RESUMO
Cereal-legume intercropping has been traditionally practiced across West Africa by farmers and provides resilience of agriculture to climate variability. Intensification of these extensive intercropping systems in order to meet future food demand is critical. This study aims at evaluating the agronomic performance of the intensification of millet-cowpea intercropping with low cowpea density, and its variation with climate variability, using an on-station experiment in Bambey, Senegal. Two trials (irrigated vs rainfed) were set up to compare millet sole- and inter-cropping with a grain and a fodder variety of cowpea, in 2018 and 2019. Two levels of fertilization were tested: 0 kg(N) ha-1 and 69 kg(N) ha-1. The two cropping years were contrasting and water stress around flowering and/or during grain filling (indicated by the Fraction of Transpirable Soil Water) was higher in 2019 than in 2018 in the rainfed experiment. In both experiment and for all treatments, land equivalent ratio (LER) in the intercropping was 1.6 and 1.4 for grain and biomass respectively. Millet aboveground biomass was significantly higher in intercropping than in sole cropping in the irrigated experiment but not in the rainfed experiment. In the rainfed experiment, the interaction between cropping system and year was significant, so that millet aboveground biomass was greater in intercropping than in sole cropping in 2018 (year of lower water stress) but not in 2019 (year of higher water stress). The effect of fertilization on millet aboveground biomass did not significantly interact with cropping system (sole vs intercrop). For grain yield, fertilization interacted significantly with the cropping system in the irrigated trial: the benefits of intercropping on millet grain yield were greater with 69 kg(N) ha-1 than with 0 kg(N) ha-1. This significant interaction could not be observed in the rainfed trial, potentially due to water stress. These results show that the level of water stress (related here to the year and to the rainfed or irrigated experiment) and that of fertilization modulate the performance of millet-cowpea intercropping in the semi-arid context of Senegal. Overall, fertilization had a stronger effect on millet grain yield than intercropping. The two strategies (intercropping and mineral fertilization) can be complementary to achieve sustainable intensification of cropping system in semi-arid areas of West Africa.
RESUMO
Smallholder farmers in sub-Saharan Africa (SSA) currently grow rainfed maize with limited inputs including fertilizer. Climate change may exacerbate current production constraints. Crop models can help quantify the potential impact of climate change on maize yields, but a comprehensive multimodel assessment of simulation accuracy and uncertainty in these low-input systems is currently lacking. We evaluated the impact of varying [CO2 ], temperature and rainfall conditions on maize yield, for different nitrogen (N) inputs (0, 80, 160 kg N/ha) for five environments in SSA, including cool subhumid Ethiopia, cool semi-arid Rwanda, hot subhumid Ghana and hot semi-arid Mali and Benin using an ensemble of 25 maize models. Models were calibrated with measured grain yield, plant biomass, plant N, leaf area index, harvest index and in-season soil water content from 2-year experiments in each country to assess their ability to simulate observed yield. Simulated responses to climate change factors were explored and compared between models. Calibrated models reproduced measured grain yield variations well with average relative root mean square error of 26%, although uncertainty in model prediction was substantial (CV = 28%). Model ensembles gave greater accuracy than any model taken at random. Nitrogen fertilization controlled the response to variations in [CO2 ], temperature and rainfall. Without N fertilizer input, maize (a) benefited less from an increase in atmospheric [CO2 ]; (b) was less affected by higher temperature or decreasing rainfall; and (c) was more affected by increased rainfall because N leaching was more critical. The model intercomparison revealed that simulation of daily soil N supply and N leaching plays a crucial role in simulating climate change impacts for low-input systems. Climate change and N input interactions have strong implications for the design of robust adaptation approaches across SSA, because the impact of climate change in low input systems will be modified if farmers intensify maize production with balanced nutrient management.
