Laboratory Study of Methane Flux from Acid Sulphate Soil in South Kalimantan

Addition of organic matter in waterlogged conditions will enhance methanogenesis process that produces greenhouse gases. Fresh organic material is considered reactive because it contains carbons that is subject to decompose, therefore, when it exposed to acid sulphate soil, both in natural condition (aeration required) and intensive (aeration not required) will lower the value of redox potential. This experiment aimed to determine the flux of methane (CH₄) from various locally available organic materials applied to acid sulphate soil. The experiment was arranged in factorial design with two factors. The first factor was the source of organic matter, i.e. fresh rice straw, fresh purun, fresh cattle manure, composted rice straw, composted purun and composted cattle manure, and control. The second factor was the management of organic matter i.e. placed on the soil surface with no tillage and mixed with soil during tillage. The results showed that application of fresh organic matter into inundated acid sulphate soil increased CH₄ fluxes up to 23.78 µg CH₄ g¹ d¹ which was higher than from composted organic matter (4.327 µg CH₄.g¹.d¹). Methane flux due to organic matter management was significantly negatively (p=0.001) correlated with soil redox potential (Eh) with R2 of - 0.76. Organic matter placed on the soil surface with no tillage produced methane flux ranged from 0.33 to 20.78 g CH₄ g¹ d¹, which was lower than methane flux produced from organic matter mixed with soil during tillage (0.38 to 27.27 g CH₄ g¹ d¹). Composting organic matter before application and mixing them with the soil through tillage are highly recommended to reduce greenhouse gas emissions from cultivated acid sulphate soils.