Pedologist

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We studied humus constituent of successively collected samples from cumulative Andisol of the Miyakonojo basin to investigate its alteration with time. Results are followed: The humus constituent of Kuronigas 4A and 2A collected from soil layers formed in a different era was similar. This suggests that the constituent of humus has not altered in thousands of years. Progression of humification in this profile was controlled by organic matter supplied to soils, therefore, in case the amount of organic matter is small, the progression degree of humification considered to be small. In almost all samples, humic acid was classified into type A, therefore, the soils of the area may be consistently made of herbaceous vegetation as conventionally reported. This has also been supported by the result of the phytolith analysis. The amount of 'free form' humic acid in buried humic layers is highly correlated with pH (NaF). This suggests that humus forms complexes with active aluminum in buried humic layers and other inorganic components in brown loam layers to retain in stable conditions.

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In this study, we attempt to evaluate the influence of forest or grassland use history on the acidity of Andosols in Nakaizu-town, Izu Peninsula. According to the analytical results, Andosols developed under the forest use tended to have stronger soil acidity and higher carbon content than the Andosols developed under grassland use. Acidification degree also differed between the Andosols developed under the broad-leaved forest and coniferous forest. Under the broad-leaved forest, the pedon with the short term forest use had low pH(H_2O) than the pedon with long term use. This may reflect on increase in the water soluble fr and organic acids. On the other hand, in the pedon developed under the coniferous forest, the soil acidity was higher under the long term forest use than short term use. This may be because of the poor litter decomposition and cation uptake to the trunk.

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A review of soil surveys shows that Tanzania has a long history of collecting soils and other land resources data. A number of inventories at different scales have been made for various land use planning objectives. The inventories at national scale are not sufficiently adequate for sound planning exercises and require further improvement. Moreover, only about 3% of the country has been mapped at detailed and semi-detailed scales to allow proper planning at village and farm level. Handling of basic soils and other land resources data are still to a great extent done manually and only a modest computerization has been done. To have a rational utilization of the country's soils and other land resources, the government is urged to deliberately invest more efforts and finances to systematically map and characterize the resources.

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