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Correct Crop Nutritional Diagnosis Using Plant Analysis (06/25/15)

I have already referred to plant analysis as a tool that growers/crop consultants can use to better diagnose nutritional problems suspected from symptoms observed in the field.

Correct Crop Nutritional Diagnosis Using Plant Analysis

I have already referred to plant analysis as a tool that growers/crop consultants can use to better diagnose nutritional problems suspected from symptoms observed in the field. I have also talked about this at crop consultant meetings and grower meetings for years, but still people send me a copy of a plant analysis report from the odd looking area and ask me what it means. The answer from such a report is ‘I don’t know’. A single plant analysis report from a stressed area compared to a chart means nothing.

The correct way to diagnose a fertility problem is to take a plant sample from a good area of the field (all the fields I have ever visited that have a nutritional problem have at least one area that looks good) and a sample from a typical problem area. When you get the report back, compare the good numbers with the bad. It would be common for the rating of copper (Cu) for example to perhaps be low (L) in both good and bad. Is it then reasonable to think that Cu is deficient in this field? I think not. If sulfur is the issue, then the good area would likely be higher testing than the bad. This would be support for sulfur being the real problem. If N is lower in the bad area compared to the good, and the good is in a higher category, then N is probably a problem. A soil sample with the plant analysis is supportive for N, P, K, salt suspicions, and Zn, but not anything else, especially sulfur.

Again, good plant nutrition diagnosis is based on paired good and bad area samples. Do not base a diagnosis on a single sample from a bad looking area.

Dave Franzen

NDSU Extension Soil Specialist

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