RESIDUE PLACEMENT AND FUNGICIDE EFFECTS ON FUNGAL COMMUNITIES IN CONVENTIONAL AND NO-TILLAGE SOILS

We investigated the effects of the fungicide captan ichloromethylthio- 4-cyclohexene-1,2-dicarboximide) and long-term conventional (CT) and n o-tillage (NT) management on the size and composition of fungal commun ities from crop residues and mineral soil. Captan and reference treatm ents 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 fun gal 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 rate s (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 soil s but there were no differences in fungal CFU. Sorghum residues had a common succession of fungi including phyllosphere colonizers (e.g., Al ternaria alternata, Epicoccum nigrum) and other common decomposer fung i (Cylindrocarpon, Fusarium, Mucor, and Phoma). Fungal communities wer e differentiated into surface residue (e.g., Alternaria, Epicoccum) an d soil (e.g., Aspergillus, Trichoderma) specialists, while buried resi dues 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 hyp hal densities in residues of both NT and CT, resulting in 23 and 7% re ductions in their decay rates, respectively. We found no evidence for differential effects of captan on the composition of the fungal commun ities in residues or soils.