How does farming remove nitrogen from soil?

Farming can remove nitrogen (N) from soil in two ways:

1. plant (crop) uptake, and
2. erosion.

Since N is an important plant nutrient, plants will remove it from the soil and incorporate the N into parts of the plant. When plant parts are harvested, that N is being removed from the soil. Plant parts that are left in the field will return a lot of the N contained in those parts to the soil.

In most soils, N will be found at highest concentrations near the surface, in soil organic matter. Many farming practices increase the rate of erosion, and it is those surface horizons high in N that will be lost first.