Tomatoes are heavy feeders, especially of nitrogen which is important for plant growth and high yields. About 40 to 50 percent of the total seasonal nitrogen can be applied at planting, With the remainder applied through the drip system over the course of the growing season. Additional nitrogen can be applied through the drip irrigation system at a rate of 8 to 10 pounds per acre per week, or 2.9 to 3.7 ounces per 1,000 square feet per week.
Foliar feeding of nitrogen, phosphorus and potassium is not effective relative to soil application of these major nutrients. Fertilizer nitrogen is available as nitrate or ammonium. Tomatoes respond favorably to nitrate nitrogen. Nitrate nitrogen is readily available to the plant and typically has low salt relative to ammonium fertilizers (ammonium nitrate, urea). Choose nitrogen fertilizers low in salt because salt levels can accumulate in the soil in a high tunnel.
Many commercial high tunnel tomato growers choose to fertilize with calcium nitrate and then alternate weekly with a fertilizer high in potassium (4-18-38), particularly during fruit ripening.
REVISED: December 3, 2015