The study was carried out in the Bougouni and Koutiala districts which comprise 41% of Sikasso's region in southern Mali (Figure 1). With a total land mass of 70, 280 km², rainfall in the region varies from 800 to 1,200 mm (Birhanu et al., 2022). Sikasso region, with a Sudanian savanna ecosystem (Cooper and West, 2017) inhabits a total population of 2.63 million (Institut National de la Statistique, 2009). The five other districts in the region include Kadiola, Kolendieba, Sikasso, Yanfolila, and Yorosso. The vegetation in the area is composed of wooded and shrub savannah which are well-preserved in the south but are severely degraded in the center and the north of the districts. All the alluvial plains are covered with a grassy savannah and gallery forest along the rivers. The soils in the region are characterized as having high erosion risk, low water storage capacity, and poor drainage conditions. The agricultural economy in the region is characterized by rainfed, small-scale crops, livestock, and integrated crop-livestock/agro-pastoral farming systems (IITA, 2016). The months of June to September contribute 80% of the total annual rainfall. The long-term (1970–2018) mean annual rainfall of the Bougouni district is 1,060 mm, and that of Koutiala is 862 mm. The long-term (1970–2018) average monthly maximum and minimum air temperatures in the two districts are 33 and 22°C in Bougouni and 34 and 23°C in Koutiala, respectively (Birhanu et al., 2022).

Data for the study was collected from multiple sources (Table 1). Population data was sourced from the national census record. In this case, two population datasets were used. The first dataset was derived from the national demographic database of 2009 (Institut National de la Statistique, 2009). This dataset was used to estimate the population in 2019 INSTAT (2011). The second data was sourced from the World Population database available at 1 km resolution (Table 1). Spatial data on land use land cover and topographic variables were obtained at 30 m resolution from satellite-derived information using GIS and Remote Sensing tools. The soil map (1:500,000) of Mali was derived from the national Terrestrial Land Resources Inventories known as “Project Inventaire des Resources Terrestre: PIRT” of 1984. The world climatological database was used to derive the climate information required for the study. Environmental factors (land use and land cover, distance to urban/ rural areas) and economic factors (distance to the road, slope, distance to river, population density) were sourced from the Malian national GIS database available at the Institute of Rulale Economy (IER). Groundwater level data was sourced from previously georeferenced databases of Birhanu and Tabo (2016) and the spatial records of IWMI (2019). The collected spatial data at different scales were brought together using GIS software and re-scaled to make the output at a district level.

The use of SBISs in rural Mali was recent, with a few years (4.5), and was on a limited land area (0.15 ha). Water was always available for household domestic use (60%), livestock water (28%), and irrigation (15 %). Female farmers are better users (64%) of irrigation systems mainly for vegetable production. The two main crops that farmers practice SBISs are Onion (49%) and Tomato (27%). Over the studied water sources in 112 farm fields, the depth of wells to irrigate vegetable crops vary from an average shallow well-depth of 19 meters to a deep well of 94 meters. The mean irrigation interval practiced by the majority of farmers (90%) was 14 h.

Water productivity according to farmers' perception was low. Summary statistics on water use and yield for major vegetable crops are shown in Table 5. The actual water use during the growing period was compared with the minimum water requirement published by the FAO database (Brouwer and Heibloem, 1986). For all crops, the actual amount of water applied was < 50% of the required minimum amount. The majority of interviewed rural households (67%) however indicated they get sufficient water from wells for irrigation practices. Few farmers witnessed dryness of soil when the interval of irrigation exceeds 2 days, implying that irrigation practices were not following proper scheduling techniques. The yield obtained with farmers' irrigation technique was much less than the national average as well; 19.5 tons/ha for Onion, and 16.5 tons/ha for Tomato (FAOSTAT, 2020). While it was possible to get production data mainly yield (Table 5), data for stover yield of Onion, Pepper and Amaranth were not available, as the leaves of these crops were directly consumed by farmers at different times. The stover left from household consumption was used for livestock feed (73%) and the remaining manure was used to improve soil nutrients.

Results of the socio-economic analysis revealed that the head of the household makes the majority of decisions about land ownership and the use of SBISs. Under the rural Malian context, household farmland belongs to the head of the family, which in the majority of cases (95%) is an adult male. Areas not under agriculture belong to the chief of the village who makes decisions on land allocation for various purposes including the implementation of SBISs. From a total of 112 farm households, the majority (65%) responded that vegetable production from the irrigation systems was controlled by the producer. The head of the household is the next person to control production. More than 56% of respondents highlighted that the producer decides on types of vegetable production. While few farmers (21%) directly fund the construction of the irrigation system on their farmland, project-initiated implementation of SBISs (77%) was established on the communal property with a decision that came from the village chief. Regarding awareness, communities are well-informed about the usefulness of SBISs. The majority (63%) responded that information comes from multi-stakeholder discussion forums and farmer-to-farmer interactions.

