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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.

Study region: Grass-reference evapotranspiration estimation by the Penman-Monteith method (PM-ETo) requires a number of climate variables which are not always available at all weather stations. Different alternative ETo equations have been developed and their utilization for various local climate conditions requires analyses of their accuracy as compared to the standardized Penman-Monteith method. There is a significant lack of data and information on this topic in the Senegal River Delta (SRD). Study focus: The objective of this study was to evaluate, calibrate and validate six ETo equations ((Trabert, Mahringer, Penman1948, Albrecht, Valiantzas1 and Valiantzas2) for the SRD. Although all six equations showed good agreement with the PM-ETo (R2 > 0.60) for daily ETo estimates, the Valiantzas2 equation was the best model for the Senegal River Delta and had the lowest root mean squared difference (RMSE) of 0.45 mm/day and the lowest percent error of estimate (PE) about 7.1%. New hydrological insights for the region: In the case of data limitations, the equations calibrated in this study are recommended for ETo estimation in the Senegal River Delta. The results of this study could be used by agricultural producers, crop consultants, university researchers, policy makers for the agricultural, hydrological, and environmental studies as well as proper allocation and use and forecasting in the SRD where lowland irrigated rice is predominant.

Study region: Reference evapotranspiration (ETo) plays a key role in irrigation systems design, water management under irrigated and rainfed production. Under the sahelian conditions in the Senegal River Valley that receives less than 300 mm annual rainfall, rice crop water use should be estimated for the sustainability of the resource. Study focus: However the Penman–Monteith (PM) equation is revealed the most accurate one; it necessitates several climatic parameters that are not always available mostly in the developing countries. The objective of this study was to evaluate the performance of 16 ETo equations against the ASCE-PM equation under the sahelian conditions at Ndiaye and Fanaye (Senegal) for alternate equation for ETo estimation with less climatic parameters. The results showed that the Hargreaves, modified Hargreaves, Ravazzani and Tralkovic equations systematically overestimated ETo with the highest percentage error of estimate (PE). In contrast, Makkink–Hansen, Oudin and Turc equations systematically underestimated ETo. Temperature based equations of Romenenko and Schendel performed relatively better at Fanaye with 5.5% and 9.6% PE, fitting slopes of 0.92 and 1.05, and mean ratio (MR) of 1.00 and 1.14, respectively. Mass transfer equations of Trabert and Mahringer also had good performance compared to the Penman–Monteith equation. New hydrological insights for the region: Overall, Valiantzas, Trabert, Romanenko, Schendel and Mahringer equations were the promising equations that could be used for reference evapotranspiration estimation in the Senegal River Valley. Keywords: Reference evapotranspiration methods, Evaluation, Senegal River basin, Sahel