The dominant factors controlling soil bacterial community variation within the tropics are poorly known. We sampled soils across a range of land use types--primary (unlogged) and logged forests and crop and pasture lands in Malaysia. PCR-amplified soil DNA for the bacterial 16S rRNA gene targeting the V1-V3 region was pyrosequenced using the 454 Roche machine. We found that land use in itself has a weak but significant effect on the bacterial community composition. However, bacterial community composition and diversity was strongly correlated with soil properties, especially soil pH, total carbon, and C/N ratio. Soil pH was the best predictor of bacterial community composition and diversity across the various land use types, with the highest diversity close to neutral pH values. In addition, variation in phylogenetic structure of dominant lineages (Alphaproteobacteria, Beta/Gammaproteobacteria, Acidobacteria, and Actinobacteria) is also significantly correlated with soil pH. Together, these results confirm the importance of soil pH in structuring soil bacterial communities in Southeast Asia. Our results also suggest that unlike the general diversity pattern found for larger organisms, primary tropical forest is no richer in operational taxonomic units of soil bacteria than logged forest, and agricultural land (crop and pasture) is actually richer than primary forest, partly due to selection of more fertile soils that have higher pH for agriculture and the effects of soil liming raising pH.

Biochar has received great attention recently due to its potential to improve soil fertility and immobilize contaminants as well as serving as a way of carbon sequestration and therefore a possible carbon sink. In this work, a series of biochars were produced from empty fruit bunch (EFB) and rice husk (RH) by slow pyrolysis at different temperatures (350, 500, and 650°C) and their physicochemical properties were analysed. The results indicate that porosity, ash content, electrical conductivity (EC), and pH value of both EFB and RH biochars were increased with temperature; however, yield, cation exchange capacity (CEC), and H, C, and N content were decreased with increasing pyrolysis temperature. The Fourier transform IR spectra were similar for both RH and EFB biochars but the functional groups were more distinct in the EFB biochar spectra. There were reductions in the amount of functional groups as pyrolysis temperature increased especially for the EFB biochar. However, total acidity of the functional groups increased with pyrolysis temperature for both biochars.

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Ammonia losses from soil following fertilization with urea may be large. This laboratory study compared the effect of four different, urea-triple superphosphate (TSP)-humic acid-zeolite, mixtures on NH 3 loss, and soil ammonium and nitrate contents, with loss from surface-applied urea without additives. The soil was a sandy clay loam Typic Kandiudult (Bungor Series). The mixtures significantly reduced NH 3 loss by between 32 and 61% compared with straight urea (46% N) with larger reductions with higher rates of humic acid (0.75 and 1 g kg )1 of soil) and zeolite (0.75 and 1 g kg )1 of soil). All the mixtures of acidic P fertilizer, humic acid and zeolite with urea significantly increased soil NH 4 and NO 3 contents, increased soil-exchangeable Ca, K and Mg, and benefited the formation of NH 4 over NH 3 compared with urea without additives. The increase in soil-exchangeable cations, and temporary reduction of soil pH may have retarded urea hydrolysis in the microsite immediately around the fertilizer. It may be possible to improve the efficiency of urea surface-applied to high value crops by the addition of TSP, humic acid and zeolite.