Properties of rice soils affecting methane production potentials: 2. Differences in topsoil and subsoil

Abstract

Methane (CH4) is one of the important greenhouse gases accounting for 15% of the total enhanced greenhouse effect. A laboratory experiment was conducted with nine soils from the Philippines and two soils from India to determine the CH4 production potential of topsoil and subsoil, and to assess the role of different fractions of soil organic C in influencing CH4 production potential. CH4 production potentials of topsoils varied in a wide range from 20 μg g−1 soil (Urdaneta soil) to 837 μg g−1 soil (Pila soil) over 100 d of incubation. In contrast, CH4 production potentials of subsoils were low (< 2 μg g−1 soil over 100 d of incubation). The topsoil was the main source of CH4 in the flooded rice soils contributing 99.95% to the total CH4 production while the subsoil contributed negligibly (0.05%). CH4 production potentials of the topsoils showed significant correlation with cation exchange capacity (CEC), total N and available K contents of soils. For the subsoils, CH4 production potentials had a significant correlation with available P and clay contents of the soils. Considering the differences in all the soil properties and the CH4 production potentials between topsoils and subsoils, a significant relationship of CH4 production potential with CEC, available K and enriched C (extra C content of topsoil compared to that of subsoil) was obtained. Two carbon fractions, water soluble C (H2O-C) and carbon mineralised under anaerobic conditions (AnMC) affected total CH4 production indirectly rather than directly.