Acid sulfate soil scover quite a large area i n the Central Plain of
Thailand which is an important rice producing region of the country. As
a result of the low pH and the low fertility of these soils , rice yields
are very low to low. To increase rice production and to maximize the net
profit , improvement of acid sulfate soils by liming and fertilizer applications
was studied and the resul t s are reported in this paper.
Four acid sulfate soil series with different pH values, depths of jarosite and suitability classes for rice, namely Rangsit very acid phase,
Rangsit, Maha Phot and Ayutthaya series were selected at eight different
' locations. The surface soil (0-20 cm) of each soil series was collected
for chemical analysis before conducting the experiment. The high yielding
and non-photoperiod sensitive variety 'RD-7' and a local photoperiod
sensitive variety were planted. Marl (a liming material), ammonium sulfate , ammonium phosphate and Thai rock phosphate were applied in a randomized
complete block design with 4 replicates .
In moderately acid s o i l s , Maha Phot and Ayutthaya series, application of
marl had little effecton yield. Applying ammonium sulfate alone (150
1
I
' kg/ha) or with Thai rock phosphate (1.250 kgfha) tended to give a high
' y i e l d . E i t h e r marl at 6.25 to 12.5 tons/ha with ammonium phosphate at
t
187.5 kg/ha or ammonium s u l f a t e alone may be applied to maximize net
p r o f i t .
In the severely acid Rangsit s o i l , r i c e responded strongly to m a r l (6.25