Compost pellets (PC) are different from non-pelletized composts in various properties including supply and retention of nutrients and production of greenhouse gases because of the micromorphology of PC. Therefore, it
is important to micro-morphologically characterize PC for its proper utilization. We investigated long-term changes in the micromorphology of cattle manure PC after its applica-tion in a soil. The PC grains were applied in a three-types soil core containing a Lowland soil, a Yellow soil, and an Andosol. The soil cores were buried in a field plot of its soil type. After 1, 6, and 18 months, the soil core was sliced into thin sections after solidifying with a polyester resin for the cross-sectional observation. Decomposition of the compost was also investigated using a glass-fiber filter bag method. Results from the investigation were as follows. 1) Weight residual ratio and carbon residual ra-tio of PC decreased rapidly in the first 6 months, and after that the decomposition became slower. 2) With the decom-position of PC, their shape was preserved, whereas their volume decreased. Estimated volume residual ratio of PC was 28 % for Lowland soil, 43 % for Yellow soil, and 39 % for Andosol after 18 months. Voids corresponding to the volume loss of PC by decomposition was formed around each PC grain. 3) PC mixed with the Yellow soil were cross-sectionally divided into curved segments by cracks whereas this separation was not observed in the Lowland soil and Andosol. 4) Internal microstructure of PC did not show a clear temporal change from 1 month to 18 months in any of the examined soils. Microstructure type was mas-sive microstructure to subangular blocky microstructure, with poor separation of peds.
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