ST. PETERSBURG, Fla. (DTN) -- Big swings in fertilizer prices have led to a decline in soil fertility around the world, according to studies by the International Plant Nutrition Institute.

Paul Fixen, IPNI senior vice president, said during a presentation at the recent 2011 Fertilizer Outlook and Technology Conference that for worldwide crop production to be sustainable, farmers must keep a balance between fertilizer applications and the amount of nutrients removed by crops.

"Declining soil fertility indicates that (the resulting) negative P and K balances require correction to avoid losses in future productivity," Fixen said.

His presentation showed that Brazil, India, China, Russia and Bulgaria had soils with varying degrees of P and K deficiency.

The U.S. also has its fair share of soils with lower levels of P and K. Fixen pointed out the Western Corn Belt, an area with traditionally high K levels, has seen large drops in median soil K levels from 2005 to 2010.

Nebraska leads the way with K down 44 parts per million followed by North Dakota with a drop of 29 ppm and South Dakota with a decline of 21 ppm. Other Western Corn Belt states with decreasing levels of K in the soil were Kansas with a drop of 20 ppm and Iowa with a decline of 11 ppm.

The Corn Belt as a whole fares even worse with the change of median P soil test levels for this same timeframe. Wisconsin soil shows a drop of 13 ppm, Illinois is down 10 ppm, Michigan is down 7 ppm and Indiana and Iowa both show a 3-ppm drop in median P levels.

"At least 50% of the Corn Belt fields will now experience immediate economic yield loss without P additions," Fixen said. "According to our research, the Corn Belt mines at least 110,000 tons of P from its soils. This is just not sustainable."

Daniel Kaiser, a nutrient management specialist at the University of Minnesota, said there are several factors at work that might explain why IPNI research shows low levels of P and K in Corn Belt soils.

First, each state has its own different points of critical levels, so what may be considered low in one state with certain types of soils might not be considered low in another state with different types of soils.

Minnesota's P test critical level, or the threshold at which P needs to be added, is set at 15 to 20 ppm while the state's K test is at 160 ppm.

"I know here in Minnesota in recent years we have played with P critical levels but we haven't changed K," Kaiser told DTN. "I know other states like Iowa they have adjusted their critical levels of K recently."

Kaiser also said the pH of soils also affects what level -- high or low -- of nutrients are present in soils. Soils with high pH levels will test low for nutrient values no matter how much fertilizer is applied, he said.

Because of both high fertilizer prices and high farm incomes, Kaiser said he has seen an upswing in grid zone samples done by Minnesota farmers in recent years. With grid zone sampling, soils can still vary in this 2.5-acre section, but nutrient levels are generally more accurate the smaller sampling you take.

"With more grid zone sampling I think this will help to clear up some of the questions about how much our soils are really lacking in some nutrients," he said.

INVESTING IN FERTILIZER PAYS

The good news, for both farmers and the fertilizer industry, is this is a reversible problem with economic benefits for those who invest in fertilizers.

In another presentation, Yao Yao, market research manager for PotashCorp, said balanced fertilization can provide a significant economic return for farmers worldwide. Based on long-term yield trials, about 30% of yield can be directly attributed to P use in U.S. corn production, he said.

"Also, the return per dollar spent on potash in 2011 in corn production is $10, while the five-year average is about $8, so you can see those who invest in fertilizer are financially rewarded," Yao said.

In addition, Yao pointed out that fertilizer cost percentage of crop revenue will remain below historic levels. While the 2006 to 2010 average was 18%, the 2011 estimate is closer to 13%, which should act as another incentive for farmers to invest in fertilizer, he said.

FARMERS 'DRAW LINE IN THE SAND'

Terry Nelson grows corn and soybeans in south-central Nebraska near Minden. As a farmer, he said he struggles with this balance of producing high yields and putting a prudent amount of fertilizer back into the soil so it remains productive while not over-applying and fouling the environment.

"I think as a farmer you almost need to just draw a line in the sand with this nutrient balance," Nelson told DTN. "You want to remain productive but you need to be profitable. It is a fine line."

He could very easily spend several hundreds of dollars an acre to fertilize his productive Kearney County farmland to high nutrient levels, he said. However, as he points out, do high nutrient levels in his soils really matter if he goes out of business because high input prices are not allowing him to be profitable?

While he believes Corn Belt farmers might have been "a bit stingy" applying fertilizer over the past five to seven years during the time of IPNI's research on P and K levels in Corn Belt soil, he does believe higher commodity prices in recent years have allowed many Corn Belt farmers to reinvest in fertilizer.

"I know over the last couple of years farmers in general have been reinvesting in their businesses with newer equipment and increased fertilizer applications with the higher incomes," he said.

Still, Nelson doesn't think farmers will go crazy increasing fertilizer application rates to high levels because of the ever-rising cost of fertilizer.

They know much they can push their soils to find that middle ground that allows them to be both productive and profitable. Farmers toe that line every day, he said.

Russ Quinn can be reached at russ.quinn@telventdtn.com

(GH/SK/AG)

© Copyright 2011 DTN/The Progressive Farmer, A Telvent Brand. All rights reserved.