nitrogen, crops, nitrogen fertilizer
Nitrate Nitrogen (NO₃-N) in the top 2 ft of soil is normally used as efficiently by crops as fertilizer nitrogen. Therefore when nitrogen fertilizer recommendations are made, the NO₃-N soil test level is subtracted from the total nitrogen requirement of the crop. The nitrogen required by most crops grown in South Dakota has been determined by extensive field calibration studies over the past 20 years by SDSU soils researchers (Table 1).
Gerwing, James R. and Gelderman, Ron, "Nitrogen Requirements of Crops" (1989). SDSU Extension Extra Archives. 242.