Harvest yields of greenhouse tomatoes grown in pine bark amended cotton gin compost

Tomatoes are the most abundantly produced greenhouse vegetable crop in the United States. The use of composted substrates has increased in recent years for the greenhouse production of many vegetables, bedding plants, and nursery crops. 'Blitz' tomatoes were grown during the spring and fall growing seasons in six substrate blends of pine bark (PB), a traditional production substrate in the southeastern US, and cotton gin compost (CGC), an agricultural by-product, to assess the potential use of CGC as a viable replacement for PB for the production of greenhouse tomatoes. Treatments ranged from 100% PB to 100% CGC. Plants grown in substrates containing CGC produced similar total yields during both seasons compared to plants grown in 100% PB. In both seasons marketable yields were similar across all treatments. Similarly, cull fruit was not different across treatments. Substrates containing 60% or more CGC had significantly higher electrical conductivity (salt) levels both initially and throughout both growing seasons than did 20 and 40% CGC and 100% PB substrates. Water holding capacity increased as the percent CGC increased in each substrate, indicating the need for adjusted irrigation volume for substrates containing CGC compared to the 100% PB. Results indicate that CGC has potential to be used as an amendment to PB in greenhouse tomato production.