the training, both adopters and non-adopters reported that their peers favored OFSP cultivation primarily due to its nutritional benefits and potential to increase income. However, social approval was limited by barriers such as high initial investment costs, limited access to information, and land constraints, which hindered uptake.

After training, subjective norms remained strongly positive, and all the trained farmers continued to perceive other peer farmers’ OFSP acceptance as driven by economic, agronomic, and nutritional benefits. This suggests that training not only validated positive social norms but also amplified them by providing tangible results. In contrast, not-trained non-adopters still perceived that their peers struggled with pest and disease management, inconsistent vine access, and market issues, indicating that the lack of training limited their exposure to successful examples or solutions. Similarly, trained adopters identified technical knowledge gaps as an ongoing perceived barrier among their peers, emphasizing that training helped them recognize and address challenges that others still face. Such patterns are also reflected in the work of Rasanjali et al., 2021, who observed that as farmers gain knowledge and resources often through structured interventions like training, their decision-making becomes more attuned to both social perceptions and practical limitations. Subjective norms, as emphasized in the TPB framework, significantly influenced farmers’ decisions to adopt OFSP. Social influences from family, peers, and community discussions can indeed play a vital role in shaping attitudes by highlighting the nutritional and market benefits of OFSP [30].

3.2.6 Perceived behavioral control.

Before the intervention, OFSP adopters acknowledged gaps in their knowledge of OFSP cultivation, while non-adopters expressed uncertainty about their ability to tackle key challenges, such as pest control and limited access to vines. The confidence of non-adopters in adopting OFSP was primarily influenced by the observed benefits and success stories of early adopters, which helped establish positive social norms. These correlations are also reflected in the work of Mwanga & Ssemakula (2011), who noted that this optimism was not always matched by a practical willingness to adopt.

After the intervention, all trained farmers reported a significant boost in their confidence in successfully growing OFSP. Farmers felt that the training enhanced their technical knowledge, improved their problem-solving skills, and provided clear explanations of best practices in pest management. They believed that the training empowered them to take control of key production variables, reinforcing their confidence in their ability to maintain OFSP cultivation. These findings align with previous research, which underscores the significance of continuous learning, risk-taking, and institutional support in strengthening perceived behavioral control and facilitating long-term adoption [35,77–79]. To provide a concise overview of how the agronomic training influenced key behavioral determinants, Table 3 summarizes the main pre- and post-training differences across the TAM and TPB constructs covered in the above sections.

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 3. Summary of key pre- and post-training differences in TAM and TPB constructs.

https://doi.org/10.1371/journal.pone.0340709.t003

3.3.1 The role of training on behavioral intention.

Before the intervention, non-adopters expressed their intention to adopt OFSP due to its nutritional value, affordability, and yield. Meanwhile, OFSP adopters indicated their commitment to continue their adoption, driven by personal factors, such as knowledge about the crop, experience, and confidence in OFSP cultivation. This aligns with the farmer study on OFSP by Adekambi et al., 2020. Of the 33 farmers trained, 17 were already adopters before the intervention, while the remaining 16 were non-adopters. After receiving agronomic training as part of this study, all 16 trained non-adopters began cultivating OFSP, highlighting the critical role of comprehensive agronomic training in influencing farmers’ adoption behavior. Trained OFSP adopters and non-adopters exhibited more proactive participation in OFSP cultivation. They actively sought information, accessed agricultural extension services, and participated in knowledge-sharing farmers’ networks, demonstrating greater confidence in managing cultivation challenges. These behavioral changes indicate a more profound commitment to improved agricultural practices, aligning with previous findings that link farmer engagement to better agricultural outcomes [15]. For trained OFSP adopters, the intention to continue OFSP adoption was motivated by increased yield, past experience with producing the crop, and its nutritional value. For trained non-adopters, the willingness to adopt stemmed from market demand for the crop and success stories from trained adopters.

Extension workers’ emphasis on the productivity and market value of OFSP further influenced the adoption decisions of trained farmers. Positive experiences with other improved root crops also motivated some non-adopters to experiment with OFSP. Moreover, agronomic training enabled one trained farmer to independently multiply and distribute vines to nine additional farmers outside the original sample. This initiative not only promotes community collaboration but also helps mitigate the risk of vine theft by increasing local access to resources.

However, not all farmers adopted. Six farmers, including one trained adopter and five untrained non-adopters, decided not to plant the vines. Their reasons included a general dislike of the crop, viewing OFSP as unimportant, vine theft, concerns about land use efficiency, and dissatisfaction with vine quality. The trained farmer expressed concerns about efficient land use, while the untrained farmers primarily highlighted the low quality of the vines and the issue of vine theft. These varied responses highlight the impact of individual preferences, psychological and social dynamics, and economic factors on adoption behavior.

3.3.2 The effect of training on OFSP yields.

While prior research (e.g., [18]) has acknowledged the role of training in agricultural technology adoption, this study also aims to provide empirical indications of its impact on OFSP yield. The provision of training led to significant agronomic benefits (yield) as shown by the trained farmers reporting higher yields, a better crop quality, and a better resistance to pests and diseases (see Fig 2). Before the intervention, baseline yields of OFSP adopters ranged from an average of 18.83 tons/ha for those in the not-trained group to an average 25.33 tons/ha for those in the trained group. After the intervention, trained adopters achieved a yield of 30.33 tons/ha (an average increase of 5 tons/ha), while not-trained adopters achieved 21.16 tons/ha (an average increase of 2.32 tons/ha). At the level of the non-adopters, those trained achieved 24.18 tons/ha on average, compared to an average of 21.54 tons/ha for those non-trained, showing that the training intervention resulted in yield increases for trained farmers, both adopters and non-adopters. These results are consistent with research findings indicating that access to quality inputs and training is critical to improving crop performance and productivity [80].

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Fig 2. Yield ton/ha between trained and not-trained OFSP adopters and non-adopters.

https://doi.org/10.1371/journal.pone.0340709.g002

The results of the two-way mixed ANOVA (see Table 4) further indicate that training has a statistically significant effect on yield (F = 4.43, p = 0.039) and intention to adopt (F = 66.41, p < 0.001). In addition, a significant interaction effect was found between adoption status and training status (F = 4.93, p = 0.010), indicating that the effect of training on yield was greater for farmers with a previous OFSP adoption status, such as adopters, compared to non-adopters. In summary, the results suggest that both training and adoption intention have a statistically significant effect on yield, with a notable interaction between the two factors, as all p-values were below the 0.05 threshold.

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 4. Two-way mixed ANOVA results of the role of training on OFSP yield of adopters and non-adopters.

https://doi.org/10.1371/journal.pone.0340709.t004