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Plants are just like people. The right nutritional balance can mean the difference between good health and that "ill" feeling. And for growers, sick plants can cost them in yields and quality.

However, many corn growers overlook the nutritional needs of their crop, said Maurice Watson, an Ohio State University Extension soil specialist with the Ohio Agricultural Research and Development Center. While the importance of soil testing is often stressed, little is mentioned of the usefulness of plant tissue analysis, Watson said.

"Plant tissue analysis really should be thought of as a compliment to soil testing," he said. "Determining the concentration of nutrients that is actually in the corn plant can provide important information about problem areas and management practices for corn production.

"Plant analysis can be used to diagnose nutritional problems that may be existing in certain areas of the field, or it can be used to monitor the crop to evaluate the overall nutrient status of the crop."

Additionally, the nutrient concentrations in the ear leaf have been shown to be most highly correlated with corn yield, Watson said.

Most soil testing laboratories also can analyze plant tissue. Such testing provides information on the concentration of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, manganese, iron, boron, copper and zinc in the corn tissue. Deficiencies -- or in some cases, too much -- of any of the nutrient concentrations can be the cause of a wide variety of field problems or management issues.

The following are some considerations that may be helpful in testing and evaluating a corn crop:

* Nitrogen (nutrient sufficient range 2.90 percent to 3.50 percent) -- Below sufficient range may be due to insufficient amount of nitrogen fertilizer or manure applied; fertilizer or manure not applied at the right time; an extremely cool season that may have reduced nitrogen release from the manure during the early plant growth stage; or extremely wet weather, caused leaching of the nitrate-nitrogen.

Above sufficient range may be due to excessive amount of nitrogen applied, or to poor plant growth because of other factors.

* Phosphorus (nutrient sufficient range 0.30 percent to 0.50 percent) -- Below sufficient range may be due to low soil phosphorus fertility; insufficient amount of phosphorus fertilizer or manure applied; or phosphorus becoming unavailable to the plant because of extremely acid soil. The soil should be limed to correct pH range.

Above sufficient range may be due to excessive amount of manure or phosphorus fertilizer applied, or to poor plant growth due to other factors.

* Potassium (nutrient sufficient range 1.91 percent to 2.50 percent) -- Below sufficient range may be due to low soil potassium fertility; insufficient amount of potassium fertilizer or manure applied; or very dry soil conditions, especially if the potassium concentration in the soil is borderline.

Above sufficient range may be due to excessive amount of manure or potassium fertilizer applied.

* Calcium (nutrient sufficient range 0.21 percent to 1.00 percent) -- Below sufficient range may be due to a very acid soil, or excessive amount of potassium applied to the soil.

* Magnesium (nutrient sufficient range 0.16 percent to 0.60 percent) -- Below sufficient range may be due to low soil magnesium levels; excessive amounts of manure or potassium fertilizer applied; or an acid soil.

* Sulfur (nutrient sufficient range (0.16 percent to 0.50 percent) -- Below sufficient range may be due to low soil organic matter; or manure or sulfur fertilizer not applied.

* Micronutrients (manganese, 20-150 ppm; iron, 21-250 ppm; boron, 4-25 ppm; copper, 6-20 ppm; zinc, 20-70 ppm) -- Below sufficient range may be due to over-liming a soil, which may reduce the availability of these micronutrients or very sandy soils, which can be low in one or more of these micronutrients.

Above sufficient range may be due to application of some waste material high in these nutrients; the over-application of fertilizer sources; or soils becoming very acid, making these nutrients highly available for plant uptake.

For plant tissue analysis, the ear leaf should be sampled when the corn is in the initial silk stage of growth, Watson said. Between 10 and 20 leaf samples should be taken randomly across each acre of the field to get an accurate analysis. He recommends not sampling dead or diseased plants.

"Nutrient concentrations within the plant can vary because of many factors," Watson said. "Consequently, knowledge of fertilizer/manure management and the weather can aid in the interpretation of the test results.

"Be sure to maintain records of the plant analysis from each field and compare them over time, to get a good idea how the nutrient levels may be changing. Remember that extra monitoring of the corn crop with plant analysis may prove very important if there are unseen nutritional problems beginning to develop."

Ed