MEASUREMENT OF SOIL MACROPORE GEOMETRY BY IMAGE-ANALYSIS OF SECTIONS THROUGH IMPREGNATED SOIL

The geometry of the soil pore space affects root growth directly by pr oviding pathways for root extension and indirectly through its effects on soil aeration and on water infiltration, redistribution and draina ge. Image analysis of sections through impregnated blocks of undisturb ed soil allows quantitative assessment of the pore space. Samples are dehydrated and impregnated with resin containing a fluorescent dye. On ce the resin has hardened, the blocks can be cut to reveal a section t hrough the structure. An image of the pore space, which is now filled with resin, can be obtained using ultra-violet light either photograph ically or digitally. Digital images are segmented into pore space and solid. Image analysis techniques can be used to classify the pore spac e into channels, fissures and packing pores. This allows appropriate m easurements to be made on each class so that stereology can be used to estimate 3-D parameters from the measurements made on the image. Vari ous indices can also be derived to quantify the pore structure.