Low grain prices are having an effect on how Iowa farmers are fertilizing this fall.

According to a press release, Iowa State scientists said most Iowa cropland contains enough phosphorus [P] and potassium [K] for optimal crop yields.

“P and K will remain in the soil for several years,” said Tom Polito, director of Student Services for the College of Agronomy.

Polito recently discussed the situation with his class, Agronomy 356 — Soil, Fertilizer and Water Management.

“The reasons the levels have built up [is because] in the past, farmers had ‘a more is better’ attitude,” he said. “Farmers used it as insurance and tended to overapply.”

The press release stated that “given the economic pressure caused by low grain prices, avoiding unnecessary fertilizer applications is particularly important this year.”

Polito added that no one knows just how the low grain prices will affect the fertilizer applications for this spring.

Justin Brach, junior in agronomy and member of Polito’s class, said farmers will be affected because prices are “the lowest in 12 years, and many people worry about another farm recession.”

According to an extension publication, “General Guide for Crop Nutrient Recommendations in Iowa,” “the most profitable long term approach to P and K in soils is to maintain soil test values at the ‘optimum’ level.”

“The optimum level of P and K varies considering the soil type throughout the state,” Polito said.

The class discussed the options available to farmers when applying fertilizer.

“Applying in the fall is usually a cheaper option, but not always,” Polito said.

ISU has been very involved in fertilizer application practices and soil testing over the years, Polito said.

“Since the 1950s, ISU has done research to determine at what levels nutrients should be applied. This long history of research continues today with soil testing programs,” he said.

Polito added the second part of ISU’s involvement with soil fertility is to get the research into the farmers’ hands through the Extension Service.

“This is where farmers and fertilizer dealers can see the research done by ISU,” he said.

Randy Killorn, ISU soil fertility specialist, said in a press release that producers do not always see actual soil-test results.

“Producers should request the results so they can evaluate their soil using information based on Iowa studies,” Killorn said. “They also can keep records of long-term trends on their land.”

Polito encourages farmers to ask for the soil testing information and explore other testing options.

“Most fertilizer dealers do free soil testing for farmers and tell farmers what to apply,” Polito said.

The nutrient-recommendation publication “PM-1688” is available for $1 from the Extension Distribution Center at (515) 294-5247. The information also is available on the Internet at www.exnet.iastate.edu/ Pages/communications/farm98/newsrel.html.