3.1. Demographic Characteristics of Farmers
All sampled farmers responded to the questionnaire, i.e., the response rate was 100%. Of the sampled population, 55.4% were females (
Table 1). The predominance of women involved in urban agriculture in four out of the six studied areas runs counter the reports of Kenmogne et al. [
32] and Saidou and Pritchard [
33], who observed stronger male-dominated farmer communities in the Nkolbisson, Mokolo, and Nkolondom areas of Yaoundé, respectively.
The lower participation of men in urban agriculture nowadays may be explained by the increasing job diversification of male farmers in Africa and beyond. Since women are often more involved in the family food supply, this could improve households’ nutrition as vegetables are often produced by women in home gardens [
34]. Half of the farmers who participated in our study were married and had completed at least secondary education. Yet, the education level of other respondents was quite low, since only 39% of the respondents had completed primary school and 8% of the respondents were illiterate. This may be the result of the rural exodus that brings youths from the villages to the city. Low education levels may affect the capacity to understand many complex issues regarding the safe management of farming practices, and thus, ultimately affects farming productivity. Such an impact of farmers’ education background on farm productivity was also found by Paltasingh and Goyari [
35] in their study on farmer education on farm productivity under varying technologies in India.
The main purposes of urban farming are enhancing the income of households (62%), improving food supply (9%), and lowering unemployment (35%). We noted that only a few participants continue farming because of family habits (27%), e.g., inheriting a farm or farmland.
The age of the participants ranged from 18–76 years, with an average of 44 (±15) years, and in all the different study areas, the mean age exceeded 40 years (
Table 2). This corroborates findings by Sotamenou and Parrot [
14] on the adaptation of compost in urban agriculture in Yaoundé and Bafoussam, Cameroon. A previous study in Yaoundé communities reported that the average age of farmers ranged between 34–36 years [
14]. In addition to unemployment and the feeding lifestyles, the level of responsibility of the people aged 18–76 years might be another reason for the high implication of farmers age ranges in vegetable production in Yaoundé. The average farm working experience was 11 (±9) years, with three to five household members involved in farming. This corresponds well with the average number of people living in households in Yaoundé, which ranges from one to more than six persons, with about 40% of households consisting of more than six members [
2]. Although farmers usually grow vegetables in more than one plot, the size of the cultivated lands is relatively small, and with increasing urbanization, the size of cultivated land is decreasing even more with time. The average size of a farm in our study was 298 m
2, which is substantially smaller than the previously reported average of 400 m
2 [
36].
All farmers practiced polyculture, with leafy vegetables as dominant crops, followed by herbs and vegetable fruits, including plants that are botanically classified as fruits, but are used as vegetables for culinary purposes. The primary cultivated species were vegetable food species such as
Amaranthus hybridus (89%),
Solanum nigrum (77%),
Corchorus olitorius (66%),
Lactuca sativa (49%), and
Vernonia amygdalina (39%).
Abelmoschus esculentus (34%) and
Solanum melangera (28%) are among the most grown vegetable fruits, while
Apium graveolens (31%),
Ocimum basilicum (22%), and
Petroselinum crispum (21%) were the most commonly grown herb species (
Table 3).
The choice of crop production was based on a combination of farmers’ consumption preferences, a preferably short vegetational cycle, and the local market demands. The vast majority of farmers in the six lowlands grew
A. hybridus and
S. nigrum primarily for self-consumption, with only the surplus sold at nearby markets. Yet,
L. sativa was primarily grown for market sale. Such kind of crop choices were also reported by Bopda et al. [
23] and Kenmogne et al. [
32] in their studies in Nkolondom and Nkolbisson, respectively.
3.2. Irrigation Water
More than half of the farmers (56%) used surface water sources (rivers) for their irrigation needs. Among the participants, 44% relied on groundwater (GW), mainly obtained from shallow dug wells built near the plots for irrigation.
