Fertilizer use efficiency

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Abstract
Objectives of this research were: 1) to determine the accuracy of the critical value method (CVM) and the Diagnosis and Recommendation Integrated System (DRIS) in confirming P and K soybean deficiencies, and 2) to determine if including nutrient concentrations in the calculation of DRIS indices helps separate limiting from non‐limiting nutrients. DRIS was slightly better than the CVM in confirming K deficiencies and much better in detecting P deficiencies. Failure of the CVM to detect P deficiencies for these data indicates that the critical value for P is too low and needs to be reevaluated. DRIS was biased in favor of diagnosing K insufficient and against detecting P deficiencies. Each time DRIS was used, it predicted at least one nutrient as limiting; therefore, several erroneous diagnoses were made. Potential hazards of this were discussed. Nutrient concentrations were used in the DRIS to calculate a dry matter index value, which helped to separate limiting from non‐limiting nutrients. This eliminated some of the incorrect insufficiency diagnoses made by DRIS. However, as with DRIS, the modified‐DRIS (M‐DRIS) was biased against detecting P deficiencies. Further work is needed to determine if detection of P deficiencies can be improved by adjusting Pin the M‐DRIS data base.

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