From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Summer 1998, No. 4


When nutrient deficiency symptoms appear in growing crops we become concerned that yields and profits will suffer. Usually that is a safe assumption, and we know that the deficiency must be corrected to optimize profits. Most farmers and crop advisers know the important deficiency symptoms in their crops and will be able to identify problems once they are visible. Unfortunately, considerable yield potential is already lost when visible symptoms appear. Some of the new tools of site-specific farming may offer opportunities to better detect and treat hidden hunger in growing crops.

All essential plant nutrients are required in at least a threshold amount throughout the life of the plant in order to support normal growth and development. If any nutrient falls short of its respective critical level at any time during the growing season, there will likely be a reduction in growth and potential yield. Even if the nutrient supply is replenished, there may have already been irreversible damage done. The critical levels for each nutrient, and the effect of deficiency, vary with stage of growth.

Deficiency symptoms are usually physiological reactions to the insufficient supply of the nutrient. They are expressed as reduced growth, abnormal color, or death of tissue. Sometimes the effect can be overcome with addition of supplemental fertilizers, but often it is too late for corrective action when the symptoms appear.

Hidden hunger, on the other hand, is less severe and does not produce the visible symptoms. Thus, it is also more difficult to detect. Analysis of plant tissue samples or in-field tissue quick tests can help identify these shortages. New electronic tools, such as the chlorophyll meter, can be used to help detect a nutrient deficiency that is developing. Researchers are experimenting with in-field measurement of light reflectance with remote-sensing scanners to detect variability that may be due to hidden nutrient deficiencies.

Plotting such measurements with global positioning system (GPS) tools and logging the data into a geographic information system (GIS) data base permit farmers and their advisers to analyze the spatial variability of the relative measurements and detect areas of the field where unseen nutrient deficiencies are possible. Then plant analysis can be used to accurately determine whether there is a deficiency developing, so that corrective action can be taken before the problem reaches the point of severely impacting yield.

As yield levels continue to increase and management is intensified, the effects of stress factors will likely be more common, and potential for hidden hunger will increase. Farmers and their advisers will benefit from using the new tools of GPS, GIS, electronic monitoring instruments, and remote sensing to help detect these developing problems and make management decisions for corrective action.


For more information, contact Dr. Harold F. Reetz, Jr., Midwest Director, PPI, 1497 N 1050 East Road, Monticello, IL 61856-9504. Phone (217) 762-2074. E-mail:
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