<P> The largest areas of fertile soils, called terra roxa (red earth), are found in the states of Paraná and São Paulo . The least fertile areas are in the Amazon, where the dense rainforest is . Soils in the Northeast are often fertile, but they lack water, unless they are irrigated artificially . </P> <P> In the 1980s, investments made possible the use of irrigation, especially in the Northeast Region and in Rio Grande do Sul State, which had shifted from grazing to soy and rice production in the 1970s . Savanna soils also were made usable for soybean farming through acidity correction, fertilization, plant breeding, and in some cases spray irrigation . As agriculture underwent modernization in the 1970s and 1980s, soil fertility became less important for agricultural production than factors related to capital investment, such as infrastructure, mechanization, use of chemical inputs, breeding, and proximity to markets . Consequently, the vigor of frontier expansion weakened . </P> <P> The variety of climates, soils, and drainage conditions in Brazil is reflected in the range of its vegetation types . The Amazon Basin and the areas of heavy rainfall along the Atlantic coast have tropical rain forest composed of broadleaf evergreen trees . The rain forest may contain as many as 3,000 species of flora and fauna within a 2.6 - square - kilometer (1 sq mi) area . The Atlantic Forest is reputed to have even greater biological diversity than the Amazon rain forest, which, despite apparent homogeneity, contains many types of vegetation, from high canopy forest to bamboo groves . </P> <P> In the semiarid Northeast, caatinga, a dry, thick, thorny vegetation, predominates . Most of central Brazil is covered with a woodland savanna, known as the cerrado (sparse scrub trees and drought - resistant grasses), which became an area of agricultural development after the mid-1970s . In the South (Sul), needle - leaved pinewoods (Paraná pine or araucaria) cover the highlands; grassland similar to the Argentine pampa covers the sea - level plains . The Mato Grosso swamplands (Pantanal Mato - grossense) is a Florida - sized plain in the western portion of the Center - West (Centro - Oeste). It is covered with tall grasses, bushes, and widely dispersed trees similar to those of the cerrado and is partly submerged during the rainy season . </P>

There are no west flowing rivers in brazil give geographical reason