Screening of 18 agroforestry species for highly acid and aluminum toxic soils of the humid tropics.

A screening trial involving 18 agroforestry species were initiated on highly acidic and Al toxic soils of Nkoemvone, Southern Cameroon, with the objective of identifying fast growing species that can be suitable for improving short fallows. Selected growth parameters evaluated were plant height, stem and crown diameter, number of stems at 3, 12 and 20 months after planting (MAP), and biomass yield at the first pruning (20 MAP). Then 9 months regrowths were evaluated for the same parameters. Outstanding height and stem diameter were observed for Indigofera zollingeriana, Inga edulis, Grewia mollis and Pterocarpus santalinoides. They reached between 6 and 9 m height and between 8 and 10 cm diameter. The best height was correlated to the best stem diameter for I. zollingeriana (8.7, 8.6), I. edulis (7.7, 10.1) and P. santalinoides (6.4, 10.3). The same four species developed a crown of more than 5 m diameter and easily out competed weed in the alley. G. mollis, Glyphea brewis, Dactiladenia barteri and I. zollingeriana had a shrubby architecture; G. mollis had up to 17 stem before the first pruning. Inga edulis and G. mollisproduced the highest total biomass, with respectively 61 and 39 t/ha dry matter. Other species with more than 20 t/ha total mass were I. zollingeriana, P. santalinoides, and Xylia xylocarpa. The first pruning stimulated shoot development, and the response of the species was similar to before the first pruning. Therefore I. edulis, P. santalinoides, G mollis and I. zollingeriana had the best growth performances and can be recommended for introduction in short fallows provided their contribution to soil fertility processes is assessed.