Biochemical Behavior of Accumulated Phosphrus in Andosol and Their Availabilities for Crop Plants and the Perspectives for Recycle Use.

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1) In order to elucidate the role of allophane fractions of plow layr in Andosol on controlling the phosphorus (P) behavior along with time, clay fractions (less than 2um) were separated from the top- and sub-soils of the experimental field by the precipitation method and ^<27>Al- and ^<29>Si- solid state nuclear magnetic resonance (NMR) spectra were measured. In relation to ^<27>Al-NMR spectra of these clay fractions, both of Al (4) and Al (6) were existed and the resonance around 50-60 ppm as an indicator of the four-co-oridinated Al was intensified higher in topsoil than in subsoil. As related the ^<29>Si-NMR spectra, the observed chemical shift in subsoil was only -79 ppm, and additional peak around -90 ppm was observed in topsoil, indicating that some changes in allophane structure were introduced along with the cultivation. However, the relationships between the behavior of accumulated P and the structure changes in allophane were still not clear.2) According to the selective dissolution method, allophane contents in topsoil were measured. Continuous application of farmyard manure to the plow layr suppressed allophane content with time, whereas it slightly increased without application. There was significantly possitive correlation between non-allophane Al content and Al-P fraction in topsoil which has been increasing with time for past more than 10 years.3) To distingwish the functions of Arbuscular Mycorrhizal (AM) root system and only the external AM hyphae on P absorption from various types of P compounds in topsoil, "double pot system -separation of the roots and hyphae compartment by a nylon net-" was used. Not only Ca-P but Al-P,Fe-P and Org-P were quite mobile in rhizosphere and hyphaesphere, and these compounds were also available for maize and pigeonpea. Glomus etunicatum, one of the active AM fungus, which was collected from topsoil in Andosol had high abilities to symbiose with rice even under submerged condition.