Effect of cultivating sorghum, marigold, and egoma (perilla) on the spore population of arbuscular mycorrhizal fungi in small plots filled with Andosol in the Southern Kyushu Region (Japan).

摘要

A small-plot (2 m x 2 m) experiment was conducted by filling the plots with Andosol (volcanic ash soil, previously uncultivated). Sorghum, marigold, and egoma (perilla) were cultivated continuously for two to four years in the plots. After the cultivation of the crops or before the cultivation of the succeeding crops, intra-row soil or soil mixed by tillage was sampled, and the spore population of arbuscular mycorrhizal fungi (AM fungi) was counted by the sieving method. Sorghum cultivation induced an increase of AM fungal spore population in the cultivated soil to a high level exceeding 40 spores per 10 g dry soil. Marigold cultivation lead to the same level of the AM fungal spore population with the fallow control soil, or increased the spore population two- to three-fold, compared with the fallow control soil. Egoma cultivation increased the spore population in the cultivated soil, compared with the fallow control soil, to ~20 to 30 spores per 10 g dry soil. Shoot dry matter production of sorghum was much higher than that of marigold and egoma, and the cultivation duration of sorghum (six months) was longer than those of marigold (three months) and egoma (four months). In the sorghum-cultivated plots, sorghum growth disorder caused by continuous cropping was observed, especially in the third- or fourth-year croppings. After the low shoot production of sorghum by continuous cropping, the spore population of mycorrhizal fungi also decreased, compared with that before the cultivation. These results suggest that sorghum cultivation without growth disorder caused by continuous cropping may induce an increase of AM fungal spore population in the cultivated soil to a high level compared with marigold and egoma cultivations. These findings may lead to the development of techniques to increase AM fungal spore population, enhance their activity in the soil, and utilize their functions in crop rotation systems in the southern Kyushu region of Japan.