Comparisons between conventional and sustainable eggplant (Solanum melongena L.) production systems
Brunson, Kathryn Estelle
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The growing consumer and environmental concerns over the use of pesticides and nitrogen based fertilizers in agriculture has emphasized the need for more information concerning the reduction of these inputs on a commercial scale. Sustainable agriculture philosophy promotes using beneficial insects and legume cover crops as a means to do so. However, information is limited as to how sustainability can be conducted on a commercial crop such as eggplant, and still be economically feasible. Field trials were conducted during 1991-93 at four locations comparing sustainable and conventional eggplant production practices. The four sites differed by soil type and cropping histories. Overwintering cover crops of crimson and subterranean clovers were used to help maintain soil fertility and populations of beneficial insects in the sustainable production system. No pesticides were used throughout the study. Velvetbean (Mucuna deeringiana L.) was incorporated into the rotation following eggplant in 1992-93 to help suppress populations of southern root-knot nematode (Meloidogyne incognita Koford and White). The conventional production system differed in that cereal rye was the plow-down cover crop and recommended fertilizer and pesticide practices were followed. Highest marketable eggplant yields were in the conventional system for each location and year. Crimson clover generally had the better yields compared to the subterranean clover but there were differences between locations and year. Regression analysis showed conventionally grown eggplant fruited earlier but that crimson clover had the potential to "catch" up in later harvests. Pest and beneficial insects populations were assessed by visual and shake sampling methods to determine differences among production systems. Shake sampling of eggplant foliage resulted in more species being recovered than did visual inspection. Weed populations differed according to location. Each location appeared to have had its own distinctive weed species. Overall percent weed cover was less in the sustainable compared to the conventional where nutsedge was the predominant problem. Use of velvetbean in the rotation in 1993 seemed to have an effect on populations of southern root-knot nematode incurred in the sustainable production. Levels were generally reduced in most locations while levels either stayed the same or increased in the conventional system that had been treated with a nematicide. Root gall and root disease severity ratings of eggplant were not significantly different between systems. The economic comparisons seemed to indicate that production costs and net returns for the conventional system were higher than for the sustainable, but sustainable yields were lower.