Saturday, August 25, 2007

Tropical soils

When we drive from Santarém to Bosque Santa Lúcia, we go from a tropical savanna environment to the Planalto (highland), where soils continue to be nutrient poor. The attached image is on BR-163, going up to the top of the hill where the Brazilian Army base, 8th-BEC, is located. This cut in the road is an excellent chance to see what our soils are all about. Some years ago I took the time to collect samples from every different layer of terrain from the top to the bottom. I ended up with more than 30 jars of samples in the approximately 120 meters in difference of altitude. Except for a very thin layer of organic soil at the top, the rest was made up of very poor soils of clays and sands rich in aluminum and ferric oxides. In some very isolated places there are also outcroppings of latterite rock, a reddish colored rock formed by millions of years of percolation of water through these minerals.

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