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Grain legumes have potential to contribute to food and nutritional security in water-scarce areas. Information on their yield, water use and water productivity (WP) would be useful for their promotion. The aim of the study was to make a comparative assessment of adaptation, yield, water use and WP of an African indigenous grain legume (bambara groundnut) and two major grain legumes (dry bean and groundnut) under rainfed, deficit and optimum irrigation conditions. Field trials were conducted during the 2015/16 and 2016/17 summer seasons in KwaZulu-Natal, South Africa, using a split-plot design arranged in completely randomised blocks with three replications. Data collected included stomatal conductance, leaf area index, timing of key phenological stages and yield. Water use was calculated as a residual of the soil water balance. Water productivity was obtained as the quotient of grain yield and water use. Crops adapted to limited soil water availability through stomatal regulation and reduction in canopy size and duration. Yield, yield components and WP varied significantly (P < 0.05) among crop species. During 2015/16, groundnut had the highest yield and WP (10 540 kg·ha-1 and 0.99 kg·m-3, respectively). During 2016/17, the highest yield and WP were observed in dry bean, 2 911 kg·ha-1 and 0.75 kg·m-3, respectively. For both seasons, dry bean had the lowest water use (143-268 mm) across all water treatments. Dry bean and groundnut out-- performed bambara groundnut with respect to yield, harvest index and WP. For any promotion of bambara groundnut as an alternative crop, there is need for crop improvement to improve yield and WP. [ABSTRACT FROM AUTHOR]

The study determined the best management practices for improved yield (Y) and water productivity (WP ET) of groundnut and bambara groundnut under different environments. Three sites representing different agro-ecological zones of KwaZulu Natal were used (Umbumbulu, Ukulinga and Wartburg). Thirty-year historic climate data from the different sites was categorised into normal and dry seasons based on probability of exceedance. Thereafter, eight strategies included were assessed against a reference scenario that represented current practices by smallholder farmers. The eight strategies included (i) early planting, (ii) recommended planting date, (iii) late planting, (iv) mulching, (v) deficit irrigation, (vi) optimum irrigation, (vii) soil bunds, and (viii) tied ridges. The Y and WP ET responses (%) to different management practices relative to the reference scenario were analysed. Frequency analyses of crop failure for every management practice were conducted. Early and late planting decreased Y and WP ET of groundnut by 35% at Ukulinga. At Umbumbulu and Wartburg, late planting increased WP ET by 60% during normal seasons. Early planting increased Y and WP ET of bambara groundnut by 30–60% at all sites during normal seasons. Both crops responded positively to mulching, especially bambara groundnut — Y and WP ET increased by up to 60% during dry seasons. Optimum irrigation increased Y by 50%, but decreased WP ET by ≈ 15% for both crops. Tied ridges improved Y and WP ET by up to 30% for both crops. Irrigation and soil water conservation practices mitigated crop failure during dry seasons. Groundnut was more prone to crop failure during dry periods compared to bambara groundnut. • Late planting improved productivity of groundnut during dry seasons. • Early planting improved productivity of bambara groundnut. • Irrigation and soil water conservation practices improved productivity and mitigated crop failure. • Bambara groundnut was hardier than groundnut during dry periods. [ABSTRACT FROM AUTHOR]

Increasing agricultural productivity has always been a prominent feature on the regional agenda due to a high incidence of food and nutrition insecurity. This review assessed the current status of irrigated agriculture in southern Africa from a water–energy–food (WEF) nexus perspective. Gaps and opportunities for improving irrigated agriculture within the context of the WEF nexus were also assessed in terms of the feasible limits to which they can be exploited. Southern Africa faces water scarcity, and climate projections show that member states will face increased physical and/or economic water scarcity by as early as 2025, which will have negative impacts on water, energy and food production. Recurrent droughts experienced across the region reaffirm the sensitive issues of food and energy insecurity as well as water scarcity. Projections of an increasing population within the region indicate increased water, energy and food demand. With agriculture already accounting for about 70% of water withdrawals, increasing the area under irrigation will place additional demand on already strained energy grids and scarce water resources. This poses the question—is increasing irrigated agriculture a solution to improving water access, food security and energy supply? While there are prospects for increasing the area under irrigation and subsequent improvement in agricultural productivity, adopting a WEF nexus approach in doing so would mitigate trade-offs and unintended consequences. Consideration of the WEF nexus in integrated resources planning and management eliminates the possibilities of transferring problems from one sector to other, as it manages synergies and trade-offs. While it is acknowledged that improving water productivity in irrigated agriculture could reduce water and energy use while increasing yield output, there is a need to decide how such savings would then be reallocated. Any intervention to increase the irrigated area should be done in the context of a WEF nexus analytical framework to guide policy and decision-making. Technical planning should evolve around the WEF nexus approach in setting targets, as WEF nexus indicators would reveal the performance and impact of proposed interventions on any of the three WEF nexus components. [ABSTRACT FROM AUTHOR]

