Evaluation of Optimal Substrates and Fertilizers for Organic Vegetable Transplant Production in Alabama

Abstract

Successful organic vegetable production requires a healthy transplant. Presently, there are several certified organic plug substrate blends available; however, the suitability and cost of these substrates are a concern to growers who often report inconsistent or poor results. There is a need to evaluate available certified organic mixes to develop recommendations for organic transplant production that will provide consistent results. In Alabama, four economically important crops for organic growers are tomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativus L.), lettuce (Lactua sativa L.) and collards (Brassica oleracea (Acephala Group) L.).

Untreated seed of ‘Celebrity’ tomato and organically produced seed of ‘General Lee’ cucumber were sown July 2006. Organic seed of ‘Red Sails’ lettuce and untreated seed of ‘Georgia Southern’ collard were sown Oct. 2006. The design was a RCBD utilizing four substrates for a total of four treatments in four replicates. Each crop was grown in one of the following substrates in 72-cell plastic market trays: Fafard Organic Formula #10 (FO), Fafard 1P (FC), Sunshine Professional Organic Blend (SO), and Sunshine LC1 (SC). Upon emergence of the true leaves, seedlings grown in FO and SO were fertilized twice weekly with 50 ppm N with a 2N-1.7P-0.83K Neptune’s Harvest Fish Hydrolysate for a total of 100 ppm N per week (Gloucester, Mass.). Seedlings grown in FC and SC were fertilized twice weekly with 50 ppm N from a standard TotalGro 20N-4.4P-16.6K water-soluble fertilizer for a total of 100 pmm N per week (SDT Industries, Winnsboro, LA).

Five plants were randomly selected per plot and harvested weekly over a three to five week period depending on the crop. Data of a number of growth parameters were collected: plant canopy height, stem diameter, total leaf area, and total fresh and dry weights of each plant’s leaves, shoots, and roots to compare relative growth under each treatment.

By last harvest of tomato and cucumber, growth in FO was statistically similar to that in FC; for lettuce and collard, growth in SO was statistically similar to FC. Results suggest growers can produce organic transplants comparable to that of conventional system but that the selection of substrates may be crop dependent.