mortiz085

Tropical regions occur between the Tropic of Cancer and the Tropic of Capricorn. The tropics include approximately 40% of the land surface and is the largest ecozone of the earth. According to Köppen (1931), the tropics are characterized by an annual mean air temperature above 18°C through­out the whole year. The largest climatic variation is introduced by the variability of precipita­tion, reaching from nearly 0 mm in the Saharan and Atacama Desert to 11,700 mm on Mt. Waialeala in Hawaii (Eswaran et al., 1992). An Afisol (Luvisol) soil derived from mudstone in Eastern Samar, Philippines According to Uehara and Gillman  (1981), "t ropical soils" is a common name used to identify any soil that occurs in the tropics. They noted that like most common names, the term lacks precision, but it is more readily understood by a larger audience than are the scientific names. In contrast, Sanchez (1976) argued against the use of the term "tropical soils" since it does not accur...

A soil at the heart of Samar, the third largest island of the Philippine archipelago, and along the Paranas-Taft road at about 300 m above sea level (within the Samar Island Natural Park) easily catches the attention of travellers. This is because it is unique: it is green in color. As far as I know, no soil with such color has yet been reported in the scientific literature. The melanterite soil near the Bagacay mining area in Samar island The dominant green color is probably due to the abundance of the secondary mineral called melanterite, a hydrated iron sulphate mineral (FeSO4.7H2 O) formed from the decomposition of pyrite or other iron minerals due to the action of surface waters. Melanterite is known to be stable only under highly acidic condition. It is commonly found in mines as a post-mining formation on mine walls, in sulfidic sedimentary and metamorphic rocks as well as in coal and lignite deposits. It indicates the possible presence of sulfuric acid and should not be handled...

The Amazon Basin is that part of South America drained by the Amazon River and its tributaries. It has a tropical climate with an annual rainfall of 1500-2500mm, and a day temperature of 30-35 degrees Celsius (Wikipedia). Much of what we now know about tropical soils was derived from many years of research in the Amazon rainforest. It is now widely known that this very important rainforest is growing on largely infertile and highly wethered soils called Ferralsols in the IUSS World Reference Base classification or Oxisols in the USDA Soil Taxonomy (see photo of typical soil profile). It has been suggested by some ecologists that the efficient nutrient cycling and the periodic dust deposition from Africa explain why the infertile soils are able to support the lush rainforest vegetation. In the recent issue of the international journal Biogeosciences Discussions, Quesada and colleagues reported the results of their interesting study on the soils in the Amazon Basin. Highlights of their f...

The classical view about soils of tropical rain forest ecosystems is that these soils are old, acidic, and infertile. It is now widely acknowledged that this view which has greatly influenced research and management of the fragile rain forest ecosystem during the last several decades is largely a misconception. Although highly weathered soils (Oxisols or Ferralsols) are the most dominant soils in the humid tropics, tropical soils range from relatively young fertile soils (e.g. Inceptisols) to the highly weathered infertile soils (e..g. Oxisols). The extent of highly weathered soils is less in geologically young areas like in much of SE Asia. More detailed investigations of rain forest soils are vital for the sustainable management of this threatened ecosystems. These could also lead to a better understanding of the response of rain forests to climate change. Navarrete et al. (2009) recently conducted a study to evaluate the physical, chemical and mineralogical characterisitics of rain ...

Weathering is the physical, chemical, and biological alteration of minerals in rocks, sediments, and soils at or near the Earth’s surface. It is an important link in the global rock cycle and is also an essential process for the formation of soils and landforms. Chemical weathering of silicate minerals which compose over 90% of the Earth’s crust, removes CO 2 from the atmosphere so it helps regulate the Earth’s climate over long time scales. Basalts are among the more easily weathered crystalline rocks thus, weathering of these rocks acts as a major CO 2 sink. Chemical weathering of rocks likewise releases nutrient elements for use by the biota in the ecosystem and also produces clay minerals which are the central components of soils. We studied the weathering of basalt by evaluating the gain and loss of elements, stream water composition, weathering indices, and clay mineral formation in the soil derived from basalt under the humid tropical conditions (average annual rainfall of ...