Using Plant Analysis to Diagnose Nutrient Deficiency Problems
Posted: June 19, 2012
There are two ways to use plant analysis. The first method is to compare the analysis of the plant tissue with standard tables of interpretive values. Since the table values are for specific plant parts sampled at a specific stage of growth, it is critical that sampling guidelines be strictly followed. The following table provides general sampling guidelines for common agronomic crops. Information on sampling other crops and plant analysis interpretation levels are available on the Penn State Agricultural Analytical Services Lab web site.
|Crop||Sampling Time||Plant Part|
|Corn||12-18” tall||Whole plant|
|Forage legumes||Bud to 10% bloom||Top 1/3 of plant|
|Small grains||Just prior to heading||Uppermost leaves|
|Soybeans||Prior to or early flowering||Uppermost full leaves|
|Forage grasses||3-4 weeks between cuttings||Top of the plant|
Remember that book values are only available for the few specific stages of growth such as those given in the table above. For annual crops the recommended sampling times are often not for the stage of growth when the problem is observed and usually they are too late to take corrective action. For perennial crops corrective action can often be taken during the next season or next cutting. A final problem with this method is that there are many environmental and cultural factors that can influence the level of a nutrient in plant tissue. Thus, book values are only ball-park estimates of sufficiency for nutrients and actual sufficiency levels can vary significantly depending on the specific conditions.
For using plant analysis to diagnose visible nutrient deficiency problems, the best approach is to take comparative samples. With this method two samples are taken for analysis. One sample is taken from the problem area and the second sample is taken from a nearby area that is as near to identical to the problem area as possible but is showing normal growth. This method can be used at any stage of growth and it eliminates the confounding effects of most of the cultural and environmental factors. When using this method the two samples must be taken at the same time and the same plant part must be sampled. Usually the newest fully developed leaves or stems are the best plant part to sample for this method. If the problem is nutritional, comparison of the nutrient levels in the two samples usually gives a direct indication of the problem.
Regardless of the method used, it is important to use all available information to interpret the plant analysis for diagnosing a nutrient deficiency. Look carefully at the symptoms on the plants, note any patterns in the field, consider the timing of the appearance of the problem. Keep in mind that not all nutrient deficiencies in plants are the result of nutrient deficiencies in the soil. Soil tests and plant analysis are often complementary. They can confirm each other, but they can also indicate when the cause of the problem is something other than a soil deficiency of the nutrient. If the soil test level is adequate but the plants are deficient, this indicates that some other factor is limiting the plants ability to take up the available nutrients. Some areas to consider include: possible interactions with other cultural practices such as tillage or pesticides; pest injury such as root worm feeding; differences in varieties or hybrids; or soil physical conditions such as compaction.
If used properly plant analysis can be a very useful tool for diagnosing plant nutritional problems and suggesting solutions to these problems. Plant analysis kits for the Penn State Agricultural Analytical Services Lab are available from your local Penn State Extension Office.
- Soil Fertility