Figure 2 shows the percentages of irrigation water sources in all study areas. Farmers from five out of the six studied lowland areas utilized water from different origins. Farmers from Mokolo used only GW to irrigate their fields, while those in Nkolbisson and Minkoameyos mainly utilized surface water (SW) (61%). Ekounou farmers equally used GW and SW. With the irrigation water sector accounting for only 7.3% of water use in Cameroon, farmers rely on potentially polluted water for irrigation because of general water scarcity. The type of irrigation water sources is one of the most critical parameters for the potential contamination of vegetables. Untreated water used for irrigation is the primary source of pathogens and heavy metal contamination in farms [
37,
38]. This may lead to the deterioration of GW quality, soil structure, and changes in physicochemical properties of lands that significantly reduces their fertility [
19].
The percentage of Mokolo farmers using GW for irrigation was significantly higher than in the other studied areas of Yaoundé. On the contrary, the percentage of farmers from Minkoameyos using GW for irrigation was significantly lower than those from the Emana, Ekounou, and Ekoumdoum sites.
3.3. Fertilizers
Vegetable production in urban areas requires several external inputs, including mineral or organic fertilizers. Of the surveyed farmers, 84.6% used fertilizers to enhance soil fertility, with the highest use in Nkolbisson (88%) and Emana (73%), yet with no significant differences in fertilizer use among the six studied lowland areas of Yaoundé (
Figure 3). Most farms in Nkolbisson belong to the neighboring Cameroonian Institute of Agricultural Research for Development or are owned by former workers of the institute, possibly explaining the relatively higher fertilizer use there compared to the other studied lowland areas. Improper farm fertilizer management can lead to nutrient contamination and other chemical pollutants into water bodies through runoff and soil erosion [
19], and such contaminants may negatively affect plants, animals, and humans [
39].
The type of fertilizers applied varied among farmers based on their availability and affordability. Of the interviewed farmers, 50% used a combination of mineral and organic fertilizers, while 28.5% utilized only organic and 6.1% only mineral fertilizers in their fields. The three most common organic fertilizers used were chicken manure (65.4%), pig manure (4.6%), and compost (8.5%). The comparison of the organic fertilizers shows that the proportion of farmers using chicken manure was significantly higher. Among the mineral fertilizers, urea was the most used type (27.7%), followed by NPK (22.3%) and ammonium sulfate (6.2%) (
Figure 4). The analysis revealed that the proportion of farmers using ammonia was statistically lower. The high popularity of chicken manure, especially compared to mineral fertilizers, such as urea or NPK, can be explained by its better availability and greater affordability. For instance, a 50 kg bag of chicken manure costs approximately Franc CFA 1200–2000 (EUR 2–3), while a 50 kg bag of mineral fertilizers costs around Franc CFA 18,000–25,000 (EUR 27–38), which is often not affordable for many smallholder farmers.
Previous studies reported that mineral fertilizer prices in different parts of Africa were not affordable for smallholder farmers (35, 36). Such farmers often revert to poultry manure to replenish soil fertility [
33]. Because of its low moisture content, chicken manure is easy to dry, thus requiring less labor, and can substantially improve the nutrient availability in the soil. It also contains less toxic and nonessential elements than mineral fertilizers [
33]. In addition, it has a higher concentration of N, P, and K per unit compared to other types of animal manure [
40,
41]. However, chicken manure application has also been reported to have some undesirable effects, such as phosphorus (P) reduction and extended stockpiling period [
42]. In some of the study areas, e.g., Nkolbisson, Emana, and Mokolo, farmers grow maize intercropped with leguminous vegetables. This practice helps to provide additional nitrogen as an environmentally friendly and more sustainable way of improving soil fertility. Nonetheless, intercropping was absent in the other three study areas, leading to higher (mostly mineral) fertilizer inputs into the environment.
