PERTANIKA JOURNAL OF TROPICAL AGRICULTURAL SCIENCE

About two-thirds of crude oil is produced in countries with tropical and subtropical climates. Many sites in these regions have been threatened by oil spills that can adversely affect soil physical, chemical and biological properties. In some tropical countries, such as Mexico, Venezuela, India, and Nigeria, studies have been conducted to evaluate the effects of petroleum spills on soil fertility, often by monitoring pasture germination or contaminant toxicity. It has been observed that most common impacts to petroleum-contaminated soil occur by two mechanisms: a) by the formation of a thin layer of hydrocarbons on soil particles that results in a reduction in field capacity and causes soil water repellency; and b) by the formation of macro-aggregates (agglomeration) of fine soil particles into coarse particles, thus causing compaction and reduced porosity in the soil. In these studies, it appears that the type and quantity of soil clays influence how severe these impacts may be, being mitigated in the presence of higher contents of smectite clays and being more intense in soils with other fine materials (silts, kaolinite clays, Fe/Al oxides). However, these results have been observed as circumstantial evidence in natural soils. To better understand the relationship between petroleum hydrocarbons and soil clays, an artificial soil system is suggested in which the type and amount of soil clay can be controlled.