INTRODUCTION
Acidification of soil is a natural process with major
ramifications on plant growth. As soils become more
acid, particularly when the pH drops below 4.5, it
becomes increasingly difficult to produce food crops.
As soil pH declines, the supply of most plant nutrients
decreases while aluminum and a few micronutrients
become more soluble and toxic to plants. These
problems are particularly acute in humid tropical
regions that have been highly weathered. According to
Sanchez and Logan (1992), for example, one third of
the tropics, or 1.7 billion hectares, is acid enough for
soluble aluminum to be toxic for most crop plants. We
will look at some of the causes of acidification and list
some of the expected results of both acidification and
the practice of liming for acid neutralization.