640 Developing Fertilizer and Substrate Practices for Organic Greenhouse Tomato Production

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  • 1 Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695

`Grace' tomatoes were grown utilizing three different growing methods: organic, conventional, and biorational (IPM and use of reduced-risk pesticides). There was one treatment per greenhouse per growing season. Treatments were rotated for each crop. Inputs for the organic system were allowable according to the Carolina Farm Stewardship Materials List for organic certification or the Organic Material Review Institute (OMRI). Organic methods were compared to conventional and biorational methods in a total of two spring and two fall crops. The conventional and biorational substrates consisted of a commercial peat/perlite blend containing a “starter” nutrient charge. The organic substrates were a coir pinebark blend and a peat/perlite/vermiculite commercial substrate without non-organic “starter nutrients” and wetting agents. Organic substrates were amended with 15% by volume vermi-compost and dolomitic lime. Organic nutrient amendments were bloodmeal, bonemeal, and potassium sulfate to provide an initial nutrient charge. Organic post-transplant fertilization practices included three commercial blends used at several application rates. Fertilizers were applied by “mixing and pouring” in Spring 1998, but were injected into the drip irrigation system for the remaining three growing seasons. Data was collected on harvest yield, fruit quality, and plant development. In the first two growing seasons, organic production resulted in the highest percentage of number1 quality fruit, but in Spring 1998, these plants were developmentally slow, resulting in lowest total yields. In the Fall 1998 and Spring 1999 crop, all measurements of growth and yield for organic production were comparable to those in conventional and biorational controls. We feel however, that additional development work is required in the organic treatments to optimize transplant production, post-plant fertilization regimes and biocontrol application.

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