Abstract:
Soil acidity is a major constraint limiting paddy productivity in the Low Country
Wet Zone (LCWZ) of Sri Lanka, while the high cost and limited availability of
conventional liming materials such as dolomite restrict their use among farmers.
Although wood ash has long been recognized as a liming agent, comparative information
on the effectiveness of locally available plant and residue-derived ashes
compared with dolomite remains limited. Therefore, this study aimed to evaluate
the comparative liming effect of different ash sources. An eight-week laboratory
incubation experiment was conducted using acidic paddy soil collected from
the Regional Rice Research and Development Centre, Bombuwela, Sri Lanka.
Treatments were arranged in a Completely Randomized Design with four replicates.
Ashes (2 t ha-1) derived from rubber (Hevea brasiliensis), cinnamon (Cinnamomum
verum), alstonia (Alstonia macrophylla), and rice husk (Oryza sativa
residue) were applied, along with dolomite and an unamended control, with recommended
rates of N, P, and K fertilizers (urea – 40 kg/ac, MOP – 44 kg/ac,
TSP – 20 kg/ac, respectively) as per Department of Agriculture guidelines. The
ashes were produced under open combustion conditions, with recorded pH ranging
from 9.5 to 12.9. Soil moisture was maintained at 50% of field capacity, and
weekly measurements of pH, EC, available P, exchangeable K, and organic matter
(OM) were conducted. All ash treatments significantly (p < 0.05) increased soil
pH compared to the control, while cinnamon ash exhibited the highest liming efficiency
in week 2, raising soil pH from 4.65 to 6.0. However, dolomite-treated soil
showed significantly (p<0.05) higher pH (5.67) in week 8. Cinnamon ash-amended
treatment increased available P (from 4.4 to 17.56 ppm) and exchangeable K (from
17.93 to 258.48 ppm) by week 8. EC values increased in all treatments, with significantly
(p<0.05) highest EC (278.25 μ S/cm) observed in cinnamon ash-treated
soil. Organic matter content improved significantly (p<0.05) in rubber (8.8%)
and alstonia (8.2%) amended treatments compared to the control. The findings
suggest that using locally available cinnamon wood ash could provide an affordable
and sustainable alternative to dolomite for ameliorating acidic soils in the
LCWZ. Field-scale validation is recommended prior to widespread agricultural
adoption.
