Inoculation of sweet potatoes with AM fungi produced on-farm increases yield in high P soil

Abstract: Vegetable farmers who grow seedlings for later outplanting to the field have the opportunity to incorporate arbuscular mycorrhizal [AM] fungus inocula into potting media to produce plants ready to benefit from the symbiosis upon outplanting. Inocula of AM fungi are available commercially or may be grown on-farm. The impact of AM fungus inoculum produced on-farm upon yield of sweet potato (Ipomoea batatus L.) was studied in a field experiment over six site-years. Rooted cuttings were inoculated with AM fungi either directly in the planting hole or were grown first in a greenhouse in potting media amended with AM fungus inoculum. Controls received the same compost and vermiculite mixture in which the inoculum was grown. Available P levels in the soil ranged from 242 to 599 kg ha^-1. Mean increase in yield of sweet potatoes of the inoculated plants for the experiment was statistically significant at 10.0 ± 1.9 % over uninoculated controls. Further, roots collected at the time of harvest indicated significantly greater colonization by AM fungi of previously inoculated plants than in controls which became colonized by the indigenous population of AM fungi. Utilization of AM fungi produced on-farm reliably increased the yield of sweet potato in high P soils.