FORESTRY UPDATE by Gary Allen Burns 11-16

Soils can be grouped by their physical and chemical properties, as well as by particle size. Sand and silt are called primary minerals since they are chemically identical to the rock they originated from. They have a round or irregular shape and consist primarily of quartz (SiO2) or other silicate minerals. Because of their size and shape, sand particles have relatively low surface areas and large pores between the particles, resulting in good aeration, but limiting water availability.

Silt particles, on the other hand, have more surface area and can hold more water.

Clay consists of secondary minerals, resulting from the physical and chemical weathering of primary minerals. In temperate zones, clays are primarily phyllosilicate clays (plate-like minerals) that have a high surface area that promote water-holding capacity.

Clays in the humid tropics are Al and Fe oxides which have cations and anions susceptible to loss through leaching. Altering the pH, however, can aid in soil absorption and retention of plant nutrients.

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