CHAPTER 2 - SOILS AND CLIMATE

Soils^[1]

Brazil is characterized by a large diversity of soil types, resulting from the interaction of the different reliefs, climates, parent material, vegetation and associated organisms. This diversity and the consequent potential uses are reflected in the regional differences.

The North of the country comprises plains and low plateaus, with an equatorial climate, high and constant temperatures and high atmospheric humidity levels. The soils are deep, highly weathered, acidic and of low natural fertility. They are commonly saturated with exchangeable aluminum, which is toxic for most plant species. These characteristics reduce considerably the productive potential of the land, unless it is managed appropriately.

In the Northeast, the climate varies from hot and humid to hot and dry (semi-arid), with a transitional semi-humid area. In this transitional area, a large proportion of the soils are of medium to high natural fertility but most are shallow due to a low degree of weathering. A moisture deficit, sometimes associated with salinity and/or high levels of sodium, is the main factor limiting agricultural production in the Northeast.

The Brazilian Central Plateau, that is characteristic of the Center West region, is a plain formed by natural erosive processes. The predominance of a hot tropical climate with accentuated dry spells during the rainy season is very characteristic of this region. There are extensive areas of deep, well-drained soils, of low natural fertility, though easily corrected by liming and fertilization. Most of the soils in this region have favorable physical characteristics and topographical conditions that permit intensive agricultural mechanization. This is the region of Brazil where most agricultural development in grain production is occurring.

Plateaus and highland areas, with several peaks higher than 2 000 metres, characterize the Southeast region. This region has a tropical climate with hot summers in the low land and mild weather in the mountain areas. The soils are predominantly deep and usually of low natural fertility.

Source: Soils and terrain database for Latin America and the Caribbean, FAO-ISRIC-UNEP, 1998. FAO-GIS Jan. 2004

TABLE 2
Extent and distribution of soils in Brazil, Brazilian nomenclature

Source: Adapted from Coelho et al., 2002.

In the Southern region, the soils originated from basic rocks and there are several sedimentary soils. The relief is very varied. A subtropical climate prevails, with well-defined seasons. The soils are fertile with a good agricultural, forestry and livestock production potential.

Table 2 presents information concerning the soil classes in Brazil, according to Embrapa (1981) and the current Brazilian Soil Classification System (Embrapa, 1999).

In Table 3 the FAO Revised Legend (FAO, 1998) nomenclature approximately equivalent to the Brazilian nomenclature is shown.

Climate

The location of 92 percent of the Brazilian territory in the inter-tropical region and at low altitudes explains the predominance of hot climates, with average temperatures above 20°C. The main climatic types are equatorial, tropical, tropical of altitude, tropical Atlantic, semi-arid and subtropical (Figure 3).

TABLE 3
Brazilian and FAO soil nomenclature

An equatorial climate dominates in the Northern region, except in Tocantins, characterized by average temperatures between 24°C and 26°C and an annual thermal amplitude (differences between the maximum and the minimum temperature registered during one year) of up to 3°C. The rains are abundant (more than 2 500 mm/year) and regular, caused by the action of the continental equatorial mass. In the winter, the area can receive cold fronts originating from the Antarctic polar mass.

Extensive areas of the Central Plateau in the Centre west, Northeast and Southeast regions are dominated by a tropical climate. In these areas, the summer is hot and humid and the winter cold and dry. Average temperatures exceed 20°C, with an annual thermal amplitude of up to 7°C. The rainfall varies from 1 000 to 1 500 mm/year.

A tropical altitude climate prevails in the high parts of the Atlantic Plateau of the Southeast, extending from the north of Paraná state in the Southern region to the south of Mato Grosso do Sul State in the Centre West region. The average temperatures are between 18° C and 22°C and annual thermal amplitude between 7°C and 9°C. The rainfall pattern is the same as that of the tropical climate. The summer rains are more intense due to the action of the Atlantic tropical mass. In the winter, the cold fronts from the Antarctic polar mass can cause frosts.

A coastal band that goes from Rio Grande do Norte state in the Northeast to Paraná State in the Southern region is influenced by the tropical Atlantic climate.

Source: GuiaNet, 2003b.

The temperatures vary between 18°C and 26°C, with an increase in thermal variation towards the south. The rainfall amounts to about 1 500 mm/year. On the coast of the Northeast, the rainfall intensifies in the autumn and in the winter. Further to the south, the rainfall is higher in the summer.

A semi-arid climate prevails in the depressions of the plateaus of the Northeastern interior and in the Rio São Francisco valley in Bahia State. It is characterized by high average temperatures, around 27°C, and a thermal amplitude of 5°C. The rainfall does not exceed 800 mm/year and is irregular. This results in the long periods of drought, the “droughts of the Northeast”.

A subtropical climate prevails to the south of the Tropic of Capricorn, in parts of São Paulo (Southeast region), Paraná (Southern region) and Mato Grosso do Sul States (Centre West region) and in the States of Santa Catarina and Rio Grande do Sul in the Southern region. It is characterized by average temperatures below 18°C, with a thermal amplitude between 9°C and 13°C. In the highest areas, the summer is mild and the winter cold, with occasional snow. Rainfall amounts to between 1 500 mm and 2 000 mm/year, well distributed between the seasons.