Over 50% of vegetables produced under SBISs are for sale. Pepper, African Eggplant, Tomato, and Okra are for sale in the majority of cases. Household consumption is relatively higher for Lettuce (59%), Onion (53%), and Amaranth (51%). With the available SBISs, the production of vegetables increased household income. The average income of each vegetable grower household during the dry season was $56 (Tomato), $60 (Onion), and $69 (Pepper). The maximum sale value was $175 (Tomato), and $260 for the other two crops. Analyzed data further revealed that SBISs contributed over 40% of household income for 31% of the respondents. Eighteen percent indicated 30% of income from the sale of vegetable crops. Additionally, 14 and 15% of respondents indicated that solar irrigation system increased their income by 20 and 10%, respectively. For the other 22% of respondents, agricultural income increased by 5%.

The use of SBISs in rural Mali had challenges as well. Fifty-five percent of respondents noted that they lacked basic skills for maintenance work in case of faulty operations or breakage of part of the systems. It was also quite common to see conflicts arising mainly on the use of donor-funded installations on land provided by the village chief. Over 86% of respondents indicated that there are conflicts on the use of the SBISs. Conflicts arose mainly on the amount and timing of irrigation for different farms owned by different farmers. There are also disagreements on the service fee to be paid to a technician in case of systems component breakdown, and few users of the system were unwilling to make a monetary contribution toward replacing damaged parts. Respondents recommended the need to have appropriate training programs on the operation of the SBISs. In addition, guidelines related to water use and systems maintenance for long-term use were recommended to be developed at the village council level (see for example Umutoni and Ayantunde, 2018).

Quite a significant area of the landscape was found to be suitable for the implementation of SBISs in each district. Suitable land area was assessed using the Boolean method using various data sets. Land areas extracted from the combination of Boolean maps have been placed on the raster layers of fuzzy maps. Therefore, the unrestricted areas determined by Boolean overlay were evaluated by fuzzy functions. As shown in Table 6 and Figures 6, 7, nearly 22% of the land area in Bougouni is suitable to implement SBISs. The figure in Koutiala is 18%. In this study, the evaluation criteria were determined and categorized based on the authors' experience and reviews from the limited available information. In the context of Mali, communes are the lower administrative structure next to districts. Villages are clustered in each commune, as such the suitability maps of Figures 6, 7 show the location of villages, names, and boundary limits of each commune. As SBISs are implemented at the village level, each suitability map provides useful guidance to target villages. Villages located in the north, north-western and central parts of the Bougouni district and the eastern and southern parts of Koutiala are found to be suitable for the implementation of SBISs. These results confirmed the findings made at the national level by Attia et al. (2022) that for example in the Sikasso region suitable areas for irrigation development using solar energy are parts located in the northeastern and southern parts. With regards to land use management practices, areas identified as not suitable for SBISs can be reforested to prevent land degradation caused by soil erosion and hence enhance the ecosystem of the landscape by acting as aquifer recharging zones.

The agricultural system in Mali heavily relies on rainfed agriculture which suffers from land degradation and a limited contribution from the small-scale irrigation system. Rising population growth and increased fragmentation of household farmland necessitate special and urgent attention to the use of CSA practices that include SBISs (IWMI, 2019; Attia et al., 2022). In communities with large household sizes (for example the average in southern Mali is 27), increasing agricultural practices with irrigation-based technologies would ensure better household food security. Most rural Malians practice traditional irrigation systems except for a few donor-funded projects. Due to the limited water lifting systems and scarce availability of water in most shallow wells, the SBISs are practiced once a year in the majority of farm fields (69%).

Irrigation practices using solar energy are still considered by rural farmers as complementary to rainfed agriculture. However, the result of our study highlighted that ~20% of the available land area in the two districts is suitable for solar-based irrigation investment. This potential, together with the untapped groundwater resource in Mali (Birhanu and Tabo, 2016), if properly managed and appropriate investments are in place, would be a game changer for the Malian agricultural system. Groundwater reserve in Mali is an untapped resource requiring due consideration along with other management practices in the changing climate condition.

Promotion and scaling of SBISs, however, are limited by the low rate of literacy level among most rural communities. The technology requires skills in implementation, maintenance, and use. However, 46% of the studied districts' rural communities do not have formal education (Sanogo et al., 2021). In situations when there are no industries or equivalent employers to provide local people with income-generating opportunities, the implementation of small-scale SBISs with the provision of required skills could be a useful option to enhance the livelihood of rural communities. This needs to include the introduction of low-cost soil water sensors that are useful to determine the minimum amount of water and frequency of irrigation (Adimassu et al., 2020; CSIRO, 2021).

The other limitation is the availability of suitable land. Land requirements, considered environmental factors, have been identified as one of the most critical factors for irrigation investments (Kahraman et al., 2009; Rabia et al., 2013). Despite being a major constraint in most developmental projects (Brewer et al., 2015), land use type is the foundation to plan and allocate land for diverse investment options (Tahri et al., 2015). For example, land with appropriate climate conditions for solar energy investments may have a lower value if the land use factor is taken into account (Carrión et al., 2008). Additionally, the dominant soil types in both districts, i.e., Regosols (in Bougouni), and Lixisols (in Koutiala) are characterized by low nutrient status and storage capacity and are susceptible to erosion. In this case, areas with Haplic Lixisols, Gleysols, and Ferric Luvisols were found to be suitable for solar-based irrigation development with the additional application of organic manure and mulches (Jalloh et al., 2011). In particular, Gleysols that are found in low-lying landscape positions with shallow groundwater reserves are better sites as they contain relatively higher organic matter and available nutrients (Jalloh et al., 2011).

