Structure investigation of soil aggregates treated with different organic matter using X ray micro tomography Strukturuntersuchung organisch behandelter Bodenaggregate mittels Mikro Röntgen Computertomographie

Soil aggregation, which is favorable for plant growth, can be modified by the presence of organic matter; farmers thus often apply different materials to promote soil aggregation and enhance its stability. However, the relationship between the type of organic matter used and the resulting properties of the aggregate structure is unclear. Using high resolution micro x ray computed tomography we investigated the internal structures of aggregates from fields to which a variety of organic material had been applied. The sampling sites are five paddy fields with rice wheat rotations four treated with different organic matters and one untreated control in southwest Japan. The organic materials used were rice straw, rice straw manure, wheat straw, and livestock manure. The soils were classified as Endogleyic Hydragric Anthrosol Clayic . Imaging samples were hand picked from bulk soil samples collected in October 2008. Tomography experiments were conducted using an X ray micro focus instrument at the Helmholtz Centre Berlin for Materials and Energy; the instrument had a spatial resolution of approximately 5 amp; 956;m. Organic substances, such as manure, root and seed, in the aggregates were observed. By thresholding the gray scale of the images, it was possible to distinguish between porous and solid phases. These imaging studies indicated that applying manure to soils effectively increased the porosity of their intra aggregates. Pores reaching from the core of the aggregate to their surfaces were observed in organic matter applied fields and sponge like pores were identified in manure fed fields. This suggests that differences in the organic fertilizers used might affect the pore network within intra aggregate