Effect of Humic acid on Growth and Yield of Tomato cv. Isabela

Humic acid, which has hormone- like activity, not only enhances plant growth and nutrients uptake but also improve stress tolerance. To determine the effect of humic acid on the yield and vegetative characteristics of tomato an experiment was conducted with tomato cv. `Isabela` in 2008 in a plastic tunnel at the Agriculture Faculty, Guilan University using randomized completely design with four treatments (0, 1, 2, 3 mg l-1 humic acid) and three replications. Humic acid was sprayed four times during the vegetation period with 10- day intervals after three weeks of planting. Results showed that humic acid could affect significantly (P)