Microbial activity of potential and actual acid sulphate soil from Kalimantan Island

Drainage on acid sulphate land causes a change in the type of acid sulfate (AS) soil, from the potential to actual due to pyrite oxidation. The alteration might cause changes in microbial composition and activity. The objective of the study was to compare the microbial activity of two types of acid sulphate (AS) soil, potential AS soil from South Kalimantan and actual AS soil from Central Kalimantan. The microbial activity of both soils was determined by measuring respiration, dehydrogenase, and nitrogenase activity. The presence of culturable soil rhizospheric microorganisms was determined by Total Plate Count methods and their nitrogen fixation function was determined by the ability of culturable rhizospheric soil bacteria to grow in semisolid nitrogen-free medium, as well as, nifH detection. The result of the research revealed that the respiration, dehydrogenase, and nitrogenase activity soil from potential (1.34 mg CO 2 .kg 1 hour −1 and 1.75 nmol C 2 H 4 .g −1 . hour −1 ) and actual AS soil (1.23 mg CO 2 .kg −1 . hour −1 and 2.00 nmol C 2 H 4 .g −1 .day −1 ) were relatively not different. However, the dehydrogenase activity of actual AS soil (6.29 μg TPF.g −1 . hour −1 ) was higher than that of potential AS soils (3.32 μg TPF.g −1 . hour −1 ). Similarly, the microbial abundance of both soils was not different and the abundance of bacteria was higher than that of fungi. The soils contained nifH genes. In both soils have been detected the presence of microbial abundance and functional microorganisms as a nitrogen fixer, a culturable phosphate solubilizer, or phytohormone producer. However, limiting factors of both soils, i.e., very acidic soil, low nutrient availability, and Al toxicity brought about the low microbial activity.