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Its average content in soils and rocks of the earth's crust is 0.12 percent, whereas
that of iron is 5 percent, of calcium 3.6 percent, of potassium 2.6 percent, and of
magnesium 2.1 percent. Thus, when phosphorus is removed from the soil by
crops, it must be replaced artificially by the addition of phosphate fertilizers.
Phosphorus is also used widely in manufacturing industries. Nearly all of the
phosphate fertilizers and phosphorus for industrial uses are obtained from
naturally occurring ...
Other resources. The quality of the soil varies, but there are large fertile areas,
including the Szczecin region, the Kujawy, the Wisla delta, and the Lublin area.
The soil is somewhat poorer in large parts of southern, central, and northern
Poland, while part of Silesia and the Sudety and the Carpathian Mountains are
characterized by brown forest soils. Less than 30 percent of the country's total
land area is wooded and, of this, some 80 percent is occupied by coniferous
timbers, with pine, ...
About 38 percent of the population is under 20 years of age, 29 percent between
20 and 40 years of age, 21 percent between 40 and 60, and 12 percent over 60
years of age. Migration. Portugal has one of the highest rates of emigration in
Europe. Before 1960 most of its migration was to Brazil and a few other Latin
American countries. In 1965 about 100,000 persons of eligible working age left
the country, while the natural population increase was 115,112. By 1970
emigration to ...
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