Potential Use of Rice Husk Biochar and Compost to Improve P Availability and Reduce GHG Emissions in Acid Sulfate Soil

Abstract

Acid sulfate soil (ASS) has major problems related to phosphorus deficiency and high potential for N2O emissions, as well as strong acidity. The objective of this study was to evaluate the effects of rice husk biochar and compost on P availability and greenhouse gas (GHG) emissions in ASS in in vitro incubation studies. An ASS was amended with two types of rice husk biochar (at rates of 0 g kg−1, 20 g kg−1, and 50 g kg−1, equivalent to 0 Mg ha−1, 20 Mg ha−1, and 50 Mg ha−1, assuming that bulk density was 1 g cm−3 and evenly applied for 10 cm in depth) and compost (at rates of 0 g kg−1, 10 g kg−1, and 20 g kg−1, equivalent to 0 Mg ha−1, 10 Mg ha−1, and 20 Mg ha−1) and incubated. Application of compost increased labile P by 100% and 200% at rates of 10 g kg−1 and 20 g kg−1, respectively. Both biochars showed an increase in NaHCO3-soluble inorganic P by 16% to 30%, decreases in NaOH-soluble inorganic P and NaHCO3-soluble organic P. N2O emissions were significantly decreased by 80% by a biochar with a higher surface area and higher NH4+ adsorption capacity at a rate of 50 g kg−1 as compared with those in un-amended soil. In contrast, compost amendment at a rate of 10 g kg−1 significantly increased N2O emission by 150%. These results suggest that in ASS, whilst compost is more effective in improving P availability, biochar is more effective in mitigating GHG emissions, emphasizing that fundamental characteristics of organic amendments influenced the outcomes in terms of desirable effects.