All are gone, except for 100 per gram of soil. There is nothing left to retain nitrogen in those soils, nothing. So you apply fertilizer. Take Santa Maria River in California as an example. This land has had methyl bromide applied 2 to 3 times a year for the last 14 years or more.
Fertilizer is applied as sidedress when strawberries are planted.
About two weeks later, the river goes up to around 150 parts per million nitrates. Ten parts per million nitrates is what the EPA tells us. It used to be three parts million but that level was increased. Not unless you'd want to die. You would destroy your kidneys pretty fast if you drank that water.