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Effects of land-use change in tropical peatlands on the microbial population and emissions of nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ) were studied in the field and laboratory. The study area covered secondary forest, paddy field and paddy-soybean rotation field in Indonesia.ATP content, and numbers of viable bacteria and fungi, cellulolytic bacteria and fungi, NH 4 + oxidizers and denitrifiers in a paddy-soybean rotation field and paddy field were reduced to 1-30% and 3-90% of those in secondary forest, respectively. The field measurements of greenhouse gas emissions showed that significantly more CH 4 was emitted from paddy field than secondary forest, but no significant difference in the emission of either N 2 O or CO 2 . The laboratory incubation experiment showed that the soil moisture level and land-use change significantly affected the emission of N 2 O, CH 4 and CO 2 . These results suggested that land-use change significantly affected the microbial population and emissions of greenhouse gases.

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An experiment was conducted to examine the accumulation and mobility of heavy metals (Zn and Cu) at different depths in three types of arable soils (Brown Lowland soil, Andosol, and Brown Forest soil) amended with cattle and pig farmyard manures for 5 years. Nitric‐perchloric acid digestion was performed for the determination of the total amounts of heavy metals, and 0.1 M hydrochloric acid extraction was performed for the determination of the amounts of soluble heavy metals. Results of the soil analysis indicated that pig farmyard manure application resulted in serious contamination of arable soils with Zn and potentially Cu. Especially, the Brown Forest soil displayed a high ability to accumulate heavy metals on the soil surface. Total‐Zn concentration in surface soils was considerably affected by the holding capacity of soluble‐Zn traction. Although the Andosol amended with pig farmyard manure showed higher concentrations of heavy metals related to the higher ability of retention on a weight basis, the soil did not contribute to high heavy metal accumulation because of its low bulk density. Heavy metals were easily leached in sandy soils such as Brown Lowland soil, and Cu was potentially stable compared with Zn. We suggest that long‐term pig farmyard manure application to the Brown Lowland soil and Andosol with a light soil texture is associated with a higher risk of groundwater pollution than the application to the Brown Forest soil.