The potential for expansion of irrigated rice under alternate wetting and drying in Burkina Faso

Highlights

• The potential for irrigated rice in Burkina Faso was estimated at 21.10 × 10⁵ ha.

• All dekads in the dry season are suitable for Alternate Wetting and Drying (AWD).

• About 25–100% of wet season dekads are suitable for AWD.

• Soil percolation was the main driver of land suitability to AWD in the wet season.

Abstract

Achieving rice self-sufficiency in West Africa will require an expansion of the irrigated rice area under water-scarce conditions. However, little is known about how much area can be irrigated and where and when water-saving practices could be used. The objective of this study was to assess potentially irrigable lands for irrigated rice cultivation under water-saving technology in Burkina Faso. A two-step, spatially explicit approach was developed and implemented. Firstly, machine learning models, namely Random Forest (RF) and Maximum Entropy (MaxEnt) were deployed in ecological niche modeling (ENM) approach to assess the land suitability for irrigated rice cultivation. Spatial datasets on topography, soil characteristics, climate parameters, land use, and water were used along with the current distribution of irrigated rice locations in Burkina Faso to drive ENMs. Secondly, the climatic suitability for alternate wetting and drying (AWD), an irrigation management method for saving water in rice cultivation in irrigated systems, was assessed by using a simple water balance model for the two main growing seasons (February to June and July to November) on a dekadal time scale. The evaluation metrics of the ENMs such as the area under the curve and percentage correctly classified showed values higher than 80% for both RF and MaxEnt. The top four predictors of land suitability for irrigated rice cultivation were exchangeable sodium percentage, exchangeable potassium, depth to the groundwater table, and distance to stream networks and rivers. Potentially suitable lands for rice cultivation in Burkina Faso were estimated at 21.1 × 10⁵ ha. The whole dry season was found suitable for AWD implementation against 25–100% of the wet season. Soil percolation was the main driver of the variation in irrigated land suitability for AWD in the wet season. The integrated modeling and water balance assessment approach used in this study can be applied to other West African countries to guide investment in irrigated rice area expansion while adapting to climate change.

Introduction

Rice consumption has steadily increased in Sub-Saharan Africa while domestic rice production hardly meets the demand. In Burkina Faso for example, the national rice self-sufficiency ratio was 30% between 2008 and 2018 (Africa Rice Center, 2018). Nonetheless, Burkina Faso’s National Rice Development Strategy (NRDS) emphasizes intensification and expansion of irrigated rice production systems to achieve rice self-sufficiency (BFNRDS, 2011). There is potential for enhancing rice production through increasing rice yield on existing land (intensification), improving rainfed lowland rice areas, and expanding areas under irrigation through diffusion and adoption of technologies (Seck et al., 2010). Among the five rice cropping systems in West Africa, i.e. rainfed upland, rainfed lowlands, irrigated lowlands, deepwater and mangrove swamps (Balasubramanian et al., 2007), the irrigated rice systems hold a promising future for several reasons: firstly, the average rice yield in irrigated lowland of 3.8 t/ha is higher than yields in rainfed lowland (2.6 t/ha), and rainfed upland (1.7 t/ha) (Dossou-Yovo et al., 2020). Secondly, due to temperature changes, rainfall variability and expected future climate change impacts in rainfed rice systems (van Oort and Zwart, 2018, Singh et al., 2017, Li et al., 2015), improvements in farmers’ adaptive capacity due to the expansion of irrigation facilities may reduce rice production losses (Birthal et al., 2015). Although irrigated rice holds tremendous potential in fulfilling many West African countries' agendas of becoming rice self-sufficient, geospatial analysis to assess potentially irrigable land is often not explored. It is therefore relevant to quantify “where” and “how much” land is potentially suitable for irrigated rice cultivation under water-saving technologies.

