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Residue Placement and Fungicide Effects on Fungal Communities in Conventional and No-Tillage Soils

Institute of Ecology, Univ. of Georgia, Athens, GA 30602

B. R. Pohlad

Division of Life Sciences, Ferrum College, Ferrum, VA 24088

D. H. Wright

Dep. of Biology, Emory Univ., Atlanta, GA 30322

*Corresponding author.

ABSTRACT

We investigated the effects of the fungicide captan (cis-N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide) and long-term conventional (CT) and no-tillage (NT) management on the size and composition of fungal communities from crop residues and mineral soil. Captan and reference treatments were established in CT and NT plots on a Hiwassee sandy clay loam soil (clayey, kaolinitic, thermic Rhodic Kanhapludult). At intervals, grain sorghum [Sorghum Bicolor (L.) Moench] litterbags and soils were collected for enumeration and identification of fungal hyphae and fungal colony-forming units (CFU) and to determine residue decomposition rates. Buried residues (CT) had higher densities of fungal hyphae but fewer fungal CFU than surface residues (NT). Buried residue decay rates (k = 0.0136 d^-1) were 3.4 times faster than surface residues (k = 0.0040 d^-1). Fungal hyphae were more abundant in NT than CT mineral soils but there were no differences in fungal CFU. Sorghum residues had a common succession of fungi including phyllosphere colonizers (e.g., Alternaria alternata, Epicoccum nigrum) and other common decomposer fungi (Cylindrocarpon, Fusarium, Mucor, and Phoma). Fungal communities were differentiated into surface residue (e.g., Alternaria, Epicoccum) and soil (e.g., Aspergillus, Trichoderma) specialists, while buried residues lacked a specialized community. Rhizopus arrhizus and Aspergillus niger showed a statistical preference for CT soils, while Penicillium verruculosum was most common in NT. Captan reduced fungal CFU and hyphal densities in residues of both NT and CT, resulting in 23 and 7% reductions in their decay rates, respectively. We found no evidence for differential effects of captan on the composition of the fungal communities in residues or soils.

Received for publication April 2, 1992.

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