Fertility Management for Tomato Production on An Extensive Green Roof

Tomato (Solanum lycopersicum) is a widely cultivated vegetable crop that serves an important role in urban agriculture.  The increasing demands for fresh, healthy, local foods in urban environments is challenging and green roofs may play a part in providing vegetable products to urban markets.  However, adequate fertility to maximize plant growth is often lacking in green roof media, especially after several years of intensive production.  Therefore, four fertility treatments were applied weekly to ‘Bush Champion II’ tomato grown in a three inch extensive green roof media mix on the Southern Illinois University campus.  The fertility treatments evaluated were: (1) vermicompost tea (from coffee grounds; 12,600 mg/kg N), 2) Miracle-Gro fertilizer (Scotts Miracle-Gro Products Inc, Maryville, OH; 16,100 mg/kg N), 3) Organic Miracle-Gro fertilizer (Scotts Miracle-Gro Products Inc; 6,900 mg/kg N), and 4) no fertilizer (0 mg/kg N).  The green roof media mix contains various gradations of expanded lightweight clay aggregate with 4 to 5% organic matter.  Although our analysis indicated that the vermicompost tea had a relatively high amount of N, most was in the organic form and was not readily available for plant uptake.  Water was applied through drip irrigation applied daily and fertility treatments were applied in 1.9 L of water for each plant once a week from transplant to the end of harvest.  Ripe tomato fruit were harvested eight times from June to August.  Plant vigor, chlorophyll content, and marketable yields were greater (P ≤ 0.05) when Miracle-Gro and Organic Miracle-Gro were used as the fertilizer source.  Subsequently, the no fertilizer and vermicompost tea application resulted in less production as lower fertility in these treatments reduced tomato plant vigor and fruit yield.  This study indicates that acceptable tomato yields can be achieved in a three-inch extensive green roof with adequate fertilizer applications.