Previous studies assessed the suitability of lands to crop cultivation at the regional and continental scales (Gumma et al., 2014, Hentze et al., 2016, Lobell and Asner, 2004, Xiong et al., 2017, Pittman et al., 2010). While these studies significantly improved our understanding of the general pattern of agricultural land, they mostly focused on the current planted areas based on satellite imagery. More holistic approaches for suitability analysis took into account the crop requirement for optimal allocation in the context of future cropland expansion. Such possibilities have been widely assessed through agricultural land suitability analysis (ALSA), a global land-use planning approach for land resources allocation in line with Sustainability Development Goals (SDGs) of the United Nations (Akpoti et al., 2019). One such approach used qualitative and parametric methods to evaluate land suitability for irrigated rice in West African Sahel based on soil units, soil fertility, and water management (Dondeyne et al., 1995). West African rice development environment has been characterized based on climate, soil, topography, land types, and rice systems with an emphasis on inland valleys (Andriesse and Fresco, 1991, Windmeijer and Andriesse, 1993, Andriesse et al., 1994). Other studies used Multi-Criteria Evaluation (MCE) to estimate map suitability for irrigation potential under current and future climate change in Ghana and Ethiopia (Schmitter et al., 2018, Worqlul et al., 2019). These methods are broadly classified as deductive which rely on physiology and other biophysical requirements.

New advances in inductive methods such as ecological niche models have provided means to take advantage of spatial big data for estimating the potential for agricultural development. A recent approach has used ecological niche modeling to map quantitatively inland valleys' suitability for rice production using machine learning methods (Akpoti et al., 2020). The approach, based on geospatial predictive modeling, uses rice occurrence along with environmental biophysical predictors of rice. Contrary to Asian conditions, where large-scale rice-growing areas can be mapped by coarse-scale MODIS data (Peng et al., 2011, Sakamoto et al., 2005, Salmon et al., 2015, Xiao et al., 2006, Xiao et al., 2005), West African rice areas are sparse in a heterogeneous environment. Thus, the application of the ecological niche modeling approach, which not only has the advantage to predict the current distribution of irrigated rice areas but also identify suitable areas for development, can aid in sustainable irrigated area expansion.

Many irrigation schemes are inefficient and irrigation water productivity is low in Burkina Faso (Dembele et al., 2012, Sawadogo et al., 2020). To improve water-use efficiency through the reduction of irrigated water use, many technologies have been introduced including alternate wetting and drying (AWD). Alternate wetting and drying is a water-saving technology developed by the International Rice Research Institute (IRRI) and is based on the fact that continuous flooding is not required for rice fields to achieve high yields (Bouman et al., 2007). Once the transplanted seedlings are well established, the field water depth can fall to a threshold depth below the soil surface for a certain period before the field is irrigated. Implementation of AWD among farmers particularly in Asia has been very site-specific in terms of the timing, frequency, and duration of the non-flooded periods. In some regions of Asia, rice fields are flooded every 6 – 8 days or 4 – 5 days depending on the soil texture (Howell et al., 2015, Norton et al., 2017, Yao et al., 2012). The IRRI’s recommendations of “safe” AWD consist of three key elements: a) flooding for 2 weeks to avoid transplanting shock and suppress weeds, b) flooding during the flowering stage to avoid yield reduction due to water stress at this sensitive stage of rice development, and c) AWD during all other periods with irrigation applied to 5 cm above the soil surface whenever water table falls to 15 cm below the soil surface (Lampayan et al., 2015). A meta-analysis of AWD applications showed that on average AWD reduced water input by 25% and increased water productivity by 24% without a yield penalty (Carrijo et al., 2017). In addition to the aforementioned benefits, AWD reduced methane emission by 53% on average (Jiang et al., 2019) and therefore has the potential to reduce water input, and greenhouse gas emission while maintaining rice yields. Studies showed that AWD can be applied in a dry environment such as the Sahelian environment of West Africa (de Vries et al., 2010, Djaman et al., 2018). These assessments showed that AWD can be deployed in both dry and wet seasons with comparable rice yields (Djaman et al., 2018) and, in some cases, better than in continuously flooded fields (de Vries et al., 2010).

Understanding the potentially irrigable land area while at the same time optimizing irrigation water use was identified as one of the priority actions in the Burkina Faso National Rice Development Strategy (BFNRDS, 2011). Thus, the objective of this study was to assess potentially irrigable lands for rice cultivation under water-saving technology in Burkina Faso. To achieve this objective, an integrated approach of two principal steps was developed and implemented. Firstly, an ensemble of models was used to assess the land suitability for irrigated rice cultivation. Secondly, a simple water balance approach was adopted to estimate the climatic suitability of AWD for water-saving. The results will provide policy makers and the development sector more insight into future suitable areas and opportunities for introducing AWD in irrigated rice systems development.