3.3.1. Organic Fertilizer Use per Square Meter
The on-farm quantity of fertilizer used per m
2 varied widely among farmers and areas studied. On average, farmers applied 2.14 (±2.16 SD) kg/m
2 organic fertilizers, ranging from 0.05–12.5 kg/m
2.
Figure 5 summarizes the amount of organic fertilizer (in kg) used per m
2 of the farm size. In the study area, the average amounts of fertilizers applied were 1.61 kg/m
2, 3.60 kg/m
2, 1.05 kg/m
2, 1.42 kg/m
2, 2.98 kg/m
2, and 1.99 kg/m
2 for Emana, Mokolo, Minkoameyos, Nkolbisson, Ekoumdoum and Ekounou, respectively.
The on-farm use of organic fertilizers in each area was evaluated using regression analysis and pairwise comparison. The results showed that the amount of organic fertilizer used per m2 in farms in the Mokolo, Emana, and Ekoumdoum areas was significantly higher than in Minkoameyos, Nkolbisson, and Ekounou.
3.3.2. Mineral Fertilizer Use per Square Meter
The use of mineral fertilizers varies from 0.01–0.50 kg/m
2, with an average of 0.08 ± 0.09 kg/m
2 (
Figure 6). In the different locations, the average quantity of fertilizers applied were 0.07 kg/m
2, 0.17 kg/m
2, 0.10 kg/m
2, 0.05 kg/m
2, 0.07 kg/m
2 and 0.05 kg/m
2 for Emana, Mokolo, Minkameyos, Nkolbisson, Ekoumdoum and Ekounou.
The results of the analysis revealed that the amounts of mineral fertilizer were significantly higher in the farms of Mokolo compared to those in the Ekounou, Nkolbisson, Emana, and Ekoumdoum areas, though there was no difference in mineral fertilizer use between farms in the Mokolo and Minkoameyos areas.
The differences in fertilizer usage between the different areas studied might have been influenced by the differences in the price of fertilizer in the respective surrounding markets of these areas. Farmers involved in animal husbandry have a greater access to comparatively less expensive organic fertilizer and are thus more likely to use comparatively larger quantities of such fertilizer on their fields. A recent study in Yaoundé reported that poultry manure was the cheapest source of N to purchase, although a larger volume was required [
33]. The authors highlighted that the application of 200 kg chicken manure would supply 7.8 kg N/ha/pa, which is lower than the Kenya Agricultural Research Institute recommended rate of 50 kg of DAP (diammonium phosphate) and 60 kg of calcium ammonium nitrate (CAN) in sub-Saharan Africa [
43,
44]. In comparison, 150 kg/ha of NPK and 50 kg/ha of urea (46% N) provide a total N loading of 53 kg/ha/pa [
33]. Our study found the highest amount of organic and mineral fertilizers was applied on farms in the Mokolo area, even though these farms tended to be smaller than those in the other study areas. This comparatively higher fertilizer use in Mokolo was probably due to the longer duration of cultivation and the soil typology there. On smaller farms, farmers often tend to overuse soil amendments to increase their productivity with little awareness of potential health and environmental effects. In addition, because of a lack of information and training on occupational health and safety, farmers often apply fertilizers with their bare hands, a practice that potentially increases long-term health hazards.
3.4. Pesticides
Pesticides, just as fertilizer applications, are common in urban agriculture in the Yaoundé lowlands. Sixty-four percent (64%) of farmers applied pesticides to control pests, weeds, and diseases that reduce yields, and only 36% did not utilize chemical pest control. The proportions of pesticides users were 91%, 70%, 19%, 67%, 72%, and 62% for the Emana, Mokolo, Minkoameyos, Nkolbisson, Ekoumdoum, and Ekounou sites, respectively (
Figure 7). The highest proportion of farmers using pesticides in their farms was found in the Emana and the lowest in the Minkoameyos area.
Compared to all studied areas, the proportion of farmers using pesticides in the Minkoameyos area was significantly lower.
