Rainfed agriculture would remain the dominant source of staple food production and the livelihood foundation of the majority of the rural populace in semi-arid West Africa. Prolonged dry spells during the growing season often lead to significant crop yield losses, a situation that is expected to be exacerbated by climate change. In this study, impacts of climate change on the sorghum production system in West Africa semi-arid tropics was analysed using the most accessible process-based crop models (DSSAT, APSIM and Samara) and simulated at six stations under rainfed conditions. The mid-century future climate predictions by 2069 indicate the productivity of grain sorghum would be diversely affected due to the differences in the GCMs projections in terms of temperature and rainfall. On the average, climate change is projected to reduce low photoperiod sensitivity genotype (CSM63E) grain yield to the tune of 13%, and by 7% for both medium photoperiod sensitivity genotype (CSM335) and high photoperiod genotype (IS15401) across the selected sites. Results also indicate that adaptation strategies like longer grain filling period and sowing date reduced the vulnerability on both the medium and high photoperiod sensitivity genotypes (CSM335 and IS15401) compared to low photoperiod sensitivity genotype (CSM63E). As obtained from the study, proper genotypic calibrations and evaluations of crop models could be used to explain the expected outcomes of future climate conditions on the diverse photoperiod sensitivity sorghum genotypes available across semi-arid area. Also, these results would serve as reliable tools towards the understanding of future climate change and adaptation options to be implemented, which could be shared among farmers and development partners interested in food security issues in West Africa semi-arid zone. (Texte integral)
Fig. 1.Map of West Africa indicating the countries and sites included in the study.in West Africa (EPA Ghana, 2001; IPCC, 2007) and there are projections of further warming of the West African region in the foreseeable future (2040-2069; Fig. 2a).The impact of climate change on West African rainfall is less clear.The analysis of historical data over the last 30 years shows that, whereas some zones experienced increased rainfall by as much as 20% to 40%, other locations experienced a decline in annual rainfall by about 15%.Future projections suggest a drier western Sahel (e.g., Senegal) but a wetter eastern Sahel (e.g., Mali, Niger; Fig. 2b).The southern locations of West Africa (e.g., Ghana) are projected to experience no change or slight increases in annual rainfall (Hulme et al., 2001).Irrespective of whether these zones will be dryer or not, there is historical evidence of shifts in rainfall patterns with extreme events (i.e., droughts and floods) becoming more frequent (Adiku and Stone, 1995) and it is probable that this trend may persist into the future. Climate change impactsThe increased warming and shifts in rainfall patterns associated with climate change would adversely affect West African agriculture, which contributes between 40% and 60% of gross domestic product (GDP).Agriculture in West Africa is dominated by a large number of smallholder farmers, who cultivate a range of cereals (e.g., millet, maize, and sorghum) and legumes (e.g., peanut, cowpea, and soya).
An integrated modelling framework is used to simulate crop productivity for current and future climate scenarios. Two crop models, Decision Support Systems for Agro-Technological Transfer (DSSAT) and the Agricultural Productions Systems sIMulator (APSIM), were calibrated and evaluated for the study site in Koutiala, Mali, simulating yields of maize, millet, and peanut for 123 households. These crop models are fed by weather data from baseline climate (1980-2009) from observed weather and future climate (2040-2069) from 5 Global Circulation Models (GCMs) were used as inputs to crop models. The models' results differ according to the crop considered. For maize, there is a decrease of grain yield across all GCMs and crop models. For sorghum, there is a slight decrease across GCMs with DSSAT, but the grain yield remains constant on average with APSIM. For peanut and millet, the results are more optimistic and grain yield increases across all cases. These outputs will then be linked to the economical the Trade-Off Analysis-Minimum Data model (TOA-MD) to assess impacts on farmer livelihoods. Further, adaptation strategies (e.g. drought and heat tolerant cultivars) will be simulated to assess their potential impact for the future. (Texte integral)
Farming in drylands is the main source of livelihood for many inhabitants of West Africa.High variability in rainfall patterns, coupled with the soaring food prices, lead to a situation in which farmers' investments to increase productivity are very risky.Improving the scientific ability to quantify risks and likely damages of climatic extremes on cropping systems can support building resilience and longer-term development goals. Process-based cropping system models are a key tool to assess the impact of weather variability and climate change, or crop management options on the farming system resilience.Given the urgency of finding solutions for sustainable development in the face of increasing climate risks, we outline here key aspects of building the scientific basis to support the desired transformation of cropping systems in West Africa.
