Abstract:
Acid sulfate soils (ASS) are not readily suitable for crop cultivation, because most crops are intolerant
to soil acidic conditions. The occurrence of ASS in the Wet Zone of Sri Lanka has been a significant
barrier to paddy cultivation. Phosphorous (P)-deficiency coupled with Aluminium (Al)-toxicity are
the key constraints for crop growth in ASS. This study aimed at investigating the changes of nutrient
availability in ASS in response to addition of biochar and different P sources under two water
management regimes. An incubation soil experiment was conducted at Regional Rice Research and
Development Center, Bombuwala as a two-factor factorial experiment in a complete randomized
design with 3 replicates for a period of one month. ASS collected from a farmer paddy field was used
for the experiment. Treatments comprised of application of Triple Super Phosphate (TSP) (35 kg/ha)
to the recommendation of the Department of Agriculture, Sri Lanka for rice crop, Rock Phosphate
(RP) as the same rate of P2O5 of TSP application, rice husk biochar (5% of dry weight of soil) and
unfertilized control soil. All treatments were evaluated under two water management regimes,
Continuous Flooding (CF) (2-cm water level above the soil) throughout the experimental period and
Alternate Wetting and Drying (AWD) (2-cm overlying water for one-week, removed and kept drying
during succeeding week). After one month, soil was sampled and analyzed for pH, electrical
conductivity, available P, Potassium (K), total Nitrogen (N), and bioavailable concentrations of Al,
Iron (Fe), Zinc (Zn), Manganese (Mn), Copper (Cu) and Cobalt (Co). Biochar addition significantly
(P<0.05) increased soil pH (CF 3.17±0.00, AWD 3.19±0.01) bioavailable K (CF 133.33±6.67 mg/kg,
AWD 153.33 ± 6.67 mg/kg) and Mn concentrations (CF 10.38±0.36 mg/kg, AWD 13.94±2.03 mg/kg)
in soil and there was no any significant influence on the availability of other metals in ASS. Across
two water management regimes, bioavailable Al concentration of soil amended with biochar was
reduced respectively by 64% and 49% compared to those of soils amended with TSP and RP. The
results indicate the potential of amending biochar to increase pH and alleviate Al toxicity in ASS
which should be further confirmed by a long-term experiment in the field.
