Contamination of soil with heavy metals such as cadmium, lead, and zinc is a major environmental problem around the world. Crops cultivated in contaminated soil can absorb high concentrations of heavy metals; so the contaminated soils must be remediated. In situ immobilization of heavy metals is an inexpensive, quick soil remediation technique. In this study, we evaluated the effectiveness of amending contaminated soil with hydroxyapatite (HAp) prepared from fish bone meal and adding secondary materials (such as lime) to immobilize heavy metals and inhibit their absorption by plants. We carried out pot experiments with spinach (Spinacia oleracea L.); experiments were conducted three times to assess changes in the effectiveness over time. When contaminated soil was amended with HAp, the soil pH increased, the exchangeable heavy metal fraction became smaller, and the amounts of heavy metals bonded to inorganic sites and to the residual fraction increased. The cadmium and zinc contents in spinach were decreased by amending the soil with HAp and lime. Lead was not detectable in any of the spinach samples. After the third experiment, the mobility and the content of heavy metals in the area of the soil that had been treated with HAp and lime was lower than in the untreated area. We concluded that HAp prepared from fish bone meal strongly immobilizes heavy metals in contaminated soil and inhibits their absorption by plants grown in the soil.

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Previous cropping of arbuscular mycorrhizal (AM) host plants is widely known to positively affect the growth of subsequent AM host plants by improving AM colonization and increasing phosphorus uptake. The objective of this study was to demonstrate the effect of previous cropping on AM colonization and growth of maize (Zea mays L., an AM host plant) in Andosol fields in Konsen, Hokkaido, Japan. We observed that AM colonization and early growth of maize were significantly higher in a plot in which maize had previously been grown than in plots in which sugar beet (Beta vulgaris L.) or white mustard (Sinapis alba L.), both of which are non-AM-host plants, had previously been grown. In addition, early growth of maize in the plot in which maize had previously been grown was less affected by a reduction in the phosphorus application rate than was the growth of maize in plots in which non-AM-host plants had previously been grown. These results suggest that using AM fungi in fields where maize is cultivated continuously may be an efficient phosphorus application method.

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