Diagnosis of Plant Nutrient Deficiency Symptoms (6/7/12)
It is important to examine plants closely, including the roots, to better diagnose problems affecting fields or parts of fields.
Some examples of environmental problems are-
- Small corn with many lower leaves showing purpling, but with both green and purple on the same leaf, separated by a sharp boundary. This is not a nutrient problem. This is probably wind damage that bent the leaves and folded them, forming a disruption of ‘plumbing’ from the leaf area producing sugars to the rest of the plant. The purple anthocyanin pigments form from the excess sugars not being able to transport to other parts of the plant. Adding a nutrient to these plants will not fix the problem. This is an environmental problem.
- Small corn with new leaves that turn yellow after a particularly cool night. This is a common environmental problem. It’s not easy being a small corn plant and having to endure 85 degrees during the day and 40 degrees that night. Top yellowing is a typical environmental response to dramatic temperature differences or an extreme thunderstorm with wind.
If environmental conditions are more mild, and top yellowing or bottom leaf firing is taking place in parts of a field, a soil test and plant analysis will help sort out if the problem is nutrient-related. Most nutrient problems are not fence-row to fence-row. They are found in areas within fields and some parts of the fields may appear perfectly normal. Take a plant sample (several plants- perhaps as many as 20- for each sample) from a problem area and another plant sample from a ‘good’ area. Dry the samples first or take them immediately to a lab that analyzes plant samples. Take a soil sample from each area also. The test results from each area will help diagnose what the problem might be. If the values for a particular nutrient are similar for both the good and problem areas, that nutrient is not a problem. If the problem area is low in both the soil sample and plant sample for a particular nutrient and the good area is high, then that nutrient is most likely deficient.
An incorrect method of using a plant analysis is to take a plant sample from a field and compare the values for nutrients against a standard chart. As a trained professional I would never use this method to diagnose a nutrient deficiency. The charts were made a long time ago, usually in places far away on varieties that have not been used in many years. Many factors have changed during that time. A recent study by Iowa State showed no relationship between plant P and K levels at a specific growth stage and yield of corn. So a plant analysis alone, even on well-studied nutrients like P and K, is not diagnostic.
Use the paired method good and problem area of plant sampling and accompany it with a soil sample. The results you receive will be far more helpful.
NDSU Extension Soil Specialist