Paddy-rice cultivation using the traditional continuous flooding method requires much water, up to 2500 L, to produce 1 kg of rice. Decreasing water availability is being exacerbated by climate dynamics, i.e., droughts and rainfall variability negatively affecting food security in developing regions, particularly Africa. Alternate wetting and drying (AWD) practice is a climate-smart water management strategy that, together with puddling (a critical field preparation process), significantly affects soil hydrological and physicochemical regimes, such as soil water dynamics and oxidation states in paddy fields. However, there are limited reviews on the effects and interaction of the AWD duration on hydrological conditions in the paddy-rice rhizosphere continuum under AWD practice at different rice growth stages. Our review synthesizes key scientific literature to examine water management and hydrological properties of paddy soils under AWD practice with climate change and sheds light on why farmers are skeptical in adopting the practice. To develop this paper, we reviewed scientific information from published journal articles, reliable reports, and our knowledge on paddy-rice cultivation and water management with climate change in Asia and Sub-Saharan Africa. Several studies confirm that AWD practice increases water–rice–crop productivity, yields, and reduces methane emissions. Limitations and challenges of AWD irrigation, including changes in soil structure that influence irrigation water application, variations in hydraulic conductivity caused by the duration and frequency of irrigation cycles, and frequent manual water level (WL) monitoring, are discussed. Opportunities to improve the integration of AWD strategies within government policies, irrigation schemes, and farmer acceptance due to skepticism, limited knowledge, and fear of unreliable water hindering adoption are highlighted. Future research suggestions include the following: (i) long-term measurement of water stress indices using infrared thermometers; (ii) seasonal suitability mapping using NDVI, GIS, and remote sensing; and (iii) application of smart sensors based on the Internet of Things (IoT) to address AWD challenges for precision water management in paddy fields with climate change.

The current water scarcity and world population increase cause the need for more food, pushing the demand on water resources due to crop production such as rice. Increasing agricultural water productivity by reducing the amount of irrigation water without affecting the yields, especially in paddy rice, is necessary. This is possible with alternate wetting and drying (AWD) irrigation. This study was conducted under greenhouse conditions at Tokyo University of Agriculture and Technology, Japan to evaluate the response of yield, water productivity and harvest index with different water regimes. The experiment was performed in pots with four water regimes as treatments and three replications, making 12 pots. The water regimes were continuous flooding irrigation as control and three AWD conditions—AWD5, AWD10 and AWD15—in which pots were irrigated when water reached 5, 10 and 15 cm soil depth, respectively, after the disappearance of surface ponding water. Yield components, harvest indexes and water productivity showed no significant difference (p < 0.05) between irrigation treatments. In this research, as there is more than a 25% reduction in water use and only 6.4% in grain yield, AWD15 was considered the best irrigation practice among the other treatments. This study provides data reference for theoretical scientific knowledge and understanding of safe AWD practice for countries facing water shortages.

Water management is a significant aspect of sustainable vegetable farming, especially in water-scarce regions. This, in addition to weed infestations, limits vegetable yields, which negatively affect food security in developing regions, particularly East Africa, where livelihoods chiefly depend on rain-fed agriculture. Vegetable farming, especially tomato cultivation, requires more water. By promoting mulching, a soil water conservation tool, we can control surface evaporation (E), which, together with irrigation, enhances effective water use and vegetable yields. The experiments for this study were conducted at the Tokyo University of Agriculture, Japan, to evaluate the influences of different irrigation conditions and poly-mulching on weed control, tomato yields, and water use efficiency. The study was conducted from May to September 2018 on a 30 m² plot in an open-ended greenhouse using drip irrigation for tomato cultivation. Three predetermined irrigation conditions of 4, 3, and 2 mm/day were applied on black poly-mulched and bare ridges. Data on soil conditions—soil temperature, as well as meteorological variables, including solar radiation and temperature—were measured using thermocouple sensors and micro-hobo weather stations, respectively, during the tomato cultivation, while yield components—growth, yield, water productivity, and sugar content—were determined after harvest. The results of a two-way ANOVA show that irrigation conditions with poly-mulching reduced the weed biomass significantly, and improved yields and water use efficiency compared to the irrigation conditions on bare ridges. The application of 4, 3, and 2 mm/day irrigation with poly-mulching significantly reduced the weed biomass by 5% compared to the same irrigation conditions on bare ridges. Similarly, 4 and 3 mm/day irrigation conditions with poly-mulching significantly increased the tomato yield by 5% compared to 2 mm/day on bare ridges. The bigger roots were concentrated and widely distributed at the shallow soil depth (0–20 cm) of the ridges with high irrigation amounts, while the small and thin roots were in deeper soil layers (30–45 cm). This study provides scientific knowledge on the application of predetermined irrigation conditions that can be (i) integrated into irrigation scheduling and (ii) adopted for regions facing water scarcity and limited or no in situ meteorological data, to improve water use efficiency for vegetable cultivation.

