The fastest way to add nitrogen to soil is by using a nitrogen fertilizer that is quickly available for plant uptake. Some common nitrogen fertilizers that can provide a rapid boost of nitrogen to the soil include ammonium sulfate, ammonium nitrate, and urea.
Ammonium sulfate is a fast-acting fertilizer that contains 21% nitrogen. It is readily available for plant uptake and can be applied to the soil or foliage.
Ammonium nitrate is another fast-acting fertilizer that contains 33% nitrogen. It is also readily available for plant uptake and can be applied to the soil or foliage.