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The Magic of Phosphorus

September 28, 2013
By: Darrell Smith, Farm Journal Conservation and Machinery Editor
Corn Sky Field

Understand the cycle to fertilize more efficiently

Harvest is in full swing, but the impact of a difficult planting season is still apparent from the combine perch. While phosphorus (P) might have been plentiful in the soil, a cold, wet spring tricked the nutrient from working its magic.

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How Corn Plants Receive Energy to Grow

"Several farmers told me that if their starter applicators got shut off or plugged, the corn that did not receive starter was a foot shorter a few weeks before tasseling," says Farm Journal Field Agronomist Ken Ferrie.

We’ll explain why in a minute. For now, understand that P helps cells elongate and divide, which is how plants grow. This unique role makes P a very important nutrient.

In this article, we’ll explain how P works. In future installments of Nutrient Navigator, we’ll tell you how, in certain seasons, the right amount of P can boost corn yield by 30 bu. to 40 bu. per acre.

Along with cell elongation and division, adequate P levels are required to transfer starches—especially sugars within a plant. "If a corn plant can’t transfer sugars, which are produced in the upper part of the plant, to other areas, the plant stops growing," Ferrie explains. "When that happens, plants take on a purple appearance. It’s similar to what happens to trees in the fall; when sugar is no longer being transferred, the leaves change color."

Corn plants need P early. "Because phosphorus is so important to early growth and development, the majority needs to be taken up early in the growing season," Ferrie says. "This is different from nitrogen, which plants can take up throughout the season."

The role of P in plant development involves two compounds in cells: ATP and ADP. "Phosphorus is constantly cycling between ATP and ADP and back," he says. "In this process, energy is released for growth. Think of it as a spring winding up and letting loose.

"It takes energy, which comes from the sun, to wind the spring or create ATP. When the plant converts ATP to ADP, that’s like letting go of the spring, and energy is released for growth and development. Then the process starts all over again," Ferrie says.

After plants pick up P from the soil, it can be consumed by animals or humans. That makes P essential to every living creature, including microbes.

Plant roots reach P three ways: interception, mass flow and diffusion. These processes occur simultaneously.

Roots intercept P as they grow through the soil. "During their rapid growth stage, corn roots grow 1" to 1½" per day," Ferrie says. "In the process, they encounter nutrients."

In mass flow, plant roots draw water from the soil, literally pulling the soil water to the plant. Nutrients are carried to the plants in the water.

In diffusion, P leaks into the soil water. The P ions move, or diffuse, from organic phosphate stored in the soil to the inorganic phosphate that plants can use by soil microbes.

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FEATURED IN: Farm Journal - October 2013

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