Water is a valuable resource for rice production, which is an integral component of food security in East Africa (EA). Rice farming is expanding in the region, with up to 90% produced on smallholder farms using traditional flooding and rain-fed methods, vulnerable to climate change and variability. Despite EA's enormous agricultural and crop potential, the region largely depends on rice imports (> 500,000 tons annually) from Asia due to rising gaps between production and consumption. Sustainable water management practices, including alternate wetting and drying (AWD), system of rice intensification (SRI), and drip irrigation are critical for paddy and upland rice production although practiced at micro-research levels with limited adoption of such technologies by smallholder farmers. Herein, we synthesize key information on smallholder irrigation agriculture development and implications for food security in changing climates in the four EA countries (Uganda, Kenya, Tanzania and Ethiopia), based on scientific literature and reports. Several studies indicate water scarcity is a major threat to rice production, while poverty and food insecurity are linked to low agricultural productivity. Although rice production has increased since 2000 because of the slight expansion of irrigation, yields are still low due to insufficient irrigation development, climate change, and variability and poor agronomic practices. Nonetheless, climate-smart water management technologies such as AWD, SRI, and drip irrigation are less used by paddy and upland rice smallholder farmers for several reasons including limited awareness, funding, and technical knowledge. Therefore, commitments of government sectors, NGOs, farmer-based organizations, and private sectors with clear policies are needed to enhance technology transfer, action research, farmer training, and innovation development. These actions are vital to promote knowledge generation and the adoption of technologies to improve water management for increased rice yields, livelihoods, and food security in changing climates.

Global concerns of decreasing water availability and food security are being exacerbated by the increasing demand for food, water quality degradation, and climate change impacts. Rice is an essential crop for food security with paddy rice cultivation largely practiced using traditional flooding conditions. Water regimes and components of the soil water balance in paddy rice catchments affect uptake of water by rice roots. Paddy management, especially puddling, significantly affects soil hydrological properties, such as hydraulic conductivity, percolation, and seepage in the paddy rhizosphere. Improved knowledge of these interactions is vital for developing sustainable water management strategies in paddy fields. Alternate Wetting and Drying (AWD) practice contributes to sustainable water management, but little is known about effects of soil wetting and drying duration on gravitational soil water flow, moisture dynamics, and hydraulic conductivity in the rice paddy rhizosphere. These factors depend on soil type, rice variety, rooting conditions, and environmental factors, such as solar radiation and temperature. Here we examine the paddy cultivation environment and soil properties under traditional continuous flooding and AWD practice. Some studies indicate that the duration and frequency of wetting and soil drying under AWD practice in paddy fields affects soil hydraulic conductivity that alters the next cycle of water application. During droughts and short rainy seasons, rainfall, soil properties, and atmospheric conditions control soil moisture dynamics in paddy fields. Limitations and challenges of applying AWD in paddy soils, including the variation of hydrological properties and the need for frequent field manual monitoring of water level (WL) head, are discussed. Implications of AWD practice on yield, water use efficiency, soil hydrology, and reduction of methane emissions, are outlined along with opportunities to improve AWD integration within government policies, irrigation schemes, and adoption by farmers. Coupled crop models can provide important insights for sustainable agricultural water management.

The increase in crop water stress due to drought variability significantly contributes to crop failure and yield reduction in developing regions. The super-absorbent polymers (SAPs)—agro-hydrogel, are promising eco-friendly solutions to minimize drought stress, improve soil health; the structure in particular, and increase water availability in the plant rhizosphere. Knowledge on the production and application of the agro-hydrogels to improve degraded soils and optimize irrigation water use during dry seasons, is limited in East Africa. In this study, two self-made cellulose-based SAPs were assessed in a pilot open-field experiment to evaluate their soil water retention abilities and irrigation water use for improved crop productivity. The research aimed to answer three major questions: (1) What is the water absorption capacity of SAPs derived from agro-waste products? (2) How do the physical properties of these SAPs influence their effectiveness in retaining moisture in soil? and (3) What is the influence of these SAPs on crop growth and yield? The cellulose-based SAPs were synthesized from sawdust and coffee husks using bulk polymerization and tested for their swelling capability in different aqueous media following the standard procedures. The effectiveness of the SAPs in agricultural applications was evaluated in the pilot open-field experiment with okra plant cultivation at the experimental site of Busitema University, main campus, located in Eastern Uganda. The SAPs were analyzed after several absorption cycles over 60 days, and three treatments defined by different SAPs (from sawdust and coffee) with 50% ET_C, 30% ET_C and control were set in a randomized complete block design (RCBD). The results indicated that SAPs-amended soils (5 g of SAPs on each plant) stored a considerable amount of water (2 L per irrigation) and released it gradually to the plant roots during plant growth. Additionally, the polymer synthesized from sawdust absorbed and retained more water (30%) than coffee husks (10%). Therefore, these results suggest that adopting SAPs could become a climate-smart and sustainable approach to water conservation, improving crop productivity and dryland farming, especially in water-scarce and saline regions.