Areas receiving annual rainfall >800 mm were found to be suitable as well. However, the spatial and temporal variability of rainfall as evidenced in southern Mali (Ebi et al., 2011; Akinseye et al., 2020; Sanogo et al., 2021) could be a limiting factor to recharge groundwater aquifers. This could also impact the sustainability of SBISs. As smallholder farmers cannot afford hydrocarbon-energized motor pumps or electrical pumps and the affordability of solar panels in many rural places as explained by Schmitter et al. (2018) makes SBISs to be an emerging climate-smart technology for most rural Malian populations. Hence, for a better result, the output of the study needs to be integrated with other intervention measures such as good agronomic practices (Traore et al., 2017) and landscape-based soil and water conservation practices (Traore and Birhanu, 2019; Birhanu et al., 2022).

In SSA, innovative irrigation systems are essential to secure smallholder farmers' year-round food production to contribute to the increased demand for food. SBISs are proven to potentially be a game changer for SSA smallholder agriculture from several aspects. SBISs are alternatives enabling smallholder farmers to grow more crops in a year by utilizing abundant sunlight and groundwater, mitigating climate change by reducing CO2 emissions (Brunet et al., 2018). SBISs can provide clean irrigation to millions of farmers, empowering their adaptive and resilient capacity by raising agricultural productivity and their incomes (Ockwell et al., 2018). SBISs can open new avenues of opportunity and potential for agricultural growth while transforming the entire range of farming systems in SSA.

Activating SBISs' game-changer potential, however, requires a long-term commitment and comprehensive ingenuity of thought and action, time, and determination across scales. Several attempts are being undertaken in SSA countries for the installation of electric pumps fed by solar energy and modern irrigation system to promote renewable energy and water use efficiency in agriculture (Noubondieu et al., 2018; Mugisha et al., 2021). Investments in west African countries (e.g., Ghana, Senegal, Mali, Gambia) focus on multiple initiatives for testing, de-risking, subsidizing, and analyzing policy reform to sustainably scale solar-powered pumps (Brunet et al., 2018; Lefore et al., 2021). SBISs as game-changer must have the ability to manage uncertainties and overcome obstacles. Enabling this ability requires adaptive approaches to overcome systemic barriers related to the lack of contextually relevant innovation bundles, appropriate end-user financing, policy frameworks biased toward large-scale irrigation and rain-fed agriculture, weak market linkages, nascent private sector investment and increasing competition for water among sectors (IWMI, 2021a). It also needs to integrate public, research, and private sector actors to respond to diverse incentives and environmental trade-offs with the underground water depletion and e-wastes (Minh et al., 2020; Lefore et al., 2021) and improve stakeholder coordination, enact more effective policies, and facilitate integration within the value chains and across sectors (Izzi et al., 2021).

In the case of Mali, enabling SBISs as a game-changer is driven by viable business and investment opportunities, appropriate finance tools, and market integration for solar entrepreneurs and irrigators. There is a growing presence of private sector solar technologies suppliers but the solar technology market can grow to reach many farmers directly when the demand for and supply of SBISs are matched. Understanding the diversity of farmers' SBISs demands, coupled with the solar irrigation suitability map (IWMI, 2021b) helps the suppliers to prioritize geographical areas for their marketing activities and business investments.

Farmers' demands are different in terms of the amount of water needed, land and water access, pump preferences, and capacity to pay for the SBISs. Tailoring the supply business models to different demands and abilities to invest is one of the necessary conditions to unpack the market bottlenecks. For example, in the areas where resource-limited and resource-poor farmers can access shallow groundwater like in areas of Dogo, Kokele, and Sibirila of Bougouni district, and N'golonianasso and M'Pessoba communes of Koutiala district, the business models should focus on supplying the solar-powered pumps with low capacity to match these farmers' ability to invest.

Finally, accelerating the SBISs requires an enabling environment in which domestic manufacturers, irrigation and input suppliers, and small processing businesses can grow. Sustainable financing models help de-risk private sector investments in irrigation markets, especially products and services that support gender and youth inclusion. Win-win partnerships between entrepreneurs, farmer groups, cooperatives, and private and public sector actors help optimize the engagement of private sector companies that supply different equipment along the continuum of agricultural water management, creating a more robust irrigation market for farmers. Multi-stakeholder dialogues and platforms are ways to engage diverse business actors to increase market density and integration (Minh et al., 2020). They also encourage collaboration and learning to drive responsive innovations to address social and gender inequality, economic empowerment, water governance, and multi-sector/stakeholder coordination to accommodate local contexts, diverse partners and stakeholders, and emerging needs for feasible and sustainable SBISs (Lefore et al., 2021).