Water, nutrients and slope position in on-farm pearl millet cultivation in the Sahel

In the Sahel, short periods of intra-seasonal drought, caused by unfavourable rainfall distribution, often have stronger effect on crop growth than fluctuations in annual rainfall. The interactive effects of nutrient deficiency and water shortage (during panicle initiation, flowering and grain filling) on yield and yield components of pearl millet (#Pennisetum glaucum$ (L.) R. Br.), were studied on-farm along a cultivated slope, during three years with close to average annual rainfall. Grain yield was correlated to plant nutrient availability but not to annual rainfall, which was explained by the capacity of the crop to compensate for damage caused by water shortage during early growth phases. The performance of each yield component was positively correlated to cumulative rainfall during the growth phase when it was formed. Leaf aera index (LAI) was very low, and leaf development followed rainfall distribution. Water and nutrients interacted during each growth phase for all fertility levels. Fertilised millet suffered less during water shortage at panicle initiation and at grain filling compared to non-fertilised millet. However, compared to favourable soil water conditions yield components were systematically lower for all treatments, indicating the synergistic effect of water and nutrients. The results suggest that water availability plays an exclusive role during flowering. Grain number dropped significantly due to water shortage and was similar for all treatments. Despite extremely high spatial variability in yields (varying with a factor 46 within the field), a significant slope effect was observed, of progressively increasing yields when moving downslope. Spatial redistribution of spatial runoff resulting in higher soil water availability on lower slope positions, contributed to the yield gradient, which was reinforced for fertilised millet... (D'après résumé d'auteur