The Effects of Alternative Media and Deficit Irrigation on Organic Vegetable Tranplant Production

In an effort to study the effectiveness of organic media and deficit irrigation in organic vegetable transplants we grew lettuce (Lactuca sativa) ‘Green Romaine’, sweet pepper (Capsicum anuum) ‘Olympus F1’, and tomato (Solanum lycopersicum) ‘West Virginia ‘63’ in three different organic media combined with three irrigation regimes.  Plants were grown for eight weeks in the commercial media Black Gold Natural and Organic Potting Mix as well as Johnny’s 512 Mix, or an autoclaved compost sourced from the university’s organic farm.  Irrigation was supplied at 80%, 100%, or 120% of initial container capacity and plants were reliant on nutrients present in the media as no supplemental fertilization was supplied.  Plants were evaluated bi-weekly in terms of height and leaf number and on alternate weeks leachate was collected in order to evaluate changes in pH and electrical conductivity.  At the end of eight weeks, plants were evaluated visually, harvested, and fresh and dry weights were collected.  Initial pH and EC was 8.4 and 270 µS.cm^-1, 6.8 and 1400 µS.cm^-1, and 7.4 and 160 µS.cm^-1, for organic farm compost, Johnny’s 512 Mix, and Black Gold respectively. Significant differences were observed in height and fresh and dry weights between organic media for lettuce, sweet pepper, and tomato transplants at the end of the experiment. Within each media treatment watering regimes did not significantly affect height, fresh and dry weight, or visual rating at the end of the experiment. Despite high initial and final pH and low EC readings, organic farm compost outperformed both Black Gold and Johnny’s mix in our experiments at least as determined by final visual ratings. Deficit irrigation at 80% of container capacity does not significantly affect growth as measured by fresh and dry weight, height, or visual rating in each of the media and plant species that were investigated. We suggest that deficit irrigation can be effectively used in organic transplant production without affecting transplant quality while minimizing nutrient loss from the media. We further postulate that initial EC and pH readings may not correlate well with the production of quality transplants and that other initial measurements of fertility may be better indicators of media quality and efficacy in producing transplants.