Sorghum is an important cereal crop cultivated by smallholder farmers of Mali, contributing significantly to their food demand and security. The study evaluated different fertilization strategies that combined organic and inorganic fertilizer applications with three sorghum varieties. The experiments were conducted over three cropping seasons (2017-2019) in three sites (Bamako, Bougouni, and Koutiala respectively) within the Sudanian region of Mali. Our results showed a significant effect of season, variety, and fertilization strategies on grain and stalk yields. Grain yield increased by 8-40% in Koutiala, 11-53% in Bougouni, and 44-110% in Bamako while the average stalk yield was above 5000 kg ha-1 with fertilized treatment compared to unfertilized treatment in the three sites. Fadda performed the best variety, mean grain yield was 23% and 42% higher than that of Soumba and Tieble, respectively. Similarly, there was a progressive increase in grain yield with an increasing level of poultry manure (PM) from 0 to 150 g/hill and cattle manure (CM) from 0 to 100 g/hill. However, the application of 100 g/hill of CM and PM plus 3 g/hill of Di-ammonium Phosphate (DAP) increased yield by 8% and 12% respectively compared to only CM or PM treatments. The results further revealed higher yield gain by 51% (Bamako), 57% (Koutiala), and 42% (Bougouni) for T10-[PM (100 g/hill) + Micro-D_DAP (3 g/hill)] equivalent to 73 kgNha-1 than others (T2-T9), but not proportionate to the highest value-cost ratio (VCR). Radar charts used to visualize sustainable intensification (SI) performance in the three domains (productivity, profitability, and environment) showed that the environmental variable has a direct influence on productivity, meanwhile profitability across the strategies ranged from low to moderate value across sites and different fertilizer strategies. Our study, therefore, recommends the use of multiple-choice fertilizer strategies includingT2-CM (50 g/hill)+PM(50 g/hill), T5-DAP-Micro-D (3 g/hill), T6-DAP41:46:00 and T9-PM(50 g/hill) alongside with improved sorghum varieties tested, for higher productivity and profitability across the region.
Abstract Sorghum production system in the semi-arid region of Africa is characterized by low yields which are generally attributed to high rainfall variability, poor soil fertility, and biotic factors. Production constraints must be well understood and quantified to design effective sorghum-system improvements. This study uses the state-of-the-art in silico methods and focuses on characterizing the sorghum production regions in Mali for drought occurrence and its effects on sorghum productivity. For this purpose, we adapted the APSIM-sorghum module to reproduce two cultivated photoperiod-sensitive sorghum types across a latitude of major sorghum production regions in Western Africa. We used the simulation outputs to characterize drought stress scenarios. We identified three main drought scenarios: (i) no-stress; (ii) early pre-flowering drought stress; and (iii) drought stress onset around flowering. The frequency of drought stress scenarios experienced by the two sorghum types across rainfall zones and soil types differed. As expected, the early pre-flowering and flowering drought stress occurred more frequently in isohyets < 600 mm, for the photoperiod-sensitive, late-flowering sorghum type. In isohyets above 600 mm, the frequency of drought stress was very low for both cultivars. We quantified the consequences of these drought scenarios on grain and biomass productivity. The yields of the highly-photoperiod-sensitive sorghum type were quite stable across the higher rainfall zones > 600 mm, but was affected by the drought stress in the lower rainfall zones < 600 mm. Comparatively, the less photoperiod-sensitive cultivar had notable yield gain in the driest regions < 600 mm. The results suggest that, at least for the tested crop types, drought stress might not be the major constraint to sorghum production in isohyets > 600 mm. The findings from this study provide the entry point for further quantitative testing of the Genotype × Environment × Management options required to optimize sorghum production in Mali.
• Crop production in West Africa is highly affected by climate variability and change. • Crop models are a key tool for designing crop management adaptation strategies. • Crop models can contribute to building climate resilient farming systems. • To achieve this, we outlined five action points that are related and interdependent.
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