PHOTOSYNTHESIS AND BIOMASS PRODUCTION BY MILLET ( PENNISETUM GLAUCUM ) AND TARO ( COLOCASIA ESCULENTA ) GROWN UNDER BAOBAB ( ADANSONIA DIGITATA) AND NÉRÉ ( PARKIA BIGLOBOSA ) IN AN AGROFORESTRY PARKLAND SYSTEM OF BURKINA FASO (WEST AFRICA)

Photosynthesis and biomass production by millet (Pennisetum glaucum) and taro (Colocasia esculenta) grown under baobab (Adansonia digitata) and nere (Parkia biglobosa) was studied at Nobere (Burkina Faso) with the aim of optimising parkland systems productivity. Millet yielded the highest biomass under Baobab and the lowest biomass was recorded in the zone close to the tree trunk of nere. In contrast, the biomass of taro was higher in heavy shaded zones under nere and the zone close to baobab's trunk. The two crops showed an increasing trend of photosynthesis rate (P-N) from tree trunk to the open area. However, the increase in the P-N of taro from tree trunk to the open field was lower compared to that of millet. By increasing its leaf area index (LAI) under shade, taro displayed higher biomass production under tree compared to the open area while an opposite trend was observed in millet. The high millet biomass production under baobab could be explained by light availability and the reduction of temperature under shade compared to the open field. The adaptation of taro to shade by increasing its LAI and thus avoiding drastic reduction in P-N under shade resulted in better biomass production under heavy shade. Therefore, it was concluded that by replacing millet with taro under dense tree crowns the productivity of agroforestry parkland systems could be increased.