SIERRA LEONE maq 4ª.indd - agrilife - Europa

3 The Agricultural Sector
42
absorbed in the vegetation and not only in the
soils. Soils are often leached, resulting in acid soils
with problems of aluminium toxicity (Powell and
William, 1993). Major crops in the humid tropics
are maize, plantains, and tree crops.
Although permanent (i.e. non shifting) tree
cropping under forest (mainly in terms of cash tree
crops such as coffee and cocoa) are present in the
country, the most widespread agrarian system18 in
Sierra Leone is that of shifting cultivation. Under
this agrarian system, also known as the slash and
burn system, the vegetation is cleared by felling
of trees, burning, and planting of crops for a
specific period of one or two years. The nutrients
of the ash provide a rapid, initially lush growth
of crop plants. However, much of the ash and
the nutrients are lost through runoff or through
leaching. Another portion of the nutrients are lost
with the harvest of the agricultural crops. Only a
portion of the nutrients are recycled.
After harvesting the planted crops, the land
is left uncultivated or idle for natural regeneration
and quickly forms secondary forest (Mazoyer
and Roudart, 2006). According to Grigg (1974) if
regeneration takes place between 20-25 years it is
denominated forest-fallow, between 6 to 10 years
bush-fallow and between 1-2 years short-fallow.
In the case of Sierra Leone the idle intervals have
been continuously decreasing since 1960’s when
a 20 year period was sustained. Nowadays the idle
period is closer to the bush-fallow levels between
4 and 7 years (NSADP, 2009). Consequently, the
soil fertility is not fully restored, contributing to
the decline in yields19 .
18 In the Guidelines for Agrarian Systems Diagnosis (FAO
1999) the following definition by Mazoyer is given for an
Agrarian system: “a mode of exploiting the environment
historically created and sustainable; adapted to the
bioclimatic conditions of a given space and responsive to
the social conditions and needs of that moment”. Several
production systems together and the interactions between
them make up an agrarian system.
19 Several authors have already pointed out the danger of the
expansion of cropping and the reduction in fallowing (idle
period) as it raises the risk of environmental degradation
(Rothenberg, 1980; Mazoyer and Roudart, 2006).
Planted crops under the shifting cultivation
system include sorghum, millet, maize,
benniseed, groundnut and other grain pulses,
cassava, sweet potato, and vegetable traditionally
grown in mixed stands, with rainfed upland rice
dominating (IFPRI, 2009). A common practice
under this agrarian system is that of keeping some
land for permanent home gardens (i.e. natural
forest is replaced and household waste is used
as nutrients). Garden production includes sweet
potatoes, groundnuts and occasionally plantain
trees. Lowland rice production is also common
and the following rice cropping processes may be
identified:
a) Traditional wet-rice cultivation which exploits
natural flooding during summer rains.
b) Rain fed lowland.
c) River basin cultivation: along the Niger River
in West Africa.
d) Irrigated rice: modern intensive form of rice
cultivation which assures optimal flooding
(about 5 cm) throughout the growing season(s),
often long enough to allow double cropping.
The original vegetation in the sub-humid
tropical zones is woodland with medium to
tall grass ground cover, nowadays turned into
woodland savannas (covering 32% of Sierra
Leone’s territory). Several plant species are grown
in these areas, with rice and maize as major
crops. Tubers are also common. Production is
mainly utilised for the household’s member selfconsumption,
and it is residually marketed.
Rice is the major food crop present in
mixed cropping. The ratio of rice to other crops
is approximately 3:1 (MAFFS & MFMR, 2004).
Mixed cropping or intercropping is carefully
coupled with relay cropping20 . Cassava has
20 Relay cropping is a multiple cropping technique where
the second crop is planted before the first having been
harvested.