Water productivity (WP) is becoming a key issue in understanding the relationship between water availability and rainfed sorghum (Sorghum bicolor L. Moench) yields in agricultural systems across sub–Saharan Africa. The objective of this study was to determine water productivity of three sorghum genotypes under different environmental conditions. Three sorghum genotypes, a hybrid (PAN8816), a commercial open-pollinated variety (Macia) and a landrace (Ujiba) were planted at two sites (Ukulinga and Mbumbulu) in South Africa during 2013/2014 and 2014/2015. High clay content in Mbumbulu lowered plant available water in the soil compared to Ukulinga. Sorghum adapted to low water availability by significantly (P < 0.05) lowering plant growth (green leaf number, plant height and canopy cover), crop physiology (chlorophyll content index and stomatal conductance), biomass and grain yield. Ujiba and PAN8816 genotypes hastened phenological development, whilst Macia delayed phenological development in response to low water availability. Total and grain WP were lower at Mbumbulu (14.93 and 7.49 kg/ha/mm) relative to Ukulinga (21.49 and 11.01 kg/ha/mm), respectively. Results showed that Macia had significantly higher (P < 0.05) WP (10.51 kg/ha/mm) relative to PAN8816 (9.34 kg/ha/mm) and Ujiba (7.90 kg/ha/mm). Lack of significant genotypic differences in grain WP highlights that all three genotypes are equally suitable for production under sub–optimal and dryland conditions. [ABSTRACT FROM AUTHOR]

Nationally recommended sorghum planting dates in South Africa are inaccurate since they are similar for all sorghum growing regions, irrespective of climatic and soil variations within agro-ecological regions The objective was to apply a well–calibrated and tested AquaCrop model to formulate optimal planting dates and best practice management recommendations for rainfed sorghum production in three different agro–ecologies of KwaZulu–Natal, South Africa (Ukulinga, Deepdale, and Richards Bay). The FAO AquaCrop model was used to generate 10 planting dates for the different agro–ecologies. Crop files for two sorghum genotypes Ujiba (landrace) and PAN8816 (hybrid) were used for model simulations, where 10 year historical climate data was considered. Seasonal rainfall, amount of soil evaporation, crop transpired water, and ground canopy cover were identified as key parameters influencing sorghum biomass, yield and water productivity. The following optimal dates were identified at Ukulinga (7 September - 24 November), Richards Bay (23 December - 3 January), and Deepdale (21 December - 3 January). These were recommended to update generic national recommendations for sorghum for agro-ecologies represented by the respective sites. High soil evaporation relative to transpiration in all agro-ecologies indicated that the low hanging fruit in improving sorghum yields was strategies use of strategies that reduce soil evaporation and increase soil water retention. Further research can look at calibrating and validating AquaCrop for best practice management recommendations suggested in this study to predict with accuracy the impact of such strategies on yield and water productivity of sorghum in various agro-ecologies. • Optimal sorghum planting dates at Ukulinga agro-ecological site were between 7 September and 24 November. • Optimal sorghum planting dates at Richard's Bay agro-ecological site were between 23 December and 3 January. • Optimal sorghum planting dates at Deepdale agro-ecological site were between 21 December and 3 January. • Rainfall was high but variable Richards Bay resulting in high soil evaporation, low transpiration and low crop yields. • Yields at Ukulinga and Deepdale were high due to high transpiration and relatively low evaporative demand. [ABSTRACT FROM AUTHOR]