DYNAMICS OF THE MYCORRHIZAL SYMBIOSIS OF CORN (ZEN MAYS L.) - EFFECTSOF HOST PHYSIOLOGY, TILLAGE PRACTICE AND FERTILIZATION ON SPATIAL-DISTRIBUTION OF EXTRA-RADICAL MYCORRHIZAL HYPHAE IN THE FIELD

Tillage and fertilization may reduce the abundance of indigenous arbus cular mycorrhizal (AM) fungi in agricultural field soils. The dynamics of hyphal abundance in soil were studied over two growing seasons at a site in eastern Canada in a corn crop grown in a sandy loam soil and over one growing season in a corn crop grown in a clay soil. Experime ntal plots in a long-term tillage experiment, had been managed under n o-tillage (NT), reduced tillage (RT) and conventional tillage (CT) for 11 years. Soil receiving each of these tillage treatments also receiv ed either inorganic (N and K) or organic (liquid dairy manure) fertili zer. Soil samples were collected from different places within each plo t: on the plant row, at 18.75 cm from the row (quarter of the inter-ro w distance) and in between two row's (mid-ron, i.e., 37.5 cm from the adjacent rows). Plant and soil samples were taken at the 12-14 leaf st age of corn (June), at silking stage (August) and at harvest (October) , in order to measure the fluctuation in soil hyphal densities and pla nt nutrients concentrations during the season. Densities of total and viable AM hyphae were greatest in the row and lowest in the mid-row. H yphal density on the row increased steeply from 12-14 leaf stage to si lking stage and decreased thereafter, No significant fluctuation of hy phal abundance was observed in the mid-row, suggesting a prevalence of AM hyphae on the row. Hyphal densities were higher in NT soil than in CT soil, while RT soil contained intermediate hyphal densities. The h ighest corn P, Zn and Cu concentrations were observed in NT and RT tre atments concurrently with the highest hyphal densities. Concentrations of K, Ca and Mg did not change with tillage or fertilization type. Ma nure application significantly increased the densities of total and vi able hyphae in the clay soil. (C) 1998 Elsevier Science B.V.