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Nutrient Diagnosis in Corn Grown on Hydric Dystrandepts: II. Comparison of Two Systems of Tissue Diagnosis¹

ABSTRACT

Recent studies suggest that the Diagnosis and Recommendation Integrated System (DRIS), which utilizes ratios of tissue nutrient concentrations rather than the concentrations themselves, consistently produces more accurate diagnoses of nutrient deficiencies and imbalances than critical concentration approaches. However, preliminary results indicated that the DRIS based on published optimum ratios of maize earleaf nutrient concentrations gave inaccurate diagnoses of N and P fertilizer responses on Hydric Dystrandepts. The objectives of this study were to evaluate several locally calibrated modifications of the DRIS and to compare their diagnostic accuracies with those of a locally calibrated critical concentration approach. The percentage of correct diagnoses [method (D) in the first paper in this series] was used to determine the diagnostic accuracy of the two approaches. Both approaches were more accurate when the critical values of nutrient concentrations or the critical values of ratios of nutrient concentrations were derived from experimental data rather than from published values. The accuracy of the DRIS approach was improved by (i) judicious selection of the high-yielding subpopulation, (ii) selecting the critical values of DRIS indexes based on their effects on diagnostic accuracy, and (iii) using 10 rather than either 3 or 36 ratios of nutrient concentrations to calculate DRIS indexes. After calibration of both approaches, the DRIS approach was 8% more accurate than the conventional approach for diagnosis of N deficiency. The two approaches were almost equally accurate for diagnosis of P deficiency.

¹ Research supported in part by the Benchmark Soils Project, a cooperative research project between the U.S. Agency for International Development and the Univ. of Hawaii, Honolulu. Part of a dissertation submitted by the Senior Author in partial fulfillment of the requirements for the Ph.D. degree at the Univ. of Hawaii.

² Graduate Student, Dep. of Agron. and Soil Sci., Univ. of Hawaii; Plant Physiologist, ARS, Temple, Tex. (formerly Associate Agronomist, Hawaiian Sugar Planters' Association); and Professor, Dep. of Agron. and Soil Sci., Univ. of Hawaii, Honolulu.

Received for publication March 9, 1981. Accepted for publication July 16, 1981.

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