Response of soil moisture, growth and biomass yield of Adansonia digitata under biochar application in Benin, West Africa

Adansonia digitata L. (hereafter, A. digitata or Baobab) is widely distributed across the African continent, but its survival is threatened by low natural regeneration, and the effects of climate change. This study investigates the effect of biochar on soil moisture, growth parameters, and biomass yield of baobab seedlings. Three doses of biochar were applied, including B0: 0 g/plant, B20: 20 g/plant, and B35: 35 g/plant at the beginning of the experiment (0 day after transplanting, DAT). Soil moisture was measured at three radial distances from the seedling stems. The results show that the average soil moisture was 2.4% lower under B20 than B0, but no significant difference was observed between B0 and B35. Moreover, the soil water content varied with the local rainfall events, showing the highest soil moisture content at 0, 10, and 45 DAT, and the lowest at 21, 24, and 51 DAT. As expected, the leaf number, stem diameter, and height of seedlings increased with time. The leaf number growth rate was overall 0.8, 0.9, and 0.5 leaves/day between 0–30, 30–60, and 60–90 DAT, respectively; but was 32%, 44%, and 39% lower under B20 than B0, and 10%, 12%, and 6% lower under B35 than B0. The soil moisture was positively correlated with dry biomass, but negatively with growth parameters, and fresh biomass. It emerges from this study that the application of biochar did not consistently improve soil water retention or baobab seedling growth, highlighting the importance of adapting application rates to local pedoclimatic conditions.