Geoscience Reference
In-Depth Information
necessary to abandon that location and slash-and-burn elsewhere. If no
area is available and if one does not wait 10-30 years before starting over
in the same location, the forest regenerates poorly for the reasons given
earlier. Its survival is compromised, and also that of the populations that
live through slash-and-burn agriculture. It is believed by some that this
explains the disappearance of the Mayan civilization.
The carbon of the burned wood comes from the CO
2
of the air
previously fixed in the wood. Thus, this cycle of incorporation and
burning does not increase the greenhouse effect. On the contrary,
charcoal is produced, which stores carbon for long in the soil (Rumpel
2006).
In view of the lack of general fertility and in absence of fertilization,
African farmers have devised methods aimed at economizing the
mineral and organic components of fertility and at reducing erosion.
These are
seed-hole agriculture
(the seeds are placed in holes where the
available fertilizers are concentrated) and
agriculture on mounds
(mounds
are raised, sometimes to a height and diameter of one metre—as for
cassava).
Low-input Cropping
The soil being deficient in almost all aspects, it will be necessary to
apply N, P, K, Ca, Mg and S in sufficient quantities, while avoiding
irreversible fixation (P), acidification and leaching (N). For ploughing,
precautions must be taken to prevent erosion of cultivated land, which
is often severe in high-rainfall regions.
Modern agriculture
CONCLUSION
Impoverished by torrential rains over tens of millions of years, the
Ferralsols concentrate in themselves the less soluble elements: iron
(cuirasses), aluminium (gibbsite) and quartz, sometimes kaolinite if
silica remains partially. Large part of the elements is removed and there
is a slow but inexorable subsidence of the soil/atmosphere interface.
The soils are almost completely depleted of all reserves needed by
plants for their growth. Thus fertilization is necessary. But this is
not simple: presence of free aluminium, lack of organic reserves and
insufficient exchange capacity leading to losses through drainage are
major problems. Added to these are erosion hazards. Agriculture thus