Farmers involved in urban lowland agriculture in Yaoundé apply different types of pesticides. The most commonly used pesticides, including six fungicides, two insecticides, one nematicide, and one herbicide, were classified according to the type and commercial brand name, active ingredient(s), and WHO classification (
Table 4). Fungicides were most frequently used (76%), followed by insecticides (66%) and nematicides (14%). Only 9% of farmers applied herbicides in their fields.
The low proportions of farmers applying herbicides in their farms can be explained by the high cost of these products, their only partial availability, and the low labor costs, with the vast majority of farmers thus preferring to manually weed their farms. A high proportion of farmers using fungicides was also reported by Tambe et al. [
46] in their study on pesticide use by smallholder’s tomato farmers in Cameroon. They reported that fungicides were the most common pesticides used among urban farmers and that most farmers apply these pesticides rather indiscriminately without using any protective gear. Moreover, another Cameroon study revealed that pesticides usage is responsible for 78% of accidental poisoning cases, 12% of suicide attempts, and 4% of criminals (thieves arrested are injected with Gramoxone or Paraquat) [
47]. Furthermore, the potential human health risk from pesticides residues in drinking water in many countries has been reported by El-Nahhal and El-Nahhal [
48].
Most farmers in our study lacked training in farming practices and knowledge on safe occupational practices. Thus, only 34% of the farmers wear personal protective clothing during irrigation, fertilizer, and pesticide applications. Even though the farmers are aware of the occupational health risks, none wear complete protective clothing, such as boots, gloves, and masks. Most farmers use only one or two pieces of personal protective gear, such as boots, raincoats, or gloves. In addition, most farmers are exposed to wastewater and often ingest some soil particles during farm work, leading to health risks [
49,
50].
More than half of the farmers generally walk in the irrigation water or wet their clothes during the irrigation process. Although 60% of farmers reported no feeling of inconvenience related to the untreated water, 40% noticed skin itching, burning, and the wretched water smell. These findings are probably due to the lack of awareness of occupational health risks and the low level of education of most of the encountered farmers. Yet, appropriate education is key to understanding safe working procedures and health risks related to certain behaviors. Asongwe et al. [
51], working with vegetable farmers in the Bamenda wetlands of Cameroon, reported that wearing personal protective gear can significantly reduce work-related threats.
3.5. Farming Practices and Explanatory Variables
A logistic model was used to understand the factors influencing the use of agricultural inputs. Four independent variables, i.e., education, land ownership, farm size, and the number of years the farm has been cultivated, significantly affected the use of fertilizers and pesticides (
Table 5).
Education is significant in negatively affecting the use of organic fertilizers. Possibly even (better) educated farmers are not sufficiently aware of the benefits of nutrient management on their farms or lack training on environmentally friendly farming techniques. Thus, there is a need to better inform and train farmers via agricultural extension agents. Cameroon’s Ministry of Agriculture often grants expenditures for organic fertilizers through NGOs or farmers’ associations. Therefore, educated farmers opt to use both types of fertilizers instead of only mineral fertilizers. Using only the latter might cause harm to environmental and human health. The integrated use of both organic and mineral fertilizers requires higher managerial skills, such as combining the two inputs in the correct proportions. Sotamenou and Parrot [
14], in their study on sustainable urban agriculture and the adoption of composts in Cameroon, found that education favors combined fertilizer use on farms.
The use of pesticides is significantly negatively associated with land ownership (
Table 5). Farmers that own the land are more interested in long-term investments, such as sustainable farming techniques and are thus less likely to use pesticides. The use of pesticides has been widely regarded as an unsustainable practice in Yaoundé because of its effect on soil, water, and human health [
47,
52]. Those who do not own the land, as many farmers living in the lowlands of Yaoundé, who often face eviction from the land, are more interested in short-term profits rather than the sustainable maintenance of soil health and thus are more prone to use pesticides. There is also an issue of awareness whereby the majority of these farmers, irrespective of land ownership, are aware that pesticides usage is harmful to soil health because of consumer organizations that sensitize them on the health risks linked to improper management of pesticides. These consumer organizations frequently hold informal debates with communities about human and environmental health issues from pesticide and other agrochemical use in farming systems.
