POST FLOOD SYNDROME AND VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI

In the past few years large areas of the Midwest and Great Plains have been inundated with water and plant P deficiency is often a problem a fter such events. Soil and plant samples were collected in 1994 in Mis souri and Iowa from sites flooded and falloff ed in 1993. Plants were P deficient during early vegetative growth in spite of soil tests indi cating adequate P availability and typical levels of starter fertilize r. The flood and fallow problem was associated with the loss of root c olonizing vesicular-arbuscular mycorrhizal (VAM) fungi that benefit th e plant by increasing uptake of P. The VAM fungi are dependent upon th e plant for growth and reproduction and loss of host significantly red uces VAM fungal populations in soil. The VAM fungal populations increa sed with the presence of a crop in the year following the hood. A gree nhouse study an the effect of flooding on VAM fungi indicates the numb er of VAM hyphae or spores producing colonization were not affected by an extended flooding period and therefore are related to the lack of host for an extended period of time in the same manner as ''long fallo w disorder'' in Australia. The research conducted indicates that the P ost Flood Syndrome was associated with the loss of VAM fungi. Use of s tarter fertilizer was beneficial in correcting Post Flood Syndrome but broadcast fertilizer application appeared to have an insignificant ef fect on reducing the P deficiency. The application of 80 Ib P/acre as starter fertilizer produced plants that were not P deficient.