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 after such events. Soil and plant samples were collected in 1994 in Missouri and Iowa from sites flooded and falloff ed in 1993. Plants were P deficient during early vegetative growth in spite of soil tests indicating adequate P availability and typical levels of starter fertilizer. The flood and fallow problem was associated with the loss of root colonizing vesicular-arbuscular mycorrhizal (VAM) fungi that benefit the plant by increasing uptake of P. The VAM fungi are dependent upon the plant for growth and reproduction and loss of host significantly reduces VAM fungal populations in soil. The VAM fungal populations increased with the presence of a crop in the year following the hood. A greenhouse study an the effect of flooding on VAM fungi indicates the number 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 fallow disorder" in Australia. The research conducted indicates that the Post Flood Syndrome was associated with the loss of VAM fungi. Use of starter fertilizer was beneficial in correcting Post Flood Syndrome but broadcast fertilizer application appeared to have an insignificant effect on reducing the P deficiency. The application of 80 Ib P/acre as starter fertilizer produced plants that were not P deficient.