The number of years the farm has been under cultivation (years of cultivation) has mixed effects on externality use. It is significantly negatively and positively associated with mineral fertilizer and pesticide use, respectively (
Table 5). Possibly farmers are aware that the long-term use of mineral fertilizers leads to diminishing productivity and soil fertility, resulting in low crop production. Yet, long-term cultivation of crops on the same piece of land leads to a build-up of pests and diseases, negatively affecting crop productivity and soil health. Therefore, farmers probably tend to address these problems through the increased use of pesticides.
There is a significant positive association between farm size and the use of a combination of organic and mineral fertilizers (
Table 5). Our findings suggest that the smaller the farm, the higher the likelihood of using higher rates of fertilizers to increase crop yield and productivity. Previous studies have also demonstrated that farm size influences the use of fertilizers. For instance, a study on fertilizer adoption in Ghana indicated that farmers were more likely not to adopt fertilizer as the farm size increased [
53]. Nkamleu [
54] reported that farm size was significantly negatively related to adopting mineral fertilizer, organic fertilizer, and integrated use of combined organic–mineral fertilizers. In this study, farmers with larger farms usually have ownership of this land and hence were interested in long-term farm management strategies, including applying combined mineral and organic fertilizers to maintain soil fertility. On the contrary, in smaller farms, where the owners do not own the land, there is a focus on producing as much as possible in the short term and to make money quickly and hence the tendency to use more inputs, in this case, fertilizers.
3.6. Farming Practices and Disease Prevalence
Our findings from the self-reported disease data show that farmers in Mokolo and Nkolbisson have the highest (95%) case of disease prevalence compared to the other studied areas. The result of the logistic regression model is reported in
Table 6.
It shows that educated farmers (above primary school level) are significantly less likely to report having malaria. This finding corroborated those reported by Spjeldnæs et al. [
55] in their study on education and knowledge that helps to combat malaria in Tanzania. These authors found that a high education status was significantly associated with high knowledge and less likelihood of contracting malaria. According to Ricci [
56], women tend to be less educated than men and thus have limited knowledge on the causes, transmission, and further appropriated treatment of malaria as the information might be available only in English or French and not in any local language. Additionally, farmers from Emana, Minkoameyos, Nkolbisson Ekoumdoum, and Ekounou are, respectively, 62%, 55%, 55%, 63%, and 48% significantly less likely to report having malaria than those in the Mokolo area. This result might be explained by the location of the Mokolo area in a slum community and the type of housing prevalent there, as poorly constructed houses facilitate the entrance of mosquito vectors and, thus, increase the risk of infection among the household members [
57].
Additionally, when farmers put on masks and gloves and are older, they are 41%, 38%, and 0.75%, respectively, significantly less likely to report contracting waterborne diseases, including typhoid, skin diseases, diarrhea, and abdominal pain. Nose masks might reduce the accidental ingestion of irrigation water. Similarly, wearing gloves might protect their hands from contacting the irrigation water and, thus, decreases the likelihood of contracting waterborne diseases. Using fertilizers significantly increases the likelihood of contracting waterborne diseases by 21%. Fertilizers, especially organic fertilizers, such as animal manure, are often stored outside. Subsequently, farmers applied the organic fertilizer using their bare hands when it was still wet, increasing the risk of infection.
Furthermore, farmers who reported facing some inconvenience, such as skin burning and itching, and are exposed to irrigation water are 14% and 33%, respectively, significantly more likely to report contracting hydric diseases. Farmers in Minkoameyos have a 33% higher risk of reporting to have headaches compared to those from Mokolo. Farmers in Minkoameyos have a 33% significantly higher risk of reporting to have headaches compared to those from Mokolo.