Check Your Soil Fertility Reserves Now

Check Your Soil Fertility Reserves Now

Nutrient balance deficits are starting to show up.

Farmers across the Corn Belt tightened their fertilizer budget belts considerably over the last two years. But a new study by the International Plant Nutrition Institute suggests that continued cuts may compromise yields in key areas.

Due to high costs, potassium and phosphorus applications took big hits last year, reports Paul Fixen, IPNI director of research. "But now we're starting to see some very negative nutrient budgets ... quantity applied minus quantity removed by crops ... for key crop areas."

"Prior to the 2009 season, much of the Corn Belt was running a P deficit with crop removal in Iowa exceeding use by 20 to 30%, and in Illinois by 50 to 60%. Realize these were the budgets prior to the recent reduction in use."

The IPNI is a not-for-profit, science-based organization with a focus on agronomic education and research support. Its database compares average soil nutrient application levels (from both commercial fertilizer and manure) to crop removal levels based on crop yield for N, P and K. A summary of the study is available at . The full report should be available at later this fall.

Assess soil nutrient balance now

While crop yields have increased significantly in recent years, many growers haven't increased fertilizer rates. "With the higher yields, crops are pulling nutrients from the soil's nutrient bank and mining the soils," points out Dan Froehlich, director of agronomy for The Mosaic Company.

"In 2009, some growers applied 35 to 40% less potassium and cut phosphorus by 15 to 20%. Many areas were at or below the critical level for these key nutrients even before the fertilizer cut backs of 2009," he adds.

He predicts, for instance, that a field testing 10 parts per million for P that doesn't receive phosphorus fertilizer would be expected to produce corn yields 20% lower than a field with soil P levels at the critical 20 ppm level.

"To maintain crop yields and farm profitability, progressive growers will definitely want to soil test immediately after harvest to get a true picture of the soil nutrient levels within each field."

Properly balancing all needed nutrients is important, not just applying nitrogen. "Growers often attempt to rely on nitrogen only. They forget potassium interacts with essential plant food nutrients and 'regulates' many essential plant processes," explains Froehlich. "Without K, plants can't optimize uptake of available N. So, the money growers spend on N may be wasted."

Ohio State research, for example, found that corn yields were reduced by 44 bushels per acre when high levels of N were used on fields with inadequate K levels. At $3.25 corn, the foregone bushels would cost the grower $143 per acre.

Likewise, adequate P is necessary for higher yields and improved grain quality because P also improves the plants' ability to use all available nutrients. Without adding P fertilizers to balance nutrition, plant N uptake is reduced. At the same time, nitrate levels in the soil increase, then may be lost.

Get a handle on your nutrient balance situation this fall, stresses Froehlich. Then with a clear picture, develop a 2010 fertility plan that'll meet crop nutrient needs and optimize production and profitability.

For more about proper crop nutrition, soil testing and the importance of balanced fertility, visit

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