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The DRIS (Diagnosis and Recommendation Integrated System) procedure for assessing nutritional status of plants by leaf analyses utilizes standard values ("norms") for nutrient ratios that have been obtained from high-yielding populations. Examination of 1086 sets of yield and analytical data from 28 field experiments with potato (Solanum tuberosum L.) conducted over a period of 8 years on irrigated Boroll soils in semi-arid southern Alberta, Canada, established ratios among Ν, Ρ, Κ, and Ca that were significantly less variable in the high-yielding ( 40 t/ha) than in the low-yielding population. Another set of ratios for N, P, K, and Mg, determined from 1260 data sets obtained from 5 years of experimentation on Spodosol soils in the temperate humid area of Nova Scotia, were similar to those from the Boroll soils. Our standard values differed from those reported for potatoes grown on South African soils. Nutrient indices of deficiency, which were computed to integrate the degree of departure of each ratio from the standard norms, 1331

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