sealPurdue News

December 2000

'Hidden hunger' threatens many crops, researcher says

WEST LAFAYETTE, Ind. – Acres of crops fail to reach yield potential every year, and a Purdue University plant pathologist says the reason often can be traced to the same source that robs humans of optimal performance: a poor diet.

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Pathologist Don Huber says crops usually get enough phosphorus, potassium and other common minerals to grow, but often can't draw sufficient micronutrients from the soil to fend off diseases. Such nutrients include the metals manganese, copper, zinc, iron and boron.

Symptoms aren't always apparent. Scientists call the phenomenon "hidden hunger."

"Plant nutrition has a big effect on the plant's susceptibility to disease," Huber says. "Micronutrients regulate a plant's physiology. Not much micronutrient is needed to mobilize a plant's disease resistance, but it is critical."

Soil composition is frequently overlooked in crop production, Huber says. Farmers and agronomists typically pay more attention to controlling insects and alien vegetation, or to weather forecasts. Huber suggests soil nutrition plays an equally important role in plant development.

In studies at four Purdue agricultural research farms and at agronomy centers in Alberta, Canada, Huber and Canadian researchers found that micronutrient deficiencies have both a direct and indirect impact on crops.

"Manganese, from a disease standpoint, plays a critical role," Huber says. "It's not only directly involved in plant photosynthesis but also in defense to disease." Soybeans, wheat, oats and barley are especially vulnerable to manganese shortages.

Wheat and corn also need adequate amounts of zinc, Huber says.

Corn is sensitive to imbalances of manganese and nitrogen, which work in concert within the plant. In extreme cases the imbalance can set off a chain of events resulting in the plant feeding off the nutrient reserves in its own cell walls to ensure kernel development, Huber says. The cannibalization weakens the plant, inviting disease.

"When the plant begins feeding on its own tissue, stalk rot can become severe," Huber says.

Other examples of micronutrient deficiencies, and the problems they can cause, include:

• Boron – Stunted growth and poor root development in alfalfa.

• Chlorine – Stunting, tip wilt, high amino acid levels in various crops.

• Copper – Leaf tip death, severe reactions to some herbicides, unusual crop lodging, melanosis (browning) of upper stem and heads, sterility and low test weight in wheat and barley.

• Iron – Stunting, chlorosis (yellowing) and short and highly branched roots in various legumes, field beans and fruit trees.

• Molybdenum – Stunting, chlorosis, breakdown and wilting of leaves in legumes and oats.

Farmers should not assume all diseases are connected to nutrient deficiencies, Huber says, but crop malnutrition occurs more frequently than might be believed.

"You see this hidden hunger in many soils, and symptoms don't always show up in some plants," Huber says. "You may have a plant that's a little stunted and the yield not as great, and you don't know why. Micronutrient deficiency may be the reason."

For farmers who suspect their crops are nutrient-starved, a plant sample analysis may be in order. If the analysis points to nutrient deficiency, there are several steps farmers can take to boost plant immunity: apply nutrients to the soil or crop; alter the soil's pH level, moisture and tillage; plant seed with better nutrient absorption characteristics; or grow crops during seasons when conditions are less likely to create plant stress.

Farmers also may consider checking the nitrogen levels in their fields, because there is a link between nitrogen and micronutrient nutrition in crops, Huber says.

"This year in Indiana we've lost up to 200 pounds of nitrogen per acre from some of our soils, almost all from denitrification – the movement of nitrogen from the soil back into the atmosphere," Huber says. "Where we've inhibited nitrification we've lost less than a fourth of that amount."

Huber's research indicated that when nitrification inhibitors were applied to soils to maintain adequate nitrogen and manganese levels for corn, yields rose 14 bushels per acre. Soybean yields following the corn increased as much as 22 bushels per acre from nitrification inhibitor use.

Nitrification inhibitor applications cost about $7.50 an acre for corn, Huber says.

Huber's micronutrient research will appear in the Encyclopedia of Plant Pathology (John Wiley & Sons Inc., New York, N.Y.). He cowrote a chapter, titled "Crop Deficiency Diseases," with Ieuan Evans and Elston Solberg, agronomy researchers at Alberta Agriculture, Food and Rural Development.

The encyclopedia is due out this fall.

Source: Don Huber, (765) 494-4652;

Writer: Steve Leer, (765) 494-8415,

Purdue News Service: (765) 494-2096;

An imbalance in nitrogen and manganese levels within corn can cause a stalk to feed on the nutrients in its own cell walls, inviting such diseases as Gibberella stalk rot. The pinkish area on the stalk is the Gibberella fungus. Purdue plant pathologist Don Huber says acres of crops fail to reach yield potential every year because they can't draw sufficient micronutrients from the soil to fend off diseases. (Photo courtesy of Don Huber)

A publication-quality photograph is available at the News Service Web site and at the ftp site. Photo ID: Huber.deficiency

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