The concept of critical nutrient concentration (CNC) as a basis for diagnosing nutritional problems is well established. The CNC implies a single point on a curve that relates nutrient concentration with yield. However, a single point is difficult to establish experimentally and, in addition, the critical point may vary under different conditions. Therefore, it seems desirable to deal with a critical nutrient range (CRN) of concentration rather than with a single concentration. Critical nutrient range is defined as: that range of nutrient concentration above which we are reasonably confident the crop is amply supplied and below which we are reasonably confident the crop is deficient. If “seasonal monitoring” of crop nutrition is to be useful, CNR values must previously be established at various growth stages during the season. Data are cited to illustrate the need for the CNR approach and for seasonal monitoring of CNR values.

Two field experiments were conducted for the purpose of establishing critical nutrient range (CNR) values for P in petioles of Russet Burhank potatoes (Solanum tuberosum L.) for use as standards in assessing plant nutrient status. The CNR is defined as the range of nutrient concentrations in plant tissue at a selected growth stage, above which the crop has an ample nutrient supply and below which the crop is nutrient‐deficient. The experiments were conducted under center‐pivot irrigation on soils classified as Quincy and Winchester loamy sands (mixed, mesic, Xeric Torripsamments). Five treatment levels from 0 to 269 kg P/ha were applied broadcast and incorporated before planting in April. Petioles were analyzed for P six times through the season, and potato yield was determined at harvest in late September. Adequate P fertilization produced maximum yields of 64 metric tons/ha on Quincy soil and 73 metric tons/ha on Winchester soil as compared with yields of only 79 to 86% of maximum without P fertilization. It was concluded that for 95 to 100% of maximum yield the estimated CNR was 0.38 to 0.45% P at the 2‐cm tuber stage in June and generally decreased with time to give a CNR of 0.14 to 0.17% P toward the end of the season 10 weeks later.

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R ECENTLY, the senior author sent a form letter to extension agronomy project leaders in each of the 49 other states. We asked how-many states had programs similar to Outlying Testing in Washington or in what ways they were different. The results indicate that very few states have programs which are similar to ours, but, in general, there is a definite interest in this area. Most states appear to have at Jeast some type of demonstration program in agronomy.Probably the most interesting result was even being asked the question, 18 of our 3 cated a definite concern over the "gap" bet and research and what to do about it. Furthe ber of respondents expressed concern over t