More than 80 percent of Liberia's soils can be used for agriculture. About 75 percent of all soils were formed on the extremely old, largely granites gneisses and other gneissic and schistic bedrock that underlie most of the country. Classed as latosols, they have been intensively leached by the heavy tropical rainfall and are of only medium to low fertility. These are the soils on which upland rice, the largest single food crop, is grown. Their limited amount of plant nutrients requires, without the use of fertilizer, a constant shifting of cultivation to new fields in order to maintain subsistence production levels. Large areas of these soils also support the country's major tree crops (see Commercial Crops, this ch.). Of the remaining soils, an estimated 17 percent, found mostly in hilly and mountainous areas, are lithosals (soils that are characterized by imperfect weathering and low humus and mineral nutrient content). Although they support tree and other woody vegetation, these soils have little value for agriculture. Other soils include sandy varieties (about 2 percent) found along the coast that are generally infertile (although they support large numbers of coconut trees, as well as oil palms), alluvial soils in the river bottoms, and swamp soils. The alluvial soils, when drained and fertilized, are well suited to growing swamp rice and other crops. Swamp soils, especially those known as half bog soils, are naturally rich in humus, and when drained they provide excellent conditions for swamp rice.
Although there have been some local soil surveys, countrywide data were insufficient in mid-1984 for a broad evaluation of soil potentials and agricultural suit abilities. For the near future, however, cultivable land to meet the needs of the subsistence population, as well as for expansion of export tree crops, was quite satisfactory. According to estimates of the Food and Agriculture Organization (FAO) in the early 1980s, only about 1,430 square miles of the country's total land area (roughly 3.9 percent) were used for cultivation. Permanent tree crops, such as rubber, coffee, and cacao, occupied 946 square miles, or two-thirds of the cultivated area; short-life crops, mainly foods, were produced on about 485 square miles. FAO also calculated that more than 21,000 square miles of additional land was in temporary bush and tree fallow-much of it at a stage available for agricultural use (see Forestry, this ch.). There was little pressure on the fallow areas in the less heavily populated rural regions, and about 80 percent of the subsistence farmers in those regions were reportedly using for crops new land on which the age of the tree or bush stands was seven or more years. The situation was different, however, in heavily peopled areas near the towns where the fallow cycle on good land has been found to be as short as four years, a period generally inadequate to allow the replacement of natural soil nutrients.
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