A great use of baking soda for tomatoes is to make an organic spray to treat tomato fungal disease.
Combine 1 gallon of water with 1 tbsp of baking soda and 2 1/2 tbsp of vegetable oil in a spray bottle. Stir and add 1/2 tsp of castile soap. Spray this solution on the foliage of tomato plants until the fungal disease disappears.