Abstract
Soils and roots of satsuma mandarin in 23 orchards in Ehime Prefecture, Japan, were surveyed for the presence of vesicular-arbuscular mycorrhizal (VAM) spores and infection. The number of VAM spores in 25g soil ranged between 160-3471, and in some orchards the percentage of VAM infection in the root was very low. A higher percentage of VAM infection was observed in orchards where the sod culture system was introduced and charcoal was applied, and in the plastic green houses where tree growth was vigorous. We observed that trees in orchards which produce the 'Hinomaru Brand' of satsuma mandarin, famous for its quality, also had a high rate of VAM infection. Proliferation of VAM fungi appeared to have been suppressed in orchards where considerable amounts of fertilizers were applied. The prolonged use of phosphorus (P) fertilizer resulting in over 50 ppm of residual PO43- in the soil caused low VAM infection in satsuma mandarin roots.
