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United States Department of Agriculture

Agricultural Research Service

Title: Suitability of Composts As Potting Media for Production of Organic Vegetable Transplants

Authors
item Clark, Sean - BEREA COLLEGE
item Cavigelli, Michel

Submitted to: Compost Science and Utilization
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 16, 2005
Publication Date: July 1, 2005
Citation: Clark, S., Cavigelli, M.A. 2005. Suitability of composts as potting media for production of organic vegetable transplants. Compost Science and Utilization. 13:150-156.

Interpretive Summary: Producers of organic vegetable transplants have relatively few potting media options that are sustainable and cost-effective. Composts, used alone or in mixtures with other materials, can serve as horticultural potting media in organic production systems. In this study we evaluated the suitability of two locally available composts as media for lettuce and tatsoi produced organically in an unheated greenhouse. One of the composts was produced from food residuals with landscape wastes as a bulking agent, while the other was generated from used horse bedding. Although the two materials had relatively similar total nitrogen contents, carbon to nitrogen ratios, and bulk densities, they performed very differently as potting media. Nitrogen released during decomposition, measured in the laboratory, was high in the compost derived from food residuals but the horse-bedding compost showed no nitrogen release during decomposition, perhaps due to high salinity. Crop production in the food-residuals compost was similar to that in a commercial peat-based potting medium with synthetic fertilizer. Crop growth in the medium consisting of horse-bedding compost, used at 100% or in a 50%/50% mixture with a commercial substrate, was unacceptable for commercial production. Although the cost per flat of the food-residuals potting material was slightly higher than that for the commercial peat-based medium, organic producers may find this additional cost insignificant since they have limited potting media options, and since they receive a price premium compared to conventional producers.

Technical Abstract: Composts, used alone or in mixtures with other materials, can serve as horticultural potting media in organic production systems. In this study we evaluated the suitability of two locally available composts as media for lettuce and tatsoi produced organically in an unheated greenhouse. One of the composts was produced from food residuals with landscape wastes as a bulking agent, while the other was generated from used horse bedding. Although the two materials had relatively similar total N contents, C:N ratios, and bulk densities, they performed very differently as potting media. Net N mineralization, measured in laboratory incubations, was high in the compost derived from food residuals but the horse-bedding compost showed net N immobilization, perhaps due to high salinity. Crop production in the food-residuals compost was statistically similar to a control treatment consisting of a commercial peat-based potting medium with synthetic fertilizer. Crop growth in the medium consisting of horse-bedding compost, used at 100% or in a 50%/50% mixture with a commercial substrate, was unacceptable for commercial production. Although the cost per flat of the food-residuals compost was slightly higher than that of the commercial peat-based medium, organic producers may find this additional cost insignificant since they have limited potting media options, and since they receive a price premium compared to conventional producers.

Last Modified: 9/20/2014
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