Acid sulfate soils (1) occupy significant
areas of alluvial coastal swamps, particularly
in the tropics. They are inundated, or at least
saturated, by water during most of the year,but
if drained the large amount of sulfide which
they contain is oxidised to sulfate resuiting
in extremely low pH values (2).
Because it is relatively tolerant of acid
conditions and suited to the topographic sites
on which such soils occur, rice is one of the
crops commonly planted on reclaimed areas.
However, under the low pH conditions existing,
toxic quantities of iron and aluminum, and
possibly manganese, cause plant damage and
retard growth (1, 3). On the other band,
CATE et al (4) have considered that the amount
of exchangeable aluminum (KCl extractable) is
reduced to insignificant levels if the land is
flooded - as it is for lowland rice growing.
On the basis of water culture experiments the
present authors (5) have suggested that the
high level of iron present in the soil solution