Make sure the nitrogen material will be 2 to 4 inches below the seed or transplant roots so it won’t harm them.
On alkaline soils, apply 1-20-0 (superphosphate) directly beneath the intended seed row or plant row before planting. Apply the superphosphate at a rate of 1 to 1½ pounds per 100 linear feet of row. Make sure the nitrogen material will be 2 to 4 inches below the seed or transplant roots so it won’t harm them. Later in the season you can apply additional nitrogen as a furrow or sidedress application. For most soils, 2 to 3 pounds of 21-0-0 (ammonium sulfate) per 100 linear feet of row, applied in the furrow and watered in, is adequate. For crops such as tomatoes, peppers and squash, make this application at first fruit set. Sidedress leafy crops such as cabbage and lettuce when they develop several sets of character leaves.