PARENT SESSION
Poster Session #34: Agroecology.
Thursday, August 9, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall
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Effects of synthetic and organic soil fertility amendments on the incidence of southern blight caused by Sclerotium rolfsii , and the abundance of soil microbial and nematode communities in conventional and organic agroecosystems.
BULLUCK, LEON1, RISTAINO*, JEAN1, 1
ABSTRACT- Organic soil amendments including cotton-gin trash, swine manure, a rye-vetch green manure, or synthetic fertilizers were applied to subplots and tillage or tillage and surface-mulch were applied to main plots to determine the impact on soil microbial and nematode communities, and the incidence of southern blight caused by Sclerotium rolfsii. Disease incidence was 67-68% in tilled plots that were amended with conventional synthetic fertilizers, whereas disease incidence was 3-20%, 12-42%, and 16-47% in organic plots that were surface-mulched with wheat straw after amendment with either a composted cotton-gin trash, swine manure, or a green manure from an incorporated rye-vetch cover crop. Propagule densities of Trichoderma species , fluorescent pseudomonad bacteria, and culturable bacteria were higher in soils with organic than synthetic fertility amendments. Numbers of bacterivorous nematodes mainly in the Families Rhabditidae, and Cephalobidae were higher initially after planting in soils amended with swine manure, composted cotton-gin trash, or rye-vetch than soils amended with synthetic fertilizer, but remained higher in soils with organic amendments than soils with synthetic fertilizers. Likewise, numbers of fungivorous nematodes were also higher initially at planting in soils with organic amendments than those with synthetic fertility amendments. Production history and time affected the abundance of the beneficial biocontrol fungi Trichoderma and Gliocladium species in grower fields studies. Propagule densities of Trichoderma and Gliocladium species were higher initially in grower fields in soils with a history of organic production than in conventional production fields, and remained higher over time in organic than conventional fields. Our data indicate that some organic amendments increased the abundance of beneficial microbes in soil and reduced the incidence of disease.
KEY WORDS: Organic agriculture, soil microbial communities, plant disease