An agricultural implement includes a chassis and a shank or shanks carried by the chassis. The shank or shanks include an on-the-go nitrate-N sensor or sensors. Nitrate-N conditions are determined for at least first and second zones at different soil depths, either by multiple sensors carried on one or multiple shanks during a single pass of the agricultural implement, a single sensor carried first at the first depth and thereafter at the second depth during multiple passes of the agricultural implement, or a sensor moved between the first and second zones during a single pass of the agricultural implement. Rates for applying additional nitrogen can be calculated from the determined conditions, and the application rates and determined conditions can be mapped.
