Effects of mycorrhizal inoculation on the uptake of slightly soluble phosphorus of groundnut, soybean and sesbania plants

In order to clarify the possibility as an inter crop for backwheat in Okinawa low phosphorus tolerance of groundnut (Arachis hypogaea) was investigated by comparison with soybean (Glycine max) and sesbania (Sesbania cannabina) in volcanic ash soil (akadama soil) and acrisols (red soil) in which phosphorus is fixed by aluminum and iron, respectively. The effects of arbuscular mycorrhizal fungi on the growth, nodulation, and phosphorus uptake of the three legumes were also examined. I found that growth of the three species declined due to the decreased amount of phosphorus fertilizer applied under akadama soil cultivation; however, groundnut showed less decline than soybean, and groundnut showed more vigorous growth than sesbania when cultivated with a small amount of phosphorus fertilizer (0% and 0.1% of phosphate absorption coefficient). The nodule weight of groundnut was similar to that of soybean and lower than that of sesbania under all phosphorus conditions. At the early growth stage, root length of soybean and sesbania was markedly decreased under phosphorus-deficient conditions, whereas that of groundnut was not. Root development during the early growth stage in groundnut appears to be secured under phosphorus-deficient conditions by the large amount of phosphorus contained in its seed. The aboveground biomass and phosphorus uptake of groundnut cultivated in red soil without arbuscular mycorrhizae were similar to those of soybean and lower than those of sesbania in superphosphate and slightly soluble phosphorus (Al-P and Fe-P) fertirizer conditions. However, the aboveground biomass and phosphorus uptake of groundnut cultivated in red soil with arbuscular mycorrhizae were similar to those of sesbania under all superphosphate conditions and higher than those of sesbania under slightly soluble phosphorus conditions. Although groundnut can develop roots in soil with low phosphorus fertility because of the large amount of phosphorous in its seed, infection with mycorrhizal fungi may be necessary to ensure sufficient continued growth.