TRACE ELEMENTS IN THE CONTINUUM PYROCLASTIC BALSALTS-SOILS-PLANTS IN THE FOUMBOT AREA (WEST-CAMEROON): IMPLICATIONS FOR ROCK FERTILIZERS TECHNOLOGY

The Noun river basin is located in the central part of the Cameroon Volcanic Line. Trace elements investigations were carried out in food plants farmed on ash basalts in the perspective of the use of these ash basalts as rock fertilizers.

The concentration of trace elements in soils reflected those ash basalts. The observed variation in trace elements between soils samples are probably controlled by the differences in the nature of the bedrock and by the relief. In addition, notorious toxic elements such as As and Cd showed low concentrations. The geochemical base of the soils compared to rocks and soils of the world, the normal range in the soils and the permissible levels do not suggest any anthropogenic influence. Some trace elements analysed in the plants have concentrations that reflect those of the soils (Al, Fe, Ti, Rb). However, some other trace elements are present in the plants in quantities higher than the concentrations found in soils: Zn, C, Cd, Mo (excluding yam), Ni (groundnut), Ba (groundnut), Sr (groundnut, bean) and B. Trace elements such as As, Cr, V are not bioavailable for all the analysed plants. Besides, trace elements such as Co, Cd, Mn, P, Sr, Ti and U are found in the normal range of concentrations in the plants while others such as Cu, Zn, Mo, Fe, Al, Ni, B, Ti, Rb, Cs and Ba are in the range of phytotoxixity and even reach or exceed the human food tolerance level (Cu). No plant shows deficiency in the analysed trace elements. The lack of toxic elements in soils developed on basalt indicate that these volcanic rocks can be suitably used in the rock fertilizers technology.

An evaluation of the fertilizing potential of pyroclastic basalts from the Foumbot area was carried out. Field tests concerned additions of 150g, 300g and 450g of basalt powders to plots of 0.25 m2 and revealed a noticeable increasing pH (5.2 to 6.4) in the soil during the early stages of growth of maize plants. The results indicate the average output with respect to the cultivated surfaces 2.855 t/ha for Ekoh, Ndon, Pouolom and Mfeusset basalts respectively and 0.274 t/ha for the zero % powder plot. The maximum. The maximum production obtained using basalt powder of the Mfeusset cone corresponds to an addition of 12 t/ha of basalt powder.