Doctoral Dissertations

Date of Award

12-2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Carl E. Sams

Committee Members

Dennis Deyton, Bonnie Ownley, Darren Robinson

Abstract

Plasticulture vegetable production is an important agricultural industry in the United States. Advantages of utilizing plastic mulch in combination with trickle irrigation and fertigation include weed control, water conservation, erosion prevention, and avoidance of disease by restricting contact of vegetables with contaminated soil.

Southern Blight, caused by the phytopathogenic fungus Sclerotium rolfsii Sacc., represents one of the major disease threats to tomato crops in the southeast United States. Integrated pre-plant soil treatments that can reduce pathogen propagule numbers and reestablish a balanced soil microecology have potential as effective, sustainable disease control strategies.

The soil treatments investigated in this study were biofumigation with incorporated Brassica cover crops, spent mushroom and poultry waste composts, solarization, and the commercial fumigant dazomet. Integrated treatments were also investigated.

Compost amendments enhanced yields (36, 91 , and 97% in 2000, 2001, and 2002, respectively) and suppressed disease in all three years (5, 7, and 33% diseased plants in 2000, 2001, and 2002, respectively). Dazomet fumigation controlled Southern Blight in all three years (8, 5, and 24% disease in 2000, 2001 , and 2002, respectively). When a full Brassica crop stand was established, as in 2002, the biofumigation treatment was effective at controlling disease and improving yields (52% fruit yield above control and 39% diseased plants in 2002). Lethal temperatures were not generated by the fall and spring solarization applications, hence, disease suppression did not occur.

Integrated treatments displayed good potential as effective pre-plant strategies. Reduced dose dazomet (199 kg/ha) plus compost treatments controlled Southern Blight to 1 % and increased yields 79% above controls in 2001.

Phospholipid fatty acid (PLFA) analysis indicated that compost-amended plots had a higher microbial biomass than controls. Signature lipid biomarker quantification revealed that the compost treatments had higher relative populations of Gram-negative bacteria and lower soil microeukaryote/fungal populations than controls.

Hierarchical cluster analysis of all PLFA biomarkers indicated that all compostbased treatments shared similar microecological profiles. Ordination modeling established a close link between improved tomato yields, high Gram-negative bacteria populations, and compost-based soil treatments.

The potential for biologically based soil treatments to be integrated into sustainable agricultural production systems is supported by the results in this research study. Both enhanced yields and lower disease incidence were observed in compost and certain biofumigation treatments. Those treatments that promote beneficial microbial community compositions were linked with improved production.

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