ABSTRACT
Approximately 5% of the 3.95 billion ha of acid soils is used for agricultural production
while 67% supports forests and woodlands (von Uexku¨ll and Mutert 1995). Plant growth in
acid soils is usually limited by low pH and=or Al toxicity. The solubility of Al and Mn in mineral soils increases rapidly when soil pH drops below a value of 5 so that low pH and
high soluble Al and Mn concentrations are interrelated. Although the availability of plant
nutrients such as P and Ca can be limiting at low soil pH (Foy 1984; Asp and Berggren
1990), Al toxicity is probably the foremost growth-limiting factor in acid soils (Andersson
1988). Root growth, and consequently water and nutrient uptake, are inhibited when dissolved
Al attains toxic levels in soil solutions.
