NATIVE SULPHUR MINERALIZATION AND MINERALIZATION RATE UNDER AEROBIC INCUBATION IN RICE-BASED SOILS

Abstract

Sulphur mineralization is a crucial process controlling the availability of sulphur for plant nutrition; however, mineralization rates are strongly dependent on temperature, incubation period and the initial sulphur status of the soil. The objective of this study was to evaluate native sulphur mineralization under aerobic conditions in two rice varieties namely Kamala and Samba Mahsuri with increasing levels of elemental sulphur (0, 20, 40 and 60 kg S ha-1). The soils were incubated at 25 ± 1 and 45 ± 1 °C for 2, 4, 6 and 8 weeks and sulphur mineralization was determined as an increase in 0.15% CaCl2 extractable sulphur during incubation. The rate of sulphur mineralization was calculated according to Janzen and Bettany (1987). The study revealed that sulphur mineralization increased with an increase in the incubation period up to 6 weeks and then decreased slightly at 8 weeks. The mineralized sulphur at 25 °C increased from 4.46 µg S g-1 at 2 weeks to 9.58 µg S g-1 at 6 weeks of incubation whereas, at 45 °C, it increased from 12.05 to 25.86 µg S g -1 during the same period. During the entire incubation period, sulphur mineralization was greater at 45 °C (20.84 µg S g -1) compared to 25 °C (7.72 µg S g 1 ). The control treatment had greater sulphur mineralization over the treatment with added sulphur and sulphur mineralization was greater in Kamala than in Samba Mahsuri. Furthermore, a progressive decrease in sulphur mineralization rate was observed with increasing incubation period from 3.36 to 2.12 µg S cm2 d-1 at 25 °C and from 9.09 to 5.74 µg S cm2 d-1 at 45 °C.