April 2, 2009

Specialist: Time, flooding, cost could affect the use of fertilizers

"Farmers will run into a time crunch when trying to apply fertilizers such as phosphorus and potassium before it is time to plant," said Jim Camberato, Purdue Extension soil fertility and plant nutrition specialist.

Much less phosphorus and potassium was applied last fall and winter than what is normally applied, and the best time to apply the fertilizers is before planting, Camberato said.

"Farmers should use soil test results, and then phosphorus and potassium can be allocated to fields and portions of fields where crops are most likely to respond to fertilizer applications," Camberato said.

Farmers can omit areas where soil tests show phosphorus and potassium levels are already sufficient for supporting optimum crop yields, he said.

"If farmers have high soil test results in phosphorus and potassium they will not get increased yield from applying phosphorus and potassium, "Camberato said. "They should take that into consideration when using soil test results."

Using phosphorus and potassium only where it is needed can help reduce the impact of high fertilizer prices.

"Now is a great time to save on fertilizer costs if soil test levels are above the maintenance limit because phosphorus and potassium are not needed to support optimum crop yields and will not need to be replaced by future fertilizer applications," Camberato said.

Not applying phosphorus and potassium fertilizer this season will not decrease crop yield, but the decision is only economically beneficial if fertilizer prices fall in the short-term, he said.

"If soil test levels are below the critical level, however, then crop yields are expected to be limited by soil phosphorus and potassium," Camberato said. "The value of the lost yield is likely greater than the cost of fertilizer, especially considering the multiple-year impact of the fertilizer application."

Farmers who were hit with flooding late in the winter also will need to address any damage the flooding did to their fields.

"If the topsoil was removed from the field by flooding, then some phosphorus and potassium will have been lost from the field as well," Camberato said. "If not, then leaching of potassium may have occurred, and soil testing should be used to monitor potassium levels."

For more information, contact Camberato at 765-496-9338 or jcambera@purdue.edu. Other fertilizer information is available at http://www.agry.purdue.edu/ext/corn/news/articles.08/PKFert-0915.html

Writer: Elizabeth Fritz, (765) 494-8402, elfritz@purdue.edu

Source: Jim Camberato, (765) 496-9338, jcambera@purdue.edu

Ag Communications: (765) 494-8415;
Steve Leer, sleer@purdue.edu
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