Young corn(Zea maysL.) and sugar beet (Beta vulgarisL.) plants were sampled in plots fertilized with different types and rates of nitrogen fertilizer during the period 1969–72. The twenty six trial fields covered a dozen different types of soil from the Montreal to the lower St. Lawrence River regions. As revealed by nitrate analysis (NO3‐N) there was a marked positive correlation between crop yield, and nitrate nitrogen from the fifth to the seventh week for corn and from the seventh to the eight week for sugar beet. Sampling prior to this was not indicative. A negative correlation was found between NO3‐N and total sugar yield for sugar beet, before the seventh week. Regression analysis, including soil NO3‐N test, showed a positive soil participation from the seventh week for corn and from the fourth week for sugar beet. The critical concentration value suggested for corn, under very adverse climatic conditions, is not less than 150–200 ppm NO3‐N. As a rule, however, the 2,000 ppm value appears to be a minimum concentration. This value may be extended to 3,000 ppm under certain conditions. As for sugar beet, a range from 10,000 to 20,000 ppa in petioles during the initial 50–56 day period, gave maximum sugar yields. During this stage, values ranging from 20,000 to 30,000 ppm of NO3‐N were considered to be overabundant.