The influence of land-use change, root abundance and macropores on saturated infiltration rate - a field study on Western Java, Indonesia

The aim of this study was to examine the infiltration rate of water and some parameters affecting it. Especially the land usage, the abundance of roots and macropores were investigated. A field study was carried out on western Java in Indonesia, on the slope of Mount Salak. The study compared four different land uses; i.e. forest, shrub areas, tree plantation and cropland since there was a high occurrence of these land uses in the area and they seemed suitable for comparison. The infiltration rate was measured with a double ring infiltrometer in 39 sampling points with at least eight locations at each land use. At 16 of these sites a soil pit was also dug, four at each land use. Root samples and soil samples were taken at six depths down to 150 cm. At the locations with soil pits, experiments with blue dye tracer were also conducted and the traces of the blue dye in the soil were photographed. Fine roots were examined both for length and weight of the sample. The soil samples were analysed at a laboratory for initial water content, bulk density, total porosity, pF-values, texture and carbon content. The differences between the four land uses were examined. A comparison in saturated infiltration rate was also conducted between tree based land uses and land uses without trees. The correlations between saturated infiltration rate and parameters such as root weight, root length and amount of macropores were investigated. The photographs of the blue dye were qualitatively evaluated and discussed. The infiltration rate showed differences when comparing shrub with forest and cropland, with shrub areas significantly lower than the other two. Plantation areas had the highest mean saturated infiltration rate 1260 mm/h. The lowest mean saturated infiltration rate was found in shrub areas where it was 580 mm/h. The comparison tree based land uses with land uses without trees showed a significant difference where the tree based land use had a higher saturated infiltration rate. Generally plantation had the highest root weights and cropland had the lowest, where as for root length cropland had generally quite high values and forest the lowest. For correlations with saturated infiltration rate, the root weight had the best significant R-value (0.66). Macropores showed a slight correlation with saturated infiltration rate. The examination of the blue dye tracer showed that the flow of infiltrating water is clearly preferential but no difference can be seen between the different land uses. There was no clear connection between the depth or spreading of the blue colour and the saturated infiltration rate. The results of this study showed that saturated infiltration rate is affected by the land usage, especially whether it is tree based land use or land use without trees. The reasons for the differences are not completely clear. There is a connection to the fine root weight and possibly to the amount of macropores. The infiltrating water was clearly preferential as it was following root paths and macropores. These results together show the importance of keeping land covered with vegetation, preferably with trees, in order to maintain the lands capacity to handle heavy rainfall. (Examensarbetet ar utfort vid Avd Teknisk vattenresurslara, TVRL)